Abhas Asthana
University of Lucknow
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Featured researches published by Abhas Asthana.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2010
Radhey M. Naik; Basant Kumar; Abhas Asthana
A kinetic spectrophotometric method for the determination of thiocyanate, based on its inhibitory effect on silver(I) catalyzed substitution of cyanide ion, by phenylhydrazine in hexacyanoferrate(II) is described. Thiocyanate ions form strong complexes with silver(I) catalyst which is used as the basis for its determination at trace level. The progress of reaction was monitored, spectrophotometrically, at 488 nm (lambda(max) of [Fe(CN)(5)PhNHNH(2)](3-), complex) under the optimum reaction conditions at: 2.5x10(-3)M [Fe(CN)(6)](4-), 1.0x10(-3)M [PhNHNH(2)], 8.0x10(-7)M [Ag(+)], pH 2.8+/-0.02, ionic strength (mu) 0.02 M (KNO(3)) and temperature 30+/-0.1 degrees C. A linear relationship obtained between absorbance (measured at 488 nm at different times) and inhibitor concentration, under specified conditions, has been used for the determination of [thiocyanate] in the range of 0.8-8.0x10(-8)M with a detection limit of 2x10(-9)M. The standard deviation and percentage error have been calculated and reported with each datum. A most plausible mechanistic scheme has been proposed for the reaction. The values of equilibrium constants for complex formation between catalyst-inhibitor (K(CI)), catalyst-substrate (K(s)) and Michaelis-Menten constant (K(m)) have been computed from the kinetic data. The influence of possible interference by major cations and anions on the determination of thiocyanate and their limits has been investigated.
Journal of The Iranian Chemical Society | 2008
Radhey M. Naik; A. Srivastava; Abhas Asthana
The oxidation of hexacyanoferrate(II) by periodate ion has been studied spectrophotometrically by registering an increase in absorbance at 420 nm (λmax of yellow colored [Fe(CN)63−] complex under pseudo first-order conditions by taking excess of [IO4−] over [Fe(CN)64−]. The reaction conditions were: pH = 9.5 ± 0.02, I = 0.1 M (NaCl) and Temp. = 25 ± 0.1 °C. The reaction exhibited first-order dependence on each [IO4−] and [Fe(CN)64−]. The effects of variations of pH, ionic strength and temperature were also studied. The experimental observations revealed that the periodate ion exists in its protonated forms viz. [H2IO6]3− and [H3IO6]2− while [Fe(CN)6]4− is present in its deprotonated form throughout the pH region selected for the present study. It has also been observed that deprotonated form of [Fe(CN)64−] and protonated forms of periodate ion are the most reactive species towards oxidation of [Fe(CN)64−]. The repetitive spectral scan is provided as an evidence to prove the conversion of [Fe(CN)64−] to [Fe(CN)63−] in the present reaction. The activation parameters have also been computed using the Eyring’s plot and found to be, ΔH‡ = 51.53 ± 0.06 kJ mol−1, ΔS‡ = −97.12 ± 1.57 J K−1 mol−1 and provided in support of a most plausible mechanistic scheme for the reaction under study.
Journal of Dispersion Science and Technology | 2010
Radhey M. Naik; Ruchi Singh; Abhas Asthana
The kinetics and mechanism of ligand substitution reaction of coordinated water in complex, [Ru(CN)5H2O]3− by two incoming naphthalene substituted ligands [Ln], that is, Ln = nitroso-R-salt (NRS) and α-nitroso-β-naphthol (αNβN) have been studied spectrophotometrically by following an increase in absorbance at λmax = 525 nm in aqueous medium in presence of anionic surfactant micelle, sodium dodecyl sulphate (SDS) at 25.0 ± 0.1°C as a function of pH, [nitro-R-salt], [α-nitroso-β-naphthol], [Ru(CN)5H2O3−], [SDS] and ionic strength(I) under pseudo-first-order conditions by taking excess [L]. The values of pseudo-first-order rate constants (kobs) were evaluated from the slope of ln(A∞ − At) versus time plots for each variation. Both systems were found to follow a dissociative mechanism (D), through the formation of an intermediate, [Ru(CN)5]3−. The activation parameters, that is, enthalpy of activation (ΔH≠) and entropy of activation (ΔS≠) were computed from the slope and intercept of ln(kf/T) versus (1/T) plot, which support the proposed mechanistic scheme.
Microchemical Journal | 2013
Radhey M. Naik; Surendra Prasad; Basant Kumar; Shiv Bali Singh Yadav; Abhas Asthana; Masafumi Yoshida
Transition Metal Chemistry | 2008
Radhey M. Naik; R. K. Tiwari; Pradeep Kumar Singh; Shiv Bali Singh Yadav; Abhas Asthana
International Journal of Chemical Kinetics | 2011
Radhey M. Naik; Ruchi Singh; Abhas Asthana
Microchemical Journal | 2015
Radhey M. Naik; Basant Kumar; Surendra Prasad; Adrian A. Chetty; Abhas Asthana
Journal of The Iranian Chemical Society | 2015
Radhey M. Naik; Abhas Asthana; Shiv Bali Singh Yadav
Transition Metal Chemistry | 2012
Radhey M. Naik; Abhas Asthana; Richa Rastogi
Transition Metal Chemistry | 2010
Radhey M. Naik; Richa Rastogi; Abhas Asthana