- Excited-state proton-coupled electron transfer within ion pairs
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The use of light to drive proton-coupled electron transfer (PCET) reactions has received growing interest, with recent focus on the direct use of excited states in PCET reactions (ES-PCET). Electrostatic ion pairs provide a scaffold to reduce reaction orders and have facilitated many discoveries in electron-transfer chemistry. Their use, however, has not translated to PCET. Herein, we show that ion pairs, formed solely through electrostatic interactions, provide a general, facile means to study an ES-PCET mechanism. These ion pairs formed readily between salicylate anions and tetracationic ruthenium complexes in acetonitrile solution. Upon light excitation, quenching of the ruthenium excited state occurred through ES-PCET oxidation of salicylate within the ion pair. Transient absorption spectroscopy identified the reduced ruthenium complex and oxidized salicylate radical as the primary photoproducts of this reaction. The reduced reaction order due to ion pairing allowed the first-order PCET rate constants to be directly measured through nanosecond photoluminescence spectroscopy. These PCET rate constants saturated at larger driving forces consistent with approaching the Marcus barrierless region. Surprisingly, a proton-transfer tautomer of salicylate, with the proton localized on the carboxylate functional group, was present in acetonitrile. A pre-equilibrium model based on this tautomerization provided non-adiabatic electron-transfer rate constants that were well described by Marcus theory. Electrostatic ion pairs were critical to our ability to investigate this PCET mechanism without the need to covalently link the donor and acceptor or introduce specific hydrogen bonding sites that could compete in alternate PCET pathways.
- Hammarstr?m, Leif,Meyer, Gerald J.,Swords, Wesley B.
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p. 3460 - 3473
(2020/04/17)
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- Conversion of Anthranilate Synthase into Isochorismate Synthase: Implications for the Evolution of Chorismate-Utilizing Enzymes
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Chorismate-utilizing enzymes play a vital role in the biosynthesis of metabolites in plants as well as free-living and infectious microorganisms. Among these enzymes are the homologous primary metabolic anthranilate synthase (AS) and secondary metabolic i
- Plach, Maximilian G.,L?ffler, Patrick,Merkl, Rainer,Sterner, Reinhard
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supporting information
p. 11270 - 11274
(2016/07/06)
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- Synthesis and chemical and biological comparison of nitroxyl- and nitric oxide-releasing diazeniumdiolate-based aspirin derivatives
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Structural modifications of nonsteroidal anti-inflammatory drugs (NSAIDs) have successfully reduced the side effect of gastrointestinal ulceration without affecting anti-inflammatory activity, but they may increase the risk of myocardial infarction with chronic use. The fact that nitroxyl (HNO) reduces platelet aggregation, preconditions against myocardial infarction, and enhances contractility led us to synthesize a diazeniumdiolate-based HNO-releasing aspirin and to compare it to an NO-releasing analogue. Here, the decomposition mechanisms are described for these compounds. In addition to protection against stomach ulceration, these prodrugs exhibited significantly enhanced cytotoxcity compared to either aspirin or the parent diazeniumdiolate toward nonsmall cell lung carcinoma cells (A549), but they were not appreciably toxic toward endothelial cells (HUVECs). The HNO-NSAID prodrug inhibited cylcooxgenase-2 and glyceraldehyde 3-phosphate dehydrogenase activity and triggered significant sarcomere shortening on murine ventricular myocytes compared to control. Together, these anti-inflammatory, antineoplasic, and contractile properties suggest the potential of HNO-NSAIDs in the treatment of inflammation, cancer, or heart failure.
- Basudhar, Debashree,Bharadwaj, Gaurav,Cheng, Robert Y.,Jain, Sarthak,Shi, Sa,Heinecke, Julie L.,Holland, Ryan J.,Ridnour, Lisa A.,Caceres, Viviane M.,Spadari-Bratfisch, Regina C.,Paolocci, Nazareno,Velázquez-Martínez, Carlos A.,Wink, David A.,Miranda, Katrina M.
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supporting information
p. 7804 - 7820
(2013/11/06)
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- PH dependence of catalysis by pseudomonas aeruginosa isochorismate - Pyruvate lyase: Implications for transition state stabilization and the role of lysine 42
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An isochorismate - pyruvate lyase with adventitious chorismate mutase activity from Pseudomonas aerugionsa (PchB) achieves catalysis of both pericyclic reactions in part by the stabilization of reactive conformations and in part by electrostatic transitio
- Olucha, Jose,Ouellette, Andrew N.,Luo, Qianyi,Lamb, Audrey L.
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experimental part
p. 7198 - 7207
(2012/07/13)
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- Entropic and enthalpic components of catalysis in the mutase and lyase activities of pseudomonas aeruginosa PchB
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The isochorismate-pyruvate lyase from Pseudomonas aeruginosa (PchB) catalyzes two pericyclic reactions, demonstrating the eponymous activity and also chorismate mutase activity. The thermodynamic parameters for these enzyme-catalyzed activities, as well a
- Luo, Qianyi,Meneely, Kathleen M.,Lamb, Audrey L.
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experimental part
p. 7229 - 7233
(2011/06/23)
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- Nueleophile specificity in anthranilate synthase, aminodeoxychorismate synthase, isochorismate synthase, and salicylate synthase
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Anthranilate synthase (AS), aminodeoxychorismate synthase (ADCS), isochorismate synthase (IS), and salicylate synthase (SS) are structurally homologous chorismate-utilizing enzymes that carry out the first committed step in the formation of tryptophan, fo
- Ziebart, Kristin T.,Toney, Michael D.
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experimental part
p. 2851 - 2859
(2011/02/26)
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- Inhibition of chorismate-utilising enzymes by 2-amino-4-carboxypyridine and 4-carboxypyridone and 5-carboxypyridone analogues
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Several 2-amino-4-carboxypyridine, 4- and 5-carboxypyridone-based compounds were prepared and tested against three members of the chorismate-utilising enzyme family, anthranilate synthase, isochorismate synthase and salicylate synthase. Most compounds exhibited low micromolar inhibition of these three enzymes. The most potent inhibitor was a 4-carboxypyridone analogue bearing a lactate side chain on the pyridyl nitrogen which exhibited inhibition constants of 5, 91 and 54 μM against anthranilate synthase, isochorismate synthase and salicylate synthase respectively. The Royal Society of Chemistry 2010.
- Payne, Richard J.,Bulloch, Esther M. M.,Kerbarh, Olivier,Abell, Chris
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scheme or table
p. 3534 - 3542
(2010/08/21)
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- Isochorismate pyruvate lyase: A pericyclic reaction mechanism?
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Isochorismate pyruvate lyase (IPL) catalyzes the cleavage of isochorismate to give salicylate and pyruvate, a key step in bacterial siderophore biosynthesis. We investigated the enzyme from Pseudomonas aeruginosa using isochorismate selectively deuterated
- DeClue, Michael S.,Baldridge, Kim K.,Kuenzler, Dominik E.,Kast, Peter,Hilvert, Donald
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p. 15002 - 15003
(2007/10/03)
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- Effects of organic salts on the rate of intramolecular general base-catalyzed piperidinolysis of ionized phenyl salicylate in the presence of cationic micelles
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Pseudo-first-order rate constants (kobs), obtained for the cleavage of ionized phenyl salicylate (PS-) at constant [NaOH], [MeCN], [CTABr]T (total concentration of cetyltrimethylammonium bromide), [Pip]T (total
- Khan,Kun
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p. 1325 - 1330
(2007/10/03)
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- Binding of sodium salicylate by β-cyclodextrin or 2,6-di-o-methyl-β- cyclodextrin in aqueous solution
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Speed of sound and conductivity experiments have been done at 298.15 K to study the encapsulation process of sodium salicylate (NASA) by β- cyclodextrin (β-CD) and 2,6-di-O-methyl-β-cyclodextrin (DIMEB) in aqueous solutions. Since the concentration of the salicyclic form (HSA), coming from the hydrolysis of SA-, is negligible at biological pH, the binding process studied in this work is that of the SA- species. The stoichiometries of the complexes DIMEB: SA- and β-CD:SA- have been found to be 1:1, as usually determined for most CD:drug complexes. Their association constants and their ionic molar conductivities at infinite dilution have been obtained by fitting the experimental conductivity data with a nonlinear regression method (NLR). For that purpose, a model based on that of Gelb and co-workers has been used. From the values of K(β-CD:SA-) = (105 ± 15) M-1 and K(DIMEB:SA-) = (140 ± 20) M-1 obtained, the bioavailability of the salicylate drug in the complexed form has been discussed.
- Junquera, Elena,Pena, Lourdes,Aicart, Emilio
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- Effects of Li+ and K+ ions on the rate of intramolecular general base-catalysed methanolysis of ionized phenyl salicylate in the absence and presence of cationic micelles in mixed H2O-CH3CN solvents
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Pseudo first-order rate constants (kobs1) for methanolysis of ionized phenyl salicylate (PS-) show a decrease of 3-5-fold with increase in CH3CN content from 2 to 60 or 70% (v/v) in mixed aqueous solvents containing 0·01 mol dm-3 LiOH and a constant content of CH3OH. At 0·01 mol dm-3 KOH, the rate constants, kobs1, reveal a decrease of 15-20% and an increase of 70-130% with increase in the CH3CN content from 2 to 30% (v/v) and from 30 to 60 or 70% (v/v) respectively. The values of ΔH? and ΔS? are not significantly affected by the presence of 2, 30 and 70% (v/v), CH3CN in mixed aqueous solvents containing 10% (v/v) CH3OH and 0.01 mol dm-3 KOH. The presence of 0.01 mol dm-3 LiOH causes the increases in ΔH? and ΔS? of 3·82 kcal mol-1 and 10·3 cal K-1 mol-1, respectively, with increase in CH3CN content from 2 to 60% (v/v) in mixed aqueous solvents containing 20% (v/v) CH3OH. An increase in the total concentration of cetyltrimethylammonium bromide ([CTABr]T) from 0·0 to 0·01 mol dm-3 decreases kobs1 by 3·6- and 4·0-fold in the presence of 0·01 mol dm-3 Li+ and K+ ion, respectively, in mixed aqueous solvents containing 2% (v/v) CH3CN and 10% (v/v) CH3OH.
- Khan, M. Niyaz,Arifin, Zainudin
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p. 301 - 307
(2007/10/03)
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- Hydrolysis of aspirin studied by spectrophotometric and fluorometric variable-temperature kinetics
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Pseudo-first-order rate constants for the hydrolysis of acetylsalicylic acid as a function of temperature have been obtained by variable-temperature kinetic experiments. A method, based on a generalization of non-isothermal analysis, has been used that takes advantage of the capabilities of modem data collection and processing systems. Both spectrophotometric and, for the first time under non-isothermal conditions, fluorometric measurements have been carried out. The results obtained are identical to those obtained under the same conditions but using traditional constant-temperature kinetic runs. This provides the possibility of reducing the amounts of time and chemicals usually spent in collecting kinetic data in mechanistic studies in solution by an order of magnitude.
- Alibrandi, Giuseppe,Micai, Norberto,Trusso, Sebastiano,Villari, Antonino
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p. 1105 - 1108
(2007/10/03)
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- Participation of two carboxyl groups in phosphodiester hydrolysis. 1. hydrolysis of bis(2-carboxyphenyl) phosphate
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The energies of rotamer conformations of bis(2-carboxyphenyl) phosphate (2), where one o-carboxy group is ionized and the other is not, have been determined by semiempirical (SAM1, AM1/SM2.1) calculations in order to approximate the probability of the pre
- Bruice, Thomas C.,Blaskó, Andrei,Petyak, Mark E.
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p. 12064 - 12069
(2007/10/03)
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- Effect of Cationic Micelles on the intramolecular General Base-catalysed Hydrolysis of Ionized Phenyl Salicylate at Different Temperatures
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An increase in the total concentration of cetyltrimethylammonium bromide (CTABr), from 0.0 to 0.12 mol dm-3 causes the pseudo-first-order rate constant for intramolecular general base-catalysed hydrolysis of ionized phenyl salicylate (PS-) to decrease by nearly five- or six-fold at constant temperature, while an increase in temperature from 30 to 58 deg C increases the first-order rate constant from 7.10*10-5 to 123*10-5 s-1 as well as decreasing the PS--micelle binding constants from 7100 to nearly 5000 dm3 mol-1.
- Khan, Mohammad Niyaz,Arifin, Zainudin
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p. 132 - 133
(2007/10/03)
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- Cationic Micellar Effect on the Kinetics of the Protolysis of Aromatic Carboxylic Acids studied by the Ultrasonic Absorption Method
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The protolysis of carboxylic acids has been kinetically studied by the ultrasonic absorption method in the presence of tetradecyltrimethylammonium bromide (TTAB) micelles in aqueous solution.The carboxylic acids studied were classified into two categories, one capable of formation of intramolecular hydrogen bond, namely the salicylic acid derivatives (SAD) and the other which cannot form the bond, namely the benzoic acid derivatives (BAD).The rate constant (γ2kf, kb), the apparent dissociation constant (Ka), and the volume change of the reaction (ΔV) were obtained.Different Ka dependences of the rate constants observed for SAD and BAD are discussed in relation to the effect of intramolecular hydrogen bond. pKa dependences were also observed for ΔV of SAD and BAD.These dependences are larger than those in aqueous solution.This result was attributed to the change of arrangement of water molecules around the solute in micellar solution and aqueous solution.
- Isoda, Teruyo,Yamasaki, Miyuki,Yano, Hiroshige,Sano, Takayuki,Harada, Shoji
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p. 869 - 874
(2007/10/02)
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- INHIBITORY EFFECT OF HYDROXIDE IONS ON THE DEGRADATION OF β-DICARBONYL COMPOUNDS PRODUCED BY THE RING OPENING OF CHROMONES IN ALKALINE MEDIUM
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A kinetic investigation is reported of the degradation of β-dicarbonyl phenolates (1) and enolates (2) produced by ring cleavage reaction of chromone, flavone, isoflavone and the corresponding 2-hydroxychromanones.Hydroxide ions were found to inhibit the cleavage of these compounds, which effect had been unknown in the field of chromonoids and β-dicarbonyl compouns.The inhibitory effect can be expressed by the equation k=(kd1K*+kd22)/(K*+).The reaction rate constants (kd1 and kd2), the equilibrium constants (K* and K), as well as the activation energy and entrophy of the degradation reaction were determined.Based upon the change of the activation energy and entropy, hydratation of the phenolates (1) and enolates (2) was found to play a very important part in the degradation.
- Zsuga, M.,Szabo, V.,Korodi, F.
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p. 111 - 119
(2007/10/02)
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- Comparison of Proton- and Electron-Transfer Equilibria and Rates for Tetraalkylhydrazines
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Relative electron-transfer equilibria for 17 tetralkylhydrazines (R4N2) were determined by measurement of their standard potentials for oxidation (E') and rates of electron loss by measurement of their standard heterogeneous electron-transfer rate constants (ks) determined from their cyclic voltammograms.These data are compared with equilibrium and rate constant measurements for proton transfer between R4N2 and salicylic acid.All measurements were in dimethyl sulfoxide containing 0.1 M tetraethylammonium perchlorate.Similar trends are found for electron and proton transfer; the most basic R4N2 examples are the most easily oxidized and the fastest both to protonate and lose an electron.The proton transfers run under these conditions show anomalous Broensted behavior; the rate of protonation of R4N2 is about twice as sensitive to change of the R groups as is the equilibrium constant, and the rate of deprotonation consequently becomes slower as the reaction becomes more exothermic.A Broensted-like plot for electron transfers was constructed by estimating the electron-transfer rate constants for all R4N2 as the same potential (called k0); electron transfer also gives anomalous Broensted behavior for R4N2.The electron-transfer rate has been previously shown to be far faster in anti lone pair conformations than in gauche ones, so that electron transfer from acrylic R4N2 involves a prior conformational equilibrium to the unstable but rapidly oxidized anti form.It is suggested that a similar gauche to anti conformational change precedes proton transfer under our conditions, and is a major contributing factor to the anomalous Broensted behavior of R4N2.
- Nelsen, Stephen F.,Kinlen, Patrick J.,Evans, Dennis H.
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p. 7045 - 7050
(2007/10/02)
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- Binary and Ternary Chelates of Scandium(III), Yttrium(III) and Lanthanum(III) with Ethyleneglycol-Bis(β-Aminoethylether)-Tetraacetic Acid as Primary and Substituted Salicylic Acids as Secondary Ligands
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Formation constants of binary and ternary complexes of the systems of the type: M-L and M-egta-L have been determined pH-metrically at 25 deg and μ=0.1 M (KNO3) in 50 percent (v/v) aqueous-ethanol medium.The order of stabilities of ternary complexes have compared with those of corresponding binary complexes, and results discussed on the basis of coulombic interactions.
- Pandey, Ashok Kumar,Chandra, M.,Agarwala, B. V.,Dey, A. K.
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