Regioselectivity in the ene-reaction of singlet oxygen with cyclic alkenes: photooxygenation of methyl-substituted 1,4-cyclohexadiene derivatives

The photooxygenation of the 1-methyl-, 2,3-dimethyl-, and 1,4-dimethylcyclohexa-1,4-dienes, which are readily available through Birch reduction, yielded the corresponding ene-products. The formed endocyclic dienes were trapped by the addition of singlet oxygen to give the corresponding bicyclic endoperoxy hydroperoxides. In the case of 1-methylcyclohexa-1,4-diene and 1,4-dimethylcyclohexa-1,4,-diene, the cis-effect determined the product distribution. Photooxygenation of 2,3-dimethylcyclohexa-1,4-dienes gave mainly exocyclic olefin, which was attributed to the lowered rotational barrier of the methyl group and increased reactivity of the methyl groups.     

Simultaneous determination of rosiglitazone and metformin in plasma by gradient liquid chromatography with UV detection

A novel, fast and simple liquid chromatographic method was developed and validated for the simultaneous determination of rosiglitazone and metformin in human plasma. The analysis was performed on a phenyl column (250 mm × 4.6 mm i.d., 5 μm) using a gradient method starting with mobile phase composed of acetonitrile:5 mM acetate buffer pH 5.5 (75:25, v/v). The flow rate was 1 mL min⁻¹. UV detection was performed at 245 nm and verapamil was used as internal standard. The total run time was less than 10 min. Sample preparation included a simple protein precipitation step with acetonitrile. Validation experiments were performed to demonstrate stability, specificity, sensitivity, linearity, accuracy, precision and robustness. The limit of quantification was 100 ng mL⁻¹ for rosiglitazone and 250 ng mL⁻¹ for metformin. The extraction recoveries were 100.02-105.0% for rosiglitazone and 105.64-103.88% for metformin. The method was applied with success to plasma samples obtained from diabetic patients undergoing treatment with rosiglitazone and metformin.     

Electrochemical studies and square-wave voltammetric determination of fenofibrate in pharmaceutical formulations

The electrochemical reduction of fenofibrate at a hanging mercury drop electrode (HMDE) was investigated by cyclic voltammetry, square-wave voltammetry, and chronoamperometry. Different buffer solutions were used over a wide pH range (3.0–10.0). The best definition of the analytical signals was found in borate buffer (pH 9.0)–tetrabutylammonium iodide mixture containing 12.5% (v/v) methanol at –1.2 V (versus Ag/AgCl). According to cyclic voltammetric studies, the reduction was irreversible and diffusion controlled. The diffusion coefficient was 2.38×10^–6 cm² s^–1 as determined by chronoamperometry. Under optimized conditions of square-wave voltammetry, a linear relationship was obtained between 0.146–4.96 g mL^–1 of fenofibrate with a limit of detection of 0.025 g mL^–1. Validation parameters such as sensitivity, accuracy, precision, and recovery were evaluated. The proposed method was applied to the determination of fenofibrate in pharmaceutical formulations. The results were compared with those obtained by a published high-performance liquid chromatography method. No difference was found statistically.     

Determination of piribedil in pharmaceutical formulations by micellar electrokinetic capillary chromatography

A fast and simple micellar electrokinetic capillary chromatographic method was developed for the analysis of piribedil in pharmaceutical formulations. The effects of buffer concentration, buffer pH, sodium dodecyl sulphate (SDS) concentration, organic modifier, applied voltage and injection time were investigated. Optimum results were obtained with a 50 mM borate buffer at pH 8.0 containing 50 mM SDS by using a fused silica capillary (50 m internal diameter, 72 cm effective length). The sample was injected hydrodynamically for 4 s at 50 mbar pressure and the applied voltage was +30 kV. The detection wavelength was set at 205 nm. Diflunisal was used as an internal standard. The analysis was performed at 25 °C and the total run time was 14 min. The method was suitably validated with respect to linearity range, limit of detection and quantification, precision, accuracy, specificity and robustness. The linear calibration range was 5–100 g mL^–1 and the limit of detection was determined as 1 g mL^–1. The method developed was successfully applied to the determination of piribedil in pharmaceutical formulations. The results were compared with a spectrophotometric method reported in the literature and no significant difference was found statistically.     

Fabrication of amperometric cholesterol biosensor based on SnO<Subscript>2</Subscript> nanoparticles and Nafion-modified carbon paste electrode

This study reports the fabrication of an amperometric cholesterol biosensor based on cholesterol oxidase (ChOx), SnO₂NPs and Nafion-modified carbon paste enzyme electrodes (CPE/SnO₂NPs-ChOx/Naf). The electrochemical characterisations of BCPE and CPE/SnO₂NPs were performed using CV and EIS. The determination of cholesterol was carried out by electrochemical oxidation of H₂O₂ at 0.6 V vs. Ag/AgCl. The CPE/SnO₂NPs-ChOx/Naf presented a linear range from 0.20 μ.mol L^?1 to 4.95 μmol L^?1 with a low limit of detection (0.04 μ.mol L^?1). In addition, the optimal values for pH and temperature were found to be 7.5 and 35°C, respectively. The CPE/SnO₂NPs-ChOx/Naf was used for the determination of cholesterol in serum samples and good results were obtained.     

Monitoring Humic Acid Photodegradation by CUPRAC Colorimetric and HPLC Determination of Dihydroxybenzoate Isomers Produced From a Salicylate Probe

Abstract

Novel analytical methods were designed for monitoring humic acid photodegradation in environmental waters. Modified CUPric Reducing Antioxidant Capacity (CUPRAC) spectrophotometric and chromatographic methods were used for the determination of dihydroxybenzoate isomers (DHBAs) produced from a salicylate probe, which was hydroxylated by hydroxyl radicals (^?OH) produced from the photodegradation of humic acid under ultraviolet A-radiation. The combined use of CUPRAC colorimetry and HPLC was shown to effectively monitor humic acid photodegradation and ^?OH generation for the first time. The formation of 2,5-dihydroxybenzoate and 2,3-dihydroxybenzoate, as major and minor products, respectively, from the hydroxylation of a salicylate probe was demonstrated by HPLC and confirmed by a modified CUPRAC method to indicate ^?OH formation from humic acid, which acted as both a generator and absorber of hydroxyl radicals. Salicylate hydroxylation showed an increase between 30 and 50?min of illumination, and was affected by the initial concentration of humic acid up to 0.01% but not by solution pH around the neutral values. Traces of Fe(III) and Mn(II) present in natural waters decreased the ^?OH production, but EDTA partly restored the probe hydroxylation by chelating these metal cations. Since humic acid-mediated ^?OH generation may aid in natural disinfection processes, this work may extend our comprehension of concentration- and time-dependent generation of ^?OH in environmental waters and of the possible effects of other antioxidants.     

The Syntheses,Structures, Fluorescence Properties and Biological Activity of two Novel Zinc(II) Complexes Controlled by the Tripodal Imidazole Ligand

Two new zinc complexes, namely Zn(L¹)ClCH₂NO(1) and {Zn(L²)CH₂NO}_n?N(CH₃)₃?ClO₄(2) (L¹ = 3,5-di(1H-imidazol-1-yl)pyridine L² = 1,3,5-tris(1-imidazolyl) benzene), have been synthesized, and characterized by IR spectra, elemental analysis, and a single crystal X-ray diffraction. Fluorescence spectroscopy indicated that two complexes presented strong DNA binding affinity constants to fish sperm DNA (FS-DNA). Gel electrophoresis assay demonstrated the ability of the complex to cleave the HL-60 DNA. Apoptotic study showed the complex exhibited significant cancer cell(KB) inhibitory rate.     

Simultaneous Determination of Rosiglitazone and Metformin in Pharmaceutical Preparations by LC

In the present study, a novel, fast and simple liquid chromatographic method was developed and validated for the simultaneous determination of rosiglitazone and metformin in pharmaceutical preparations. The separation was achieved on a phenyl column (250 × 4.6 mm i.d., 5 μm) using a mobile phase composed of acetonitrile:10.0 mM phosphate buffer pH 5.5 (70:30, v/v). The flow rate was 1 mL min⁻¹. UV detection was performed at 245 nm and verapamil was used as internal standard. The developed method was validated in terms of stability, specificity, sensitivity, linearity, accuracy, precision and robustness. The limit of quantification was 0.02 μg mL⁻¹ for both drugs. The method developed was successfully applied to the simultaneous determination of rosiglitazone and metformin in pharmaceutical preparations. The results were compared to two methods reported in the literature and no significant difference was found statistically.