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Dive into the research topics where Abhas Asthana is active.

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Featured researches published by Abhas Asthana.


Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy | 2010

Kinetic spectrophotometric method for trace determination of thiocyanate based on its inhibitory effect

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

The kinetics and mechanism of oxidation of hexacyanoferrate(II) by periodate ion in highly alkaline aqueous medium

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

The Kinetics and Mechanism of Ligand Substitution Reaction of Aquapentacyanoruthenate(II) with Nitroso-R-salt and α-Nitroso-β-Naphthol in Presence of Anionic Surfactant Micelle

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

Ligand substitution kinetic assay of antitubercular drug isoniazid in pure and pharmaceutical formulations

Radhey M. Naik; Surendra Prasad; Basant Kumar; Shiv Bali Singh Yadav; Abhas Asthana; Masafumi Yoshida


Transition Metal Chemistry | 2008

Kinetic determination of silver at trace level based on its catalytic effect on a ligand substitution reaction

Radhey M. Naik; R. K. Tiwari; Pradeep Kumar Singh; Shiv Bali Singh Yadav; Abhas Asthana


International Journal of Chemical Kinetics | 2011

The kinetics and mechanism of the substitution reactions of the aquapentacyanoruthenate(II) ion with naphthalene-substituted ligands in aqueous medium

Radhey M. Naik; Ruchi Singh; Abhas Asthana


Microchemical Journal | 2015

Catalytic ligand exchange reaction between hexacyanoferrate(II) and 4-cyanopyridine applied to trace kinetic analysis of palladium(II)

Radhey M. Naik; Basant Kumar; Surendra Prasad; Adrian A. Chetty; Abhas Asthana


Journal of The Iranian Chemical Society | 2015

Comparative study of the catalytic effect of Ag(I) and Hg(II) on the exchange of cyanide by 4-cyanopyridine in hexacyanoferrate(II): a kinetic approach

Radhey M. Naik; Abhas Asthana; Shiv Bali Singh Yadav


Transition Metal Chemistry | 2012

Metal exchange kinetics: uncatalyzed replacement of Ni(II) from tetramethylenediaminetetraacetatonickel(II) complex by Cu(II)

Radhey M. Naik; Abhas Asthana; Richa Rastogi


Transition Metal Chemistry | 2010

Kinetics and mechanism of the ligand substitution reaction between aquapentacyanoruthenate(II) and 4-cyanopyridine in the presence of anionic surfactant micelles

Radhey M. Naik; Richa Rastogi; Abhas Asthana

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Surendra Prasad

University of the South Pacific

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