Ravi Joshi

Free radical scavenging behavior of folic acid: evidence for possible antioxidant activity.

The free radical scavenging properties and possible antioxidant activity of folic acid are reported. Pulse radiolysis technique is employed to study the one-electron oxidation of folic acid in homogeneous aqueous solution. The radicals used for this study are CCl(3)O(2)(*), N(3)(*), SO(4)(*-), Br(2)(*-), *OH, and O(*-). All these radicals react with folic acid under ambient condition at an almost diffusion-controlled rate producing two types of transients. The first transient absorption maximum is around 430 nm, which decays, and a simultaneous growth at around 390 nm is observed. Considering the chemical structure of folic acid, the absorption maximum at 430 nm has been assigned to a phenoxyl radical. The latter one is proposed to be a delocalized molecular radical. A permanent product has been observed in the oxidation of folic acid with CCl(3)O(2)(*) and N(3)(*) radicals, with a broad absorption band around 370-400 nm. The bimolecular rate constants for all the radical-induced oxidation reactions of folic acid have been measured. Folic acid is seen to scavenge these radicals very efficiently. In the reaction of thiyl radicals with folic acid, it has been observed that folic acid can not only scavenge thiyl radicals but can also repair these thiols at physiological pH. While carrying out the lipid peroxidation study, in spite of the fact that folic acid is considerably soluble in water, we observed a significant inhibition property in microsomal lipid peroxidation. A suitable mechanism for oxidation of folic acid and repair of thiyl radicals by folic acid has been proposed.

Influence of I− anions on the formation and stabilization of copper nanoparticles

Abstract Copper nanoparticles have been prepared by the reduction of copper(II) sulfate in an aerated water using sodium borohydride at room temperature and stabilized by inorganic anion. Mechanistic steps for the stabilization provided by iodide anion was studied using pulse radiolysis technique. Various inorganic anions have been used to stabilize Cu nanoparticles and compared for their stabilization efficiency. The synthesized nanoparticles exhibit a distinct absorption maximum in the region 560–565 nm. The average size as estimated from TEM micrographs has been found to be in the range 8–10 nm.

Bilirubin as an anti precipitant against copper mediated denaturation of bovine serum albumin: formation of copper-bilirubin complex.

BR forms a beautiful 1:1 greenish complex with Cu2+, having a characteristic absorption maximum at 343 nm. To our knowledge, this is the first metal complex of bilirubin in aqueous solution so far to be reported. It has also been shown that bilirubin (BR) at a concentration more than protein binding capacity has a definite role as an anti precipitant of bovine serum albumin by excess copper. At a concentration of 1 x 10(-3) moll-1 of the Cu-BR complex, the colour becomes greenish black. The rate of formation of this Cu-BR complex when BR extracts copper from copper-albumin complex as obtained in our experiment is 34.981 mol-1 s-1. The Cu-BR complex is stable at a pH ranging from 3.5 to 13.2, and also can scavenge radicals like CCl3OO., eaq- and OH.. Addition of excess copper sulfate to the solution of this complex causes a greenish black precipitate which can be re dissolved in HCl but insoluble in 99% ethanol. The complex does not give positive test in Gmelin reaction for bile pigments. The fluorescence spectrum of the complex in solution exhibits a peak at 450 nm when excited at 343 nm. The precipitated complex is insoluble in a number of solvents like ether, xylene, benzene, acetone, chloroform-methanol mixture and DMSO. These results show that BR may protect mammals from copper poisoning.

Hydrogen bonding in neutral and cation dimers of H2Se with H2O, H2S, and H2Se.

Structures, hydrogen bonding, and binding energies of H(4)SeA (A = O, S, Se) dimers and their cation radicals have been studied using DFT-B3LYP, MP2, and CCSD methods with 6-31++G(d,p), cc-pVTZ, and aug-cc-pVTZ basis sets. The binding energy (BE) order of the most stable neutral and cationic dimers have been found to be (H(2)Se···HOH) > (H(2)Se···HSH) > (H(2)Se···HSeH), and (H(2)Se···SeH(2))(+) > (H(2)Se···SH(2))(+) > (HSe···HOH(2))(+), respectively, by B3LYP/6-31++G(d,p) and MP2/aug-cc-pVTZ methods. Higher electronegativity of the heteroatom has been found to result in more stability of the neutral dimer but less of the cationic dimer. Among neutral dimers, structure with more electronegative heteroatom acting as proton donor has been found to be more stable. However, the hemibonded structure has been found to be more stable for the dimer cation radical unless the ionization potentials of the involved heteroatoms are very different, e.g., H(4)SeO(+). Vibrational frequency calculation suggests that an increase in electronegativity of A-atom results in a decrease in Se-H bond strength in H(4)SeA and H(4)SeA(+) dimers. The calculated values of Mulliken atomic charge/spin and hydrogen bond lengths of the dimers and their radical cations have also been discussed.

Effect of solvent viscosity, polarity and pH on the charge transfer between tryptophan radical and tyrosine in bovine serum albumin: a pulse radiolysis study

The effect of viscosity, solvent polarity and pH of the medium on the reaction of a protein, bovine serum albumin (BSA), with organohalo-peroxyl radical in aqueous solution has been studied using pulse radiolysis technique. Unlike in dilute aqueous solution, electron transfer from tyrosine to tryptophan radical in BSA has been clearly observed at a viscosity of 7.7 centiPoise (cP). The oxidation of BSA, tryptophan and tyrosine in different media has also been compared with those taking place in dilute aqueous solution. The effect of solvent characteristics on the observed charge transfer has been discussed.

Charge transfer between tryptophan and tyrosine in casein: a pulse radiolysis study

Charge transfer from tyrosine to tryptophan radicals in bovine milk casein, as observed using pulse radiolysis technique, is reported. The reactions of casein with hydroxyl, azide, Br(2)(*-) and CCl(3)O(2)(*) radicals have also been studied. Radical transformation was found to take place at a rate of 1.5 x10(4) s(-1). The effect of pH, oxidising radical and the proximity of tyrosine and tryptophan on this radical transformation, as well as repair of the casein radical by ascorbate, have also been studied.

Hydrated electrons in water-in-oil microemulsion: a pulse radiolysis study

Abstract Half-life and yield of hydrated electron in water-in-oil microemulsion of cetyl trimethylammonium bromide-water-1-pentanol-cyclohexane system has been studied. Dose distribution calculation suggests scavenging of electrons that are generated in cyclohexane by water pools and hydroxyl radical generation by direct water radiolysis only. Dose distribution, half-life of e aq − , generation and solvation of e aq − in this system and its comparison with other systems have been discussed.

Base line radioactivity levels in Kaiga site soil and its migration to biosphere

The effects of variation in different parameters on the environmental distribution of base line 137Cs and 40K activities in Kaiga environment and their migration into biosphere are discussed. Transfer factors of these radionuclides from soil to different parts of commonly available plants in this region were estimated. Base line radioactivity levels in soil at Kaiga were higher as compared to pre-operational values reported from other power station sites in India and were mainly attributed to the very high precipitation rate prevailing in this area. Also, this area being an undisturbed forest land, fallout activities are re-circulated to the soil by the decay of parts of trees.40K and 137Cs activity levels in leaves of shallow rooted plants were found to be higher as compared to that in deep rooted trees. Transfer factors of soil to plant parts revealed that there is no major bio-accumulation of 137Cs in any parts of Colocassia esculenta (L.) and Chromolaena odorata (L.) King & Robinson. Comparison of 40K/137Cs ratio between soil and different parts of these plants has revealed that uptake of K is relatively more efficient as compared to that of Cs, presumably because of the faster kinetics of K due to its larger atom inventory in the soil.

Free radical reactions of pyridoxal (vitamin B6): a pulse radiolysis study

Redox reactions of pyridoxal (P-OH) with e¯aq, .OH, N.3, SO.4¯ and various organo-haloperoxyl radicals have been studied using pulse radiolysis technique. The rate constants for the reaction of P-OH or P-O¯ with the above-mentioned radicals and the transient absorption spectra have been measured. The transients formed in the reaction of hydrated electron and oxidizing radicals with pyridoxal have been assigned. An attempt has been made to find a correlation between the rate constants and Taft parameter for the reactions with the organo-haloperoxyl radicals. It has also been observed that the one-electron oxidized radical of pyridoxal is repaired by uric acid. The reduction potential for the P-OH.+/P-OH couple at pH 7, as measured by cyclic voltammetry, has been found to be +1.11 V vs. NHE.

Pulse radiolytic studies of metallic clusters in a quaternary microemulsion system

The radiation-chemical reduction of Tl+, Co2+ and Ni2+ ions in water-in-oil microemulsion has been described. Rate constants for the reduction of the metal ions by e-aq were found to be much lower compared to those in aqueous solution. The absorption spectrum and the rate constants of formation of the transient intermediates of metal clusters were correlated with the water-pool size, surrounding environment and compared with data in aqueous solution. Tl2+ reacts with Cd2+ with k = 1.1 × 108 M-1 s-1. Reactions of Tl2+ and Co+ with Ag+ leads to the formation of Ag metal particles. No reaction was observed from Cd+ to Tl+ or Co2+. The results are discussed in terms of dynamic exchange of materials between the polar cores of microemulsion. This exchange facilitates formation of silver particles.