K. N. Rao

One-electron reduction of thionine studied by pulse radiolysis

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.

Identity of intermediates formed on photolysis of CH2I2 and CHI3 in 3-methylpentane at 77 K

Abstract Transient intermediates formed on photolysis of CH2I2 and CHI3 in 3MP glass at 77 K have been characterized from their optical absorption and stable products analysis. Variation of stable products yields and intensity of absorption bands in presence of benzene, which is known to lessen solute clustering by molecular complex formation, has indirectly indicated solute aggregation at 77 K and formation of solute cations by energy transfer from excited solute molecules.

Separation and identification of the products of the photodegradation of 7-amino-4-methylcoumarin and the mechanism of its photodegradation

Abstract The separation of the products of the photodegradation of 7-amino-4-methylcoumarin (C120), a laser dye, has been achieved by a reverse phase high performance liquid chromatography method. Two reverse phase columns (C6 and ODS) were used to optimize the separation conditions and various mixtures of methanol and water served as the mobile phase. The chromatograms representing the separation of the photolyte from the photoproducts under various experimental conditions are also shown. The fluorescent photodegradation product in an oxygenated methanolic solution of the dye has been separated by column chromatography assisted by thin layer chromatography and high performance liquid chromatography. The structure of the compound has been ascertained by mass spectrometric and IR spectroscopic analysis and found to be 7-amino-3-hydroxy-4-methyl-coumarin. A mechanism is suggested for the formation of this product by the interaction of singlet oxygen and the dye. On the basis of the behaviour of the dye in degassed solutions, a general scheme is postulated to represent the photobleaching of C120.

The radiation-induced oxidation of n-heptane

Abstract The radiation-induced oxidation of n-heptane is studied at ⋍ 30°C. The yields of individual heptanols and heptanones have been measured. n-heptanol and heptaldehyde were not observed in this system. The yield of heptanone isomers was found to be in the ratio 2:2:1. Scavenger studies were carried out to elucidate the mechanism of the oxidation reaction. It is postulated that excited states of heptane lead to the formation of ketones and the excited state leading to 3-heptanone is different from the one leading to the other two isomers.

Radiation protection of vitamins in aqueous systems. Part II. A comparative study in fluid and frozen aqueous systems

Abstract A study of the radiation induced decomposition of the B-group vitamins has been carried out in aqueous media at room temperature as well as in rigid matrices at low temperature. The detailed results on the effect of glucose and oxygen as protective additives at the different temperatures are presented in the case of Thiamine (Vitamin B1). Comparative data are given on the extent of decomposition of this and other vitamins of the B-group at room temperature and at 193 K. The importance of these results in connection with the radiation sterilization of pharmaceutical preparations is indicated.

Transient spectra and decay kinetics of semithionine radicals in sodium dodecylsulphate micellar media

Abstract The transient spectra and decay kinetics of semithionine species produced by the photoreduction of thionine by ferrous ions were studied in sodium dodecylsulphate (SDDS) micellar media. The results were compared with data obtained for a homogeneous aqueous medium. It was found that, whereas in the homogeneous aqueous medium there is evidence for the interaction of the semithionine species with ferrous ions, particularly at higher pH values and high ferrous ion concentrations, this is not the case in the micellar medium. Further, the decay of the semithionine species which is a kinetically second-order dismutation process in the homogeneous aqueous medium becomes pseudo first order in the SDDS micellar medium and is attributable to re-oxidation of semithionine by ferric ions adsorbed on the same micelle surface. From a comparison of the spectra in the two media at different pH values it is inferred that the species is more likely to be the doubly protonated semithionine TH. 32+ form in the micelle in the pH range 0 – 2.5. Addition of high concentrations of electrolytes such as NaCl had no effect on the spectrum of the species in the micellar medium, but the decay reverted to second order. This has been interpreted in terms of displacement of the ferric ions from the micelle surface into the bulk aqueous phase such that dismutation becomes the only pathway available for semithionine decay. The dismutation rate was found to decrease with increases in the concentration of the micellized surfactant in qualitative agreement with the pseudophase model of micellar kinetics.

Radiation initiated polymerisation of phenyl methacrylate

Abstract Radiation initiated polymerisation of phenyl methacrylate has been studied at various dose rates and temperature. Predominant chain transfer to the monomer was observed and ktran/kp the chain transfer constant ratio was found to be 4 x 10 -2 · k p k t 1 2 value determined by the kinetic data and the molecular weight data were 0.0821 and 0.0198, respectively. IR studies of polymer at low conversion showed the presence of terminal unsaturation which disappeared at saturation conversion, thus showing its participation in the formation of a three dimensional network.

Effect of 60Co γ-rays on polyphenyl methacrylate obtained by γ-ray irradiation

Abstract Polyphenyl methacrylate of different molecular weights Mn 13000, 34500 and crosslinked polymer prepared by 60Co γ-irradiation has been irradiated with 60Co γ-rays at 300 K. G(scission) of the 13000 molecular weight polymer was 15. The crosslinked polymer undergoes both degradation and crosslinking. G(x) value determined for that polymer is ∼ 9. The gaseous product consists largely of CO with some CO2 and H2. Hydrocarbon gases were not detected. The yield of H2 is only to the extent of 2–5% of the total gas and it is assumed that majority of scission takes place at the ester linkage. On the basis of the estimation of phenol and benzene, a mechanism for degradation and crosslinking is proposed.

Riboflavin as a new versatile solute for the determination of OH radical rate constants by the competition kinetic technique

Riboflavin (RF) has been used as a standard for the determination of OH radical rate constants by the competition kinetic method. In oxygenated solutions its radiolytic decomposition was found to closely correspond to G(-RF) = (12)GOH. Its rate constant was first evaluated by employing ethanol as the standard and taking kOH+C2H5OH = 1.85 × 109 dm3mol-1s-1. The kOH+RF value was found to be constant (= 1.2 ± 0.05 × 1010dm3mol-1s-1) over the pH range 1–11. Using this value the rate constant for reaction of a number of other solutes have been determined and compared with literature values. The advantages of riboflavin over other standard solutes are discussed.

Radiation effects on chlorobenzoic acids in aqueous solutions

Abstract The effect of gamma rays on aqueous solutions of orthochlorobenzoic acid (OCBA), metachlorobenzoic acid (MCBA) and parachlorobenzoic acid (PCBA) have been studied. The H atom rate constants for OCBA and MCBA have been determined in a degassed solution of 0.8 N H2 SO4 using isopropanol as the competitor and determining G(H2) at different concentration ratios of the competitors. Similarly, the OH radical rate constants have been determined for all three chlorobenzoic acids at pH 7.0 in oxygenated solution using isopropanol as the competitor and measuring acetone yields at different concentration ratios of the chlorobenzoic acids and isopropanol. The hydrated electron rate constants were measured at pH 11 by measuring the decay of the e − aq in presence of the chlorobenzoic acids. G(CO2), G(H2O2) and G(Cl−) have also been measured and their yields have been discussed. Paper chromatography of the products revealed 4–6 components in each case.