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- Author or Editor: S. Mandal x
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Abstract
Dilute aqueous solutions of cytosine were irradiated with60Co 
-rays under N2O saturated conditions at different pH and in the presence of Cu(II) ions at neutral pH. The base degradation decreased from neutral to acidic and basic conditions. In the presence of metal ions at neutral pH conditions there was a significant increase in the base degradation compared to that in the absence of metal ions under similar conditions. From the difference absorption spectra and fluorescence behavior of the irradiated solutions it was observed that the major radiolytic products of cytosine under different conditions are cytosine glycols, 5-hydroxycytosine, hydroxy-hydrocytosine and cytosine dimers. The yields of dimers is maximum in neutral conditions and it decreased from basic to acidic conditions. However, in the presence of Cu(II) ions formation of cytosine dimers is completely restricted and there is an increase in the yields of cytosine glycol, hydroxy-hydrocytosine and 5-hydroxycytosine. From the post-radiolytic changes in absorption and fluorescence behavior of irradiated solutions, it is revealed that some of the radiolytic products, namely cytosine glycol and hydroxy-hydrocytosine decompose to 5-hydroxycytosine and cytosine, respectively.
Abstract
Reactions of carbonate radical (CO3 –), generated by photolysis or by radiolysis of a carbonate solution with nickel(II)-iminodiacetate (Ni(II)IDA) were studied at pH 10.5 and ionic strength (I)==0.2 mol·dm–3. The stable product arising from the ligand degradation in the complex is mainly glyxalic acid. Time-resolved spectroscopy and transient kinetics were studied using flash photolysis. From the kinetic data it was suggested that the carbonate radical initially reacts with Ni(III)IDA with a rate constant (2.4±0.4)·106 dm3·mol–1·s–1 to form a Ni(II)IDA species which, however, undergoes a first-order transformation (k=2.7·102·s–1) to give a radical intermediate of the type Ni(II)RNHCHCO 2 – ) which rapidly forms an adduct containing a Ni–C bond. This adduct decays very slowly to give rise to glyoxalic acid. From a consideration of equilibrium between Ni(II)IDA and Ni(III)IDA, the one electron reduction potential for the Ni(III)IDA/Ni(II)IDA couple was determined to be 1.467 V.
Abstract
Reactions of carbonate (CO 3 –· ) and bicarbonate (HCO 3 · ) radicals generated by photolysis of a carbonate or bicarbonate solution at pH 11.2 and 8.5, respectively, with Co(II) complexes of iminodiacetic acid (IDA) and ethylenediaminetetraacetic acid (EDTA) have been studied. The rate constants for the reactions were in the order of 106–107 dm3mol–1s–1. From the time-resolved spectroscopy of the products formed after reaction of CO 3· –· or HCO 3 · , it is observed that CO 3 –· or HCO 3 · oxidize the metal center to its higher oxidation state.
Abstract
When an aqueous solution of Na2[Mo(V)2O4EDTA] (ethylene diamine tetraacetate) was photolyzed in the presence of excess KBr and K2S2O8 at neutral pH, the complex was found to be oxidized due to the reactions of Br 2 –. and SO 4 –. , respectively. Oxidation of the complex was also observed due to the reactions of the complex with radiolytically generated Br 2 –. and SO 4 –. radicals. When the oxidation of the complex with SO 4 –. was conducted in an unbuffered solution, a chain reaction was observed in the oxidation of the complex. The time resolved kinetics for the formation and decay of different transient intermediates and the relevant rate constants were investigated with a flash photolysis technique, and a probable mechanism for the oxidation process was given.
Abstract
The yields for the loss of chromophore of Ni(II) and Cu(II) complexes of metronidazole,G(-Ni(II)M) andG(-Cu(II)M), reached almost zero when their aqueous solutions were 
-irradiated in the presence, of 0.4 mol·dm–3 of MeOH, EtOH,i-PrOH andt-BuOH in aerated medium. However, under N2O saturated conditions, these yields attained limiting values which suggests that the hydroxyalkyl radicals, derived from the alcohols by reaction with OH, react with the complexes in deaerated medium. But in aerated medium they react preferentially with O2. The rate constants for the reactions of the different hydroxyalkyl radicals with the complexes have been determined by the flash photolysis technique and the plausible mechanisms for the reactions have been suggested.
Clay from the Nagrotta area of Jammu (J & K State, India) was calcined at various temperatures. The products were analysed by X-ray diffraction. The mode of loss of hydroxyl group from the structure with respect to temperature is discussed. The results were supplemented by differential thermal analysis. The calcined products were subjected to lime reactivity tests and the data obtained were correlated with those of the above study to investigate the pozzolanic activity at various temperatures.
