Keerti M. Naik

Elucidation of binding mechanism of hydroxyurea on serum albumins by different spectroscopic studies

ObjectivesThe interaction of hydroxyurea (HU) with serum albumins (SAs) has not been investigated so far. However, it necessitates the interaction study of HU with SAs in phosphate buffer of pH 7.4.MethodsThe binding of HU on bovine serum albumin (BSA) and human serum albumin (HSA) was studied in vitro under simulated physiological conditions by spectroscopic methods viz., fluorescence, FT-IR, UV–vis absorption, synchronous fluorescence and three-dimensional fluorescence.ResultsThe Stern-Volmer plot indicated the presence of dynamic quenching mechanism in the interaction of HU with SAs. The number of binding sites, n and binding constants, K were obtained at various temperatures according to the double logarithm regression curve. The result of FT-IR spectra, UV–vis absorption, synchronous fluorescence and three-dimensional fluorescence spectra showed that the conformation of SAs has been changed in the presence of HU. The thermodynamic parameters were calculated according to van’t Hoff equation and discussed.ConclusionThis kind of study of interaction between BSA and HSA with HU would be useful in pharmaceutical industry, life sciences and clinical medicine.

Kinetics and mechanism of oxidation of L-leucine by alkaline diperiodatocuprate(III) — A free radical intervention, deamination and decarboxylation

AbstractThe kinetics of oxidation of L-leucine by diperiodatocuprate (III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.10 mol dm − 3 was studied spectrophotometrically. The reaction between L-leucine and DPC in alkaline medium exhibits 1:4 stoichiometry (L-leucine: DPC). The reaction is of first order in [DPC] and has less than unit order in both [L-leucine] and [alkali]. However, the order in [L-leucine] and [alkali] changes from first order to zero order as their concentration increase. Intervention of free radicals was observed in the reaction. Increase in periodate concentration decreased the rate. The oxidation reaction in alkaline medium has been shown to proceed via a monoperiodatocuprate (III) – L-leucine complex, which decomposed slowly in a rate-determining step followed by other fast steps to give the products. The main oxidative products were identified by spot test and GC-MS. The reaction constants involved in the different steps of the mechanism were calculated. Graphical AbstractThe title reaction was studied spectrophotometrically and a suitable mechanism was proposed. The thermodynamic quantities of different steps of the mechanism were evaluated. The active species of DPC was found to be [Cu(H2IO6)(H2O)2].

Electrochemical response of hydroxyurea by different voltammetric techniques at carbon paste electrode

A simple and novel electroanalysis of hydroxyurea (HU) drug at carbon paste electrode has been investigated for the first time using cyclic, linear sweep and differential pulse voltammetric techniques. The oxidation of HU is irreversible and exhibits a diffusion controlled process and is pH dependent. The oxidation mechanism is proposed. The dependence of the current on pH, the concentration, nature of buffer, and scan rate is investigated to optimize the experimental conditions for the determination of HU. It was found that the optimum buffer for the determination of HU was pH 7.0, a physiological pH. In the range of 0.2 to 1.0 mM, the current measured by differential pulse voltammetry presents a good linear property as a function of the concentration of HU with a limit of detection of 6.52 μM. In addition, reproducibility, precision and accuracy of the method were checked as well. The developed method was successfully applied to HU determination in pharmaceutical formulation and human urine. The method finds its applications in quality control laboratories and pharmacokinetics.

RP-HPLC Method for the Estimation of 6-Mercaptopurine in spiked human plasma and pharmaceutical formulations

AbstarctA simple, rapid and accurate reverse-phase high-performance liquid chromatography (RP-HPLC) method for the determination of 6-mercaptopurine (6-MP) in pharmaceutical formulations and spiked human plasma samples has been developed and validated. The assay of the drug was performed on a CLC C18 (5 μm, 25 cm × 4.6 mm i.d.) with UV detection at 325 nm. The mobile phase consisted of methanol-water mixture in the ratio of 90: 10, and a flow rate of 1 mL/min was maintained. The standard curve was linear over the range of 25–150 μg/mL (r2 = 0.9964). Analytical parameters have been evaluated. Between and within-day precision and accuracy were acceptable down to the limit of quantification of 9.5 μg/mL in plasma. The proposed method was validated for accuracy and precision. Statistical analysis proves that the method was found to be simple, precise, accurate, rapid and reproducible and can be used for the routine determination of 6-mercaptopurine. The proposed method was successfully applied to the determination of 6-mercaptopurine in spiked human plasma and pharmaceutical formulations. The method will be useful for routine quality control analysis.

Thermodynamic quantities for different steps involved in the mechanism of the oxidation of 6-mercaptopurine by diperiodatocuprate(III) in aqueous alkaline medium

The kinetics of oxidation of 6-mercaptopurine (6-MP) by diperiodatocuprate(III) (DPC) in aqueous alkaline medium at a constant ionic strength of 0.01 mol/dm3 was studied spectrophotometrically. The reaction between DPC and 6-MP in an alkaline medium exhibits 1:4 stoichiometry (6-MP:DPC). The reaction is of first order in [DPC] and has less than unit order in both [6-MP] and [alkali]. However, the order of [6-MP] and [alkali] changes from first order to zero order as their concentration increases. Intervention of free radicals was observed in the reaction. An increase in periodate concentration decreases the rate. The oxidation reaction in an alkaline medium has been shown to proceed via a monoperiodatocuprate(III)–6-MP complex, which decomposes slowly in a rate-determining step followed by other fast steps to give the products. The main oxidative products were identified by spot test, IR, GC-MS and HPLC studies. The reaction constants involved in the different steps of the mechanism are calculated. The activation parameters with respect to a slow step of the mechanism are computed and discussed, and thermodynamic quantities are also determined.

Mechanistic aspects of uncatalyzed and ruthenium(III) catalyzed oxidation of 1,4-dioxane by a copper(III) periodate complex in aqueous alkaline medium

Oxidation of 1,4-dioxane (Dio) by a copper(III) periodate complex (DPC) has been investigated spectrophotometrically both in the absence and presence of a ruthenium(III) catalyst in aqueous alkaline medium at 298 K. Stoichiometry of (1:8) was observed in both the reactions and the order of the reaction with respect to [DPC] was unity while the order with respect to [Dio] was <1 over the concentration range studied. Order with respect to [OH−] and [IO4−] had negative order in both cases. Order with respect to [Ru(III)] was unity. The activation parameters (ΔH# = 38 ± 2 kJ mol−1, ΔS# = −164 ± 15 J K−1 mol−1 and ΔG# = 87 ± 4 for uncatalyzed and ΔH# = 34 ± 3 kJ mol−1, ΔS# = −43 ± 2 J K−1 mol−1 and ΔG# = 47 ± 3 for catalyzed reaction) with respect to the slow step of the proposed mechanism were computed and thermodynamic quantities were also calculated. Kinetic studies suggest that [Cu(OH)2(H3IO6)]− is the reactive copper(III) species and [Ru(H2O)5(OH)]2+ is the reactive Ru(III) species.