Unsymmetrical disulfide and sulfenamide synthesis via reactions of thiosulfonates with thiols or amines

The reactivity of thiosulfonates with nucleophilic reagents was investigated. When reactions of thiosulfonates with thiols were performed, unsymmetrical disulfides were obtained in excellent yields. This procedure could employ numerous aryl or alkyl thiols. On the other hand, reactions of thiosulfonates with amines proceeded in the presence of a copper catalyst. The procedure was performed efficiently in air, and afforded the corresponding sulfenamides.     

Ammonium iodide-mediated electrosynthesis of unsymmetrical thiosulfonates from arenesulfonohydrazides and thiols

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Determination of sulfur dioxide in solutions by pyridinium bromide perbromide and titrimetric and flow injection procedures

Sulfur dioxide can be determined by its reaction with pyridinium bromide perbromide using photometric titrations and flow injection procedures. Both methods are useful down to 30 ppm, and are unaffected by ammonia or nitrogen dioxide. Both mercury(II) and EDTA interfere under some circumstances.     

Effects of aromatic thiols on thiol-disulfide interchange reactions that occur during protein folding

The folding of disulfide containing proteins from denatured protein to native protein involves numerous thiol-disulfide interchange reactions. Many of these reactions include a redox buffer, which is a mixture of a thiol (RSH) and the corresponding disulfide (RSSR). The relationship between the structure of RSH and its efficacy in folding proteins in vitro has been investigated only to a limited extent. Reported herein are the effects of aliphatic and especially aromatic thiols on reactions that occur during protein folding. Aromatic thiols may be particularly efficacious as their thiol pK(a) values and reactivities match those of the in vivo catalyst, protein disulfide isomerase (PDI). This investigation correlates the thiol pK(a) values of aromatic thiols with their reactivities toward small molecule disulfides and the protein insulin. The thiol pK(a) values of nine para-substituted aromatic thiols were measured; a Hammett plot constructed using sigma(p-) values yielded rho = -1.6 +/- 0.1. The reactivities of aromatic and aliphatic thiols with 2-pyridyldithioethanol (2-PDE), a small molecule disulfide, were determined. A plot of reactivity versus pK(a) of the aromatic thiols had a slope (beta) of 0.9. The ability of these thiols to reduce (unfold) the protein insulin correlates strongly with their ability to reduce 2-PDE. Since the reduction of protein disulfides occurs during protein folding to remove mismatched disulfides, aromatic thiols with high pK(a) values are expected to increase the rate not only of protein unfolding but protein folding as well.     

Rhodium-catalyzed alkyne hydrothiolation with aromatic and aliphatic thiols

Alkyne hydrothiolation is a potentially attractive method for the formation of vinyl sulfides, which are valuable synthetic intermediates. Known methods for hydrothiolation using alkyl thiols are quite limited. We report herein that Tp*Rh(PPh3)2 (Tp* = hydrotris(3,5-dimethylpyrazolyl)borate) is a highly active catalyst for alkyne hydrothiolation with alkyl and aryl thiols. Hydrothiolation using alkyl thiols proceeds with excellent regioselectivity, providing convenient access to branched alkyl vinyl sulfides, which are difficult to synthesize by other means. A mixture of regioisomers is obtained when using aryl thiols, with the branched isomer as the major product, opposite that reported for other Rh complexes.     

ortho-Acidic aromatic thiols as efficient catalysts of intramolecular Morita-Baylis-Hillman and Rauhut-Currier reactions

ortho-Mercaptobenzoic acid and ortho-mercaptophenols were discovered as efficient thiol catalysts of both the intramolecular Morita-Baylis-Hillman (MBH) and Rauhut-Currier (RC) reaction. High reaction rates were achieved under mildly basic, aqueous conditions. The unprecedented catalytic activity of these protic nucleophiles could originate from a Brønsted acid induced destabilization of intermediate thioethers and thus represent a unique mechanism of multifunctional Lewis base catalysis.     

Photodissociation of aromatic thiols and disulfides

For the first time, the quantum yields of cleavage of SS and SH bonds in a disulfide and a thiol and also the extinction coefficient of the photoinduced aminophenylthiyl radical were determined, on the basis of which the relation of the photodissociation quantum yield to the energy of an absorbed quantum was observed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 540–543, March, 1990.     

Estimating uncertainty in analytical procedures based on chromatographic techniques

Chromatographic techniques are very frequently used in analytical procedures for the separation, determination and identification of a wide spectrum of analytes present in samples with complex and sometimes variable matrices. However, the estimation of uncertainty of the final results does not include the uncertainties associated with the actual chromatographic process. In effect, such results cannot always be treated as a reliable source of analytical information. In this paper we present the basic terms, sources of uncertainty, and methods of calculating the combined uncertainty that any presentation of final determinations should include.     

Kinetics of OH reactions with aliphatic thiols

The kinetics of OH reactions with 1–4 carbon aliphatic thiols have been investigated over the temperature range 252–430 K. OH radicals were produced by flash photolysis of water vapor at λ > 165 nm and detected by time-resolved resonance fluorescence spectroscopy. All thiols investigated react with OH at nearly the same rate; k(298 K) = 3.2–4.6 × 10^?11 cm³ molecule^?1 s^?1, -E_act = 0.6–1.0 kcal/mol, A = 0.6–1.2 × 10^?11 cm³ molecule^?1 s^?1. CH₃SH and CH₃SD react with OH at identical rates over the entire temperature range investigated. We conclude that the dominant reaction pathway is addition to the sulfur atom.     

Oxirane ring opening reactions with thiols catalyzed by lanthanide complexes

LnCl₃ (Ln = Ce,Sm) and Eu(fod)₃ act as Lewis-acid catalysts in stereo- and regioselective epoxide ring opening reactions with thiols under mild conditions in CH₂Cl₂.     

Ring opening of aziridines by aromatic thiols followed by amino-substitution

Ring opening of 2-aziridinecarboxylic acid methyl ester by a number of aromatic thiols under solvent-free and non-catalytic conditions resulted in bis-arylsulfanyl propanoic acid esters.     

Repair reactions of pyrimidine-derived radicals by aliphatic thiols

Pyrimidinyl radicals of various structures (Pyr*) were generated in aqueous and alcohol-containing solutions by means of pulse radiolysis to determine the rate constants of their repair reactions by different thiols (RSH = cysteamine, 2-mercaptoethanol, cysteine, and penicillamine): Pyr* + RSH --> PyrH + RS*. C5-OH and C6-OH adduct radicals of the pyrimidines react with thiols with k9 = (1.2-10.0) x 10(6) dm3 mol(-1) s(-1). Similar repair rate constants were found for uracil- and thymine-derived N1-centered radicals, k31 = (1.5-6.1) x 10(6) dm3 mol(-1) s(-1). However, pyrimidine radical anions protonated at their C6 position and C6-uracilyl radicals, with carbonyl groups at their C5 position, react with thiols faster, with k24 = (0.5-7.6) x 10(7) dm3 mol(-1) s(-1) and k14 = (1.4-4.8) x 10(7) dm3 mol(-1) s(-1), respectively. Quantum chemical calculations, at the B3LYP/6-31G(d,p) and self-consistent reaction field polarizable continuum model level point to the combined effects of the energy gap between interacting molecular orbitals, charge distribution within different pyrimidine-derived radicals, and the coefficients of the atomic orbitals as the possible reasons for the differences in the rate constants of repair.     

Substituent dependence of the reactions of [RuCl2(PPh3)3] with bulky aromatic thiols

2,4,6-trialkylbenzenethiols react with [RuCl2(PPh3)3] to give Ru products with the alkyl substituents forming M-C sigma bonds, carbene, carbene with a S alpha-heteroatom, agostic hydrogen interaction or a simple tetrahedral Ru(II) species, depending on the substituent.     

Determination of dissolved thiols using solid-phase extraction and liquid chromatographic determination of fluorescently derivatized thiolic compounds

A method employing solid-phase extraction coupled with HPLC separation of thiol-monobromobimane (mBBr) derivatives was developed and optimized to quantify dissolved thiols at concentrations as low as 0.1 nM for glutathione (GSH) and gamma-glutamylcysteine (gammaEC) in natural waters. The reducing reagent, tri-n-butylphosphine (TBP), is needed for complete derivatization. At the optimal addition of TBP ([TBP]/[mBBr] = -0.4-1.6), no interference from copper was observed. The thiol fluorescence signal was totally suppressed if the mole ratio of TBP to mBBr was 2.6 or greater. Consistent recovery of thiols standards in a NaCl solution (0.5 M) was obtained using the Waters HLB reversed-phase resin, and blank levels of GSH and gammaEC were extremely low (less than 0.03 nM). The detection limits for GSH, gammaEC and phytochelatin-2 (PC-2) were 0.03, 0.03, and 0.06 nM, respectively.     

Self-assembled monolayers of aromatic thiols stabilized by parallel-displaced pi-pi stacking interactions

Parallel-displaced pi-pi stacking interactions have been known to be the dominant force in stabilizing the double helical structure of DNA and the tertiary structure of proteins. However, little is known about their roles in self-assembled monolayers of other large pi molecules such as aromatic thiols. Here we report on a systematic study of the self-assembled monolayers of four kinds of anthracene-based thiols, 9-mercaptoanthracene (MA), (4-mercaptophenyl) (9-anthryl) acetylene (MPAA), (4-mercaptophenyl) (10-nitro-9-anthryl) acetylene (MPNAA), and (4-mercaptophenyl) (10-carboxyl-9-anthryl) acetylene (MPCAA) on Au(111), in which a spacer and different functional groups (NO2 and COOH) are intentionally designed to introduce and thus allow the investigation of various intermolecular interactions, in addition to pi-pi interactions in the base molecules. We find that all molecules form long-range-ordered monolayers and, more interestingly, that these assembled monolayers exhibit essentially the same fundamental packing structure. On the basis of high-resolution scanning tunneling microscopy observations, we propose the space-filling models for the observed superstructures and demonstrate that all superstructures can be understood in terms of the parallel-displaced pi-pi stacking interactions, despite the presence of competing dipole-dipole and H-bonding interactions associated with these specially designed functional groups.     

High-performance liquid chromatographic separation and indirect fluorescence detection of thiols

A fluorescent post-column reaction detection scheme has been devised for selective determination of thiols. The post-column reagent is 40 microM Cd2+ and 100 microM 8-hydroxyquinoline-5-sulfonic acid (HQS) in non-complexing buffer at pH 10. HQS complexes Cd2+ to form a fluorescent product. Thiols in the HPLC effluent compete for complexation of the Cd2+, resulting in a decrease in the fluorescence response. Detection limits of 0.2 microM (0.04 ppm) are achieved for cysteine, homocysteine and glutathione in a 5 min separation. Recoveries from spiked synthetic urine samples are 87-120%.     

Place exchange reactions of alkyl thiols on gold nanoparticles

The kinetics and equilibrium position of place exchange (alkylthiol-for-alkylthiol) reactions of gold nanoparticles are reported. These reactions were monitored via a gas chromatography analysis of structurally similar incoming and outgoing alkylthiols, as a function of time. The place exchange reactions described here proceed to an equilibrium position, where Keq approximately 1. The product-time data follow Langmuir diffusion kinetics.     

Chemical amplification methods for the sequential determination of trace amounts of ruthenium by titrimetric and spectrophotometric procedures

Two simple, inexpensive and rapid iodometric and spectrophotometric procedures were developed for trace amount determination of ruthenium. The proposed methods were based on the oxidation of ruthenium(II or III) with sodium periodate at pH 2.4-3.6, masking the excess periodate with sodium molybdate. The released iodate was then allowed to react with KI at pH 3, with subsequent determination of the released iodine spectrophotometry as triiodide at 350 nm or iodometry with 0.005 M sodium thiosulphate. This procedure offers an 18- and 15-fold amplification per Ru(II) or Ru(III) ion, respectively. Alternatively, the produced iodine was extracted with CHCl(3), shaken with an aqueous solution of sodium sulphite and the produced iodide ion was then allowed to react with bromine (or sodium periodate). The released iodate was subsequently determined by iodometry or spectrophotometry after addition of KI. The bromine and sodium periodate oxidation procedures offered 90- and 360-fold amplification per ruthenium(III) ion, and 108- and 432-fold amplification per ruthenium(II) ion. Ruthenium(IV) content was determined by these procedures after prior reduction to Ru(III) with sulphurous acid. The binary mixtures Ru(II)-Ru(III); Ru(III)-Ru(IV) and Ru(II)-Ru(IV) in aqueous solution at concentration 0.05 mug ml(-1) were successfully analyzed by the developed procedures. The utility of the proposed methods for the analysis of ruthenium in its complexes was demonstrated. Natural seawater and seawater spiked with ruthenium were analyzed satisfactorily.     

Determination of water in thiols by Karl Fischer titration

Water in thiol-containing samples may be determined by titration with Karl Fischer reagent after conversion of the thiol into a thioether. Both acrylonitrile and N-ethylmaleimide have been found to be suitable reagents.