Shaista Bano

Spectrophotometric interaction of the oxidation of captopril by hexacyanoferrate(III) in an alkaline medium: a kinetic and mechanistic approach

Spectrophotometric kinetic interaction of the oxidation of captopril (CPL) by hexacyanoferrate(III) (HCF(III)) in an alkaline medium has been studied spectrophotometrically. The reaction showed firstorder kinetics. The rate of the reaction increased with an increase in alkali concentration. Increasing ionic strength increased the rate of the reaction.A mechanism involving the formation of a complex between CPL and HCF(III) has been proposed. The reaction constants involved in the mechanism have been evaluated. There is a good agreement between the observed and calculated rate constants under different experimental conditions. Investigations at different temperatures allowed the determination of the activation parameters with respect to the slow step of the proposed mechanism.

Resonance Rayleigh Scattering Spectra, Nonlinear Scattering Spectra of Selected Cephalosporins-Cd(II) Chelate with Titan Yellow and Their Analytical Applications

Three simple and highly sensitive methods were designed for the determination of cephalosporins antibiotics (CFs) such as cefpodoxime proxetil (CFPD), cefdinir (CFDN), and cefuroxime axetil (CFRX) by means of the enhancement effect on resonance Rayleigh scattering (RRS) and nonlinear scattering such as second-order scattering (SOS) and frequency doubling scattering (FDS) intensities. All CFs under this project reacts with Cd(II) in BR buffer medium of pH 3.4 to form 1:1 cationic chelate which further react with titan yellow to form 2:1 ion association complexes as a result, RRS, SOS, and FDS intensities were markedly enhanced. The increments of scattering intensities were directly proportional to the concentration of CFs antibiotics in a certain range. The detection limit for the three CFs were 1.73–2.38 ng ml−1 for RRS method, 5.12–5.67 ng ml−1 for SOS, 6.25–7.26 ng ml−1 for FDS method, respectively. Among them the RRS method exhibited the highest sensitivity and the CFPD system was more sensitive then other antibiotics systems. The optimum reaction conditions, the effects of coexisting substances, the structure of ternary complexes, and the reaction mechanism were discussed. The methods were applied to the determination of CFs in pharmaceutical samples with satisfactory results.

Kinetics and Mechanism of Oxidation of D-Penicillamine by Potassium Hexacyanoferrate(III) Ions in Aqueous Solution in the Presence of Sodium Dodecyl Sulphate and Cetyltrimethylammonium Bromide

The effect of cationic surfactant cetyltrimethylammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulphate (SDS) on the rate of oxidation of D-penicillamine by alkaline hexacyanoferrate(III) has been studied by spectrophotometrically at different temperatures. The effect of CTAB and SDS on the rate of reaction has been observed at even below the critical micelle concentration (CMC) of the surfactants, indicating binding of the substrate with the surfactants. On the basis of the kinetic results, the mechanism of the reaction has been proposed. The kinetic data have been rationalized in terms of Manger and Portnoys model for micellar inhibition and binding parameters (viz. binding constants, partition coefficient, free energy transfer from water to micelle, etc.); activation parameters have also been evaluated.

Fluorescence Enhancement of Levosulpiride Upon Coordination with Transition Metal Ions and Spectrophotometric Determination of Complex Formation

Abstract Absorbance and fluorescence spectral pattern of levosulpiride in absence and presence of first row transition metal ions (Mn-Zn) has been studied at room temperature under physiological condition. The fluorescence spectra of the drug in presence of different concentrations of transition metal ions showed enhancement in fluorescence intensity of levosulpiride. The photophysical changes owing to the direct interaction between metal ion and the amide nitrogen of levosulpiride has been described in terms of CHEF (chelating enhancement fluorescence) effect. The absorption spectra of the drug at different pH exhibited two isosbestic points at 255 and 275 nm respectively, indicating the presence of three chemical species in solution. The ratio of the drug to metal ions is found to be 2:1 and the log K of the resulting complex was determined spectrophotometrically and potentiometrically. The apparent ionization constant of levosulpiride is found to be 8.98. The low value of stability constant suggests that complexes may dissolve and the drug can be absorbed.

Development of spectrofluorimetric methods for the determination of levosulpiride in pharmaceutical formulation

Simple, accurate, rapid, and sensitive spectrofluorimetric methods for the determination of levosulpiride in pharmaceutical formulation were developed utilizing its fluorescence reaction with Fe3+ (method A) and Al3+ (method B). The calibration curves were found to be linear in the concentration range 0.239–3.44 μg/mL and 0.310–2.730 μg/mL with limit of detection 0.005 μg/mL and 0.0032 μg/mL, respectively, for method A and method B. The reaction conditions were studied and optimized. In addition, the complexation of Mg2+ and Ca2+ was also studied. In all cases, an enhancement in fluorescence emission of levosulpiride upon formation of complex with metal ions was observed. A 2: 1 (drug: metal) stoichiometry for all the complexes was established. Benesi-Hildebrand method was applied for calculation of association constant at 25 and 35°C. The thermodynamic parameters obtained in this study revealed that the interaction process was spontaneous and mainly ΔS-driven.

Interaction of Clofazimine with Divalent Metal Ions: A Fluorescence Quenching Study

The interaction of clofazimine (CFZ) with divalent metal cations was studied by measuring fluorescence quenching spectra, synchronous fluorescence spectra and ultraviolet spectra. The fluorescence quenching spectra of CFZ in the presence of metal ions showed that metal ions quenched the fluorescence of CFZ. The quenching constants were determined using the Stern–Volmer equation. The binding constants (log K) and binding site were obtained. The thermodynamic parameters obtained in this study revealed that the interaction between CFZ and metal ions was mainly driven by a hydrophobic force. The conformational changes of CFZ were investigated by synchronous spectrum studies.

Spectroscopic and Substitution Kinetic Studies of Hexacyanoferrate(II) Complexes by EDTA Catalysed with Mercury(II)

Kinetics and mechanism of substitution of cyanide ion in hexacyanoferrate(II) by EDTA catalysed by mercury(II) has been studied spectrophotometrically at 365 nm in potassium hydrogen phthalate buffer of pH = 5.0 and ionic strength, I = 0.1 M, maintained by (KNO 3) at 25 0 C. Effect of the pH and concentration of the EDTA, (Fe(CN) 4- 6) on the rate of reaction has been studied. The kinetics and mechanism of the reaction has been shown through dissociative mechanism. The mechanism of ligand substitution in the complex together with the kinetic data has been shown. The catalytic activity of mercury(II) has also been studied as a function of its concentration. The maximum reaction product was detected at pH = 5 after which a decline in absorption occurs followed by precipitation. It is an inexpensive method to identify and remove the cyanide ion in solution even in very low concentration of the order of 10 -4 M.