- A REINVESTIGATION OF THE OXIDATION OF CYSTEINE BY Br2(1-)(.) AND I2(1-)(.). EVIDENCE FOR CySBr(1-) AND CySI(1-).
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The existence of the species CySBr(1-) and CySI(1-), which may be regarded as complexes between the thiyl radical from cysteine and bromide or iodide ions, is reported, and their properties discussed in relation to other sulphur- and halogen- containing species which also, have a three-electron half-order bond.The oxidation of cysteine by I2(1-)(.) is shown to be much more complex than hitherto reported, and pH-dependent equilibria involving iodine atoms, iodide ions, cysteine, and cysteinyl radicals are described.The first measured rate constant for the reaction of iodine (as I3(1-)) with a thiol is also reported.
- Packer, John E.
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- Mechanism of oxidation of L-Cysteine by Tetraoxoiodate(VII) in aqueous acid medium
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The kinetics and mechanism of the oxidation of L-cysteine by tetraoxoiodate(VII) ion in aqueous acid medium has been studied at 0.03 δ[H+] δ0.1 mol dm-3- under pseudo-first order conditions of an excess of tetraoxoiodate(VII) concentration at 1 = 0.11 mol dm-3- (NaClO4). The reaction obeys the rate expression:-d [IO4-]/dt = {k3K1K2 [H+] + k5} [RSH][IO4 -] Addition of AcO- and NO3 - had no effect on the reaction but the rate of reaction decreased with increase in ionic strength of the medium. Increase in dielectric constant decreased the rate of reaction. The rates are consistent with a mechanism which involves the formation of free radicals which subsequently dimerized into disulfides. The reaction has been rationalized on the basis of the inner-sphere electron transfer mechanism.
- Ukoha, Pius O.,Ujam, Oguejiofo T.,Iyun, Johnson F.,Okereke, Solomon E.O.
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- Hierarchical cystine flower based electrochemical genosensor for detection of Escherichia coli O157:H7
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This work reports on a facile and reproducible approach to synthesize novel organic flowers of cystine (CysFls) with high uniformity. These 3D flower-like structures have a purely hierarchical arrangement, wherein each petal is composed of several cystine molecules with an average size of 50 μM, as determined by transmission electron microscopy. The CysFls were self-assembled onto a gold electrode and were utilized as matrices for the covalent immobilization of an Escherichia coli O157:H7 (E. coli) specific probe oligonucleotide that was identified from the 16s rRNA coding region of the E. coli genome. This fabricated CysFl platform sought to provide improved fundamental characteristics to electrode interface in terms of electro-active surface area and diffusion coefficient. Electrochemical impedance spectroscopy revealed that this genosensor exhibits a linear response to complementary DNA in the concentration range of 10-6 to 10-15 M with a detection limit of 1 × 10-15 M. Under optimal conditions, this genosensor was found to retain about 88% of its initial activity after being used for 6 times. This journal is the Partner Organisations 2014.
- Pandey, Chandra Mouli,Tiwari, Ida,Sumana, Gajjala
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- Electrocatalytic oxidation of cysteine on a nafion-ruthenium oxide pyrochlore chemically modified electrode
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The electrocatalytic oxidation of cysteine (CySH) to cystine (CyS-SCy) was noticed on the Nafion-ruthenium oxide pyrochlore chemically modified electrode. The electrocatalytic oxidation was mediated by the RuVI/IV redox sites in the oxide pyrochlore network in terms of the Michaelis-Menten kinetics. The obtained heterogeneous catalytic rate constant (kc) and transfer coefficient (α) are 6.33 s-1 and 0.99, respectively.
- Zen, Jyh-Myng,Senthil Kumar, Annamalai,Chen, Jyh-Cheng
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- Simple and facile preparation of silver-polydopamine (Ag-PDA) core-shell nanoparticles for selective electrochemical detection of cysteine
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Selective and sensitive non-enzymatic electrochemical detection of cysteine (CySH) is achieved in the present work using a polydopamine capped silver nanoparticles (Ag-PDA) modified indium tin oxide (ITO) electrode. Efficient redox properties, synergistic effects and the specific steric hindrance associated with the Ag-PDA core-shell nanoparticles provide higher selectivity and larger sensitivity for CySH detection over other competitive bio-thiols namely, homo-cysteine and glutathione. A simple one-step method is used for the preparation of Ag-PDA core-shell nanoparticles. The structure, morphology and composition of Ag-PDA nanoparticles are characterized by using field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), UV-visible (UV-vis) and Fourier transform infra red (FTIR) spectroscopic techniques. Electrochemical characteristics are investigated by using cyclic voltammetry (CV) and linear sweep voltammetry (LSV). These studies clearly reveal the formation of Ag-PDA nanocomposite on the ITO electrodes and their corresponding redox properties. Non-enzymatic electrochemical detection of CySH is carried out using Ag-PDA modified ITO electrodes in 0.1 M PBS (pH = 5.0) aqueous solution. Under the optimized conditions, this particular electrochemical biosensor exhibits a perfect linear calibration plot in the concentration range between 0.05 μM and 300 μM. Further, a sensitivity value of 0.023 μA μM-1 and a lower detection limit of 0.02 μM are determined for CySH detection. Moreover this Ag-PDA modified ITO electrode is applied further for the determination of CySH in human blood serum samples and the results are promising and satisfactory, suggesting the possible analytical application of this biosensor for the determination of CySH in biological samples.
- Thota, Raju,Ganesh
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- Kinetic Studies on the Role of Dioxygen in the Cooper-Catalyzed Autoxidation of Cysteine
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Kinetic studies on a role of dioxygen in the copper-catalyzed autoxidation of cysteine in glycylglycine-phosphate buffers have been carried out.The rate of autoxidation was obtained by measuring the consumption of cysteine.It has been revealed that cysteine is oxidized by a "sequential mechanism".The reaction pathway can be shown by Eqs. 1, 2, 3, and 4; cysteine is oxidized not only by copper(II) species, but also by copper(I)-O2 adducts: Cu(II)-L + CyS- = L-Cu(II)-CyS- (1) L-Cu(II)-CyS- -> Cu(I)-L + CySradical (2) Cu(I)-L + O2 = L-Cu(I)-O2 (3) L-Cu(I)-O2 + Cy S- + 2H+ -> Cu(II)-L + CySradical + H2O2 (4) Here, L represents ligands including cysteine.The oxidation step (4) catalyzed by the Cu(I)-O2 species was proposed to be rate-determining.
- Hanaki, Akira
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- An unusual electrochemical oxidation of phenothiazine dye to phenothiazine-bi-1,4-quinone derivative (a donor-acceptor type molecular hybrid) on MWCNT surface and its cysteine electrocatalytic oxidation function
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Phenothiazine (PTZ), a thiazine class heterocyclic compound, is a well-known electron donating system and has been widely used as a starting compound to prepare various phenothiazine dyes and pharmaceutically important compounds. Quinones and its derivatives are constituents of biologically active molecules serve as excellent electron-acceptor systems. Oxidation of PTZ by chemical and electrochemical methods often resulted into monohydroxylation of benzene ring moiety, S-oxidized and polymerized compounds as end products. Electrochemical oxidation of PTZ on a multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode in pH 7 phosphate buffers solution (PBS) has been investigated in this work. A highly redox active surface confined PTZ-bi-1,4-quinone derivative (PTZ-biQ) on MWCNT modified glassy carbon electrode, designated as GCE/MWCNT@PTZ-biQ, as a product was unusually observed. The GCE/MWCNT@PTZ-biQ showed well-defined redox peaks at E1/2 = -0.07 and +0.29 V vs Ag/AgCl corresponding to surface confined electron-transfer behavior of the bi-quinone (acceptor) and PTZ-cationic radical species (donor) respectively. No such electrochemical characteristics were noticed when unmodified GCE was subjected to the electrochemical oxidation of PTZ. Existence of PTZ-biQ was confirmed by XRD, Raman spectroscopy, FT-IR and GC-MS (methanolic extract of the active layer) analyses. Position of biQ in PTZ-biQ as 1,4-quinone isomer was confirmed by observation of absence of copper-complexation with 1,4-quinone and H2O2 electrochemical reduction reactions at -0.1 V vs Ag/AgCl unlike to the specific copper-complexation and H2O2 reduction with 1,2-quinone isomer in pH 7. Cysteine (CySH) oxidation was studied as a model system to understand the electron-transfer function of the MWCNT@PTZ-biQ. A highly selective electrocatalytic oxidation and sensing by amperometric i-t and flow injection analysis of CySH at low oxidation potential, 0.3 V vs Ag/AgCl in pH 7 PBS with detection limit values (signal-to-noise ratio = 3) of 11.10 μM and 110 nM respectively, without any interference from other biochemicals like uric acid, dopamine, nitrite, citric acid and H2O2, unlike the conventional chemically modified electrodes with serious interference's, have been demonstrated.
- Shanmugam, Ranganathan,Barathi, Palani,Zen, Jyh-Myng,Kumar, Annamalai Senthil
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- Selective detection of cysteine/cystine using silver nanoparticles
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The selective detection of cysteine and cystine amino acids over other standard amino acids was possible with the naked eye using silver nanoparticles (AgNPs) in a simple procedure at room temperature. The change in color and the aggregation of NPs were studied using UV-vis spectroscopy and transmission electron microscopy, respectively. It was observed that when the derivative and substructures of cysteine were employed as analytes the detection was possible only when there is free SH or S-S group present in the analytes. The method was extended to a dipeptide 'cys-gly' as a model peptide where the detection was successful due to the presence of SH moiety.
- Athilakshmi, Jeyaraman,Mohan, Manikkavalli,Chand, Dillip Kumar
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- Cysteine oxidation reactions catalyzed by a mononuclear non-heme iron enzyme (OvoA) in ovothiol biosynthesis
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OvoA in ovothiol biosynthesis is a mononuclear non-heme iron enzyme catalyzing the oxidative coupling between histidine and cysteine. It can also catalyze the oxidative coupling between hercynine and cysteine, yet with a different regio-selectivity. Due to the potential application of this reaction for industrial ergothioneine production, in this study, we systematically characterized OvoA by a combination of three different assays. Our studies revealed that OvoA can also catalyze the oxidation of cysteine to either cysteine sulfinic acid or cystine. Remarkably, these OvoA-catalyzed reactions can be systematically modulated by a slight modification of one of its substrates, histidine.
- Song, Heng,Her, Ampon Sae,Raso, Fiona,Zhen, Zhibin,Huo, Yuda,Liu, Pinghua
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- A cytotoxic tantalum(v) half-sandwich complex: A new challenge for metal-based anticancer agents
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Despite the biological relevance of complexes of various transition metals, tantalum complexes have long been neglected by bioinorganic chemists. Herein, we demonstrate potential chemotherapeutic applicability of the [Ta(η5-Cp?)Cl2(salaph)] (1) complex, containing deprotonated Schiff base 2-{(E)-[(2-hydroxyphenyl)imino]methyl}phenol (H2salaph), which shows strong cytotoxicity in cancer cells, related to the induction of apoptosis and apoptosis-related processes, but shows low cytotoxicity in healthy cells.
- ?tarha, Pavel,Trávní?ek, Zdeněk,Dvo?ák, Zdeněk
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- Reactive sulfur species: Kinetics and mechanisms of the oxidation of cysteine by hypohalous acid to give cysteine sulfenic acid
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Cysteine sulfenic acid has been generated in alkaline aqueous solution by oxidation of cysteine with hypohalous acid (HOX, X = Cl or Br). The kinetics and mechanisms of the oxidation reaction and the subsequent reactions of cysteine sulfenic acid have been studied by stopped-flow spectrophotometry between pH 10 and 14. Two reaction pathways were observed: (1) below pH 12, the condensation of two sulfenic acids to give cysteine thiosulfinate ester followed by the nucleophilic attack of cysteinate on cysteine thiosulfinate ester and (2) above pH 10, a pH-dependent fast equilibrium protonation of cysteine sulfenate that is followed by rate-limiting comproportionation of cysteine sulfenic acid with cysteinate to give cystine. The observation of the first reaction suggests that the condensation of cysteine sulfenic acid to give cysteine thiosulfinate ester can be competitive with the reaction of cysteine sulfenic acid with cysteine.
- Nagy, Peter,Ashby, Michael T.
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- Redox Chemistry of [Fe2(CN)10]4-. Part 4 Reaction with L-Cysteine
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L-Cysteine reduces [Fe2(CN)10]4- to [Fe2(CN)10]6- in a two stage process, a rapid reduction to [Fe2(CN)10]6- followed by a slower second order reaction involving HSCH2CH (NH3+CO2- and a conjugate base.
- Beckford, Floyd A.,Bennet, Deon,Dasgupta, Tara P.,Stedman, Geoffrey
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- New Approaches to the Synthesis of Cystine Peptides Using N-Iodosuccinimide in the Construction of Disulfide Bridges
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N-Halosuccinimides have been found to convert cysteine, S-(acetamidomethyl)-, S-(p-methoxybenzyl)-, or S-(p-methylbenzyl)cysteine into cystine.N-Iodosuccinimide, the mildest reagent among N-halosuccinimides, is applied successfully in the synthesis of (Arg8)-vasopressin and oxytocin by a fully automated process of solid-phase peptide synthesis or by cyclizing the released thiol peptides in DMF-CH2Cl2.These simple and synthetically useful methods have led to the fully automated solid-phase synthesis of (Cys5,Cys12)human growth hormone releasing factor (1-29)-NH2 and apamin based on the combined process of stepwise addition of Boc-amino acids and controlled stepwise formation of the disulfide bonds.These new approaches may be useful in the synthesis of larger and more complex cystine peptides.
- Shih, Hsiencheng
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- Synthesis of Cystine-peptide by a New Disulphide Bond-forming Reaction using the Silyl Chloride-Sulphoxide System
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Methyltrichlorosilane or tetrachlorosilane in trifluoroacetic acid, in the presence of diphenylsulphoxide, is found to cleave various S-protecting groups of cysteine to form cystine directly by the reduction-oxidation reaction; this new disulphide bond forming reaction is successfully applied to the syntheses of oxytocin and human brain natriuretic peptide.
- Akaji, Kenichi,Tatsumi, Tadashi,Yoshida, Makoto,Kimura, Tooru,Fujiwara, Yoichi,Kiso, Yoshiaki
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- The Reaction of Cysteine with the Pentacyanonitrosylferrate(2-) Ion
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The title reaction has been studied and it has been found that in the presence of oxygen a catalytic path for the oxidation of cysteine to cystine is established.The rate law is presented, and the mechanism is discussed on the basis of observed effects of the reagent concentrations on the extrapolated initial absorbance of the solution at 522 nm, and on the experimental pseudo-first-order rate of disappearance of colour.Cyanide ion has a remarkable influence on the course of the reaction.
- Morando, Pedro J.,Borghi, Elena B.,Schteingart, Lydia M. de,Blesa, Miguel A.
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- A simple and efficient fluorescent sensor for histidine
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A simple coordination complex terpyridine-CuCl2 is found to be an efficient fluorescent sensor for histidine in aqueous solution with up to 1004 fold fluorescence enhancement.
- Huang, Zeng,Du, Jiao,Zhang, Jing,Yu, Xiao-Qi,Pu, Lin
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- Reactive sulfur species: Kinetics and mechanisms of the reaction of cysteine thiosulfinate ester with cysteine to give cysteine sulfenic acid
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(Chemical Equation Presented) The kinetics and mechanisms of the reaction of cysteine with cysteine thiosulfinate ester in aqueous solution have been studied by stopped-flow spectrophotometry between pH 6 and 14. Two reaction pathways were observed for pH > 12: (1) an essentially pH-independent nucleophilic attack of cysteinate on cysteine thiosulfinate ester, and (2) a pH-dependent fast equilibrium protonation of cysteine sulfenate that is followed by rate-limiting comproportionation of cysteine sulfenic acid with cysteinate to give cystine. For 6 pH 12, the rate-determining reaction between cysteinate and cysteine thiosulfinate ester becomes pH-dependent due to the protonation of their amine groups. Hydrolysis of cysteine thiosulfinate ester does not play a role in the aforementioned mechanisms because the rate-determining nucleophilic attack by hydroxide is relatively slow.
- Nagy, Peter,Lemma, Kelemu,Ashby, Michael T.
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- Adduct Formation and Absolute Rate Constants in the Displacement Reaction of Thiyl Radicals with Disulfides
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The displacement reaction of thiyl radicals with disulfides is shown to proceed via a transient adduct radical by using time-resolved pulse radiolysis techniques.The relatively long-lived adduct (t1/2 > 100 μs) formed in the forward reaction of the equilibrum RS. + RSSR . is suggested to be a sulfuranyl radical with the unpaired electron located in an antibonding ?* orbital within a trisulfide bridge.These species exhibit optical absorptions in the UV, e.g., λmax = 375 +/- 10 nm and ε = (3.4 +/- 0.4)*103 M-1 cm-1 for the all-methylated radical, and have been identified in aqueous and methanolic solutions.Equilibrum constants of K = 180 +/- 30 and 60 +/- 20 M-1 have been evaluated for the systems with R = CH3 and cysteine residue, respectively, via two different methods.The corresponding forward reactions occur with k(RS. + RSSR) = 3.8*106 and 7.7*105 M-1 s-1, respectively.
- Bonifacic, M.,Asmus, K.-D.
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- Electrochemical behavior of L-cysteine and its detection at ordered mesoporous carbon-modified glassy carbon electrode
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In this paper, the electrochemical behavior of L-cysteine (CySH) was investigated thoroughly at an ordered mesoporous carbon-modified glassy carbon (OMC/GC) electrode. The voltammetric studies showed there were three anodic peaks for the electrooxidation of CySH in the pH range of 2.00-5.00; however, one peak disappeared above pH 5.00. This behavior has never been reported before. Through the studies of the effect of pH on the distribution fractions (δ) of the four chemical species of CySH, we conclude only CySH 2+ (H3A+) and CyS- (HA-) are the electroactive substances and should be responsible for the electrooxidation of CySH. And for the first time, we successfully established the exact and systemic mechanisms based on the electroactive species to explain CySH oxidation at different pH values. On the other hand, a sensitive CySH sensor was developed based on an OMC/GC electrode, which shows a large determination range (18-2500 μmol L-1), a high sensitivity (23.6 μA mmol L-1), and a remarkably low detection limit (2.0 nmol L-1, which is the lowest value ever reported for direct CySH determination on the electrodes) at pH 2.00. At pH 7.00, the modified electrode can be still used to readily detect CySH in the range of the physiological levels. These make OMC/GC electrode a promising candidate for efficient electrochemical sensors for the detection of CySH.
- Zhou, Ming,Ding, Jie,Guo, Li-Ping,Shang, Qing-Kun
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- Formation, characterization and electrochemical properties of novel tetrasubstituted cobalt phthalocyanines bearing tetrahydropyran, furan and coumarin moieties
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Cobalt phthalocyanines (CoPcs) bearing peripherally tetrasubstituted tetrahydropyran (thp) or furan (fur) moieties were formed and spectroscopically characterized. Structural elucidations of 4-(tetrahydropyran-2-methoxy)phthalonitrile (1) and 4-(furan-2-methylthio)phthalonitrile (2) were confirmed via single crystal X-ray analysis. The redox properties of CoPc-thp (3) and CoPc-fur (4) were investigated via cyclic and squarewave voltammetry as well as UV-Vis spectroelectrochemistry. Glassy carbon electrodes (GCEs) modified with 3, 4 and a previously reported coumarin (cou) substituted CoPc (CoPc-cou, 5), were tested for their electrocatalytic activities toward l-cysteine. While the bare GCE and 4-GCE showed no peaks for l-cysteine oxidation in the 0.0-0.70 V potential window; 3-GCE and 5-GCE showed peaks at 0.42 V and 0.52 V, respectively. Kinetic parameters were determined by chronoamperometry studies. l-Cysteine oxidation using 3-GCE was found to proceed at a faster rate than 5-GCE.
- Chohan, Sumayya,Booysen, Irvin Noel,Mambanda, Allen,Akerman, Matthew Piers
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- Efficient oxygen consumption by hydroxo(protoporphyrinato)iron(III) adsorbed on magnesium oxide powder in the presence of cysteine
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The oxygen reduction ability of hydroxo(protoporphyrinato)iron(III) (HEM) adsorbed on powdery supports in the presence of cysteine was investigated using a Clark-type oxygen electrode. All of the oxygen consumption rates for HEM adsorbed on powdery supports having different surface basicity values (CaO > MgO > TiO2) were larger than the cases of HEM in aqueous solution and of MgO suspension without HEM in the presence of cysteine. Maximum oxygen consumption rate was obtained in the case of the HEM/MgO system. This result suggests that the optimum surface basicity of powdery support is necessary to achieve efficient oxygen consumption. From the measurements for ESR and Raman spectra of the HEM/MgO system, we confirmed the change for the iron valence of HEM from III to II in the presence of cysteine. The production of cystine through the dimerization of cysteinyl radicals in the reaction mixture was also confirmed by the measurements of ESR spectra and capillary electrophoresis (CE). A possible mechanism for accelerating the oxygen consumption rate of the HEM/MgO system in the presence of cysteine is discussed, concerning the effect of the catalytic ability of MgO on the turnovers of iron valence.
- Noda, Hiroyuki,Ohya, Hiroaki,Kamada, Hitoshi
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- Iron(III)–salen ion catalyzed s-oxidation of L-cysteine and s-alkyl-L-cysteines by H2O2: Spectral, kinetic and electrochemical study
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The H2O2 oxidation of L-cysteine and s-alkyl-L-cysteines (s-met-L-cys, s-et-L-cys & s-pro-L-cys) catalyzed by iron(III)–salen (salen = N,N′-bis(salicylidene)ethylenediaminato) complexes in aqueous CH3CN proceeds through Michaelis–Menten kinetics. The rate constant (k) values correlate well with Hammett σ constants, which gives the positive reaction constant (ρ = 1.5–1.9) value. The CV of oxoiron(IV)-salen ion shows a clear oxidation peak at 1.28 V in 0.1 M phosphate buffer (PB) solution using 0.1 M tertiary butyl ammonium perchlorate (TBAP) as supporting electrolyte at 266 K. The rate of the reaction is highly sensitive to the length of the alkyl chains present in the L-cysteines, pH and solvent composition of the medium. The calculated binding constant values (Kf) in the range of 117–613 M?1, indicate that iron(III)–salen complexes carrying electron donating substituents in the salen ligand have higher binding constant values compared to those carrying electron withdrawing substituents. Product analysis shows the conversion of L-cys to its disulfide and s-alkyl-L-cys to the corresponding sulfoxides. Based on the spectral and kinetic data the plausible mechanism has been proposed.
- Karuppasamy, Periyakaruppan,Thiruppathi, Dharmaraj,Ganesan, Muniyandi,Rajendran, Thangamuthu,Rajagopal, Seenivasan,Sivasubramanian, Veluchamy Kamaraj
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- DNA sensors and aptasensors based on the hemin/G-quadruplex-controlled aggregation of Au NPs in the presence of L-cysteine
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L-cysteine induces the aggregation of Au nanoparticles (NPs), resulting in a color transition from red to blue due to interparticle plasmonic coupling in the aggregated structure. The hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme catalyzes the aerobic oxidation of L-cysteine to cystine, a process that inhibits the aggregation of the NPs. The degree of inhibition of the aggregation process is controlled by the concentration of the DNAzyme in the system. These functions are implemented to develop sensing platforms for the detection of a target DNA, for the analysis of aptamer-substrate complexes, and for the analysis of L-cysteine in human urine samples. A hairpin DNA structure that includes a recognition site for the DNA analyte and a caged G-quadruplex sequence, is opened in the presence of the target DNA. The resulting self-assembled hemin/G-quadruplex acts as catalyst that controls the aggregation of the Au NPs. Also, the thrombin-binding aptamer folds into a G-quadruplex nanostructure upon binding to thrombin. The association of hemin to the resulting G-quadruplex aptamer-thrombin complex leads to a catalytic label that controls the L-cysteine-mediated aggregation of the Au NPs. The hemin/G-qaudruplex-controlled aggregation of Au NPs process is further implemented for visual and spectroscopic detection of L-cysteine concentration in urine samples.
- Niazov-Elkan, Angelica,Golub, Eyal,Sharon, Etery,Balogh, Dora,Willner, Itamar
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- Determination of a small quantity of cystine in the presence of a large amount of cysteine
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A procedure is described to precisely determine a very small amount of cystine in the presence of a large amount of cysteine. After completely modifying cysteine with N-ethylmaleimide, the remaining reagent was reacted with DL-homocysteine. Cystine was determined, after being reduced with dithiothreitol, by the reaction with ninhydrin carried out under acidic conditions. The procedure makes it possible to precisely determine the amount of cystine present with cysteine in a concentration ratio of 1:2,000. By employing this procedure, auto-oxidation of cysteine to cystine in a mixture for the L-cysteine α, β-elimination reaction was investigated.
- Yamagata, Shuzo,Iwama, Tomonori
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- Oxidation of L-Thiols in the Presence of Iron(III) Complex Ions Anchored to Asymmetric Polymers. A Kinetic and Conformational Investigation
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The H2O2 oxidation of L-cysteine in the presence of enantiomeric systems formed by + (FeT) ions anchored to ordered poly(D-glutamate) (FeTD) or poly(L-glutamate) (FeTL) matrices has been studied at pH 7 (tetpy=2,2',2'',2'''-tetrapyridyl).The reaction follows a total third-order kinetics (kox=6.1x104 M-2 s-1, 26 deg C) and does not exhibit any stereoselectivity.These results markedly differ, in terms of both rate law and chiral discrimination, from those obtained under similar conditions by using optically active o-dihydroxy substrates, such as L-ascorbic acid, L-adrenaline, and L-dopa.They also differ from those obtained with reduced L-glutathione, which follows a total second-order kinetics (k=6.4 M-1 s-1, 26 deg C).In the absence of hydrogen peroxide, evidence is produced for the formation of a stable, polymer-supported, FeIIIT-cysteinate complex, to which no stereoselectivity is associated because of the high conformational mobility of the axially bound substrate.This complex is characterized by electron paramagnetic resonance (EPR) signals (10 K) at g=2.20, 2.15, and 1.92 and by a rather slow, +>-dependent kinetics of formation (k=12.7 M-1 s-1, 26 deg C) that are suggestive of a ligand-exchange process at the polymer-shielded active sites, within an outer-sphere compound involving the entering substrate molecule.Conformational energy calculations on the noncovalent diastereomeric adducts show the absence of a sterically preferred pathway for the closest approach of cysteine to the central metal ion and support the hypothesis of the ligand-interchange reaction on steric and geometric grounds.Implications of these effects on the absence of stereoselectivity in the reaction investigated are briefly discussed.
- Pispisa, B.,Paradossi, G.,Palleschi, A.,Desideri, A.
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- Reduction of RuVI≡N to RuIII - NH3 by Cysteine in Aqueous Solution
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The reduction of metal nitride to ammonia is a key step in biological and chemical nitrogen fixation. We report herein the facile reduction of a ruthenium(VI) nitrido complex [(L)RuVI(N)(OH2)]+ (1, L = N,N′-bis(salicylidene)-o-cyclohexyldiamine dianion) to [(L)RuIII(NH3)(OH2)]+ by l-cysteine (Cys), an ubiquitous biological reductant, in aqueous solution. At pH 1.0-5.3, the reaction has the following stoichiometry: [(L)RuVI(N)(OH2)]+ + 3HSCH2CH(NH3)CO2 → [(L)RuIII(NH3)(OH2)]+ + 1.5(SCH2CH(NH3)CO2)2. Kinetic studies show that at pH 1 the reaction consists of two phases, while at pH 5 there are three distinct phases. For all phases the rate law is rate = k2[1][Cys]. Studies on the effects of acidity indicate that both HSCH2CH(NH3+)CO2- and -SCH2CH(NH3+)CO2- are kinetically active species. At pH 1, the reaction is proposed to go through [(L)RuIV(NHSCH2CHNH3CO2H)(OH2)]2+ (2a), [(L)RuIII(NH2SCH2CHNH3CO2H)(OH2)]2+ (3), and [(L)RuIV(NH2)(OH2)]+ (4) intermediates. On the other hand, at pH around 5, the proposed intermediates are [(L)RuIV(NHSCH2CHNH3CO2)(OH2)]+ (2b) and [(L)RuIV(NH2)(OH2)]+ (4). The intermediate ruthenium(IV) sulfilamido species, [(L)RuIV(NHSCH2CHNH3CO2H)(OH2)]2+ (2a) and the final ruthenium(III) ammine species, [(L)RuIII(NH3)(MeOH)]+ (5) (where H2O was replaced by MeOH) have been isolated and characterized by various spectroscopic methods.
- Wang, Qian,Man, Wai-Lun,Lam, William W. Y.,Yiu, Shek-Man,Tse, Man-Kit,Lau, Tai-Chu
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- A waste-free and highly effective catalytic system for the oxidation of cysteine to cystine
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A new three-component catalytic system, water/ionic liquid/metal phthalocyanine complex, was studied for the oxidition of cysteine to prepare cystine. It was found that the water/ 1-n-hexyl-3-methylimidazolium tetrafluoroborate ([hmim][BF4])/iron (II) phthalocyanine (Fe IIPc) system exhibited an excellent catalytic activity in the oxidition of cysteine. Cystine was obtained with 98% isolated yield in 12 h at the temperature of 80 °C. Further more, the catalytic system can be easily recovered and recycled in the following run without apparent reduction in catalytic activity.
- Zhao, Xinhua,Kong, Aiguo,Zhang, Xinhua,Shan, Chongchong,Ding, Hanming,Shan, Yongkui
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- Kinetic Studies of the Oxidation of Thiols by Coenzyme PQQ
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Kinetic studies on the oxidation of thiols by coenzyme PQQ are carried out under anaerobic conditions.A bell-shaped pH-rate profile having a maximum rate at around pKa of the thiol is observed.The rate-determining step changes between acidic and basic sides of the profile indicating the existence of at least one intermediate in the course of the reaction.
- Itoh, Shinobu,Kato, Noboyuki,Mure, Minae,Ohshiro, Yoshiki
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- Real-time monitoring of "self-oxidation" of cysteine in presence of Cu2+: novel findings in the oxidation mechanism
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A novel approach for investigation of a mechanism and rate of "self-oxidation" of cysteine in the presence of Cu2+ is presented. Continuous monitoring was performed using simple, low-cost, and widely available commercial ion-selective electrode for Cu2+. Presented procedure provides a complete real-time picture of overall oxidation process and has revealed a sequentially organized process, with the domination of certain reactions in each stage. A plausible mechanism, in the light of the previously reported explanation, has been proposed to account for the experimental results together with an adequate scheme of the overall process. The dependence of both the pH (measurements were performed at pH 5, 7, 8) and the concentration of the initially present Cu2+ is presented and discussed. Additionally, information into the process was collected by experiments performed in oxygen-free atmosphere and changes in the mechanism of oxidation, at weakly alkaline pH values, were observed. Information presented in this study can be utilized in advanced biochemical monitoring systems, when considering the importance of the position of cysteine and cysteine containing peptides in metabolic processes.
- Buzuk, Marijo,Brini?, Slobodan,Vladislavi?, Nives,Brali?, Marija,Buljac, Ma?a,Ron?evi?, Ivana ?kugor
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- Ru(III)-catalyzed oxidation of cysteine hydrochloride by methylene blue in acidic medium; synergetic effect of Cu(II): A kinetic study
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Cysteine hydrochloride and methylene blue (MB) interact in a molar ratio of 2:1 in acidic medium forming cystine and dihydromethylene blue, and the reaction is catalyzed by Ru(III). At low concentrations (ca. 2.0 × 10 -8 M), Cu(II) does not catalyze the reaction significantly but at this concentration level the catalytic activity of Ru(III) is found to be augmented by the addition of Cu(II) and the kinetics of Ru(III)-catalyzed reaction has been studied in the absence and in the presence of externally added Cu(II). The reaction follows a half-order kinetics in MB that increases to 3/4 on increasing [MB] beyond 1.5 × 10-5 M in the Ru-catalyzed reaction, In the Ru-Cu catalyzed reaction; the order in MB is 3/4 even at lower concentrations of MB. The order in cysteine is unity. The rate decreases on increasing [MB] in both cases but attains a limiting value at higher concentrations of MB (ca. >2.0 × 10-5 M) in the presence of Ru(III) alone. The rate increases on increasing [H+) and in Ru-catalyzed reaction, an optimum is noticed. The rate increases linearly with increasing [Ru(III)], but equilibration of the catalyst with other ingredients of the reaction system decreases the rate. The FTIR spectra of the reaction system exhibit time-dependent changes in the stretching as well as bending modes of - SH group. The synergetic effect of Cu(II) has been attributed to its ligation with cysteine and its subsequent interaction with Ru(II) produced in situ in the system. 2008 Wiley Periodicals, Inc.
- Chaturvedi,Mishra
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- COPPER-CATALYZED AUTOXIDATION OF CYSTEINE. THE AMOUNT OF HYDROGEN PEROXIDE PRODUCED UNDER VARIOUS CONDITIONS AND THE STOICHIOMETRY OF THE REACTION.
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Hydrogen peroxide is shown to be produced as an intermediate from oxygen in the copper-catalyzed autoxidation of cysteine. The amounts of cysteine oxidized and of hydrogen peroxide formed varied depending on the reaction conditions employed. The peroxide upon forming was spontaneously utilized for the oxidation of cysteine. As a result, the ratio of the concentration of hydrogen peroxide formed to cysteine oxidized is variable depending on the conditions. But, in dilute solutions, where the oxidation by the peroxide was slow, a stoichiometric relation of 2:1 was obtained between cysteine consumed and hdyrogen peroxide produced. The rate of autoxidation is dependent on the concentration of oxygen dissolved. The double reciprocal plot of the rate against the concentration of oxygen gives a straight line, which indicates a possibility of the Michaelis-Menten type mechanism concerning the reoxidation or oxygenation of Cu(I) species.
- Hanaki,Kamide
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- Mechanism of the 2-ethyl-3-hydroxy-6-methylpyridinium 2-nitroxysuccinate reduction in nitrite-generating systems
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The nitrite-generating activity of 2-ethyl-3-hydroxy-6-methylpyridinium 2-nitroxysuccinate as a promising NO-donor has been investigated in reactions with various reducing agents. Reduction of the NO-donor with cysteine was analyzed using a kinetic modeling method. The calculated rate constants satisfactorily describe the experimental data, thereby confirming the proposed reaction mechanism.
- Fedorov, Boris S.,Kormukhina, Alexandra Yu.,Kotel'nikov, Alexander I.,Pokidova, Olesya V.,Psikha, Boris L.
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- Metal organic frameworks as nitric oxide catalysts
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The use of metal organic frameworks (MOFs) for the catalytic production of nitric oxide (NO) is reported. In this account we demonstrate the use of Cu 3(BTC)2 as a catalyst for the generation of NO from the biologically occurring substrate, S-nitrosocysteine (CysNO). The MOF catalyst was evaluated as an NO generator by monitoring the evolution of NO in real time via chemiluminescence. The addition of 2, 10, and 15-fold excess CysNO to MOF-CuII sites and cysteine (CysH) resulted in catalytic turnover of the active sites and nearly 100% theoretical yield of the NO product. Control experiments without the MOF present did not yield appreciable NO generation. In separate studies the MOF was found to be reusable over successive iterations of CysNO additions without loss of activity. Subsequently, the MOF catalyst was confirmed to remain structurally intact by pXRD and ATR-IR following reaction with CysNO and CysH.
- Harding, Jacqueline L.,Reynolds, Melissa M.
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- Kinetics of oxidation of L-cysteine by trans- And cis-CoIII and FeIII complexes based on α- And γ-diimine schiff base ligands
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Kinetics of oxidation of L-cysteine by Co and Fe complexes based on a- and y-diimine Schiff base ligands were studied in aqueous solution. Pairs of trans and cis isomers of the metal complexes were used in the studies. Kinetic measurements were performed, at 25 °C and constant pH and ionic strength under pseudo-first order condition, in which the concentration of cysteine was around two orders of magnitude greater than that of the metal complex. The observed rate constant was obtained by following the change in absorbance of the reaction mixture with time at a predetermined wavelength. The overall rate constant and order of the reaction with respect to cysteine and metal complex were determined. For both metal ions studied, the oxidation rate constant for the trans isomer was higher than that for the cis isomer. This was attributed to the contribution of the steric factor and the trans effect. The effects of substituents and the nature of the metal ion on the reaction, rate are discussed.
- Abdel-Halim, Hamzeh M.,Abu-Surrah, Adnan S.,Baker, Hutaf M.
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- Reduction of vanadium(IV) to vanadium(III) by cysteine methyl ester in water in the presence of amino polycarboxylates
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The reduction behavior of vanadium(IV) by several thiolate compounds in water was investigated in the presence of amino polycarboxylates. Vanadium(IV) can be reduced by cysteine methyl ester in the presence of edta or cydta to yield [VIII(edta or cydta)(H20)]-, respectively.
- Kanamori, Kan,Kinebuchi, Yoshiko,Michibata, Hitoshi
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- Efficient Amino-Sulfhydryl Stapling on Peptides and Proteins Using Bifunctional NHS-Activated Acrylamides
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Widely used reagents in the peptide functionalization toolbox, Michael acceptors and N-hydroxysuccinimide (NHS) activated esters, are combined in NHS-activated acrylamides for efficient chemoselective amino-sulfhydryl stapling on native peptides and proteins. NHS-activated acrylamides allow for a fast functionalization of N-terminal cysteines (k2=1.54±0.18×103 M?1 s?1) under dilute aqueous conditions, enabling selectivity over other nucleophilic amino acids. Additionally, the versatility of these new bioconjugation handles was demonstrated in the cross-linking of in-chain or C-terminal cysteines with nearby lysine residues. NHS-activated acrylamides are compatible with the use of other cysteine selective reagents, allowing for orthogonal dual-modifications. This strategy was successfully applied to the late-stage functionalization of peptides and proteins with a PEG unit, fluorescent probe, and cytotoxic agent. The level of molecular control offered by NHS-activated acrylamides is expected to promote amino-sulfhydryl stapling technology as a powerful strategy to design functional bioconjugates.
- Silva, Maria J. S. A.,Faustino, Hélio,Coelho, Jaime A. S.,Pinto, Maria V.,Fernandes, Adelaide,Compa?ón, Ismael,Corzana, Francisco,Gasser, Gilles,Gois, Pedro M. P.
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supporting information
p. 10850 - 10857
(2021/04/15)
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- Reduction of an asymmetric Pt(IV) prodrug fac-[Pt(dach)Cl3(OC(=O)CH3)] by biological thiol compounds: kinetic and mechanistic characterizations
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An asymmetric Pt(IV) prodrug fac-[Pt (dach)Cl3(OC(=O)CH3)] (dach = 1,2-diaminocyclohexane) was synthesized, and the reduction of the Pt(IV) prodrug by three biological thiols glutathione (GSH), cysteine (Cys) and homocysteine (Hcy) was investigated by a stopped-flow spectrometer. All the reductions were followed by an overall second-order reaction with first-order in both [Pt(IV)] and [thiol]. The reduction of the Pt(IV) prodrug occurred through a chloride bridge (Pt-Cl-S) mediated two electron transfer process. Therefore, the coordinated chloride possesses a better bridging effect than the oxygen atom from the coordinated –CH3COO? of the Pt(IV) prodrug. A reactivity trend of k′Cys > k′GSH > k′Hcy is found, illustrating that the reactivity is followed by the trend of Cys > GSH > Hcy in pH 7.4 buffer. Graphical abstract: Transition state is formed between the axially coordinated chloride of the platinum(IV) complex and the sulfur atom from the thiol/thiolate group of Cys/Hcy/GSH.[Figure not available: see fulltext.].
- Huo, Shuying,Ma, Dongying,Song, Changying,Sun, Jingjing,Wang, Yafang
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p. 623 - 631
(2021/11/22)
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- Amphiphilic Iodine(III) Reagents for the Lipophilization of Peptides in Water
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We report the functionalization of cysteine residues with lipophilic alkynes bearing a silyl group or an alkyl chain using amphiphilic ethynylbenziodoxolone reagents (EBXs). The reactions were carried out in buffer (pH 6 to 9), without organic co-solvent or removal of oxygen, either at 37 °C or room temperature. The transformation led to a significant increase of peptide lipophilicity and worked for aromatic thiols, homocysteine, cysteine, and peptides containing 4 to 18 amino acids. His6-Cys-Ubiquitin was also alkynylated under physiological conditions. Under acidic conditions, the thioalkynes were converted into thioesters, which could be cleaved in the presence of hydroxylamine.
- Hari, Durga Prasad,Mishra, Abhaya Kumar,Tessier, Romain,Waser, Jerome
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supporting information
p. 17963 - 17968
(2021/07/20)
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- CYSTINE DIAMIDE ANALOGS FOR CYSTINURIA
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This document discloses novel cystine analogs, methods of making cystine analogs, compositions containing cystine analogs and methods of using such analogs for inhibiting cystine stone formation and treatment of cystinuria.
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Paragraph 0023; 0177-0178
(2021/06/22)
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- Enhanced Light-Driven Hydrogen Production by Self-Photosensitized Biohybrid Systems
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Storage of solar energy as hydrogen provides a platform towards decarbonizing our economy. One emerging strategy for the production of solar fuels is to use photocatalytic biohybrid systems that combine the high catalytic activity of non-photosynthetic microorganisms with the high light-harvesting efficiency of metal semiconductor nanoparticles. However, few such systems have been tested for H2 production. We investigated light-driven H2 production by three novel organisms, Desulfovibrio desulfuricans, Citrobacter freundii, and Shewanella oneidensis, self-photosensitized with cadmium sulfide nanoparticles, and compared their performance to Escherichia coli. All biohybrid systems produced H2 from light, with D. desulfuricans-CdS demonstrating the best activity overall and outperforming the other microbial systems even in the absence of a mediator. With this system, H2 was continuously produced for more than 10 days with a specific rate of 36 μmol gdcw?1 h?1. High apparent quantum yields of 23 % and 4 % were obtained, with and without methyl viologen, respectively, exceeding values previously reported.
- Martins, Mónica,Toste, Catarina,Pereira, Inês A. C.
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supporting information
p. 9055 - 9062
(2021/03/15)
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- Biological activity and photocatalytic properties of a naphthyl-imidazo phenanthroline (HNAIP) ligand and its [Ir(ppy)2(HNAIP)]Cl and [Rh(ppy)2(HNAIP)]Cl complexes
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The synthesized 2-(hydroxy-1-naphtyl)imidazo-[4,5-f][1,10]phenanthroline (HNAIP) ligand and its new iridium ([Ir(ppy)2(HNAIP)]Cl) and rhodium ([Rh(ppy)2(HNAIP)]Cl) complexes, being ppy = 2-phenylpiridinate, show cytotoxic effects in SW480 (colon adenocarcinoma) and A549 (epithelial lung adenocarcinoma) cells. They all are cytotoxic in the tested cell lines. HNAIP and [Rh(ppy)2(HNAIP)]+ are the most cytotoxic, whereas [Ir(ppy)2(HNAIP)]+ displays negligible cytotoxicity towards A549 cells and moderate activity towards SW480. The interaction of all three compounds with Bovine Serum Albumin (BSA), L-glutathione reduced (GSH), nicotinamide adenine dinucleotide (NADH) and DNA was studied to explain the differences found in terms of cytotoxicity. None of them are able to interact with BSA, thus excluding bioavailability due to plasma protein interaction as the possible differentiating factor in their biological activity. By contrast, small differences have been observed regarding DNA interaction. In addition, taking advantage of the emission properties of these molecules, they have been visualized in the cytoplasmic region of A549 cells. Inductively coupled plasma mass spectrometry (ICP-MS) experiments show, in turn, that the internalization ability follow the sequence [Rh(ppy)2(HNAIP)]+ > [Ir(ppy)2(HNAIP)]+ > cisplatin. Therefore, it seems clear that the cellular uptake by tumour cells is the key factor affecting the different cytotoxicity of the metal complexes and that this cellular uptake is influenced by the hydrophobicity of the studied complexes. On the other hand, preliminary catalytic experiments performed on the photo-oxidation of GSH and some amino acids such as L-methionine (Met), L-cysteine (Cys) and L-tryptophan (Trp) provide evidence for the photocatalytic activity of the Ir(III) complex in this type of reactions.
- Rubio, Ana R.,Fidalgo, Jairo,Martin-Vargas, Judit,Pérez-Arnaiz, Cristina,Alonso-Torre, Sara R.,Biver, Tarita,Espino, Gustavo,Busto, Natalia,García, Bego?a
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- Redox Activity of Ce(IV)-Substituted Polyoxometalates toward Amino Acids and Peptides
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Redox reactions between polyoxometalates (POMs) and biologically relevant molecules have been virtually unexplored but are important, considering the growing interest in the biological applications of POMs. In this work we give a detailed account on the redox behavior of CeIV-substituted polyoxometalates (CeIV-POMs) toward a range of amino acids and peptides. CeIV-POMs have been shown to act as artificial proteases that promote the selective hydrolysis of peptide bonds. In presence of a protein, a concomitant reduction of CeIV to CeIII ion is frequently observed, leading us to examine the origins of this redox reaction by first using amino acid building blocks as simple models. Among all of the examined amino acids, cysteine (Cys) showed the highest activity in reducing CeIV-POMs to CeIII-POMs, followed by the aromatic amino acids tryptophan (Trp), tyrosine (Tyr), histidine (His), and phenylalanine (Phe). While the redox reaction with Cys afforded the well-defined product cystine, no oxidation products were detected for the Trp, His, Tyr, and Phe amino acids after their reaction with CeIV-POMs, suggesting a radical pathway in which the solvent likely regenerates the amino acid. In general, the rate of redox reactions increased upon increasing the pD, temperature, and ionic strength of the reaction. Moreover, the redox reaction is highly sensitive to the type of polyoxometalate scaffold, as complexation of CeIV to a Keggin (K) or Wells-Dawson (WD) polyoxotungstate anion resulted in a large difference in the rate of redox reaction for both Cys and aromatic amino acids. The reduction of CeIVK was at least 1 order of magnitude faster in comparison to CeIVWD, in accordance with the higher redox potential of CeIVK in comparison to CeIVWD. The reaction of CeIVPOMs with a range of peptides containing redox-active amino acids revealed that the redox reaction is influenced by their coordination mode with CeIV ion, but in all examined peptides the redox reaction is favored in comparison to the hydrolytic cleavage of the peptide bond.
- Abdelhameed, Shorok A. M.,De Azambuja, Francisco,Parac-Vogt, Tatjana N.,Vandebroek, Laurens
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supporting information
(2020/07/06)
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- Electrochemical Evidence in Mechanism of Toxicity of Mefenamic Acid Overdose in the Presence of Glutathione and N-Acetyl-L-Cysteine
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In this study, the electrochemical oxidation of mefenamic acid was investigated in the presence of glutathione and N-acetyl-L-cysteine. The results revealed that the mefenamic acid was involved in a catalytic reaction with glutathione and N-acetyl-L-cysteine. This investigation presents some electrochemical evidence for the mechanism of action of these compounds in mefenamic acid poisoning.
- Amani, Ameneh,Amooshahi, Parvaneh,Khazalpour, Sadegh
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- Scalable synthesis of orthogonally protected β-methyllanthionines by indium(III)-mediated ring opening of aziridines
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Lantibiotics are a class of peptide antibiotics with activity against most Gram-positive bacteria. Lanthionine (Lan) and β-MeLan are unusual thioether-bridged, non-proteinogenic amino acids, which are characteristic features of lantibiotics. In this paper, we report the facile stereoselective synthesis of β-methyllanthionines with orthogonal protection by nucleophilic ring opening of aziridines. This method leads to an expedient access to β-methyllanthionines and allows production of over 30 g of β-methyllanthionine in a single batch.
- Li, Ziran,Gentry, Zachary,Murphy, Brennan,Vannieuwenhze, Michael S.
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supporting information
p. 2200 - 2203
(2019/03/26)
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- Biomimetic catalytic oxidative coupling of thiols using thiolate-bridged dinuclear metal complexes containing iron in water under mild conditions
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A green and efficient approach to disulfides via oxidative coupling of thiols was developed by adopting a biomimetic thiolate-bridged iron-ruthenium complex as the catalyst. Using environmentally friendly oxygen as the oxidant, a wide range of thiols including biologically important molecules can be smoothly converted into corresponding disulfides in water. Notably, two potential intermediate species were successfully isolated and unambiguously characterized, which is essential to reveal the detailed mechanism of this transformation. This catalytic system represents a rare and desired heteronuclear bimetallic scaffold for understanding the biological process of S-S bond formation from the viewpoint of bioinspired catalysis.
- Zhang, Yahui,Yang, Dawei,Li, Ying,Zhao, Xiangyu,Wang, Baomin,Qu, Jingping
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p. 6492 - 6502
(2019/11/20)
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- An l-cysteine-mediated iodide-catalyzed reaction for the detection of I-
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In this study, a highly selective and eco-friendly fluorescent sensor consisting of upconversion (UCNPs) and gold nanoparticles (AuNPs) was developed for the detection of iodide (I-). The negatively charged AuNPs were able to electrostatically adsorb on the positively charged UCNPs, leading to the fluorescence quenching of the UCNPs. In the presence of l-cysteine, AuNPs were released from the surface of the UCNPs and aggregated due to the Au-S interactions that occurred between the AuNPs and l-cysteine, which resulted in the fluorescence recovery of the UCNPs. Upon the addition of I-, the fluorescence of the UCNPs was gradually quenched meaning that I- catalyzes the oxidation of l-cysteine, preventing the aggregation of AuNPs and forming a fluorescence resonance energy transfer system. The I--catalyzed oxidation reaction provides a method for the l-cysteine-triggered sensor to detect I-, using l-cysteine to modulate the fluorescence signal in an eco-friendly manner. Based on the above special detection strategies, this sensor has excellent selectivity for I- even in a complex matrix such as urine, which is much better than most assays for I-. Under the optimal conditions, the sensor allows the quantitative analysis of I- with a detection limit of 55 nM. The high selectivity, sensitivity and environmental friendliness of the sensor proves that it has the potential for the detection of I- in actual samples. Most importantly, the excellent results of the sensor for the detection of I- in urine prove that the probe can be used as an ideal tool in clinic diagnoses.
- He, Kaili,Chen, Hongyu,Wu, Cuiyan,Liu, Meiling,Zhang, Youyu
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p. 1398 - 1403
(2019/01/21)
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- Crystal-facet-dependent denitrosylation: Modulation of NO release from S-nitrosothiols by Cu2O polymorphs
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Nitric oxide (NO), a gaseous small molecule generated by the nitric oxide synthase (NOS) enzymes, plays key roles in signal transduction. The thiol groups present in many proteins and small molecules undergo nitrosylation to form the corresponding S-nitrosothiols. The release of NO from S-nitrosothiols is a key strategy to maintain the NO levels in biological systems. However, the controlled release of NO from the nitrosylated compounds at physiological pH remains a challenge. In this paper, we describe the synthesis and NO releasing ability of Cu2O nanomaterials and provide the first experimental evidence that the nanocrystals having different crystal facets within the same crystal system exhibit different activities toward S-nitrosothiols. We used various imaging techniques and time-dependent spectroscopic measurements to understand the nature of catalytically active species involved in the surface reactions. The denitrosylation reactions by Cu2O can be carried out multiple times without affecting the catalytic activity.
- Ghosh, Sourav,Roy, Punarbasu,Prasad, Sanjay,Mugesh, Govindasamy
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p. 5308 - 5318
(2019/05/29)
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- Iterative synthetic strategies and gene deletant experiments enable the first identification of polysulfides in: Saccharomyces cerevisiae
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New evidence on the role of H2S as a gasotransmitter suggests that the true signalling effectors are polysulfides. Both oxidized polysulfides and hydropolysulfides were synthesized and their presence in S. cerevisiae was observed for the first time. A single gene-deletant approach allowed observation of the modulation of polysulfide species and levels.
- Pilkington, Lisa I.,Deed, Rebecca C.,Parish-Virtue, Katie,Huang, Chien-Wei,Walker, Michelle E.,Jiranek, Vladimir,Barker, David,Fedrizzi, Bruno
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supporting information
p. 8868 - 8871
(2019/08/01)
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- An Organodiselenide with Dual Mimic Function of Sulfhydryl Oxidases and Glutathione Peroxidases: Aerial Oxidation of Organothiols to Organodisulfides
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A novel organodiselenide, which mimics sulfhydryl oxidases and glutathione peroxidase (GPx) enzymes for oxidation of thiols by oxygen and hydrogen peroxide, respectively, into disulfides has been presented. The developed catalyst oxidizes an array of organothiols into respective disulfides in practical yields by using aerial O2 to avoid any reagents/additives, base, and light source. The synthesized diselenide also catalyzes the reduction of hydrogen peroxide into water by following the GPx enzymatic catalytic cycle with a reduction rate of 49.65 ± 3.7 μM·min-1.
- Rathore, Vandana,Upadhyay, Aditya,Kumar, Sangit
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supporting information
p. 6274 - 6278
(2018/10/05)
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- Selective Photooxidation of Sulfides Catalyzed by Bis-cyclometalated IrIII Photosensitizers Bearing 2,2′-Dipyridylamine-Based Ligands
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A new family of heteroleptic bis-cyclometalated IrIII complexes with formula [Ir((Formula presented.))2((Formula presented.))]Cl ((Formula presented.) =2-phenylpyridinate and (Formula presented.) =2,2′-dipyridylamine or N-benzylated 2,2′-dipyridylamines, were synthesized, characterized, and successfully used as photosensitizers in the catalytic photooxidation of an array of dialkyl, dibenzyl, alkyl aryl, and diaryl sulfides, as well as sulfur-containing amino acids. Furthermore, the reactions proceeded with optimal chemoselectivity, and atom economy under mild conditions. Experimental observations support a dual mechanism in which singlet oxygen and superoxide are the actual oxidants.
- Vaquero, Mónica,Ruiz-Riaguas, Alba,Martínez-Alonso, Marta,Jalón, Félix A.,Manzano, Blanca R.,Rodríguez, Ana M.,García-Herbosa, Gabriel,Carbayo, Arancha,García, Bego?a,Espino, Gustavo
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supporting information
p. 10662 - 10671
(2018/07/31)
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- Ferroelectric Perovskite Oxide@TiO2 Nanorod Heterostructures: Preparation, Characterization, and Application as a Platform for Photoelectrochemical Bioanalysis
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This work reports the first synthesis and characterization of a ferroelectric perovskite oxide-based heterostructure as well as its application for photoelectrochemical (PEC) bioanalytical purposes. Specifically, exemplified by [KNbO3]1-x[BaNi1/2Nb1/2O3-δ]x (KBNNO), the ferroelectric perovskite oxides were prepared by solid-state synthesis, while the TiO2 nanorod (NR) arrays were obtained via a hydrothermal method. Using the technique of pulsed laser deposition (PLD), KBNNO were then deposited on TiO2 NRs to form KBNNO@TiO2 NR heterostructures. Various characterization techniques were applied to reveal compositional and structural information on the as-fabricated sample, and favorable alignment existed between the two components as displayed by the PEC test. In the detection of l-cysteine, the as-fabricated KBNNO@TiO2 NRs demonstrated good performance in terms of sensitivity and selectivity. This work revealed the potential of ferroelectric perovskite oxide and its heterostructures for innovative PEC bioanalytical applications, and we hope it will generate more interest in the development of various ferroelectrics-based heterostructures for advanced PEC bioanalysis.
- Yu, Li-Min,Zhu, Yuan-Cheng,Liu, Yi-Li,Qu, Peng,Xu, Mao-Tian,Shen, Qi,Zhao, Wei-Wei
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p. 10803 - 10811
(2018/09/12)
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- Dialkyl Dicyanofumarates as Oxidizing Reagents for the Conversion of Thiols into Disulfides and Selenols into Diselenides
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Aliphatic and aromatic thiols react smoothly with dialkyl dicyanofumarates in CH2Cl2 at room temperature to give the corresponding disulfides in excellent yields. Aliphatic 1,2-, 1,3-, and 1,4-dithiols afford cyclic disulfides. Analogous reaction courses were observed for selenols, and the required diselenides also formed in nearly quantitative yields. In all of the reactions, dialkyl dicyanosuccinates formed as 1:1 mixtures of diastereoisomers as the only other product. Cysteamine (2-mercaptoethylamine) behaved differently; the Michael addition of the primary amine group led to the complete consumption of the dicyanofumarate, and the formation of the disulfide containing an enamine moiety occurred without the formation of dicyanosuccinate.
- Mlostoń, Grzegorz,Capperucci, Antonella,Tanini, Damiano,Hamera-Fa?dyga, Ró?a,Heimgartner, Heinz
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p. 6831 - 6839
(2017/09/11)
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- Kinetics and thermodynamics of oxidation mediated reaction in L-cysteine and its methyl and ethyl esters in dimethyl sulfoxide-d6 by NMR spectroscopy
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L-Cysteine (L-Cys), L-Cysteine methyl ester (L-CysME) or L-Cysteine ethyl ester (L-CysEE), when dissolved in dimethyl sulfoxide, undergoes an oxidation process. This process is slow enough and leads to nuclear magnetic resonance (NMR) spectral changes that could be monitored in real time. The oxidation mediated transition is modeled as a pseudo-first order kinetics and the thermodynamic parameters are estimated using the Eyring's formulation. L-Cysteine and their esters are often used as biological models due to the remarkable thiol group that can be found in different oxidation states. This oxidation mediated transition is due to the combination of thiol oxidation to a disulfide followed by solvent-induced effects may be relevant in designing cysteine-based molecular models.
- Dougherty, Ryan J.,Singh, Jaideep,Krishnan
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p. 196 - 200
(2016/11/29)
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- 3,6-Di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz) mediated metal-free mild oxidation of thiols to disulfides in aqueous medium
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Thiols are efficiently oxidized to disulfides (RSSR) in the presence of 3,6-di(pyridin-2-yl)-1,2,4,5-tetrazine (pytz) in aqueous medium, as well as in the absence of a solvent under mild and metal-free conditions. A broad range of alkyl, aryl and heterocyclic symmetrical disulfides can be easily obtained in almost quantitative yields. The X-ray single crystal structure of 2-aminocyclopent-1-ene-1-carbothioic dithioperoxyanhydride (disulfide obtained from 2-aminocyclopentene-1-dithiocarboxylic acid, ACDA) is reported. The reaction mechanism has been studied thoroughly. It is shown that the reaction proceeds through the formation of an organosulphur radical. Pytz interacts with thiol to accept one electron and produces an organosulphur radical. Pytz ultimately accepts two electrons to form H2pytz and is capable of oxidizing 2 equivalents of thiols.
- Samanta, Suvendu,Ray, Shounak,Ghosh, Abhisek Brata,Biswas, Papu
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p. 39356 - 39363
(2016/06/01)
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- Substrate and pH-Dependent Kinetic Profile of 3-Mercaptopropionate Dioxygenase from Pseudomonas aeruginosa
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Thiol dioxygenases catalyze the synthesis of sulfinic acids in a range of organisms from bacteria to mammals. A thiol dioxygenase from the bacterium Pseudomonas aeruginosa oxidizes both 3-mercaptopropionic acid and cysteine, with a ～70 fold preference for 3-mercaptopropionic acid over all pHs. This substrate reactivity is widened compared to other thiol dioxygenases and was exploited in this investigation of the residues important for activity. A simple model incorporating two protonation events was used to fit profiles of the Michaelis-Menten parameters determined at different pH values for both substrates. The pKs determined using plots of kcat/Km differ at low pH, but not in a way easily attributable to protonation of the substrate alone and share a common value at higher pH. Plots of kcat versus pH are also quite different at low pH showing the monoprotonated ES complexes with 3-mercaptopropionic acid and cysteine have different pKs. At higher pH, kcat decreases sigmoidally with a similar pK regardless of substrate. Loss of reactivity at high pH is attributed to deprotonation of tyrosine 159 and its influence on dioxygen binding. A mechanism is proposed by which deprotonation of tyrosine 159 both blocks oxygen binding and concomitantly promotes cystine formation. Finally, the role of tyrosine 159 was further probed by production of a G95C variant that is able to form a cysteine-tyrosine crosslink homologous to that found in mammalian cysteine dioxygenases. Activity of this variant is severely impaired. Crystallography shows that when un-crosslinked, the cysteine thiol excludes tyrosine 159 from its native position, while kinetic analysis shows that the thioether bond impairs reactivity of the crosslinked form.
- Fellner, Matthias,Aloi, Sekotilani,Tchesnokov, Egor P.,Wilbanks, Sigurd M.,Jameson, Guy N.L.
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p. 1362 - 1371
(2016/03/19)
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- Electropolymerization of cobalt tetraamino-phthalocyanine at reduced graphene oxide for electrochemical determination of cysteine and hydrazine
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We describe a simple and elegant electropolymerization method to prepare highly stable tetraamino functionalized cobalt phthalocyanine (pTACoPc) at electrochemically reduced graphene oxide (RGO). The described method efficiently bridges the excellent physicochemical properties of RGO with the rich redox chemistry of TACoPc. Graphene oxide was electrochemically reduced to RGO at the electrode surface along with concominent electropolymerization of TACoPc. The electrochemical studies showed that RGO on pTACoP/GCE increased effective surface area, reduced charge transfer resistance and enhanced electrochemical signal. The RGO-pTACoPc film modified electrode exhibits excellent electrocatalytic ability to oxidize cysteine and hydrazine. To determine cysteine, the RGO-pTACoPc sensor displayed a linear concentration range of 50 nM to 2.0 μM, detection limit of 18.5 nM and sensitivity of 10.19 nA nM-1 cm-2. Besides, the sensor displayed a linear concentration range of 50 nM to 2.6 μM, detection limit of 10 nM and sensitivity of 1.62 nA nM-1 cm-2 to determine hydrazine. The electrocatalytic ability of RGO-pTACoPc shows better performance over other cobalt phthalocyanine derivatives. Furthermore, the described sensor exhibited long-term storage stability, good repeatability and reproducibility. The practical applicability of the sensor has been assessed in biological and water samples.
- Mani, Veerappan,Huang, Sheng-Tung,Devasenathipathy, Rajkumar,Yang, Thomas C. K.
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p. 38463 - 38469
(2016/05/19)
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- Rethinking Cysteine Protective Groups: S-Alkylsulfonyl-l-Cysteines for Chemoselective Disulfide Formation
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The ability to reversibly cross-link proteins and peptides grants the amino acid cysteine its unique role in nature as well as in peptide chemistry. We report a novel class of S-alkylsulfonyl-l-cysteines and N-carboxy anhydrides (NCA) thereof for peptide synthesis. The S-alkylsulfonyl group is stable against amines and thus enables its use under Fmoc chemistry conditions and the controlled polymerization of the corresponding NCAs yielding well-defined homo- as well as block co-polymers. Yet, thiols react immediately with the S-alkylsulfonyl group forming asymmetric disulfides. Therefore, we introduce the first reactive cysteine derivative for efficient and chemoselective disulfide formation in synthetic polypeptides, thus bypassing additional protective group cleavage steps.
- Sch?fer, Olga,Huesmann, David,Muhl, Christian,Barz, Matthias
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supporting information
p. 18085 - 18091
(2016/12/16)
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- The Anticancer Activity of Organotelluranes: Potential Role in Integrin Inactivation
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Organic TeIV compounds (organotelluranes) differing in their labile ligands exhibited anti-integrin activities in vitro and anti-metastatic properties in vivo. They underwent ligand substitution with l-cysteine, as a thiol model compound. Unlike inorganic TeIV compounds, the organotelluranes did not form a stable complex with cysteine, but rather immediately oxidized it. The organotelluranes inhibited integrin functions, such as adhesion, migration, and metalloproteinase secretion mediation in B16F10 murine melanoma cells. In comparison, a reduced derivative with no labile ligand inhibited adhesion of B16F10 cells to a significantly lower extent, thus pointing to the importance of the labile ligands of the TeIV atom. One of the organotelluranes inhibited circulating cancer cells in vivo, possibly by integrin inhibition. Our results extend the current knowledge on the reactivity and mechanism of organotelluranes with different labile ligands and highlight their clinical potential.
- Silberman, Alon,Kalechman, Yona,Hirsch, Shira,Erlich, Ziv,Sredni, Benjamin,Albeck, Amnon
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p. 918 - 927
(2016/05/24)
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- Fused Selenazolinium Salt Derivatives with a Se-N+ Bond: Preparation and Properties
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Convenient methods for the preparation of stable, fused selenazolinium salt systems with a Se-N+ bond have been developed. The mechanism for the formation of the selenazole cycle was investigated in detail by conducting multinuclear NMR experiments. The ability of these compounds to form stable inner salts was demonstrated. We have shown the glutathione peroxidase (GPx) like properties of selenazolopyridinium salts by oxidizing sulfur-containing natural amino acids, as well as aromatic and heteroaromatic aldehydes. The molecular structures of most of the compounds were confirmed by X-ray diffraction studies.
- Arsenyan, Pavel,Vasiljeva, Jelena,Belyakov, Sergey,Liepinsh, Edvards,Petrova, Marina
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supporting information
p. 5842 - 5855
(2015/09/15)
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- Oxidation of thiols to disulfides by dioxygen catalyzed by a bioinspired organocatalyst
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2,3-Dihydro-2,2,2-triphenylphenanthro[9,10-d]-1,3,2-λ5-oxazaphosphole serves as good catalyst for the oxidation of thiophenol, cysteine and glutathione to their disulfides by molecular oxygen. The kinetics of the reactions unveiled an overall second order rate equation for all reactions and pure dioxygen chemistry for all three substrates. The formation of an unstable hydroperoxide from the catalyst is assumed to be a key step during the reaction.
- Bagi, Nárcisz,Kaizer, József,Speier, Gábor
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p. 45983 - 45986
(2015/06/08)
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- Bovine serum albumin triggered waste-free aerobic oxidative coupling of thiols into disulphides on water: An extended synthesis of bioactive dithiobis(phenylene)bis(benzylideneimine) via sequential oxidative coupling-condensation reactions in one pot from aminothiophenol and benzaldehyde
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Bovine serum albumin (BSA) has been explored for aerobic oxidative coupling of thiols (aromatic, heterocyclic as well as aliphatic) "on water" towards formation of disulphides (SS) without using any metal/non-metal complexes, bases and additives, which renders the process environmentally benign and economically attractive with good recyclability (up to four cycles). The developed green protocol was further extended for synthesis of diallyldisulphide (DADS), an important constituent of natural occurring allicin. Among various synthesized disulphides, bis(2-aminophenyl)disulphide, obtained by oxidative coupling of 2-aminothiophenol in BSA, was further utilized for condensation with benzaldehyde in the same pot thus enabling easy access to bioactive dithiobis(phenylene)bis(benzyldeneimine). This is the first example of BSA catalysed sequential (oxidation/condensation) reaction where one SS and two CN bonds are formed solely "on water."
- Saima,Lavekar, Aditya G.,Kumar, Rajesh,Sinha, Arun K.
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p. 113 - 123
(2015/04/14)
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- A novel gold nanoparticle decorated nanocrystalline zeolite based electrochemical sensor for the nanomolar simultaneous detection of cysteine and glutathione
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In this work, highly dispersed gold nanoparticle decorated nanocrystalline zeolite was synthesized by the electrostatic interaction between the functionalized gold nanoparticles and functionalized nanocrystalline zeolite. An electrochemical sensor based on the gold nanoparticle decorated nanocrystalline zeolite was developed for the nanomolar simultaneous detection of cysteine and glutathione with high sensitivity, selectivity, and remarkably low detection limit. A wide linear range was obtained from 2 nM to 800 μM and 3 nM to 800 μM with a limit of detection of 0.3 nM and 0.6 nM for cysteine and glutathione, respectively. The analytical performance of the developed sensor was demonstrated in the determination of cysteine and glutathione in commercial pharmaceutical preparations with satisfactory results even in the presence of several amino acids. The proposed methodology provides promising application in clinical diagnostic and drug analysis.
- Kaur, Balwinder,Srivastava, Rajendra,Satpati, Biswarup
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p. 95028 - 95037
(2015/11/24)
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- Design, Synthesis, and Cardioprotective Effects of N-Mercapto-Based Hydrogen Sulfide Donors
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Hydrogen sulfide (H2S) is a signaling molecule which plays regulatory roles in many physiological and/or pathological processes. Therefore, regulation of H2S levels could have great potential therapeutic value. In this work, we report the design, synthesis, and evaluation of a class of N-mercapto (N-SH)-based H2S donors. Thirty-three donors were synthesized and tested. Our results indicated that controllable H2S release from these donors could be achieved upon structural modifications. Selected donors (NSHD-1, NSHD-2, and NSHD-6) were tested in cellular models of oxidative damage and showed significant cytoprotective effects. Moreover, NSHD-1 and NSHD-2 were also found to exhibit potent protective effects in a murine model of myocardial ischemia reperfusion (MI/R) injury.
- Zhao, Yu,Yang, Chuntao,Organ, Chelsea,Li, Zhen,Bhushan, Shashi,Otsuka, Hiro,Pacheco, Armando,Kang, Jianming,Aguilar, Hector C.,Lefer, David J.,Xian, Ming
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p. 7501 - 7511
(2015/10/05)
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- Nitric oxide and nitroxyl products from the reaction of L -cysteine with trans-[RuNO(NH3)4P(OEt)3](PF6)3
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The reaction between the trans-[RuNO(NH3)4P(OEt)3](PF6)3 and L-cysteine (RS-) was studied over a pH range of 2.0-7.4. In this reaction, the concentrations of NO and HNO produced varied as a function of the pH of the solution. The first step of this reaction proceeded quickly [k1 = (3.5 ± 0.3) × 103 M-1 s-1, pH = 3.5, 25 C] and resulted in the formation of trans-[Ru(NH3)4P(OEt)3N(O)SR]2+, which dissociated to yield trans-[Ru(NH3)4P(OEt)3NO·]2+ and RS·. However, trans-[Ru(NH3)4P(OEt)3N(O)SR]n-1 can react with a second L-cysteine, yielding trans-[Ru(NH3)4P(OEt)3N(O)(SR)2]+ [k2 = (3.6 ± 0.1) M-1 s-1, pH = 3.5, 25 C]. Therefore, the trans-[Ru(NH3)4P(OEt)3NO·]2+ species released NO and the trans-[Ru(NH3)4P(OEt)3N(O)(SR)2]n-2 species released HNO.
- Pereira, José Clayston Melo,Souza, Maykon Lima,Franco, Douglas Wagner
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p. 1005 - 1011
(2015/03/04)
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- Flavin-catalyzed aerobic oxidation of sulfides and thiols with formic acid/triethylamine
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An efficient and practical catalytic method for the aerobic oxidative transformation of sulfides into sulfoxides, and thiols into disulfides with formic acid/TEA in the presence of a new, readily available, and stable flavin catalyst 5d is described. This journal is the Partner Organisations 2014.
- Murahashi, Shun-Ichi,Zhang, Dazhi,Iida, Hiroki,Miyawaki, Toshio,Uenaka, Masaaki,Murano, Kenji,Meguro, Kanji
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supporting information
p. 10295 - 10298
(2014/08/18)
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- Amino acid and water-driven tunable green protocol to access S-S/C-S bonds via aerobic oxidative coupling and hydrothiolation
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A green methodology utilizing a natural supplement such as l-arginine in conjunction with water and oxygen led to oxidative coupling of thiols into disulfides (S-S bond) whereas thiol-yne coupling to access vinyl sulfides (C-S bond) was facilitated in a nitrogen atmosphere. The tunable protocol offers several advantages such as low catalyst loading, high yields, clean reaction, no over-oxidation of the S-S bond besides being metal/base/waste-free. The synthesis of ubiquitous cystine and glutathione disulfide in the same catalytic system is an added advantage and the catalytic system has been recycled up to seven times. the Partner Organisations 2014.
- Shard, Amit,Kumar, Rajesh,Saima,Sharma, Nidhi,Sinha, Arun K.
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p. 33399 - 33407
(2014/08/18)
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- Natural low-molecular mass organic compounds with oxidase activity as organocatalysts
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Organocatalysts, low-molecular mass organic compounds composed of nonmetallic elements, are often used in organic synthesis, but there have been no reports of organocatalysts of biological origin that function in vivo. Here, we report that actinorhodin (ACT), a natural product derived from Streptomyces coelicolor A3(2), acts as a biocatalyst.We purified ACT and assayed its catalytic activity in the oxidation of L-ascorbic acid and L-cysteine as substrates by analytical methods for enzymes. Our findings were as follows: (i ) oxidation reactions producing H2O2 proceeded upon addition of ACT to the reaction mixture; (ii ) 5ACT was not consumed during the reactions; and (iii ) a small amount (catalytic amount) of 6ACT consumed an excess amount of the substrates. Even at room temperature, atmospheric pressure, and neutral pH, 7ACT showed catalytic activity in aqueous solution, and ACT exhibited substrate specificity in the oxidation reactions. These findings reveal ACT to be an organocatalyst. ACT is known to show antibiotic activity, but its mechanism of action remains unknown. On the basis of our results, we propose that 8ACT kills bacteria by catalyzing the production of toxic levels of H2O2. We also screened various other natural products of bacterial, plant, 9and animal origins and found that several of the compounds exhibited catalytic activity, 10suggesting that living organisms produce and use these compounds as biocatalysts in nature.
- Nishiyamaa, Tatsuya,Hashimotoa, Yoshiteru,Kusakabeb, Hitoshi,Kumanoa, Takuto,Kobayashia, Michihiko
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p. 17152 - 17157
(2015/04/16)
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- Nitrite reduction mediated by the complex RuIII(EDTA)
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Reported is the first example of a ruthenium(iii)-complex, Ru III(EDTA) (EDTA4- = ethylenediaminetetraacetate), that mediates O-atom transfer from nitrite to the biological thiols cysteine and glutathione, leading to the formation of [RuIII(EDTA)(NO +)]0. However, at pH below 5.0, the coordinated nitrite ion in the [RuIII(EDTA)(NO2)]2- complex undergoes proton-assisted decomposition, resulting in the formation of a [RuIII(EDTA)(NO+)]0 species. the Partner Organisations 2014.
- Chatterjee, Debabrata,Shome, Sanchari,Jaiswal, Namita,Banerjee, Priyabrata
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p. 13596 - 13600
(2014/11/08)
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- S-aroylthiooximes: A facile route to hydrogen sulfide releasing compounds with structure-dependent release kinetics
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We report the facile preparation of a family of S-aroylthiooxime (SATO) H2S donors, which are synthesized via a click reaction analogous to oxime formation between S-aroylthiohydroxylamines (SATHAs) and aldehydes or ketones. Analysis of cysteine-triggered H2S release revealed structure-dependent release kinetics with half-lives from 8-82 min by substitution of the SATHA ring. The pseudo-first-order rate constants of substituted SATOs fit standard linear free energy relationships (p = 1.05), demonstrating a significant sensitivity to electronic effects.
- Foster, Jeffrey C.,Powell, Chadwick R.,Radzinski, Scott C.,Matson, John B.
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supporting information
p. 1558 - 1561
(2014/04/17)
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- (NH 4) 6Mo 7O 34·4H 2O as an efficient, selective, and reusable catalyst for the oxidation of thiols to disulfides using potassium bromate
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Ammonium molybdate, (NH 4) 6Mo 7O 34·4H 2O, is found to be an efficient and selective catalyst for the oxidation of thiols to corresponding disulfides using potassium bromate in aqueous acetonitrile as the solvent. Among various solvents tested, CH3CN/H2O showed better results in terms of the reaction yield and rate. In the absence of (NH4)6Mo 7O24·4H2O, the oxidation reaction is not selective for the formation of disulfides. The catalyst can be easily recovered after completion of the reaction and reused without any significant loss of its activity. [Supplementary materials are available for this article. Go to the publisher's online edition of Phosphorus, Sulfer, and Silicon and the Related Elements for the following free supplemental files: Additional text and figures.]
- Bayraq, Samad Shoghpour,Nikseresht, Ahmad,Khosravi, Iman
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supporting information
p. 1236 - 1243
(2013/09/23)
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- Thiol-dependent recovery of catalytic activity from oxidized protein tyrosine phosphatases
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Protein tyrosine phosphatases (PTPs) play an important role in the regulation of mammalian signal transduction. During some cell signaling processes, the generation of endogenous hydrogen peroxide inactivates selected PTPs via oxidation of the enzyme's catalytic cysteine thiolate group. Importantly, low-molecular weight and protein thiols in the cell have the potential to regenerate the catalytically active PTPs. Here we examined the recovery of catalytic activity from two oxidatively inactivated PTPs (PTP1B and SHP-2) by various low-molecular weight thiols and the enzyme thioredoxin. All monothiols examined regenerated the catalytic activity of oxidized PTP1B, with apparent rate constants that varied by a factor of approximately 8. In general, molecules bearing low-pKa thiol groups were particularly effective. The biological thiol glutathione repaired oxidized PTP1B with an apparent second-order rate constant of 0.023 ± 0.004 M-1 s -1, while the dithiol dithiothreitol (DTT) displayed an apparent second-order rate constant of 0.325 ± 0.007 M-1 s -1. The enzyme thioredoxin regenerated the catalytic activity of oxidized PTP1B at a substantially faster rate than DTT. Thioredoxin (2 μM) converted oxidized PTP1B to the active form with an observed rate constant of 1.4 × 10-3 s-1. The rates at which these agents regenerated oxidized PTP1B followed the order Trx > DTT > GSHand comparable values observed at 2 μM Trx, 4 mM DTT, and 60 mM GSH. Various disulfides that are byproducts of the reactivation process did not inactivate native PTP1B at concentrations of 1-20 mM. The common biochemical reducing agent tris(2-carboxyethyl)phosphine regenerates enzymatic activity from oxidized PTP1B somewhat faster than the thiol-based reagents, with a rate constant of 1.5 ± 0.5 M-1 s-1. We observed profound kinetic differences between the thiol-dependent regeneration of activity from oxidized PTP1B and SHP-2, highlighting the potential for structural differences in various oxidized PTPs to play a significant role in the rates at which low-molecular weight thiols and thiol-containing enzymes such as thioredoxin and glutaredoxin return catalytic activity to these enzymes during cell signaling events.
- Parsons, Zachary D.,Gates, Kent S.
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p. 6412 - 6423
(2013/10/01)
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- Nitrite reduction mediated by heme models. Routes to NO and HNO?
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The water-soluble ferriheme model FeIII(TPPS) mediates oxygen atom transfer from inorganic nitrite to a water-soluble phosphine (tppts), dimethyl sulfide, and the biological thiols cysteine (CysSH) and glutathione (GSH). The products with the latter reductant are the respective sulfenic acids CysS(O)H and GS(O)H, although these reactive intermediates are rapidly trapped by reaction with excess thiol. The nitrosyl complex FeII(TPPS)(NO) is the dominant iron species while excess substrate is present. However, in slightly acidic media (pH ≈ 6), the system does not terminate at this very stable ferrous nitrosyl. Instead, it displays a matrix of redox transformations linking spontaneous regeneration of FeIII(TPPS) to the formation of both N2O and NO. Electrochemical sensor and trapping experiments demonstrate that HNO (nitroxyl) is formed, at least when tppts is the reductant. HNO is the likely predecessor of the N2O. A key pathway to NO formation is nitrite reduction by FeII(TPPS), and the kinetics of this iron-mediated transformation are described. Given that inorganic nitrite has protective roles during ischemia/reperfusion (I/R) injury to organs, attributed in part to NO formation, and that HNO may also reduce net damage from I/R, the present studies are relevant to potential mechanisms of such nitrite protection.
- Heinecke, Julie L.,Khin, Chosu,Pereira, Jose Clayston Melo,Suárez, Sebastián A.,Iretskii, Alexei V.,Doctorovich, Fabio,Ford, Peter C.
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supporting information
p. 4007 - 4017
(2013/04/23)
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