- Oxyhalogen-sulfur chemistry - Kinetics and mechanism of the oxidation of cysteamine by acidic iodate and iodine
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The oxidation of cysteamine by iodate and aqueous iodine has been studied in neutral to mildly acidic conditions. The reaction is relatively slow and is heavily dependent on acid concentration. The reaction dynamics are complex and display clock behavior, transient iodine production, and even oligooscillatory production of iodine, depending upon initial conditions. The oxidation product was the cysteamine dimer (cystamine), with no further oxidation observed past this product. The stoichiometry of the reaction was deduced to be IO 3- + 6H2NCH2CH2SH → I- + 3H2NCH2CH2S-SCH 2CH2NH2 + 3H2O in excess cysteamine conditions, whereas in excess iodate the stoichiometry of the reaction is 2IO3- + 10H2NCH2CH2SH → I2 + 5H2NCH2CH2S-SCH 2CH2NH2 + 6H2O. The stoichiometry of the oxidation of cysteamine by aqueous iodine was deduced to be I2 + 2H2NCH2CH2SH → 2I- + H 2NCH2CH2S-SCH2CH2NH 2 + 2H+. The bimolecular rate constant for the oxidation of cysteamine by iodine was experimentally evaluated as 2.7 (mol L -1)-1 s-1. The whole reaction scheme was satisfactorily modeled by a network of 14 elementary reactions.
- Chanakira, Alice,Chikwana, Edward,Peyton, David H.,Simoyi, Reuben H.
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- Oxidation of aminothiols by molecular oxygen catalyzed by copper ions. Stoichiometry of the reaction
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Catalysis of oxidation of aminothiols by copper ions was studied depending on the structure of aminothiols and pH of the medium. The catalytic reaction proceeds in the inner coordination sphere of Cu+. At pH 7-9, oxidation of bidentate aminothiols involves reduction of O2 to H 2O2. At pH 9-13, oxidation of chelating aminothiols is accompanied by reduction of O2 to H2O, whereas oxidation of weak-chelating aminothiols still proceeds by the former mechanism. In this process, the thiolate anions coordinated to the Cu+ ions lose one electron each and are oxidized to amino disulfides, which go from the inner sphere of the Cu+ complex into a solution. Procedures developed for the determination of amino disulfides, the chemiluminescence determination of H2O2 in the presence of aminothiols as luminescence quenchers, and a modified polarographic procedure for the determination of O2 allowed us to establish that oxidation of aminothiols is not accompanied by catalytic decomposition of H2O2 that formed.
- Bagiyan,Koroleva,Soroka,Ufimtsev
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- Peroxidase-Catalyzed Chemiluminescence-Delay of Luminol for Determination of Traces of Copper(II)
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Delayed chemilumunescence (CL) was observed in the copper(II)-catalyzed oxidation of cysteamine with oxygen in the presence of horseradish peroxidase (HRP) and luminol.After preferential catalytic oxidation of cysteamine by both Cu(II) and HRP, a HRP-catalyzed luminol CL reaction was subsequently commenced with hydrogen peroxide accumulated from the catalytic oxidation.Thus, a delay time from the reaction initiation to a sharp flash of CL was observed.The HRP-catalyzed CL-delay of luminol was applied to the determination of Cu(II).The delay time was linearly correlated with the Cu(II) concentration over the range from the detection limit of 5.0*10-9 to 1.5*10-5 M.The detection limit of the present method is a factor of 30 times better than that of the conventional luminol CL method.The relative standard deviation of the delay time in five succesive experiments was 3.2percent at 1.0*10-7 M of Cu(II).The present method was highly sensitive compared to the conventional luminol CL method.
- Katayama, Atsushi,Kamidate, Tamio,Watanabe, Hiroto
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- Characterization of the nonheme iron center of cysteamine dioxygenase and its interaction with substrates
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Cysteamine dioxygenase (ADO) has been reported to exhibit two distinct biological functions with a nonheme iron center. It catalyzes oxidation of both cysteamine in sulfur metabolism and N-terminal cysteine-containing proteins or peptides, such as regulator of G protein signaling 5 (RGS5). It thereby preserves oxygen homeostasis in a variety of physiological processes. However, little is known about its catalytic center and how it interacts with these two types of primary substrates in addition to O2. Here, using electron paramagnetic resonance (EPR), M?ssbauer, and UV-visible spectroscopies, we explored the binding mode of cysteamine and RGS5 to human and mouse ADO proteins in their physiologically relevant ferrous form. This characterization revealed that in the presence of nitric oxide as a spin probe and oxygen surrogate, both the small molecule and the peptide substrates coordinate the iron center with their free thiols in a monodentate binding mode, in sharp contrast to binding behaviors observed in other thiol dioxygenases. We observed a substrate-bound B-type dinitrosyl iron center complex in ADO, suggesting the possibility of dioxygen binding to the iron ion in a side-on mode. Moreover, we observed substrate-mediated reduction of the iron center from ferric to the ferrous oxidation state. Subsequent MS analysis indicated corresponding disulfide formation of the substrates, suggesting that the presence of the substrate could reactivate ADO to defend against oxidative stress. The findings of this work contribute to the understanding of the substrate interaction in ADO and fill a gap in our knowledge of the substrate specificity of thiol dioxygenases.
- Wang, Yifan,Davis, Ian,Chan, Yan,Naik, Sunil G.,Griffith, Wendell P.,Liu, Aimin
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- Detailed mechanistic investigation into the S-nitrosation of cysteamine
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The nitrosation of cysteamine (H2NCH2CH 2SH) to produce cysteamine-S-nitrosothiol (CANO) was studied in slightly acidic medium by using nitrous acid prepared in situ. The stoichiometry of the reaction was H2NCH2CH2SH + HNO 2 → H2NCH2CH2SNO + H 2O. On prolonged standing, the nitrosothiol decomposed quantitatively to yield the disulfide, cystamine: 2H2NCH2CH 2SNO → H2NCH2CH2S-SCH 2CH2NH2 + 2NO. NO2 and N 2O3 are not the primary nitrosating agents, since their precursor (NO) was not detected during the nitrosation process. The reaction is first order in nitrous acid, thus implicating it as the major nitrosating agent in mildly acidic pH conditions. Acid catalyzes nitrosation after nitrous acid has saturated, implicating the protonated nitrous acid species, the nitrosonium cation (NO+) as a contributing nitrosating species in highly acidic environments. The acid catalysis at constant nitrous acid concentrations suggests that the nitrosonium cation nitrosates at a much higher rate than nitrous acid. Bimolecular rate constants for the nitrosation of cysteamine by nitrous acid and by the nitrosonium cation were deduced to be 17.9 ± 1.5 (mol/L)-1 s-1 and 6.7 ×104 (mol/L) -1 s-1, respectively. Both Cu(I) and Cu(II) ions were effective catalysts for the formation and decomposition of the cysteamine nitrosothiol. Cu(II) ions could catalyze the nitrosation of cysteamine in neutral conditions, whereas Cu(I) could only catalyze in acidic conditions. Transnitrosation kinetics of CANO with glutathione showed the formation of cystamine and the mixed disulfide with no formation of oxidized glutathione (GSSG). The nitrosation reaction was satisfactorily simulated by a simple reaction scheme involving eight reactions.
- Morakinyo, Moshood K.,Chipinda, Itai,Hettick, Justin,Siegel, Paul D.,Abramson, Jonathan,Strongin, Robert,Martincigh, Bice S.,Simoyi, Reuben H.
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- Fluorescein Chemiluminescence-Delay Method for the Determination of Ultratrace Amounts of Copper(II)
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A delayed chemiluminescence (CL) was observed in the copper(II)-catalyzed oxidation of cysteamine with oxygen in the presence of fluorescein (FL) and horseradish peroxidase.The delayed CL reaction of FL was applied to the determination of Cu(II).The delay time was correlated linearly with Cu(II) concentration over the range from 5.0 * 10-9 M to 1.0 * 10-6 M.
- Kamidate, Tamio,Kuniya, Isao,Segawa, Tadashi,Watanabe, Hiroto
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- A kinetic study of the oxidations of 2-mercaptoethanol and 2-mercaptoethylamine by heteropoly 11-tungsto-1- vanadophosphate in aqueous acidic medium
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The kinetics of oxidation of 2-mercaptoethanol and 2-mercaptoethylamine by the heteropoly 11-tungsto-1- vanadophosphate anion, [PVVW11O40]4-, have been studied spectrophotometrically in aqueous perchloric acid at 25°C. EPR and optical studies show that [PVVW11O40]4- is reduced to the one-electron reduced heteropoly blue, [PVIVW11O40]5-, whilst the thiols are oxidized to the corresponding disulphides, RSSR. Spectrophotometric titrations show that the stoichiometry of both reactions is 1:1. At constant pH, the reactions show simple second-order kinetics with first-order dependence of rate on both [oxidant] and [thiol]. At constant [thiol], the rate of the reaction increases with increasing pH. Plots of kobs/[thiol]t versus 1/[H+] are linear with finite intercepts, showing that both the undissociated thiol (RSH) and thiolate ion (RS-) are reactive species. Generation of RS· from RSH proceeds via a separated-concerted proton-electron transfer mechanism. The reaction of thiolate ion is a simple outer-sphere electron transfer reaction. By applying the Marcus theory, the self-exchange rate constants for the couples HOCH2CH2S·/HOCH2CH2S- and H3N+CH2CH2S·/H3N+CH2CH2S- were evaluated as 3 × 109 and 2.2 × 108 M-1 s-1, respectively, at 25°C.
- Shanmugaprabha, Thangamariyappan,Selvakumar, Karuppaiah,Rajasekaran, Kasi,Sami, Ponnusamy
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- Self-Polymerization Promoting Monomers: In Situ Transformation of Disulfide-Linked Benzoxazines into the Thiazolidine Structure
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Polybenzoxazines obtained especially from green synthons are facing challenges of the requirement of high ring-opening polymerization (ROP) temperature of the monomer, thus affecting their exploration at the industrial front. This demands effective structural changes in the monomer itself, to mediate catalyst-free polymerization at a low energy via one-step synthesis protocol. In this regard, monomers based on disulfide-linked bisbenzoxazine were successfully synthesized using cystamine (biobased) and cardanol (agro-waste)/phenol. Reduction of the disulfide bridge in the monomer using dithiothreitol under mild conditions in situ transformed the oxazine ring in the monomer, via neighboring group participation of the -SH group in a transient intermediate monomer, into a thiazolidine structure, which is otherwise difficult to synthesize. Structural transformation of ring-opening followed by the ring-closing intramolecular reaction led to an interconversion of O-CH2-N containing a six-membered oxazine ring to S-CH2-N containing a five-membered thiazolidine ring and a phenolic-OH. The structure of the monomer with the oxazine ring and its congener with the thiazolidine ring was characterized by spectroscopic methods and X-ray analysis. Kinetics of structural transformation at a molecular level is studied in detail, and it was found that the reaction proceeded via a transient 2-aminoethanethiol-linked benzoxazine intermediate, as supported by nuclear magnetic resonance spectroscopy and density functional theory studies. The thiazolidine-ring-containing monomer promotes ROP at a substantially low temperature than the reported mono-/bisoxazine monomers due to the dual mode of facilitation of the ROP reaction, both by phenolic-OH and by ring strain. Surprisingly, both the monomer structures led to the formation of a similar polymer structure, as supported by thermogravimetric analysis and Fourier transform infrared study. The current work highlights the benefits of inherent functionalities in naturally sourced feedstocks as biosynthons for the new latest generation of benzoxazine monomers.
- Monisha, Monisha,Sahu, Sangeeta,Lochab, Bimlesh
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p. 4408 - 4421
(2021/10/20)
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- Mechanistic scrutiny of the oxidations of thiol-containing drugs cysteamine and d-penicillamine by cis-diamminetetrachloroplatinum(IV)
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Cysteamine (CA) and d-penicillamine (Pen) are the thiol-containing drugs and good antioxidants. Their reactions with a cisplatin Pt(IV) prodrug cis-diamminetetrachloroplatinum(IV) (cis-[Pt(NH3)2Cl4]) were investigated by use of rapid scan, stopped-flow, and mass spectral techniques. The kinetic traces are biphasic in nature, encompassing a faster reduction of cis-[Pt(NH3)2Cl4] to cisplatin followed by slow substitutions on cisplatin. The reduction reactions were demonstrated to follow overall second-order kinetics over a wide pH range. The observed second-order rate constants versus pH profiles were established at 25.0°C and 1.0?M ionic strength, indicating a huge increase of reaction rate with the increase of pH. However, the oxidations of CA and Pen by cis-[Pt(NH3)2Cl4] displayed different reaction stoichiometric ratios as revealed by the spectrophotometric titration experiments. Accordingly, CA was oxidized to CA-disulfide while Pen-sulfinic acid and Pen-disulfide were identified as the major products in the case of Pen via mass spectral analysis. The above similarities and differences are rationalized in terms of the proposed reaction mechanisms, which encompass similar rate-determining reactions for both CA and Pen, but involve disparate and faster followed-up reactions. Rate constants of the rate determining were derived at 25.0°C and 1.0?M ionic strength. A consequent species reactivity analysis revealed that the species -SCH2CH2NH3+ of CA and the species +H3NCH(COO?)CMe2S? of Pen played a predominant role toward the reduction of cis-[Pt(NH3)2Cl4] from pH 5 to 8, which also is a critical pH region for most of drugs.
- Zhou, Li,Li, Tiejian,Sun, Ying,Tian, Hongwu,Gao, Cunxiu,Liu, Chunli,Kong, Lingli,Zhang, Guimin,Shi, Tiesheng
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supporting information
p. 548 - 557
(2020/12/18)
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- Selective, Modular Probes for Thioredoxins Enabled by Rational Tuning of a Unique Disulfide Structure Motif
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Specialized cellular networks of oxidoreductases coordinate the dithiol/disulfide-exchange reactions that control metabolism, protein regulation, and redox homeostasis. For probes to be selective for redox enzymes and effector proteins (nM to μM concentrations), they must also be able to resist non-specific triggering by the ca. 50 mM background of non-catalytic cellular monothiols. However, no such selective reduction-sensing systems have yet been established. Here, we used rational structural design to independently vary thermodynamic and kinetic aspects of disulfide stability, creating a series of unusual disulfide reduction trigger units designed for stability to monothiols. We integrated the motifs into modular series of fluorogenic probes that release and activate an arbitrary chemical cargo upon reduction, and compared their performance to that of the literature-known disulfides. The probes were comprehensively screened for biological stability and selectivity against a range of redox effector proteins and enzymes. This design process delivered the first disulfide probes with excellent stability to monothiols yet high selectivity for the key redox-Active protein effector, thioredoxin. We anticipate that further applications of these novel disulfide triggers will deliver unique probes targeting cellular thioredoxins. We also anticipate that further tuning following this design paradigm will enable redox probes for other important dithiol-manifold redox proteins, that will be useful in revealing the hitherto hidden dynamics of endogenous cellular redox systems.
- Becker, Katja,Busker, Sander,Felber, Jan G.,Maier, Martin S.,Poczka, Lena,Scholzen, Karoline,Theisen, Ulrike,Thorn-Seshold, Julia,Thorn-Seshold, Oliver,Zeisel, Lukas,Arnér, Elias S. J.,Brandst?dter, Christina
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supporting information
p. 8791 - 8803
(2021/06/27)
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- Accelerated reduction and solubilization of elemental sulfur by 1,2-aminothiols
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Nucleophilic 1,2-aminothiol compounds readily reduce typically-insoluble elemental sulfur to polysulfides in both water and nonpolar organic solvents. The resulting anionic polysulfide species are stabilized through hydrogen-bonding interactions with the proximal amine moieties. These interactions can facilitate sulfur transfer to alkenes.
- Stoffel, Jonathan T.,Riordan, Kimberly T.,Tsui, Emily Y.
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supporting information
p. 12488 - 12491
(2021/12/04)
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- BIODEGRADABLE CATIONIC POLYMERS AND USES THEREOF
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Disclosed herein are poly(hydroxylalkyleneimine disulfide)polymers, which have both desirable transfection properties and reduced toxicity.
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Paragraph 0184
(2019/02/24)
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- Preparation method for amidation based folic acid sulfydryl derivative
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The invention discloses a preparation method for an amidation based folic acid sulfydryl derivative. The preparation method comprises the following steps: 1) utilizing an oxidant hydrogen peroxide foroxidizing a compound containing an amido functional group and a sulfydryl functional group into disulfide containing a S-S bond, wherein amino groups at the two ends of the disulfide lay up foundation for next-step amidation reaction, and the hydrogen peroxide is hydrogen peroxide with preferable concentration of 30%; 2) adding a catalyst and a water absorbent into the product disulfide in the step 1), wherein amino groups on the disulfide generate amidation reaction with folic acid to obtain a folic acid derivative containing a disulfide bond; and 3) adding a reducing agent into the productin step 2) for cracking the disulfide bond in the folic acid derivative, thereby obtaining a target product with sulfydryl at the tail end. According to the preparation method disclosed by the invention, 4-dimethylamiopryidine (DMAP) is taken as a catalyst, and N,N'-dicyclohexylcarbodiimide (DCC) is taken as the water absorbent, so that reaction speed is high, the whole reaction process time is greatly shortened, and production efficiency is greatly improved.
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Paragraph 0043; 0045; 0046
(2018/04/03)
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- A METHOD FOR PREPARATION OF REDUCIBLE DEGRADABLE HYPERBRANCHED POLYMERIC MICELLES
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Provided are a reducible degradable hyperbranched-polymer nanomicelle and a method for preparation thereof and an application thereof. Cystamine and polyethylene glycol diglycidyl ether are polymerized by means of a nucleophilic addition mechanism; in one step, a hyperbranched polymer alternatingly arising from cystamine and polyethylene glycol structural units is synthesized and obtained; then, a hyperbranched nanomicelle is formed by means of self-assembly during the process of dialysis. The hyperbranched-polymer chain segments contain both tertiary aminos and disulfide bond structural units and have pH- and reduction responsiveness, and the hyperbranched three-dimensional cavity structure imparts a drug-carrying ability to the nanomicelle.
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Paragraph 0042; 0043
(2019/01/04)
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- Glutathione and endosomal pH-responsive hybrid vesicles fabricated by zwitterionic polymer block poly(L-aspartic acid) as a smart anticancer delivery platform
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Zwitterionic hybrid block copolymer based nanocarriers are ideal candidates for drug delivery applications due the higher resistance to nonspecific protein adsorption in complex media compared to nonionic polymers. Especially, zwitterionic poly(2-methacryloyloxyethyl phosphorylcholine) p(MPC) based nanocarriers can maintain its stability during circulation in complex media, such as serum. Thus, a series of bioreducible and pH-responsive zwitterionic/amphiphilic block copolymers, poly(2-methacryloyloxyethyl phosphorylcholine)50-block-poly(L-aspartic acid)n (p(MPC)50–b–p(AA)n) (n = 10, 25, 50, 75), bearing a degradable disulfide linker have been synthesized and exploited as dual-stimuli-responsive drug delivery vehicle of the chemotherapeutic drug, doxorubicin (Dox). Dox was successfully loaded into uniform vesicles (～ 100 nm) fabricated from p(MPC)50–b–p(AA)n and the release performance was investigated under different pH conditions and with a range of concentrations of the reducing agent, 1,4-dithiothreitol (DTT). At physiological conditions, increasing concentrations of DTT resulted in faster Dox release from vesicles. Dox release at elevated DTT concentrations was more effective at pH 5.5 than at pH 7.5. Blank vesicles were non-toxic over a wide concentration range when tested in normal cell lines (0.01–100 μg/mL). Vesicles efficiently encapsulated Dox and the dual stimuli-responsive disassembly results demonstrated controlled and sustained release of Dox tin 4T1 cancer cells to confer dose-dependent cytotoxicity. Thus, the bioreducible and pH sensitive vesicles appear to be a promising theranostic platform for drug delivery applications.
- Johnson, Renjith P.,Uthaman, Saji,Augustine, Rimesh,Zhang, Yu,Jin, Hua,Choi, Chang In,Park, In-Kyu,Kim, Il
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- Polydopamine as a Catalyst for Thiol Coupling
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In biological systems, disulfide bonds are formed efficiently under mild conditions without the release of harmful byproducts. Inspired by nature, we report a biomimetic polydopamine (PDA) catalyst for oxidative thiol coupling. This reaction was accelerated with only a small amount of PDA particles in neutral, weakly alkaline, and even weakly acidic aqueous media at room temperature under an air atmosphere. The catalytic particles were facilely separated and were reused without a decrease in activity. The entire process is totally biofriendly, including the synthesis of the PDA particles. This route is especially useful for the synthesis of pharmaceutical molecules. S-imulating nature: Inspired by disulfide bond formation mechanisms in nature, we demonstrate that polydopamine particles can be used as a promising biomimetic catalyst for the thiol coupling reaction in aqueous media under mild conditions. This approach involves no harmful chemicals and produces no waste products except for water.
- Du, Yong,Yang, Hao-Cheng,Xu, Xiao-Ling,Wu, Jian,Xu, Zhi-Kang
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p. 3822 - 3825
(2016/01/26)
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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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- Dendritic polymers with enhanced amplification and interior functionality
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Poly(ester-acrylate) and poly(ester/epoxide) dendrimers. These materials can be synthesized by utilizing the so-called “sterically induced stoichiometric” principles. The preparation of the dendrimers is carried out by reacting precursor amino/polyamino-functional core materials with various branch cell reagents. The branch cell reagents are dimensionally large, relative to the amino/polyamino-initiator core and when reacted, produce generation=1 dendrimers directly in one step. There is also a method by which the dendrimers can be stabilized and that method is the reaction of the dendrimers with surface reactive molecules to pacify the reactive groups on the dendrimers.
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- Aerobic oxidation of thiols to disulfides catalyzed by diaryl tellurides under photosensitized conditions
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Aerobic oxidation of thiols is efficiently catalyzed by diaryl tellurides such as bis(4-methoxyphenyl) telluride under photosensitized conditions to give the corresponding disulfides in good to excellent yields. In this catalytic system, the tellurone oligomer, produced by the reaction of a telluride with singlet oxygen, is assumed to be the active species and is capable of oxidizing 4 equiv of a thiol.
- Oba, Makoto,Tanaka, Kazuhito,Nishiyama, Kozaburo,Ando, Wataru
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experimental part
p. 4173 - 4177
(2011/06/26)
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- Enhanced sensitivity and selectivity of chemosensor for malonate by anchoring on gold nanoparticles
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A novel organic-inorganic nanohybrided receptor 4 functionalized with bis-thiourea arms and then assembled on gold nanoparticles was synthesized. The preorganized system possesses phenylthiourea units for the spectrophotometric sensing of dicarboxylates, especially malonate, based on changes in the surface plasmon absorption of the gold nanoparticles (GNPs). The intensity of the absorbance band increases gradually with the concentration of dicarboxylates increasing. But such an ion-selective change in the plasmon band was not observed in control tests carried out by mono-thiourea-modified GNPs, receptor 3 and the free receptor 2. As it is shown from the association constants, derived from quantitative titrations, receptor 4 can selectively recognize dicarboxylate anions of shorter carbon chain, and has the highest affinity to malonate. The interaction properties for anions of receptor 4 were evaluated by 1H NMR and UV-vis spectroscopic methods.
- Liu, Yanyun,Liu, Yun,Liang, Zhongshi,Li, Xiangyang,Liu, Shunying,Yu, Jiahui
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experimental part
p. 531 - 538
(2012/02/02)
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- Selenium and sulfur in exchange reactions: A comparative study
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Cysteamine reduces selenocystamine to form hemiselenocystamine and then cystamine. The rate constants are k1 = 1.3 × 105 M-1 s-1; k-1 = 2.6 × 107 M-1 s-1; k2 = 11 M-1 s-1; and k-2 = 1.4 × 103 M-1 s-1, respectively. Rate constants for reactions of cysteine/selenocystine are similar. Reaction rates of selenium as a nucle'phile and as an electrophile are 2-3 and 4 orders of magnitude higher, respectively, than those of sulfur. Sulfides and selenides are comparable as leaving groups.
- Steinmann, Daniel,Nauser, Thomas,Koppenol, Willem H.
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experimental part
p. 6696 - 6699
(2010/12/24)
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- Catalytic oxidation of thiol compounds by novel fuel cell-inspired co-porphyrin and co-imidazole catalysts
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The catalytic performance of pyrolyzed carbon-supported cobalt-nitrogen donor (CoN4) catalysts for the oxidation of thiol compounds by dioxygen in aqueous solution was studied. This paper continues our previous line of research, which was inspired by the electrocatalytic reduction of oxygen on pyrolyzed carbon-supported cobalt-porphyrins and related tetra-coordinated nitrogen donor-transition metal complexes (MeN4, where Me stands for a transition metal atom). Both pyrolyzed carbon-supported Co-imidazole and Co-porphyrin exhibited fast catalytic oxidation of the different thiols. The rate of oxidation of different thiols on the pyrolyzed CoN4 catalysts was compared to the homogeneous rate of oxidation using 5,10,15,20-tetrakis(4- sulfonatophenyl)porphyrin Co(II) tetrasodium salt as catalyst. Based on the cobalt content, the heterogeneous catalysts always outperformed the homogeneous one, and at times even exhibited 4,100-fold better catalysis. The dependence of the catalytic rate of oxidation on the preparation temperature was investigated, showing an optimal catalysis at ～650 °C for the cobalt-imidazole catalyst. The decrease in catalytic performance after heat treatment at elevated temperature was attributed to the formation of cobalt metal acting as a generator of carbon nanotubes.
- Goifman, Anatoly,Gun, Jenny,Gelman, Faina,Ekeltchik, Irina,Worch, Eckhard,Lev, Ovadia
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- Oxidation of thiol compounds by molecular oxygen in aqueous solutions
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Side self-oxidation of thiols was studied. It was found that these reactions in neutral and alkaline solutions are induced by impurities of variable-valence metals. The ability of transition metals to catalyze oxidation of thiols changes in the order Cu > Mn > Fe > Ni ? Co. The plot of the self-oxidation rate vs. pH passes through a maximum whose position on the pH scale depends on both the nature of metal and the structure of the thiol oxidized. For thiols having different structures, the kinetic orders in reactions catalyzed by copper ions differently vary with pH, which is apparently associated with the formation of complexes possessing different catalytic activity.
- Bagiyan,Koroleva,Soroka,Ufimtsev
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p. 1135 - 1141
(2007/10/03)
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- Metal ion catalysis in model electron transfer reactions?
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The reactions of a phenazine dye, methylene blue with sulfydryl substrates have been investigated in acidic medium in presence of metal ions Cu II and RuIII. The substrates are the functional parts of active biomolecules and our investigation reveals that the kinetics of these reactions are appreciably influenced by the environmental and the steric factors. The mechanistic conclusions partly explain the complexity of biochemical processes involving these substrates.
- Mishra
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p. 297 - 304
(2007/10/03)
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- Reaction of ascorbic acid with S-nitrosothiols: Clear evidence for two distinct reaction pathways
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Ascorbate reacts with S-nitrosothiols generally, in the pH range 3-13 by way of two distinct pathways, (a) at low [ascorbate], typically below ～1 × 10-4 mol dm-3 which leads to the formation of NO and the disulfide, and (b) at higher [ascorbate] when the products are the thiol and NO. Reaction (a) is Cu2+-dependent, and is completely cut out in the presence of EDTA, whereas reaction (b) is totally independent of [Cu2+] and takes place readily whether EDTA is present or not. For S-nitrosoglutathione (GSNO) the two reactions can be made quite separate, although for some reactants the two reactions overlap. In reaction (a), ascorbate acts as a reducing agent, generating Cu+ from Cu2+, which in turn reacts with RSNO forming initially NO, Cu2+ and RS-. The latter can then play the role of reducing agent for Cu2+, leading to disulfide formation. Ascorbate will initiate reaction when the free thiolate has initially been reduced to a very low level by the synthesis of RSNO from a large excess of nitrous acid over the thiol. Reaction (b) is interpreted in terms of nucleophilic attack by ascorbate at the nitroso-nitrogen atom, leading to thiol and O-nitrosoascorbate which breaks up, by a free-radical pathway, to give dehydroascorbic acid and NO. A similar pathway is the accepted mechanism in the literature for the nitrosation of ascorbate by nitrous acid and alkyl nitrites. The rate constant for the Cu2+-independent pathway increases sharply with pH and analysis of the variation of the rate constant with pH identifies a reaction pathway via both the mono- and di-anion forms of ascorbate, with the latter being the more reactive. As expected the entropy of activation is large and negative. Some aspects of structure-reactivity trends are discussed.
- Holmes, Anthony J.,Williams, D. Lyn H.
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p. 1639 - 1644
(2007/10/03)
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- The reaction of S-nitrosothiols with thiols at high thiol concentration
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Reactions of S-nitrosothiols (RSNO) with their corresponding thiols (RSH) present in a large excess (>20-fold) proceed readily to give the disulfide. Ammonia is formed together with some nitrite anion, and these constitute >90% of the 'nitrogen' products. This is in marked contrast with the reaction at low thiol concentration, where nitric oxide is the major initial 'nitrogen' product, which is rapidly converted in the presence of oxygen in water to nitrite anion. Also in marked contrast to the 'low thiol concentration' reaction, the reaction at high thiol concentration is not affected by added Cu2+, nor by the metal-ion scavenger EDTA. Kinetically all reactions were excellent first-order processes, and the reactions were also strictly first order in thiol concentration. A large range of nitrosothiols were studied and the generality of the reaction established. Some reactions of RSNO with other thiols (R'SH) were examined and the results readily interpreted in terms of a prior rapid equilibrium transnitrosation. The pH dependence for the reaction of S-nitrosocysteine with cysteine clearly showed that the reactive species is the cysteine thiolate anion. The results are discussed along with those of two other recent reports of these reactions, in terms of thiolate attack initially at the nitroso nitrogen atom, and subsequently at sulfur atoms, eliminating RSSR and yielding hydroxylamine, which is rapidly reduced by thiolate ion to ammonia. The results are also discussed in connection with the release of NO from nitrosothiols and with the important biological consequences, both for the in vivo reactions of NO and for the potential of nitrosothiols as NO-releasing drags for medical use.
- Dicks, Andrew P.,Li,Munro, Andrew P.,Swift, Helen R.,Williams, D. Lyn H.
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p. 789 - 794
(2007/10/03)
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- Phosphate radical induced oxidation of thiols in aqueous solution
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Photolysis of thiols, viz., cysteine, cysteamine and dithiothreitol in aqueous solution at natural pH in the presence of peroxydiphosphate (PDF) has been carried out in a quantum yield reactor using a medium pressure mercury lamp. The respective disulphides, viz., cysteine, cysteamine and oxidised dithiothreitol are found as the products of oxidation. The rates of formation of disulphides have been followed spectrophotometrically by measuring the absorbance at 280 nm. The intensity of light has been measured using peroxydisulphate solution as a standard chemical actinometer. The quantum yields of disulphide formation are found to depend on [PDP] as well as on [thiol] and are independent of the intensity of incident light. A mechanism involving photolysis of peroxydiphosphate giving phosphate radical anion followed by a chain propagation step involving disulphide radical anion has been proposed.
- Kumar, Maram Ravi,Adinarayana, Mundra
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p. 346 - 349
(2007/10/03)
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- A kinetic approach to characterize the electrostatic environments of thiol groups in proteins
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In this study, we synthesized a zwitterionic DTNB derivative, 5-(2- aminoethyl)-dithio-2-nitrobenzoate (ADNB), and characterized its reactions with several cationic, anionic, and neutral thiols. Reactions with ADNB, unlike those with DTNB, are relatively insensitive to electrostatic environments and ionic strengths. At relatively low ionic strength, rate ratios, k(ADNB)/k(DTNB), varied from 0.22 for reactions with low-molecular- weight cationic thiols to 3.0 for those with low-molecular-weight anionic thiols. A k(ADNB)/k(DTNB) ratio of ~200 for Cys-34 of BSA appears to reflect a very anionic environment. k(ADNB)/k(DTNB) ratios of ~6 and ~1, respectively, for canine and equine serum albumins, which have Glu-82 → Asp and Glu-82 → Ala substitutions suggest Glu-82 is the most important anionic residues affecting the reactivity of Cys-34 in BSA. k(ADNB)/k(DTNB) ratios appear to be useful for characterizing electrostatic environments of thiol groups in proteins.
- Zhang, Hao,Le, Min,Means, Gary E.
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p. 356 - 364
(2007/10/03)
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- Controlled oxidation of thiols to disulfides by diazenecarboxamides
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New reagents were developed and were found to be convenient and selective oxidants of various thiols (including glutathione, cysteamine and dithiothreitol) to disulfides under mild reaction conditions.
- Kosmrlj, Janez,Kocevar, Marijan,Polanc, Slovenko
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p. 3917 - 3919
(2007/10/03)
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- Design and synthesis of a bifunctional label for selection of β-lactamase displayed on filamentous bacteriophage by catalytic activity
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A bifunctional activity label 1c has been constructed for the selection of active β-lactamases displayed on filamentous bacteriophage. It features an original 6-sulfonylamido-penam sulfone moiety, as β-lactamase suicide-inhibitor, and a biotinyl residue, for separation by affinity chromatography, connected through a linker including a cleavable disulfide bond. The inhibitor 28 resulted from coupling of methoxymethyl 6-aminopenicillinate 8 with N-protected (aminoethoxy)ethoxyethanesulfonyl chloride 23, followed by oxidation into the corresponding sulfone 25, and usual deprotections. The biotinyl ester 32 reacted with 3-(2-aminoethyldithio)propanoic acid 31 as linker, to give 33 which was further activated as pentafluorophenol ester 34b. Final coupling of the building blocks 28 and 34b gave the target label 1c.
- Marchand-Brynaert, Jacqueline,Bouchet, Michele,Touillaux, Roland,Beauve, Cecile,Fastrez, Jacques
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p. 5591 - 5606
(2007/10/03)
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- The mechanism of nitric oxide formation from S-nitrosothiols (thionitrites)
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S-Nitrosothiols (RSNO) are easily made by electrophilic nitrosation of thiols and are a convenient source of nitric oxide. Reaction occurs readily (in many cases) in aqueous buffer at pH 7.4 to give in addition the corresponding disulfide RSSR. If oxygen is not rigorously excluded from the solution, then the nitric oxide is converted quantitatively to nitrite ion, whereas in the absence of oxygen nitric oxide can be detected using a commercial NO-probe. Reaction, however, only occurs (apart from the photochemical pathway) if Cu2+ is present. There is often enough Cu2+ in the distilled water-buffer components to bring about reaction, but decomposition is halted if Cu2+ is complexed with EDTA. Experiments with the specific Cu+ chelator neocuproine however show that the true effective reagent is Cu+, formed by reduction of Cu2+ with thiolate ion. Kinetic experiments show that the most reactive nitrosothiols are those which can coordinate bidentately with Cu+, and there is a wide range of reactivity amongst the structures studied. Reactivity is crucially dependent on the concentrations of Cu2+ and RS-. Reaction also occurs, although somewhat more slowly, if the source of copper is the CuII complex with the tripeptide diglycyl-L-histidine (GGH) or as the CuII complex with human serum albumin (HSA). This allows the possibility that nitrosothiols could in principle generate nitric oxide in vivo using the naturally occurring sources of CuII. Rapid exchange of the NO-group in RSNO with thiols occurs, again in aqueous buffer at pH 7.4. This reaction has been established as a nucleophilic substitution reaction by the thiolate ion at the nitroso nitrogen atom. The implications of these results with regard to possible involvement of nitrosothiols in vivo are discussed.
- Williams, D. Lyn H.
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p. 1085 - 1091
(2007/10/03)
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- Catalysis by Cu2+ of nitric oxide release from S-nitrosothiols (RSNO)
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The decomposition of a range of S-nitrosothiols (thionitrites) RSNO, based on cysteine derivatives, yields in water at pH 7.4 nitrite ion quantitatively.If oxygen is rigorously excluded then no nitrite ion is formed and nitric oxide can be detected using an NO-probe.The reaction is catalysed by trace quantities of Cu2+ (there is often enough present in distilled water samples) and also to a lesser extent by Fe2+, but not by Zn2+, Cu2+, Mg2+, Ni2+, Co2+, Mn2+, Cr3+ or Fe3+.The rate equation (measuring the disappearance of the absorption at ca. 350 nm due to RSNO) was established as v = k*2+> + k' over a range of 2+> typically 5-50 μmol dm-3.The constant term k' represents the component of the rate due to residual Cu2+ in the solvent and buffer components, together with the spontaneous thermal reaction.Decomposition can be virtually halted by the addition of EDTA.Reactions carried out in the presence of N-methylaniline gave a quantitative yield of N-methyl-N-nitrosoaniline, but a negligible yield when oxygen was rigorously excluded.Values of the second-order rate constant k were obtained for a range of S-nitrosothiols.Reactivity is highest for the S-nitrosothiols derived from cysteamine and penicillamine, when Cu2+ can be complexed both with the nitrogen atom of the nitroso group and the nitrogen atom of the amino group, via a six-membered ring intermediate.If there is no amino (or other electron donating group) present, reaction is very slow (as for RSNO derived from a tert-butyl sulfide).N-Acetylation of the amino group reduces the reactivity drastically as does the introduction of another CH2 group in the chain.There is evidence of a significant gem-dimethyl effect.Kinetic results using the S-nitrosothiols derived from mercaptoacetic, thiolactic and thiomalic acids suggests that coordination can also occur via one of the oxygen atoms of the carboxylate group.EPR experiments which examined the Cu2+ signal showed no spectral change during the reaction suggesting that the mechanism does not involve oxidation and reduction with Cu2+ Cu+ interconversion.
- Askew, Stuart C.,Barnett, D. Jonathan,McAninly, John,Williams, D. Lyn H.
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p. 741 - 746
(2007/10/02)
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- Oxidation of 2-mercaptoethanol and 2-mercaptoethylamine by III>2O4+ in aqueous media
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The stoichiometry, kinetics and mechanisms of the oxidation of HSCH2CH2OH (1) and HSCH2CH2NH3+ (2) by III>2O4+(bpy=2,2'-bipyridine) to the corresponding disulphides have been investigated in aqueous HClO4.The oxidation is found to be first order each in reductants and the oxidant and the dependence of the second order rate constants on +> approximates to k2=a+b +>-1.Results have been rationalized in terms of plausible free radical mechanisms.
- Iyun, J. Femi,Musa, Kabir Y.,Ayoko, G. Adefikayo
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p. 635 - 638
(2007/10/03)
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- Method for production of cystamine and alkylene oxide adduct thereof, additive for aqueous lubricant, and aqueous lubricant
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Cystamine is produced by a method which comprises reacting a 2,2-dialkyl thiazolidine represented by the general formula(1): wherein R1 and R2 independently are alkyl groups of 1 to 5 carbon atoms, with a peroxide in the presence of water. An alkylene oxide adduct of cystamine is produced by a method which comprises reacting the reaction mixture obtained as described above further with an alkylene oxide. These cystamine and alkylene oxide adduct of cystamine are useful as an additive for an aqueous lubricant.
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- Synthesis of peptides containing a sulfinamide or a sulfonamide transition-state isostere
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A versatile synthesis of peptides incorporating the sulfinamide or sulfonamide transition-state analogue is described. Apart from the easily accessible Gly-Xxx isosteres used as haptens to elicit catalytic antibodies, other amino acids than Gly can be prepared by α-alkylation of the sulfonamide containing peptides. This is illustrated with the synthesis of a potential HIV-protease inhibitor 27.
- Moree, Wilna J.,Van Gent, Liesbeth C.,Van Der Marel, Gijs A.,Liskamp, Rob M. J.
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p. 1133 - 1150
(2007/10/02)
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- Kinetics and Equilibria of Thiol/Disulfide Interchange Reactions of Selected Biological Thiols and Related Molecules with Oxidized Glutathione
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Rate constants for reaction of coenzyme A and cysteine with oxidized glutathione (GSSG) and equilibrium constants for the reaction of coenzyme A, cysteine, homocysteine, cysteamine, and related thiols with GSSG by thiol/disulfide interchange were determined over a range of pD values by NMR spectroscopy.The rate constants for reaction of the thiolate anion forms of coenzyme A and cysteine with GSSG suggest that reduction of GSSG by coenzyme A and cysteine is a mechanistically uncomplicated SN2 reaction.Equilibrium constants for the thiol/disulfide interchange reactions show a strong dependence on the Bronsted basicity of the thiolate anion.In a similar way, ΔE0', the difference between the half-cell potentials for the RSSR/RSH and GSSG/GSH redox couples, is linearly dependent on the difference between the pKA values of RSH and glutathione: ΔE0' = 64ΔpKA - 7.7 where ΔE0' is in units of mV.The reducing strength at a given pH is also determined by the fraction of the thiol present in the reactive thiolate form.At pD 7, the half-cell potentials for coenzyme A, cysteine, homocysteine, and cysteamine are close to that of glutathione, the major intracellular thiol redox system, which suggests that small changes in the intracellular redox potential can cause significant changes in the intracellular distribution of these biological thiols between their reduced and oxidized forms.
- Keire, David A.,Strauss, Erin,Guo, Wei,Noszal, Bela,Rabenstein, Dallas L.
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p. 123 - 127
(2007/10/02)
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- Synthesis of Nickel(II), Coper(II), Zinc(II), and Cadmium(II) Complexes of 2-pyrrole and 2-pyrrole by the Electrochemical Cleavage of a Disulphide Bond: the Crystal Structure of Bis 2-thiophenolato..
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The electrochemical oxidation of anodic metal (nickel, copper, zinc, or cadmium) in acetonitrile solutions of the Schiff bases derived from 2-pyrrolecarbaldehyde and bis(2-aminophenyl)disulphide (H2L2) or cysteamine (H2L2') gives compounds , or .The crystal structure of bisthiophenolato>zinc(II) is orthorhombic, space group Pbca with a = 13.764(3), b = 17.819(1), c = 16.593(2) Angstroem, and Z = 8.The zinc atom has ZnS2N2 distorted tetrahedral stereochemistry and the pyrrolic nitrogen atoms are not co-ordinated.
- Castro, Jesus,Romero, Jaime,Garcia-Vazquez, Jose A.,Duran, Maria L.,Castineiras, Alfonso,et al.
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p. 3255 - 3258
(2007/10/02)
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- A Comparative Study of the Kinetics of Selenol/Diselenide and Thiol/Disulfide Exchange Reactions
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The kinetics of symmetrical selenol/diselenide and thiol/disulfide exchange reactions involving selenocysteamine/selenocystamine and cysteamine/cystamine have been studied in D2O solution by NMR spectroscopy.The rate of selenol/diselenide exchange is so fast that resonances for the selenol and diselenide forms are coalesced in (1)H NMR spectra of millimolar selenocysteamine/selenocystamine mixtures at pD > 2-3.In contrast, the rate of thiol/disulfide exchange is so slow that separate, sharp resonances are observed for both cysteamine and cystamine in mixtures atconcentrations up to at least 0.2 M from pD 13.Rate constants for the selenol/diselenide exchange reaction were determined by line shape analysis of exchange-broadened resonances, while those for thiol/disulfide exchange were determined by an inversion-transfer method.The rate constants at 25 deg C for exchange by reaction of D3N(1+)CH2CH2X(1-) with D3N(1+)CH2CH2XXCH2CH2ND3(1+) are as follows: X = Se, k = 1.65 * 1E7 L/mol*s; X = S, k = 68.0 L/mol*s.When the differences in the acidities of the selenol and thiol groups are accounted for, selenocysteamine/selenocystamine exchange is 1.2 * 1E7 times faster than cysteamine/cystamine exchange at physiological pH.
- Pleasants, Joan C.,Guo, Wei,Rabenstein, Dallas L.
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p. 6553 - 6558
(2007/10/02)
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- Kinetics and Mechanism of the Autoxidation of 2-Aminoethanethiol and Ethanethiol Catalyzed by Cobalt(II) 4,4',4'',4'''-Tetrasulfophthalocyanine in Aqueous Solution
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The kinetics of autoxidation of 2-aminoethanethiol to 2-aminoethyl disulfide and ethanethiol to ethyl disulfide as catalyzed by cobalt(II) 4,4',4'',4'''-tetrasulfophthalocyanine (CoIITSP) were investigated.The following general rate law found to hold for both substrates over the pH range 8.8-13.5: ν = -d->/dt = kobsdT->.Evidence for a mechanism that proceeds via a dimeric catalytic center that is bridged by the RS- anion has been obtained.In the proposed mechanism, electron transfer from the Co(II) metal center to bound dioxygen was considered to the rate-determining step.Hydrogen peroxide and mercaptan radical were identified as reaction intermediates in the autoxidation of both substrates.These intermediates react further to produce the correponding disulfide, RSSR. as the final product of the autoxidation. kobsd was found to be of the following general form: kobsd = (k31K21 + (k32K22K'1/aH+) + (k33K23K'1K'2/aH+2))/1/aH+) + (K'1K'2/aH+2))(1 + (aH+/K'a12))>, where k3i and K2i are the rate constants for the electron transfer and the equilibrium constants for substrate complexation of the ith catalytic center, respectively, K'1 and K'2 are the apparent acid dissociation constants of the pyrrole groups of CoIITSP-RS--CoIITSP and CoIITSP-RS--CoIITSP-, respectively, and K'a1 is the apparent acid dissociation constant of RCH2CH2SH.
- Leung, Ping-Sang K.,Hoffmann, Michael R.
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p. 434 - 441
(2007/10/02)
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- Organic Disulfides and Related Substances. 47. Some Novel Types of Aminoalkyl Disulfides
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Several novel types of amino disulfides are reported, together with their stabilities in D2O (i.e., resistance to disproportionation).These disulfides contain the group H2N(CH2)2, known to be radioprotective, as an R group in alkenyl and arylene systems of the structure RSSCH2-C.=C.-CH2SSR.The disulfides (5-7) were synthesized by reactions of 2-aminoethanethiol with novel thiosulfonates (1-3).
- Singh, Pramod K.,Field, Lamar
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- Growth-enhancing cystamine derivatives
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Cystamine derivatives of the formula: STR1 [wherein n represents 2 or 3, R1 and R2 each represents a hydrogen atom, or an alkyl group optionally substituted by a hydroxy, amino, alkylamino or dialkylamino group, or represents a cycloalkyl or aryl group, and X1 represents a group selected from the formulae =N--CN, =N--NO2, =N--COR3, =N--COOR3, =N--NH--CONH2, =N--SO2 R3, =CH--NO2, =CH--SO2 R3, =C(CN)2, =C(CN)COOR3 and =C(CN)CONH2 (wherein R3 represents an alkyl or aryl group), or R1 represents a hydrogen atom, R2 represents an alkyl group optionally substituted by a hydroxy, amino, alkylamino or dialkylamino group, or represents a cycloalkyl or aryl group and X1 represents an oxygen or sulphur atom] have been found to be useful in the promotion of the growth of non-human animals including birds. Prcesses for the preparation of the cystamine derivatives and compositions containing them for administration to non-human animals are described.
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- Polymer-Supported Diaryl Selenoxide and Telluroxide as Mild and Selective Oxidizing Agents
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Polystyrene-bound diaryl selenoxide and telluroxide have been prepared, which behaved as mild oxidizing agents for thiols to disulfide, phosphines to phosphine oxides, hydroquinone and catechol to p- and o-benzoquinones, and thioketones to oxo compounds.The telluroxide completed these reactions in shorter periods or under milder conditions than the selenoxide.In addition, they effected novel solvent-dependent reactions of thioamides involving thioureas to 1,2,4-thiadiazoles or to nitriles.In nonacidic solvents, the dehydrosulfurization to nitriles occured in preference to the oxidative dimerization to 1,2,4-thiadiazoles, but an acidic solvent such as acetic acid promoted the latter reaction.
- Hu, Nan Xing,Aso, Yoshio,Otsubo, Tetsuo,Ogura, Fumio
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p. 879 - 884
(2007/10/02)
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- Interaction of Thiols with n-Type Cadmium Sulfide and n-Type Cadmium Selenide in Aqueous Solutions: Adsorption of Thiolate Anion and Efficient Photoelectrochemical Oxidation to Disulfides
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Organic thiols, RSH=cysteamine, 2-mercaptoethanol, penicillamine, or cysteine, effectively suppress photoanodic decomposition of n-CdS and n-CdSe in aqueous solutions and undergo efficient controlled potential photoelectrochemical oxidation to the corresponding disulfides, RSSR.Photovoltage (the extent to which oxidation occurs at potentials negative of the thermodynamic potential) of greater than 700 mV is observed for certain thiols upon excitation of the semiconductor anode with light of energy greater than the band gap.As electrodes for preparative electrosynthesis, both illuminated n-CdS and n-CdSe offer significant electrical energy savings compared to conventional electrochemical oxidation in the dark at a Pt electrode.The oxidation of RSH to RSSR at n-CdS and n-CdSe has been studied under various conditions: high current efficiencies, typically measured to be greater than 98percent, are found at high and low pH for all RSH studied except glutathione which is oxidized with about 60percent current efficiency.Attempted controlled potential oxidation of glutathione at n-CdS leads to decomposition of the electrode.No S/Se exchange occurs at the surface of n-CdSe in the efficient photoelectrochemical oxidation of RSH to RSSR, as determined by Auger spectroscopy.The output parameters at n-CdS and n-CdSe depend on the nature of the functional groups on the RSH.The best energy conversion performance is achieved with a 1 M solution of cysteamine at pH 11 with an efficiency for conversion of 501.7-nm light (30 mW/cm2) to electricity of 14.5percent (without electrode decomposition) with a photovoltage of 670 mV when n-CdS is used as a photoanode.In contrast, a 1 M glutathione solution at pH 11 yields an efficiency of only 0.6percent (with electrode decomposition) with a photovoltage of 510 mV under the same conditions.Both capacitance-voltage and photocurrent-voltage measurements show that the flat-band potentials, EFB, of n-CdS and n-CdSe are shifted to more negative values (by up to 0.7 V) by the strong adsorption of RS(1-).Unfortunately, a simple Langmuir model does not explain the concentration dependence of adsorption of RS(1-) and detailed comparisons of binding properties cannot be made.
- Natan, Michael J.,Thackeray, James W.,Wrighton, Mark S.
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p. 4089 - 4098
(2007/10/02)
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- MILD AND SELECTIVE OXIDATIONS WITH POLYSTYRENE-BOUND DIARYL SELENOXIDE
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Polystyrene-bound diaryl selenoxide is sohwn to behave as a mild oxidizing agent for thiol to disulfide, sulfide to sulfoxide, phosphine to phosphine oxide, and hydroquinone to benzoquinone.In addition, it effects solvent-dependent reactions of thioamide to nitrile in usual solvent and to thiadiazole in acetic acid.
- Hu, Nan Xing,Aso, Yoshio,Otsubo, Tetsuo,Ogura, Fumio
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p. 603 - 606
(2007/10/02)
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- Molybdenum(VI) Complexes of Schiff Bases Derived from Salicylaldehyde and 2-Aminoethanethiol (Cysteamine)
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The reaction of salicylaldehyde and 2-aminoethanethiol (cysteamine) in methanol results in two distinct products: a yellow oil, 2-(2"-mercaptoethyliminomethyl)phenol, and a yellow crystalline solid, 2,2'-bisphenol, which is an oxidation product of the former.The latter compound may also be prepared from salicylaldehyde and 2,2'-dithio-bis(ethylamine)(cystamine)in methanol. 2-(2"-Mercaptoethyliminomethyl)phenol reacts with MoO2(acac)2 (acac=pentane-2,4-dionate) in methanol to yield a red crystalline solid with empirical formula MoO2(mep) .This red solid exists as a dimer in the solid state.It forms adducts with dimethyl sulfoxide, hexamethylphosphoric acid triamide and pyridine. 2,2'-bisphenol reacts with MoO2(acac)2 to yield a pale yellow solid.It is a monomeric compound whose formula is MoO2(dbp) bisphenolate>.It does not form an adduct and is decomposed by an excess of tetramethylammonium hydroxide in methanol.
- Goh, Wai-Kah,Lim, Meng-Chay
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p. 2235 - 2242
(2007/10/02)
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- Bis(p-methoxyphenyl) Selenoxide as a Mild and Selective Oxidizing Agent
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The title compound oxidized thiolsto disulfides, sulfides to sulfoxides, hydroquinone or catechol to benzoquinones, and phosphine to phosphine oxide in high yields under very mild conditions.In addition, it functioned as a useful reagent for the syntheses of 1,2,4-thiadiazole derivatives from thioureas or thioamides.
- Ogura, Fumio,Yamaguchi, Hachiro,Otsubo, Tetsuo,Tanaka, Hiroyuki
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p. 641 - 642
(2007/10/02)
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- Transformation of DAEP under Various Oxidative Conditions
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14C-DAEP was subjected to four different oxidative conditions, and the products were identified.On peracid oxidation in dichloromethane, DAEP gave the oxon (1) predominantly, and 2-acetylaminoethyl dimethoxyphosphinyl disulphide (3), N-acetylcysteamine (10), its oxidized dimer (11) and a further oxidation product of compound (11).This indicates that an unstable phosphorus oxythionate was initially formed, which lost sulfur, was rearranged, and hydrolyzed to give these products.Under other conditions, phosphinyl disulfide 3 was not found.DAEP was metabolized in vitro with a rat liver microsome-NADPH system via oxydation.The aqueous reaction condition prevented the formation of compound 3 from the intermediate, which predominated as well as the oxon formation under anhydrous or close conditions.The formation of various products with sunlight irradiation on glass plates or on bean leaves could be interpreted by oxidation at P=S, C1 and C2 positions, demethylation, and deacetylation, followed by further transformation.The initial formation of phosphorus oxythionate seems to play an important role in the oxidation of the organothionophosphorus compound.
- Miyamoto, Toru,Yamamoto, Izuru
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p. 1991 - 1998
(2007/10/02)
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