Theoretical and electrochemical analysis of dissociative electron transfers proceeding through formation of loose radical anion species: reduction of symmetrical and unsymmetrical disulfides

Electrochemical Cyanation of Alcohols Enabled by an Iodide-Mediated Phosphine P(V/III) Redox Couple

We report herein a mild electrochemical method to transform alcohols into their corresponding nitriles by using commercially available reagents. This protocol accepts substrates with various functional groups including those that are susceptible to oxidative decomposition. Mechanistic studies revealed a critical iodide-mediated phosphine electrochemical oxidation pathway leading to the alkoxyphosphonium intermediate, followed by nucleophilic substitution by a cyanide nucleophile. This method demonstrates the use of electrochemistry in replacing azo-type reagents in direct nucleophilic substitution and homologation of alcohol substrates.

Unraveling redox pathways of the disulfide bond in dimethyl disulfide: Ab initio modeling

CONTEXT

In cellular environments, the reduction of disulfide bonds is pivotal for protein folding and synthesis. However, the intricate enzymatic mechanisms governing this process remain poorly understood. This study addresses this gap by investigating a disulfide bridge reduction reaction, serving as a model for comprehending electron and proton transfer in biological systems. Six potential mechanisms for reducing the dimethyl disulfide (DMDS) bridge through electron and proton capture were explored. Thermodynamic and kinetic analyses elucidated the sequence of proton and electron addition. MD-PMM, a method that combines molecular dynamics simulations and quantum-chemical calculations, was employed to compute the redox potential of the mechanism. This research provides valuable insights into the mechanisms and redox potentials involved in disulfide bridge reduction within proteins, offering an understanding of phenomena that are challenging to explore experimentally.

METHODS

All calculations used the Gaussian 09 software package at the MP2/6-311 + g(d,p) theory level. Visualization of the molecular orbitals and electron densities was conducted using Gaussview6. Molecular dynamics simulations were performed using GROMACS with the CHARMM36 force field. The PyMM program (Python Program for QM/MM Simulations Based on the Perturbed Matrix Method) is used to apply the Perturbed Matrix Method to MD simulations.

Long-Life, High-Rate Rechargeable Lithium Batteries Based on Soluble Bis(2-pyrimidyl) Disulfide Cathode

Organosulfides are promising candidates as cathode materials for the development of electric vehicles and energy storage systems due to their low-cost and high capacity properties. However, they generally suffer from slow kinetics because of the large rearrangement of S-S bonds and structural degradation upon cycling in batteries. In this paper, we reveal that soluble bis(2-pyrimidyl) disulfide (Pym2 S2 ) can be a high-rate cathode material for rechargeable lithium batteries. Benefiting from the superdelocalization of pyrimidyl group, the extra electrons prefer to be localized on the π* (pyrimidyl group) than σ* (S-S bond) molecular orbitals initially, generating the anion-like intermedia of [Pym2 S2 ]2- and thus decreasing the dissociation energy of the S-S bond. It makes the intrinsic energy barrier of dissociative electron transfer depleted, therefore the lithium half cell exhibits 2000 cycles at 5 C. This study provides a distinct pathway for the design of high-rate, long-cycle-life organic cathode materials.

Disulfide radical anion as a super-reductant in biology and photoredox chemistry

Disulfides are involved in a broad range of radical-based synthetic organic and biochemical transformations. In particular, the reduction of a disulfide to the corresponding radical anion, followed by S-S bond cleavage to yield a thiyl radical and a thiolate anion plays critical roles in radical-based photoredox transformations and the disulfide radical anion in conjunction with a proton donor, mediates the enzymatic synthesis of deoxynucleotides from nucleotides within the active site of the enzyme, ribonucleotide reductase (RNR). To gain fundamental thermodynamic insight into these reactions, we have performed experimental measurements to furnish the transfer coefficient from which the standard E0(RSSR/RSSR˙-) reduction potential has been determined for a homologous series of disulfides. The electrochemical potentials are found to be strongly dependent on the structures and electronic properties of the substituents of the disulfides. In the case of cysteine, a standard potential of E0(RSSR/RSSR˙-) = -1.38 V vs. NHE is determined, making the disulfide radical anion of cysteine one of the most reducing cofactors in biology.

Mesolysis of an asymmetric diphenyldisulfide radical anion studied by γ-ray and pulsed-electron radiolyses

Diaryldisulfides are known to undergo S-S bond cleavage upon one-electron reduction, which is called mesolysis of radical anions, to form the corresponding arylthiyl radical and anion. In this study, we prepared (4-cyanophenyl)(4'-methoxyphenyl)disulfide (MeOSSCN), and the mesolytic profiles were investigated by γ-ray and pulsed-electron radiolyses in 2-methyltetrahydrofuran. As a result of radiolysis of MeOSSCN at room and lower temperatures, the formation of the methoxythiyl radical was recognized upon mesolysis of the radical anion. This observation indicated that intramolecular electron transfer in the radical anion occurred, and the stepwise mechanism was operative after the attached electron occupied the antibonding σ*-orbital for promoting the S-S bond cleavage. According to the Arrhenius expression for the decay rates of the radical anion, the activation energy and frequency factor were determined. DFT calculations provided the bond dissociation energy and bond length for the S-S bond and charge distribution on the S atoms in the radical anion. The substituent effects on the mesolysis process are discussed.

Effects of Substitution on Cytotoxicity of Diphenyl Ditelluride in Cultured Vascular Endothelial Cells

Among organic–inorganic hybrid molecules consisting of organic structure(s) and metal(s), only few studies are available on the cytotoxicity of nucleophilic molecules. In the present study, we investigated the cytotoxicity of a nucleophilic organotellurium compound, diphenyl ditelluride (DPDTe), using a cell culture system. DPDTe exhibited strong cytotoxicity against vascular endothelial cells and fibroblasts along with high intracellular accumulation but showed no cytotoxicity and had less accumulation in vascular smooth muscle cells and renal epithelial cells. The cytotoxicity of DPDTe decreased when intramolecular tellurium atoms were replaced with selenium or sulfur atoms. Electronic state analysis revealed that the electron density between tellurium atoms in DPDTe was much lower than those between selenium atoms of diphenyl diselenide and sulfur atoms of diphenyl disulfide. Moreover, diphenyl telluride did not accumulate and exhibit cytotoxicity. The cytotoxicity of DPDTe was also affected by substitution. p-Dimethoxy-DPDTe showed higher cytotoxicity, but p-dichloro-DPDTe and p-methyl-DPDTe showed lower cytotoxicity than that of DPDTe. The subcellular distribution of the compounds revealed that the compounds with stronger cytotoxicity showed higher accumulation rates in the mitochondria. Our findings suggest that the electronic state of tellurium atoms in DPDTe play an important role in accumulation and distribution of DPDTe in cultured cells. The present study supports the hypothesis that nucleophilic organometallic compounds, as well as electrophilic organometallic compounds, exhibit cytotoxicity by particular mechanisms.

Mechanistic Investigation and Optimization of Photoredox Anti-Markovnikov Hydroamination

The reaction mechanism and the origin of the selectivity for the photocatalytic intermolecular anti-Markovnikov hydroamination of unactivated alkenes with primary amines to furnish secondary amines have been revealed by time-resolved laser kinetics measurements of the key reaction intermediates. We show that back-electron transfer (BET) between the photogenerated aminium radical cation (ARC) and reduced photocatalyst complex (Ir(II)) is nearly absent due to rapid deprotonation of the ARC on the sub-100 ns time scale. The selectivity for primary amine alkylation is derived from the faster addition of the primary ARCs (as compared to secondary ARCs) to alkenes. The turnover of the photocatalyst occurs via the reaction between Ir(II) and a thiyl radical; the in situ formation of an off-cycle disulfide from thiyl radicals suppresses this turnover, diminishing the efficiency of the reaction. With these detailed mechanistic insights, the turnover of the photocatalyst has been optimized, resulting in a >10-fold improvement in the quantum yield. These improvements enabled the development of a scalable flow protocol, demonstrating a potential strategy for practical applications with improved energy efficiency and cost-effectiveness.

Covalent Linkages of Molecules and Proteins to Si-H Surfaces Formed by Disulfide Reduction

Thiols and disulfide contacts have been, for decades, key for connecting organic molecules to surfaces and nanoclusters as they form self-assembled monolayers (SAMs) on metals such as gold (Au) under mild conditions. In contrast, they have not been similarly deployed on Si owing to the harsh conditions required for monolayer formation. Here, we show that SAMs can be simply formed by dipping Si-H surfaces into dilute solutions of organic molecules or proteins comprising disulfide bonds. We demonstrate that S-S bonds can be spontaneously reduced on Si-H, forming covalent Si-S bonds in the presence of traces of water, and that this grafting can be catalyzed by electrochemical potential. Cyclic disulfide can be spontaneously reduced to form complete monolayers in 1 h, and the reduction can be catalyzed electrochemically to form full surface coverages within 15 min. In contrast, the kinetics of SAM formation of the cyclic disulfide molecule on Au was found to be three-fold slower than that on Si. It is also demonstrated that dilute thiol solutions can form monolayers on Si-H following oxidation to disulfides under ambient conditions; the supply of too much oxygen, however, inhibits SAM formation. The electron transfer kinetics of the Si-S-enabled SAMs on Si-H is comparable to that on Au, suggesting that Si-S contacts are electrically transmissive. We further demonstrate the prospect of this spontaneous disulfide reduction by forming a monolayer of protein azurin on a Si-H surface within 1 h. The direct reduction of disulfides on Si electrodes presents new capabilities for a range of fields, including molecular electronics, for which highly conducting SAM-electrode contacts are necessary and for emerging fields such as biomolecular electronics as disulfide linkages could be exploited to wire proteins between Si electrodes, within the context of the current Si-based technologies.

Direct effects of low-energy electrons on including sulfur bonds in proteins: a second-order Møller-Plesset perturbation (MP2) theory approach

In an attempt to describe how low-energy electrons (LEEs) damage the polypeptide chain at disulfide bridges, ab initio electronic structure estimates on LEE interactions with cysteine-cysteine (Cys-Cys) disulfide bond model have been performed. Here, the fundamental mechanisms in LEE impression on S-S and C-S bond ruptures in the Cys-Cys model have been discussed. The electronic energy was calculated using the MP2 method with a Hartree-Fock exchange during the SCF and the Møller-Plesset correlation energy correction on the converged HF orbitals with 6-311++G(d,p) atomic orbital basis set. Further, six more sets of diffuse s and p functions with extra basis on the sulfur and relevant carbon atoms were used to describe the added electron to located away as much as possible from the nuclei in anions. The bonds rupture mechanisms involve the primary placement of LEEs to the π* orbital of the model to construct the shape-resonance state following by an adiabatic or nonadiabatic electron migration to either S-S or C-S bond σ* orbital. The formed radical anion undergoes S-S or C-S bonds cleavage by energy barriers of ca. 5.68 and 9.19 kcal/mol, respectively, to produce either (2-amino-2-carboxyethyl) sulfanyl (cysteine radical), aziridine-2-carboxylic acid or mercapto-L-cysteine lesions. In SMD solvent, calculations suggest electronically stable of the formed π* and σ* states by solvation, something that induces either S-S or C-S bond break even when the electron energy is near zero. The required barrier energy of only 0 to < 0.4 eV indicates a high kinetic favorable fragmentation for involved sulfur polypeptides with LEEs.Communicated by Ramaswamy H. Sarma.

Alternating Current Electrolysis for the Electrocatalytic Synthesis of Mixed Disulfide via Sulfur-Sulfur Bond Metathesis towards Dynamic Disulfide Libraries

A novel approach of electrolysis using alternating current was applied in the sulfur–sulfur bond metathesis of symmetrical disulfides towards unsymmetrical disulfides. As initially expected, a statistical distribution in disulfides was obtained. Furthermore, the influence of electrode polarisation by alternating current was investigated on a two‐disulfide matrix. The highly dynamic nature of this chemistry resulted in the creation of dynamic disulfide libraries by expansion of the matrices, consisting of up to six symmetrical disulfides. In addition, mixing of matrices and stepwise expanding of a matrix by using alternating current electrolysis were realised.

Inorganic hydrogen polysulfides: chemistry, chemical biology and detection

Recent studies suggest that inorganic hydrogen polysulfides (H2 Sn , n ≥ 2) play important regulatory roles in redox biology. Modulation of their cellular levels could have potential therapeutic value. This review article focuses on our current understanding of the biosynthesis, biofunctions, fundamental physical/chemical properties, detection methods and delivery techniques of H2 Sn . LINKED ARTICLES: This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc.

A trisulfur radical anion (S3˙−) involved sulfur insertion reaction of 1,3-enynes: sulfide sources control chemoselective synthesis of 2,3,5-trisubstituted thiophenes and 3-thienyl disulfides

Cascade cyclization reactions of S₃˙⁻in situ generated from S₂⁻ with 1,3-enynes for the chemoselective synthesis of 2,3,5-trisubstituted thiophenes and 3-thienyl disulfides controlled by sulfide salts are developed.

Amine Induced Retardation of the Radical-Mediated Thiol-Ene Reaction via the Formation of Metastable Disulfide Radical Anions

The effect of amines on the kinetics and efficacy of radical-mediated thiol-ene coupling (TEC) reactions was investigated. By varying the thiol reactant and amine additive, it was shown that amines retard thiyl radical-mediated reactions when the amine is adequately basic enough to deprotonate the thiol affording the thiolate anion, e.g., when the weakly basic amine tetramethylethylenediamine was incorporated in the TEC reaction between butyl 2-mercaptoacetate and an allyl ether at 5 mol %, the final conversion was reduced from quantitative to <40%. Alternatively, no effect is observed when the less acidic thiol butyl 3-mercaptopropionate is employed. The thiolate anion was established as the retarding species through the introduction of ammonium and thiolate salt additives into TEC formulations. The formation of a two-sulfur three-electron bonded disulfide radical anion (DRA) species by the reaction of a thiyl radical with a thiolate anion was determined as the cause for the reduction in catalytic radicals and the TEC rate. Thermodynamic and kinetic trends in DRA formations were computed using density functional theory and by modeling the reaction as an associative electron transfer process. These trends correlate well with the experimental retardation trends of various thiolate anions in TEC reactions.

The thiolation of pentafluorobenzene with disulfides by C–H, C–F bond activation and C–S bond formation

A metal-free thiolation reaction between pentafluorobenzene and disulfides by C–H, C–F bond activation and C–S bond formation is reported.

Positively Charged Combinatory Drug Delivery Systems against Multi-Drug-Resistant Breast Cancer: Beyond the Drug Combination

The formation and development of cancer is usually accompanied by angiogenesis and is related to multiple pathways. The inhibition of one pathway by monotherapy might result in the occurrence of drug resistance, tumor relapse, or metastasis. Thus, a combinatory therapeutic system that targets several independent pathways simultaneously is preferred for the treatment. To this end, we prepared combinatory drug delivery systems consisting of cytotoxic drug SN38, pro-apoptotic KLAK peptide, and survivin siRNA with high drug loading capacity and reductive responsiveness for the treatment of multi-drug-resistant (MDR) cancer. With the help of positive charge and the synergistic effect of different drug, the combinatory systems inhibited the growth of doxorubicin-resistant breast cancer cells (MCF-7/ADR) efficiently. Interestingly, the systems without siRNA showed more superior in vivo anticancer efficacy than those with siRNA which exhibited enhanced in vitro cytotoxicity and pro-apoptotic ability. This phenomenon could be attributed to the preferential tumor accumulation, strong tumor penetration, and excellent tumor vasculature targeting ability of the combinatory micelles of SN38 and KLAK. As a result, a combinatory multitarget therapeutic system with positive charge induced tumor accumulation and vasculature targeting which can simultaneously inhibit the growth of both tumor cell and tumor vasculature was established. This work also enlightened us to the fact that the design of combinatory drug delivery systems is not just a matter of simple drug combination. Besides the cytotoxicity and pro-apoptotic ability, tumor accumulation, tumor penetration, or vascular targeting may also influence the eventual antitumor effect of the combinatory system.

The Effect of Liposomes on the Kinetics and Mechanism of the Photocatalytic Reduction of 5,5'-Dithiobis(2-Nitrobenzoic Acid) by Triethanolamine

Recently, the addition of negatively charged liposomes was shown to increase the quantum yield of the photocatalytic reduction of 5,5'-dithio(2-nitrobenzoic acid) (H₂DTNB) to 2-nitro-5-thiobenzoic acid (H₂NTB) by triethanolamine using meso-tetra(4-(N-methylpyridinium)porphyrinato zinc chloride as photosensitizer. In this work, we investigate in detail the kinetics of this photocatalytic reaction both in homogeneous solution and at the surface of negatively charged liposomes, to unravel the effects of liposomes on the mechanism of the photoreaction. In homogeneous solution, the reaction is initiated by oxidative quenching. Both static (singlet) and dynamic (triplet) quenching of the photosensitizer contribute to the formation of the photoproduct. In these conditions, the reaction is limited by the low efficiency of reductive regeneration of the photosensitizer, compared to charge recombination. Upon adsorption of the positively charged photosensitizer to the negative surface of the liposomes, however, both static and dynamic oxidative quenching become ineffective due to electrostatic repulsion of the dianionic DTNB^2- from the negatively charged membrane. In such conditions, photoreduction occurs via reductive quenching, showing that the addition of liposomes can truly modify the mechanism of photocatalyzed redox reactions.

Self-assembled monolayer formation of a (N5)Fe(ii) complex on gold electrodes: electrochemical properties and coordination chemistry on a surface

A coordinatively unsaturated Fe^II complex bearing a pentadentate ligand (N,N',N'-tris(2-pyridyl-methyl)-1,2-diaminoethane) functionalized with a cyclic disulfide group has been prepared in order to graft reactive metal entities as self-assembled monolayers (SAMs) on gold electrodes. Prior to grafting, exogenous ligand exchange has been investigated by cyclic voltammetry (CV) in solution, showing that the nature of the first coordination sphere (N₅)Fe^II-X (X = Cl^-, OTf^-, MeCN, acetone) can be tuned, thanks to the control of the chemical conditions. The Fe^II complex has been immobilized on gold electrodes by spontaneous (passive) adsorption as well as by an electro-assisted method. The resulting SAMs were characterised by XPS and AFM analyses. CV experiments implementing these SAMs as working electrodes showed that the first coordination sphere of the grafted Fe^II complex can be controlled by adjusting the chemical conditions, similarly to the studies in a homogeneous solution. Finally, the supported Fe^II complex proved to be reactive with superoxide generated at the electrode surface by reduction of dissolved dioxygen. Under the employed conditions, leaking of the metal complex was not observed.

Iodide-Photocatalyzed Reduction of Carbon Dioxide to Formic Acid with Thiols and Hydrogen Sulfide

The photolysis of iodide anions promotes the reaction of carbon dioxide with hydrogen sulfide or thiols to quantitatively yield formic acid and sulfur or disulfides. The reaction proceeds in acetonitrile and aqueous solutions, at atmospheric pressure and room temperature by irradiation using a low-pressure mercury lamp. This transition-metal-free photocatalytic process for CO₂ capture coupled with H₂ S removal may have been relevant as a prebiotic carbon dioxide fixation.

Electrochemical and spectroscopic insights of interactions between alizarin red S and arsenite ions

ARS molecules are deprotonated in the presence of arsenite ions. The deprotonated form of ARS molecules show increase of charge transfer resistance and decrease of diffusion coefficient.

Chiral 1,2-dithiine as a sulfur rich electron acceptor

Both enantiomers of a 1,2-dithiine containing two 1-phenylethyl groups of the same chirality were selectively synthesized and electrochemically and spectro-electrochemically characterized.

Understanding intrinsically irreversible, non-Nernstian, two-electron redox processes: a combined experimental and computational study of the electrochemical activation of platinum(IV) antitumor prodrugs

Six-coordinate Pt(IV)-complexes are prominent prodrug candidates for the treatment of various cancers where, upon two-electron reduction and loss of two axial ligands, they form more familiar, pharmacologically active four-coordinate Pt(II) drugs. A series of electrochemical experiments coupled with extensive density functional calculations has been employed to elucidate the mechanism for the two-electron reduction of Pt(IV)(NH3)2Cl2L2 to Pt(II)(NH3)2Cl2 (L = CH3COO(-), 1; L = CHCl2COO(-), 2; L = Cl(-), 3). A reliable estimate for the normal reduction potential E(o) is derived for the electrochemically irreversible Pt(IV) reduction and is compared directly to the quantum chemically calculated reduction potentials. The process of electron transfer and Pt-L bond cleavage is found to occur in a stepwise fashion, suggesting that a metastable six-coordinate Pt(III) intermediate is formed upon addition of a single electron, and the loss of both axial ligands is associated with the second electron transfer. The quantum chemically calculated reduction potentials are in excellent agreement with experimentally determined values that are notably more positive than peak potentials reported previously for 1-3.

Hammett correlations as test of mechanism of CO-induced disulfide elimination from dinitrosyl iron complexes

The use of Hammett correlations provide experimental evidence for an unusual role of the frontier molecular orbitals of an iron dinitrosyl unit in CO induced reductive elimination of disulfide.

Switching on/off the chemisorption of thioctic-based self-assembled monolayers on gold by applying a moderate cathodic/anodic potential

An in situ and real-time electrochemical method has been devised for quantitatively monitoring the self-assembly of a ferrocene-labeled cyclic disulfide derivative (i.e., a thioctic acid derivative) on a polycrystalline gold electrode under electrode polarization. Taking advantage of the high sensitivity, specificity, accuracy, and temporal resolution of this method, we were able to demonstrate an unexpectedly facilitated formation of the redox-active SAM when the electrode was held at a moderate cathodic potential (-0.4 V vs SCE in CH3CN), affording a saturated monolayer from only micromolar solutions in less than 10 min, and a totally impeded SAM growth when the electrode was polarized at a slightly anodic potential (+0.5 V vs SCE in CH3CN). This method literally allows for switching on/off the formation of SAMs under "soft" conditions. Moreover the cyclic disulfide-based SAM was completely desorbed at this potential contrary to the facilitated deposition of a ferrocene-labeled alkanethiol. Such a strikingly contrasting behavior could be explained by an energetically favored release of the thioctic-based SAM through homolytic cleavage of the Au-S bond followed by intramolecular cyclization of the generated thiyl diradicals. Moreover, the absence of a discernible transient faradaic current response during the potential-assisted adsorption/desorption of the redox-labeled cyclic disulfide led us to conclude in a potential-dependent reversible surface reaction where no electron is released or consumed. These results provide new insights into the formation of disulfide-based SAMs on gold but also raise some fundamental questions about the intimate mechanism involved in the facilitated adsorption/desorption of SAMs under electrode polarization. Finally, the possibility to easily and selectively address the formation/removal of thioctic-based SAMs on gold by applying a moderate cathodic/anodic potential offers another degree of freedom in tailoring their properties and in controlling their self-assembly, nanostructuration, and/or release.

Electron capture by the thiyl radical and disulfide bond: ligand effects on the reduction potential

The effect of non-polar and polar ligands and of monovalent cations on the one-electron reduction potential of the thiyl radical and the disulfide bond was evaluated. The reduction potentials E° for the CH3S(.)-nL/CH3S(-)-nL and CH3SSCH3-L/CH3SSCH3(.-)-L redox couples were calculated at the B3LYP, M06-2X and MP2 levels of theory, with n=1, 2 and L=CH4, C2H4, H2O, CH3OH, NH3, CH3COOH, CH3CONH2, NH4(+), Na(+), K(+) and Li(+). Non-polar ligands decrease the E° value of the thiyl radical and disulfide bond, while neutral polar ligands favour electron uptake. Charged polar ligands and cations favour electron capture by the thiyl radical while disfavouring electron uptake by the disulfide bond. Thus, the same type of ligand can have a different effect on E° depending on the redox couple. Therefore, properties of an isolated ligand cannot uniquely determine E°. The ligand effects on E° are discussed in terms of the vertical electron affinity and reorganization energy, as well as molecular orbital theory. For a given redox couple, the ligand type influences the nature of the anion formed upon electron capture and the corresponding reorganization process towards the reduced geometry.

Reactions of CH3SH and CH3SSCH3 with gas-phase hydrated radical anions (H2O)n(•-), CO2(•-)(H2O)n, and O2(•-)(H2O)n

The chemistry of (H(2)O)(n)(•-), CO(2)(•-)(H(2)O)(n), and O(2)(•-)(H(2)O)(n) with small sulfur-containing molecules was studied in the gas phase by Fourier transform ion cyclotron resonance mass spectrometry. With hydrated electrons and hydrated carbon dioxide radical anions, two reactions with relevance for biological radiation damage were observed, cleavage of the disulfide bond of CH(3)SSCH(3) and activation of the thiol group of CH(3)SH. No reactions were observed with CH(3)SCH(3). The hydrated superoxide radical anion, usually viewed as major source of oxidative stress, did not react with any of the compounds. Nanocalorimetry and quantum chemical calculations give a consistent picture of the reaction mechanism. The results indicate that the conversion of e(-) and CO(2)(•-) to O(2)(•-) deactivates highly reactive species and may actually reduce oxidative stress. For reactions of (H(2)O)(n)(•-) with CH(3)SH as well as CO(2)(•-)(H(2)O)(n) with CH(3)SSCH(3), the reaction products in the gas phase are different from those reported in the literature from pulse radiolysis studies. This observation is rationalized with the reduced cage effect in reactions of gas-phase clusters.

Radiolytic Reduction Characteristics of Artificial Oligodeoxynucleotides Possessing 2-Oxoalkyl Group or Disulfide Bonds

A number of advances have been made in the development of modified oligodeoxynucleotides (ODNs), and chemical or physical properties of which are controlled by external stimuli. These intelligent ODNs are promising for the next generation of gene diagnostics and therapy. This paper focuses on the molecular design of artificial ODNs that are activated by X-irradiation and their applications to regulation of hybridization properties, conformation change, radiation-activated DNAzyme, and decoy molecules.