• P N Moorthy

      Articles written in Journal of Chemical Sciences

    • Differential pulse polarographic study of thiamine (vitamin B1) in neutral and acidic aqueous solutions

      P N Moorthy Kamal Kishore K N Rao

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      The differential pulse (dp) polarograms of thiamine in neutral aqueous solutions exhibited six peaks at low depolarizer concentration (⋦10−4 mol dm−3) and only three peaks at concentrations ≥10−3 mol dm−3. Only one of these was found to correspond to the diffusion-controlled reduction of this compound at the dme and this was shown to be an irreversible two-electron process. The kinetic parameters derived from the dp polarograms were found to be in good agreement with those calculated from classical polarograms and were:E1/2=−1·261 Vvs SCE,ana=0·54 andD≈3·5×10−6 cm2 sec−1 for 10−3 mol dm−3 thiamine in 0·1 mol dm−3 acetate buffer (pH 6·5). The reduction product has been identified as dihydrothiamine. The effect of pH on the dpp of thiamine was studied in the pH range 0–7. In the pH region 5·5 to 7·0 only one peak attributable to the B1+ form of thiamine is present. In the pH region 3·5–5·5 another dpp peak attributable to the protonated form (B1H2+) of thiamine was also observed. At pHs less than 3 only one peak was observed which could be attributed to the doubly protonated form (B1 H23+) of thiamine. Surfactants like triton-X-100 and CTABr were found to inhibit the electroreduction of thiamine due to the strong adsorption of these compounds on the dme. Thiamine itself was found to have an inhibitory effect on its own electroreduction, although to a smaller extent.

    • Spectral and fluorimetric studies on the effect of surfactants on thionine

      S N Guha P N Moorthy K N Rao

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      The effect of surfactants on the absorption and emission properties of thionine (TH+) have been studied in detail. Among the various surfactants investigated sodium lauryl sulphate (SLS) has marked effect on these properties. Changes in the absorption spectrum and the decrease in fluorescence intensity at [SLS] below the critical micelle concentration (CMC) are attributed to the formation of a dye-surfactant complex. At [SLS] above CMC, the restoration of dye spectrum with increased extinction coefficient at the λmax and a small but definite red shift of the λmax are interpreted as due to the incorporation of the dye into the SLS micelle. The absorbance and spectral shift data suggest the thionine cation to be localized near the micelle Stern layer in the case of SLS micelles but completely outside the micelle in the aqueous environment in the case of CTABr. From the absorbance and fluorescence data, the association constant for the formation of the TH+-SLS complex in the premicellar region, and the binding constant for the incorporation of the dye into the micelle in the micellar region have been computed. The values of both these constants were found to increase markedly in the presence of electrolytes.

    • Photoprocesses in sodium decyl sulphate micellar media

      D B Naik P N Moorthy

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      The absorption and fluorescence behaviour of thionine dye in sodium decyl sulphate (sds) medium has been studied in detail. The transient spectra and kinetics of decay of semithionine species produced by photoreduction of thionine by ferrous ions has-been studied using flash photolysis technique. The results have been compared with those in neat aqueous medium and in sodium lauryl sulphate (sls) media published earlier. It was found that the decay of semithionine which is kinetically second order in neat aqueous medium becomes pseudo first order as in thesls medium; however unlike in the latter case, the pseudo first order rate decreases with increasing surfactant concentration at all concentrations of ferric ion. The effect of electrolyte concentration on transient semithionine spectra and decay kinetics has also been studied. It was found that with increasing NaCl concentration the transient absorbance decreases and the decay slowly reverts back to second order as in aqueous medium. Insds medium as compared tosls a much higher concentration of NaCl is needed for the reaction to become second order which is attributed to stronger binding of ferric ions to thesds micelles.

    • One-electron reduction of thionine studied by pulse radiolysis

      S N Guha P N Moorthy K Kishore D B Naik K N Rao

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      One-electron reduction of thionine has been studied by using the technique of nanosecond pulse radiolysis and kinetic spectrophotometry. H,eaq as well as radicals derived from methanol, ethanol, isopropanol, THF, dioxane andt-butanol by H atom abstraction were used as reductants. The rate constants for the transfer of electrons from these radicalts to thionine were directly determined from the pseudo first-order formation rates of the product, semithionine and the one-electron reduction potential of thionine estimated. The absorption spectrum of semithionine in its different conjugate acid-base forms was found to be in agreement with previously reported spectra and the decay of the species was second order. By monitoring transient absorbance changes as a function of pH, twopKa values were observed and, based on the effect of ionic strength on the second-order decay constants of the species were assigned to the equilibria described.

    • Pulse radiolysis study of one-electron oxidation of thionine in aqueous solutions

      K Kishore S N Guha P N Moorthy

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      One-electron oxidation of thionine has been studied using specific oxidizing radicals such as ClTl(II) and N3 generated by pulse radiolysis of aqueous solutions. The semioxidized thionine exhibited threepK’s indicating four conjugate acid-base forms. N3 radicals were found to be less efficient in oxidizing thionine as compared to Cl2, Tl2+ and Tl(OH)+. The rate constants for electron abstraction from thionine by Cl2, Tl2+, Tl(OH)+, Tl(OH)2 and N3 were evaluated. The spectra of different protonated forms of semioxidized thionine and the extinction coefficients at λmax are presented. Reaction of OH radicals with thionine gave transient products whose spectra and acid-base properties were different from those of semioxidized thionine. The rate constant for formation of the product transient agrees well with competition kinetic value for reaction of OH with thionine reported earlier.

    • One-electron reduction of toluidine blue. A pulse radiolysis study

      J Mahadevan S N Guha K Kishore P N Moorthy

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      The technique of nanosecond pulse radiolysis has been used to study the one-electron reduction of toluidine blue. Apart from H andeaq various organic reducing radicals derived from isopropanol, tetrahydrofuran, cytosine etc. have been employed. The rate constants for the one-electron reduction was evaluated from build up traces. By monitoring the absorbance changes as a function of pH, twopKa values were obtained suggesting the existence of the species in three conjugate acid-base forms. The spectra of the different protonated forms were monitored and their characteristic features have been presented here. In the case of H-atoms it has been observed that in addition to the electron-transfer reaction, other processes like adduct formation also appear to be taking place. Using the redox titration method, with radicals of known redox potential the one-electron reduction potential of toluidine blue was also evaluated (vs. NHE).

    • One-electron oxidation of toluidine blue. A pulse radiolysis study

      J Mahadevan S N Guha K Kishore P N Moorthy

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      The one-electron oxidation of toluidine blue by specific oxidising radicals such as Cl2, Tl(II), N3, Br2 etc. has been studied by employing the pulse radiolysis technique. The Br2 radical was found to be less efficient in oxidising toluidine blue as compared to Cl2., Tl+2 and N3. The semioxidised species exhibited only onepKa indicating the presence of two conjugate acid-base forms whose spectral and kinetic features were evaluated. Reaction of OH radicals with the dye gave rise to a transient species which exhibited spectral and kinetic features different from that of the semioxidised species indicating that the mode of reaction of OH is different.

    • Pulse radiolysis of some aromatic sulphoxides in aqueous solutions

      K Kishore G R Dey P N Moorthy

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      Reactions ofeaq and H-atoms with aromatic sulphoxides such as dibenzyl, diphenyl and di-4-chlorophenyl sulphoxides have been studied at various pH values and the spectral and kinetic properties of the transients determined.eaq addition to dibenzyl sulphoxide was found to lead to the scission of the C−S bond giving benzyl radicals, but such bond breakage was not observed in other cases.

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