Electrochemical reduction of 4-aminopyrimidine and cytosine in dimethyl sulfoxide

The electrochemical reduction in dimethyl sulfoxide of cytosine (4-amino-2-hydroxypyrimidine) and one of its model compounds (4-aminopyrimidine) has been examined. Initially, each pyrimidine (RH) undergoes a reversible, diffusion-controlled one-electron reduction of the 3,4 N=C double bond to the radical anion (RH⁻, which can dimerize or can react with the parent compound (father-son reaction) to form the neutral free radical (RH₂) and the pyrimidine anion (R⁻); the radical can dimerize or be further reduced, perhaps after effectve protonation; the anion forms a redox couple with Hg(1)−Hg(0). Other coupled reactions, which may occur under suitable conditions, include reaction between anionic dimer (⁻RH−RH⁻) and RH, proton-assisted decomposition of dimer to form reducible RH₃⁺, and deamination of the two-electron reduction product (RH₃), which is a gem diamine, to generate 2-hydroxypyrimidine or pyrimidine itself. The effects on the electrochemical redox pattern of added water, strong acid (HClO₄), weak acid (chloroacetic and benzoic acids), and strong base (Et₄NOH) are described.     

Study of sulfur dioxide reduction mechanism in dimethyl sulfoxide

The electroreduction of sulfur dioxide in DMSO has been studied by normal and dp polarography, controlled-potential coulometry and cyclic voltammetry. Results suggest that the main process in the electrochemical reduction of sulfur dioxide in DMSO is a one-electron reversible reduction, followed by a reduction product dimerization according to:

$\begin{array}{l}{SO}_2+\mathit{e}?{SO}_2^{?}\\ 2{SO}_2^{?}\underset{K_f}{\overset{K_d}{?}}{S}_2{O}_4^{2?}\end{array}$

The behavior of the electrochemical parameters as function of depolarizer concentration and potential scan rate is consistent with the mechanism mentioned. In this case there is a transition between a pure kinetic control and a fast equilibrated dimerization.Moreover, the main process of SO₂ discharge is complicated by secondary reactions. Therefore, polarographic measurements have been also carried out with Na₂S₂O₄ solutions in DMSO. Furthermore, the influence that the nature and concentration of the supporting electrolyte exert on SO₂ reduction in DMSO has been studied.     

Reactions between a superoxide anion and alkyl bromides in dimethyl sulfoxide

The activation parameters of the reactions between a superoxide anion (O₂^·−) and alkyl bromides are measured. An ab initio study of the transition states for various mechanisms of this reaction is performed. The mechanism of radical separation in a polar solvent becomes competitive upon an increase in the number of alkyl groups in an alkyl bromide molecule and depends on their arrangement relative to a reaction center.     

Electrochemical investigation of 1,3,5-triphenylformazan and its nitro derivatives in dimethyl sulfoxide.

Cyclic voltammetric (CV) and chronoamperometric (CA) behaviors of 1,3,5-triphenylformazan (TPF), 3-(p-nitrophenyl)-1,5-diphenylformazan (PNF) and 3-(m-nitrophenyl)-1,5-diphenylformazan (MNF) were studied in dimethyl sulfoxide medium. TPF was found to give a single sharp cathodic CV peak corresponding to a gain of one-electron per molecule. The diffusion coefficient and the number of electrons transferred were calculated using the Baranski equation with the CV-data obtained by an ultramicroelectrode. Standard rate constants for the reduction were calculated by the Klingler-Kochi technique. The electrochemical data obtained support the mechanism proposed by Umemoto.     

Electrochemical determination of the superoxide ion concentration from KO2 dissolved in dimethyl sulfoxide.

An electrochemical determination of the O2- concentration from KO2 in DMSO solution using steady state microelectrode voltammetry shows that the KO2/DMSO method with the combined use of a crown compound or sonication is a reliable and simple technique for introduction of O2- to the biomimitic reaction system.     

Thermolysis of dimethyl sulfoxide

The thermal decomposition of dimethyl sulfoxide at small extent of reaction has been studied at temperatures of 297-350°C and pressures of 10–400 Torr. The major products CH₄, C₂H₄, and SO₂ were shown to follow first-order kinetics. The activation energies for production of each was about 48 kcal·mole^?1. A chain mechanism has been postulated in the light of the results of isotopic substitution experiments.     

Carbocation-forming reactions in dimethyl sulfoxide

Mesylate derivatives of 3-aryl-3-hydroxy-beta-lactams and thiolactams react in DMSO-d(6) by first-order processes to give alcohol products. Substituent effect studies implicate carbocation intermediates (ion-pairs) that are captured by DMSO-d(6) to give transient oxosulfonium ions. Rapid reaction of the oxosulfonium ions with trace amounts of water leads to the alcohol product and regenerates DMSO-d(6). H(2)(17)O labeling studies show that (17)O is incorporated into the DMSO. The mesylate derivatives of endo- and exo-2-hydroxy-2-phenylbicyclo[2.2.1]heptan-3-one also react in DMSO-d(6) to give the alcohol products. Ion-pair intermediates that capture DMSO giving unstable oxosulfonium ions are again proposed. Exo-2-phenyl-endo-bicyclo[2.2.1]heptyl trifluoroacetate readily eliminates trifluoroacetic acid in DMSO-d(6) via a cationic mechanism involving loss of the endo-trifluoroacetate leaving group as well as an exo-hydrogen. The O-methyl oxime derivative of alpha-chloro-alpha,alpha-diphenylacetophenone reacts in DMSO-d(6) to give 1-methoxy-2,3-diphenylindole, a product derived from cyclization of a cationic intermediate. A common ion rate suppression provides further evidence for a cationic mechanism. The triflate derivative of pivaloin reacts by a cationic mechanism in DMSO-d(6) to give rearranged products. The rate is even faster than in highly ionizing solvents such as trifluoroethanol or trifluoroacetic acid. 1-Adamantyl mesylate reacts in DMSO-d(6) by a first-order process (Y(OMs) = -4.00) to give a long-lived oxosulfonium ion, 1-Ad-OS(CD(3))(2)(+), which can be characterized spectroscopically. This oxosulfonium ion reacts only slowly with water at elevated temperatures to give 1-adamantanol. DMSO is therefore a viable solvent for k(s), k(C), and k(Delta) cationic processes.     

Electrochemical behavior of superoxide anion radical towards quinones: a mechanistic approach

Research on Chemical Intermediates - Among the reactive oxygen species, the superoxide anion radical (O 2 ·? ) has a fundamental role in several biological functions. Consequently, its...     

Vinylation of pyrroles in dimethyl sulfoxide

A number of 1-vinylpyrroles were obtained in up to 97% yields by base-catalyzed addition of substituted pyrroles to acetylene in dimethyl sulfoxide at 80–100°C.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 213–214, February, 1977.     

Preferential solvation of lysozyme by dimethyl sulfoxide in binary solutions of water and dimethyl sulfoxide

To reveal the denaturation mechanism of lysozyme by dimethyl sulfoxide (DMSO), thermal stability of lysozyme and its preferential solvation by DMSO in binary solutions of water and DMSO was studied by differential scanning calorimetry (DSC) and using densities of ternary solutions of water (1), DMSO (2) and lysozyme (3) at 298.15 K. A significant endothermic peak was observed in binary solutions of water and DMSO except for a solution with a mole fraction of DMSO (x ₂) of 0.4. As x ₂ was increased, the thermal denaturation temperature T _m decreased, but significant increases in changes in enthalpy and heat capacity for denaturation, ΔH _cal and ΔC _p, were observed at low x ₂ before decreasing. The obtained amount of preferential solvation of lysozyme by DMSO (∂g ₂/∂g ₃) was about 0.09 g g⁻¹ at low x ₂, indicating that DMSO molecules preferentially solvate lysozyme at low x ₂. In solutions with high x ₂, the amount of preferential solvation (∂g ₂/∂g ₃) decreased to negative values when lysozyme was denatured. These results indicated that DMSO molecules do not interact directly with lysozyme as denaturants such as guanidine hydrochloride and urea do. The DMSO molecules interact indirectly with lysozyme leading to denaturation, probably due to a strong interaction between water and DMSO molecules.     

Cyclopolymerization of diallylamine derivatives in dimethyl sulfoxide

Diallyl quaternary ammonium chlorides, bromides and N-alkyldiallylamine hydrochlorides were polymerized with ammonium persulfate (APS) in dimethyl sulfoxide (DMSO). The dependences of yield and molecular weight of polymers on polymerization conditions were examined and quaternary ammonium chlorides were found to have better polymerizability than bromides. The poly(diallyl quaternary ammonium chlorides) obtained with APS—DMSO system are expected to have quite high molecular weights, as determined from the measurement of limiting viscosity numbers of the polymers in NaCl aqueous solution.     

Polymerization of vinylene carbonate in dimethyl sulfoxide

Pure vinylene carbonate polymerizes readily in dimethyl sulfoxide solutions upon initiation by azobisisobutyronitrile (AIBN). The monomer conversion is characterized by a limiting value which appears to be a function of the temperature and the initial concentrations of both the initiator and the monomer. Increasing both initiator concentration and temperature results in higher final conversions, whereas a maximum conversion is indicated for initial monomer concentrations in the range of 80% to 90%. Principal kinetic quantities were found to be adequately represented by the equations k_d = 24.3 × 10⁵ exp {?11300/RT} and k_p(f/k_t)^1/2 = 46.3 × 10⁵ exp {?8900/RT} for the temperature range of 50–80°C. The average degree of polymerization was found to be affected by chain transfer to the solvent. A value of 5.8 × 10^?4 was determined for the corresponding chain transfer constant.     

Base-catalyzed dehydration of aldoximes in dimethyl sulfoxide

Conclusions A convenient method is proposed for the alkaline dehydration of aldoximes into nitriles in the presence of KOH in dimethyl sulfoxide at 140°.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 3, pp. 690–691, March, 1976.     

Thermodynamic properties of resveratrol in dimethyl sulfoxide

In this article, the enthalpies of dissolution of resveratrol in dimethyl sulfoxide (DMSO) were measured using a RD496-2000 Calvet microcalorimeter at 298.15?K under atmospheric pressure. The differential enthalpy (??_dif H _m) and molar enthalpy (??_sol H _m) of dissolution of resveratrol in DMSO were determined, and the relationship between heat and the amount of solute was also established. Based on the thermodynamic and kinetic knowledge, the corresponding kinetic equation, half-life, ??_sol H _m, ??_sol S _m, ??_sol G _m, the relative partial molar enthalpy (??_sol H _m(partial)) and the relative apparent molar enthalpy (??_sol H _m(app)) of the dissolution process were obtained. The results showed that this study not only provided a simple method for the determination of the half-life for a drug, but also offered a theoretical reference for the clinical application of resveratrol.     

Effects of microsolvation on uracil and its radical anion: uracil(H2O)n (n = 1-5)

Microsolvation effects on the stabilities of uracil and its anion have been investigated by explicitly considering the structures of complexes of uracil with up to five water molecules at the B3LYPDZP++ level of theory. For all five systems, the global minimum of the neutral cluster has a different equilibrium geometry from that of the radical anion. Both the vertical detachment energy (VDE) and adiabatic electron affinity (AEA) of uracil are predicted to increase gradually with the number of hydrating molecules, qualitatively consistent with experimental results from a photodetachment-photoelectron spectroscopy study [J. Schiedt et al., Chem. Phys. 239, 511 (1998)]. The trend in the AEAs implies that while the conventional valence radical anion of uracil is only marginally bound in the gas phase, it will form a stable anion in aqueous solution. The gas-phase AEA of uracil (0.24 eV) was higher than that of thymine by 0.04 eV and this gap was not significantly affected by microsolvation. The largest AEA is that predicted for uracil(H2O)5, namely, 0.96 eV. The VDEs range from 0.76 to 1.78 eV.