Voltammetric Analysis of the Novel Atypical Antipsychotic Drug Quetiapine in Human Serum and Urine

The electrooxidative behaviour and determination of quetiapine (QTP), a dibenzothiazepine derivative and antipsychotic agent, on a glassy carbon disc electrode was investigated using cyclic (CV), linear sweep (LSV), differential pulse (DPV) and Osteryoung square wave voltammetry (OSWV). Fully validated DP and SW voltammetric procedures are described for the determination of QTP. QTP in pH 3.5 acetate buffer solution presents a well-defined anodic response, studied by the proposed methods. This main response was due to the irreversible, diffusion-controlled, one-electron and one-proton oxidation of the aliphatic nitrogen of the piperazine ring. Under optimal conditions, a detection limit of 4.0 × 10⁻⁸ mol L⁻¹ for DPV and 1.33 × 10⁻⁷ mol L⁻¹ for OSWV, and a linear calibration graph in the range from 4.0 × 10⁻⁶ to 2.0 × 10⁻⁴ mol L⁻¹ were obtained for both methods. The procedure was successfully applied to the determination of the drug in tablets, human serum and human urine with good recoveries. The detection limits were 6.20 × 10⁻⁷ mol L⁻¹ and 5.92 × 10⁻⁷ mol L⁻¹ in human serum and 1.44 × 10⁻⁷ mol L⁻¹ and 1.31 × 10⁻⁶ mol L⁻¹ in human urine, for the DPV and OSWV method, respectively.     

Anodic voltammetric behavior and determination of cefixime in pharmaceutical dosage forms and biological fluids

The voltammetric behavior of cefixime was studied using cyclic, linear sweep, differential pulse and square wave voltammetric techniques. The oxidation of cefixime was irreversible and exhibited diffusion controlled process depending on pH. The oxidation mechanism was proposed and discussed. Different parameters were tested to optimize the conditions for the determination of cefixime. The dependence of current intensities and potentials on pH, concentration, scan rate, nature of the buffer was investigated. According to the linear relationship between the peak current and the concentration, differential pulse (DPV) and square wave (SWV) voltammetric methods for cefixime assay in pharmaceutical dosage forms and biological fluids were developed. For the determination of cefixime were proposed in acetate buffer at pH 4.5, which allows quantitation over the 6 × 10⁻⁶-2 × 10⁻⁴ M range in supporting electrolyte and spiked serum sample; 8 × 10⁻⁶-2 × 10⁻⁴ M range in urine sample; 6 × 10⁻⁶-1 × 10⁻⁴ M range in breast milk samples for both techniques. The repeatability, reproducibility, precision and accuracy of the methods in all media were investigated. No electroactive interferences from the excipients and endogenous substances were found in the pharmaceutical dosage forms and in the biological samples, respectively.     

Development and Validation of an RP-HPLC Method for Determination of Valganciclovir in Human Serum and Tablets

This paper describes the validation of an isocratic high-performance liquid chromatographic method for the assay of valganciclovir in raw materials, tablets and human serum samples. Valganciclovir and fluvastatin (internal standard) were well separated using a reversed phase column and a mobile phase consisting of a mixture of acetonitrile:methanol:KH₂PO₄ (0.02 M) (40:20:40; v/v/v) (at pH 5.0). The mobile phase was pumped at 1.0 mL min⁻¹ flow rate and valganciclovir was detected by diode-array detection at 255 nm. The retention times for valganciclovir and fluvastatin were 3.41 and 5.60 min, respectively. A linear response (r > 0.999) was observed in the range of 10–30,000 ng mL⁻¹ in mobile phase and serum. The limit of detection and limit of quantification were found as 2.95 and 9.82 ng mL⁻¹ in mobile phase and 1.73 and 5.77 ng mL⁻¹ in human serum samples, respectively. Validation parameters as precision, accuracy, selectivity, reproducibility and system suitability tests were also determined. The method can be used for valganciclovir assay of tablets and human serum samples as the method separates valganciclovir from tablet excipients and endogenous substances.

     

Transition structures, energetics, and secondary kinetic isotope effects for cope rearrangements of cis-1,2-divinylcyclobutane and cis-1,2-divinylcyclopropane: a DFT study

The minimum energy reaction paths and secondary kinetic isotope effects (KIE) for the Cope rearrangements of cis-1,2-divinylcyclobutane and cis-1,2-divinylcyclopropane obtained by (U)B3LYP calculations are reported. Both reactions proceed through endo-boatlike reaction paths, and have aromatic transition states. The predicted activation energies are in agreement with the experimental data. The reaction paths of the rearrangements are intervened by enantiomerization saddle points of the products (and the reactant in the case of divinylcyclobutane). The calculated KIEs are similar in the two systems, and consistent with the geometries of the transition structures. There is computational evidence that the isotope effect associated with the conversion of a pure sp(2) C-H bond into a pure sp(3) one might be the same in all molecules. The predicted KIEs agree with experiment for divinylcyclopropane, but not for divinylcyclobutane.     

Oxidative polymerization of diphenylamine: A mechanistic study

The mechanism of oxidative polymerization of diphenylamine is considered. The kinetic study of diphenylamine polymerization and of the structure and molecular-mass characteristics of the reaction products has shown that the degree of oxidation of intermediates plays the key role in polyrecombination. The relationship between the polymerization procedure and the molecular mass of polydiphenylamine was revealed.     

DNA and PNA sensing on mercury and carbon electrodes by using methylene blue as an electrochemical label

Described here are the electrochemical parameters for MB on binding to DNA at hanging mercury drop electrode (HMDE), glassy carbon electrode (GCE), and carbon paste electrode (CPE) in the solution and at the electrode surface. MB, which interacts with the immobilized calf thymus DNA, was detected by using single-stranded DNA-modified HMDE or CPE (ssDNA-modified HMDE or CPE), bare HMDE or CPE, and double-stranded DNA-modified HMDE or CPE (dsDNA-modified HMDE or CPE) in combination with adsorptive transfer stripping voltammetry (AdTSV), differential pulse voltammetry (DPV), and alternating current voltammetry (ACV) techniques. The structural conformation of DNA and hybridization between synthetic peptide nucleic acid (PNA) and DNA oligonucleotides were determined by the changes in the voltammetric peak of MB. The PNA and DNA probes were also challenged with excessive and equal amount of noncomplementary DNA and a mixture that contained one-base mismatched and target DNA. The partition coefficient was also obtained from the signal of MB with probe, hybrid, and ssDNA-modified GCEs. The effect of probe, target, and ssDNA concentration upon the MB signal was investigated. These results demonstrated that MB could be used as an effective electroactive hybridization indicator for DNA biosensors. Performance characteristics of the sensor are described, along with future prospects.     

Determination of the volatile constituents and total phenolic contents of some endemic Stachys taxa from Turkey

The total phenolic contents and the essential oil compositions of the previously unknown Stachys taxa (Labiatae), including Stachys pinardii Boiss, Stachys cretica L. subsp. mersinaea (Boiss.) Rech., and Stachys aleurites Boiss. & Heldr., all endemic to Turkey, were studied. Their essential oil compositions were investigated by GC-MS. It was found that the main constituents were α-curcumene (34.10%) for S. cretica, cedrandiol (25.26%) and caryophyllene dioxide (22.15%) for S. pinardii, and (Z)-β-caryophyllene (31.60%) for S. aleurites. The total phenolic contents, by the Folin-Ciocalteu colorimetric method, of the S. pinardii, S. cretica subsp. mersinaea, and S. aleurites methanolic extract were found to be 600.74±0.23, 1200.94±0.11, and 900.61±0.06 mg gallic acid equivalent (GAE)/100 g in dried herb, respectively. Published in Khimiya Prirodnykh Soedinenii, No. 2, pp. 141–143, March–April, 2006.     

NH2‐Functionalized Multi Walled Carbon Nanotubes Decorated with ZnO Nanoparticles and Graphene Quantum Dots for Sensitive Assay of Pimozide

In this study, a novel and sensitive electrochemical nanosensor for the determination of antipsychotic drug Pimozide (PZ) is proposed using NH₂ functionalized multi walled carbon nanotubes (NH₂fMWCNT) decorated with and ZnO nanoparticles (ZnONPs) co‐catalyzed by graphene quantum dots (GQDs). Prior to electrochemical analyses of PZ, the designed nanosensor was well characterized in terms of surface morphology by scanning electron microscopy (SEM) and SEM armed with EDX analysis. Electrochemical impedance spectroscopy (EIS) employed to investigate the electron transfer capability and cyclic voltammetry (CV) technique was used to successfully compare the redox response of PZ on the surface of modified and unmodified electrode. The designed nanosensor response was linear between 6.25×10^?11–1.20×10^?7 M concentration range of PZ with a limit of detection value as 1.02×10^?11 M. The influence of interfering agents was further studied to examine the selectivity of the designed sensor. A rapid screening of PZ as is required in pharmaceutical and biological samples underscores the paramount importance of nano based electrochemical sensor for its sensitive and selective detection.     

Thermally stimulated current observation of trapping centers in an undoped Tl4Ga3InSe8 layered single crystal

Thermally stimulated current measurements are carried out on as‐grown Tl₄Ga₃InSe₈ layered single crystal in the temperature range 10–160 K with different heating rates. Experimental evidence is found for two shallow trapping centers in Tl₄Ga₃InSe₈. They are located at 17 and 27 meV. The trap parameters have been determined by various methods of analysis, and they agree well with each other. It is concluded that in these centers retrapping is negligible, as confirmed by the good agreement between the experimental results and the theoretical predictions of the model that assumes slow retrapping. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Singular 1-soliton and Periodic Solutions to the Nonlinear Fisher-Type Equation with Time-Dependent Coefficients

In this article,we establish exact solutions for the variable-coefficient Fisher-type equation.The solutions are obtained by the modified sine-cosine method and ansatz method.The soliton and periodic solutions and topological as well as the singular 1-soliton solution are obtained with the aid of the ansatz method.These solutions are important for the explanation of some practical physical problems.The obtained results show that these methods provide a powerful mathematical tool for solving nonlinear equations with variable coefficients.