Sudhindra N. Bhattacharyya

Photodegradation of phenol by visible light in the presence of colloidal Fe2O3

Abstract The photocatalytic degradation of phenol in visible light was observed following different irradiation procedures. The reaction follows first-order kinetics, although adsorption effects appear, especially in the case of Fe2O3 immobilized in ordinary beach sand. The apparent rate constant ϰap and initial reaction rate are dependent on the pH, and reach a maximum at pH 5.5.

Radiation-induced inactivation of enzymes—A review

In vitro studies on the indirect effects of radiation on enzymes have been reviewed. For a better understanding an attempt has been made to classify radiation-induced inactivation of enzymes based on structural features of enzyme molecules. Oxygen effect on enzyme inactivation has also been emphasized. Inactivation caused by reactions with water-derived free radicals as well as with some inorganic and organic free radicals has been discussed.

Size effect in the photochemical generation of hydrogen from water by colloidal Fe2O3 particles

Abstract Colloidal Fe2O3 particles of various dimensions were prepared. Their crystal structure and optical properties were studied. These particles were used as photosensitizers for steady state water photolysis. The yield of H2 generated is dependent on the particle size and the concentration of the colloids. The pH dependence is different for different particle sizes. The effects of methylviologen (MV2+) as an electron relay and CH3OH as a hole scavenger on the H2 yield were also studied.

Colloidal ferric oxide: a new photosensitizer for grafting acrylamide onto cellulose acetate films

Abstract The photografting of acrylamide onto cellulose acetate films using light of wavelength > 380 nm is discussed. The semiconducting properties of colloidal Fe 2 O 3 (bandgap 2.2 eV) is used for photosensitizing the reaction. Degree of grafting is dependent upon the concentration of the photosensitizer as well as that of the monomer. Methyl viologen (MV 2+ ) is used to prevent e − −h + recombination.

Radiosensitization of thymine by copper(II) and nickel(II) complexes of metronidazole

Aqueous solutions of thymine (10(-3) mol dm(-3)) were irradiated with Co 60 gamma-rays in the absence and presence of metronidazole as well as its Cu(II) and Ni(II) complexes (10(-4) mol dm(-3)) under different conditions. The yields for the loss of thymine and those for the formation of the products of radiolysis were determined by hplc. The degradation of thymine when compared with that in the absence of metronidazole was not significantly altered. However, it increased significantly when the radiolysis of thymine was carried out in the presence of the Cu(II) and Ni(II) complexes of metronidazole. All three compounds were found to promote the formation of thymine glycol although the increase was more significant for the metal complexes than for free metronidazole. The higher radiosensitizing efficiency observed with the metal complexes as compared with that for free metronidazole is due to their higher rate of oxidation of the transient thymine-OH radical adduct. The reduction of the sensitizers results in the formation of the nitro-anion radical which in the case of the Cu(II) complex undergoes intramolecular electron transfer to the metal centre leading to the formation of Cu(I).

Extraction and separation of Zr, Nb and Hf by Aliquat 336 and its mixtures with TOPO from acidic thiocyanate media

Presence of thiocyanate ions results in appreciable extraction of Zr(IV) by Aliquat 336 from low aqueous HCl acidities, i.e., 0.1 to 4.5M. The variation of concentrations of HCl, thiocyanate and Aliquat 336 greatly influences the extent of extraction. Mixtures of Aliquat 336 and TOPO result in synergistic extraction of Zr and Hf from acidic thiocyanate media, the extracted species being the disolvate with TOPO. By controlled adjustment of HCl, SCN− and Aliquat 336 concentrations, separation of Zr, Nb and Hf is possible. A maximum separation factor (DNb/DZr) of 3675 has been achieved under certain conditions.

Toxicity of free and various aminocarboxylic ligands sequestered copper(II) ions to Escherichia coli.

Cytotoxicity of free Cu(II) ions and its complexes of EDTA, NTA or IDA in Escherichia coli (AB 4401) wild type cells were assessed by cell inactivation assay. In order to understand the toxic effects of these additives, membrane status by AFM vis-à-vis K(+) ion efflux were followed in the absence and in the presence of Cu(II) ions or its complexes. This was coupled with the determinations of cellular copper concentrations by atomic absorption spectrometry. The observed results show that free copper ions are more cytotoxic and cause considerable plasma membrane damage compared to that of Cu-EDTA, Cu-NTA and Cu-IDA. Determination of cellular copper reveals that Cu(2+) and Cu-NTA are able to enter inside the cells while Cu-EDTA and Cu-IDA fail to do that. This may be attributed to the electron affinity of free Cu(2+) ions and Cu-NTA, which help in binding with histidine present in copper transport proteins. In addition to cytotoxicity, genotoxicity of free copper and its complexes were also assessed on E. coli isogenic DNA repair proficient and repair-deficient strains. In contrast to free Cu(2+) ions, Cu-NTA does not cause any significant cytotoxicity but render greater genotoxicity.

Radiation-induced changes in flavin fluorescence of dihydroorotate dehydrogenase

The effect of gamma-radiation on the flavin moiety of dihydroorotate dehydrogenase was studied by fluorescence spectroscopy. Irradiation of aerated solutions (0-7 Gy) led to a small increase in fluorescence intensity, but with higher doses a decrease in intensity was observed. The increase in fluorescence intensity after irradiation at low doses may be attributed to protein unfolding, leading to greater exposure of flavin groups and a concomitant increase in separation between the flavin moiety and the iron-sulphur centre. This was confirmed by fluorescence quenching studies using potassium iodide as quencher. The Stern-Volmer constant calculated for iodide quenching indicates a two-fold increase in the fraction of flavin moiety being accessible to the quencher after 6.6 Gy. No spectral change was observed when unirradiated or irradiated enzyme was denatured with guanidine hydrochloride. However, a decrease in fluorescence intensity in the case of irradiated samples indicated a radiation-induced decrease in the flavin fluorophore. The flavin fluorophore loss in dihydroorotate dehydrogenase was also determined using aerated, argon-saturated or nitrous oxide-saturated solutions. H and OH radicals were found to have nearly equal contributions in damaging the flavin moiety of dihydroorotate dehydrogenase.

Effect of Iron (III) Ions on the Radiosensitivity of Uracil

Aqueous solutions of uracil(U) in the presence of iron(III) were irradiated with 60Co gamma-rays both in the presence and in the absence of dissolved oxygen. The products of radiolysis (uracil dimer, cis- and trans-uracil glycol, hydroxy-dihydrouracil and isobarbituric acid) were separated by means of paper chromatography using n-butanol: water (86:14) as the solvent. Radiolytic reduction of Fe(III) and the formation of Fe(II) were followed spectrophotometrically. In the absence of any additive, G(-U) is approximately 1.3, but with Fe(III) added G(-U) approaches a limiting value of 3.3 and the yield of cis-glycol increases. Radiosensitization by Fe(III) is found to be different from that of oxygen, which results in the yield of cis glycol decreasing and the yields of trans glycol and isobarbituric acid increasing. The mechanisms involved are discussed.

Gamma radiolysis of copper (II) nitrilotriacetate in aqueous solution

Aqueous solutions of copper (II) nitrilotriacetate (CuIINTA) were irradiated with 60Co-gamma rays in deaerated conditions as well as in the presence of various scavengers such as O2, N2O, NO–3, HCOO– and aliphatic alcohols. Both e–aq and H were found to reduce the metal ion directly. In the presence of scavengers such as HCOO– the reduced complex decomposes to yield Cu2O. The reaction of OH with the complex leads to the production of iminodiacetic acid (IDA) and the carbonyl compounds, formaldehyde and glyoxalic acid. It is argued that HCHO is formed in the system by the decomposition of transient CuIIINTA formed by oxidation of the metal ion by OH; CHOCOOH, on the other hand, is produced from the radical formed by hydrogen abstraction by OH from the α-carbon atom of the ligand. The rate constants for the two reactions have been evaluated by competition kinetic studies as (1.02 ± 0.06)× 109 dm3 mol–1 s–1 and (3.3 ± 0.3)× 108 dm3 mol–1 s–1 respectively. In the presence of the scavengers, N2O or NO–3 the metal ion is ultimately reduced to Cu2O. However, in the presence of aliphatic alcohols and in the absence of any scavenger, CuIINTA solutions acquired a red colour on radiolysis which was highly sensitive to oxygen. These red solutions were found to have characteristic broad absorption spectra, and these are ascribed to the presence of copper–carbon linkages. When the radiolysis was carried out in presence of oxygen neither the red coloration nor precipitation of Cu2O was observed.