Platinum nanoparticles–decorated graphene-modified glassy carbon electrode toward the electrochemical determination of ascorbic acid,dopamine, and paracetamol

In the present study, we report the synthesis and characterization of platinum nanoparticles decorated graphene (GPtNPs) nanocomposite toward the electrochemical determination of ascorbic acid (AA), dopamine (DA), and paracetamol (PCT). GPtNPs demonstrated synergistic catalytic activity with enhanced currents in all of the measurements when compared with graphene-modified glassy carbon electrode (G-GCE) and bare GCE. The nanocomposite exhibited low overpotential for AA oxidation and good peak-to-peak separation of 218.0, 218.0, and 436.0 mV for AA–DA, DA–PCT, and AA–PCT, respectively. Cyclic voltammetry (CV) and chronoamperometry (CA) determination of AA, DA, and PCT showed wide linearity ranges. CV determination of AA exhibited linearity range from 300 μM to 20.89 mM and from 22.02 to 39.87 mM. DA determination using CV exhibited linearity range from 5 to 104 μM and from 114 to 684 μM, whereas CA determination of PCT showed a linearity range from 20 μM to 6.43 mM. Differential pulse voltammetry determinations of AA, DA, and PCT exhibited low detection limits of 300, 5, and 5 μM, respectively.     

Thermal studies of furosemide–caffeine binary system that forms a cocrystal

Thermal techniques, differential scanning calorimetry (DSC), and hot stage microscopy (HSM) have been used to study the interactions between furosemide and caffeine that are known to form a 1:1 cocrystal. This system has been used as an example to study the probable mechanism of cocrystal formation when the individual components, which are polymorphic, are heated. The study indicates that the phase transition of the low temperature stable polymorph of furosemide initiates cocrystal formation. This result suggests increased mass transfer rate can trigger cocrystal formation. The binary phase diagram (composition–temperature plots) of furosemide–cocrystal–caffeine system was determined from the DSC curves. The results imply that the cocrystal forms eutectic with caffeine but not with furosemide. This study has thus exemplified the use of DSC in understanding binary phase system where the two components form a cocrystal.     

Physicochemical and dissolution properties of ezetimibe–aspirin binary system in development of fixed-dose combinations

Journal of Thermal Analysis and Calorimetry - The objective of this work was to investigate binary pharmaceutical mixtures of ezetimibe (EZT) and aspirin (ASA) in order to identify whether the...     

Four-membered ring cyclic ketene –O,O–, –O,S–, –O,N–, –S,S–, –S,N–, and –N,N–acetals and their corresponding cations: a computational study

A systematic computational study of four-membered cyclic ketene –O,O–, –O,S–, –O,N–, –S,N– and –N,N-acetals as well as their protonated analogs have been performed at the second order M?ller Plesset level with a polarized triple zeta basis set. The main purpose of this study was to make predictions about the nucleophilicity of these systems and the variations in nucleophilicity with the hetero atoms. Our calculations suggest that all six target molecules are good nucleophiles, and that the N,N analog is the strongest and the S,S analog the weakest nucleophile. Our results include molecular geometries, bond lengths, proton affinities, vibrational frequencies, and calculated charges.     

Rapid analysis of caffeine in various coffee samples employing direct analysis in real-time ionization–high-resolution mass spectrometry

The development and use of a fast method employing a direct analysis in real time (DART) ion source coupled to high-resolution time-of-flight mass spectrometry (TOFMS) for the quantitative analysis of caffeine in various coffee samples has been demonstrated in this study. A simple sample extraction procedure employing hot water was followed by direct, high-throughput (<1 min per run) examination of the extracts spread on a glass rod under optimized conditions of ambient mass spectrometry, without any prior chromatographic separation. For quantification of caffeine using DART-TOFMS, an external calibration was used. Isotopically labeled caffeine was used to compensate for the variations of the ion intensities of caffeine signal. Recoveries of the DART-TOFMS method were 97% for instant coffee at the spiking levels of 20 and 60 mg/g, respectively, while for roasted ground coffee, the obtained values were 106% and 107% at the spiking levels of 10 and 30 mg/g, respectively. The repeatability of the whole analytical procedure (expressed as relative standard deviation, RSD, %) was <5% for all tested spiking levels and matrices. Since the linearity range of the method was relatively narrow (two orders of magnitude), an optimization of sample dilution prior the DART-TOFMS measurement to avoid saturation of the detector was needed.     

Simultaneous quantification of nimesulide,phenylpropanolamine, caffeine and chlorpheniramine in rat plasma by RP–HPLC/PDA method and application to pharmacokinetic studies in healthy rat subjects

Simultaneous determination of nimesulide, phenylpropanolamine, chlorpheniramine and caffeine in rat plasma by reversed-phase high performance liquid-chromatography (RP–HPLC) with photodiode array (PDA) detection method was developed and validated. Sample preparation based on a simple extraction procedure consisting of deproteination and extraction with methanol solution followed by volume make up with the aqueous component of the mobile phase obtained best recoveries of the analytes. The chromatographic conditions were optimized and the analytes were separated on XBridge™ C₁₈ (3.5 μm, 4.6 × 150 mm) column in isocratic elution with the mobile phase composition of acetonitrile and 10 mM ammonium acetate buffer (pH 4.0, 0.1% formic acid) (18:82 v/v%) at the flow rate of 1 mL min⁻¹ and the effluents were monitored in the wavelength range of 220–275 nm. The method was linear for all analytes over the following concentration (ng mL⁻¹) ranges: nimesulide 250–4000; phenylpropanolamine 100–1500; chlorpheniramine 20–500; and caffeine 10–100. Acceptable precision, accuracy and recoveries were obtained for quality control (QC) samples at three concentrations (low QC, middle QC and high QC). The percentage of relative standard deviation (% RSD) of Inter and intra-run precision of all molecules was <15% and the percentage of accuracy was 100 ± 10. The analytes were more stable in rat plasma at different storage conditions. Finally the method was efficiently applied to pharmacokinetics study in rat plasma.     

Reactivity of the Ge–H,Sn–H,P–H,and Se–H Bonds in Radical Abstraction Reactions

The experimental data for the liquid- and gas-phase reactions of atoms and radicals with organoelement compounds R _{n – 1}E–H

Poly(aquachlorobis(1,10–phenanthroline)copper(II)iodidemonohydrate)/GCE for simultaneous determination of caffeine and theophylline in human serum,tea, and tablet samples

This paper presents metal complex based polymer film modified electrode for simultaneous determination of caffeine, and theophylline. Potentiodynamic fabrication of poly(aquachlorobis(1,10– phenanthroline)copper(II)iodidemonohydrate) modified glassy carbon electrode (poly(ACP₂CuIH)/GCE) was verified using cyclic voltammetric and electrochemical impedance spectroscopic techniques. In contrast to the unmodified glassy carbon electrode, the poly(ACP₂CuIH)/GCE in equi-molar mixture of theophylline and caffeine revealed sufficiently separated oxidative peaks with much enhanced peak current showing electrocatalytic property of the polymer film towards the oxidation of theophylline and caffeine. Under optimized solution pH and square wave voltammetric parameters, oxidative peak current response of poly(ACP₂CuIH)/GCE showed linear dependence on the concentration of caffeine and theophylline in the concentration range 1.0–200.0 µM with limit of detection 8.92 × 10^-3 µM for theophylline, and 1.02 × 10^{-2 µ}M for caffeine. Spike recovery in the range 97.0-102.4% for theophylline, and 95.4-100.0% for caffeine, interference recovery in the range 96.0–101.0% for theophylline, and 95.7–104.3% for caffeine, agreement of the detected amounts of theophylline and caffeine in tablet samples with the nominal values, and stability of the modified electrode all validated the developed method for simultaneous determination of theophylline and caffeine in wide range of real samples. The method was applied for simultaneous determination of both theophylline and caffeine in three tea brands (Black lion, Addis, and Wush wush), pharmaceutical tablet brands (Panadol extra, and Theodrine), and human blood serum samples making the method an excellent candidate.     

Application of CE–ICP–MS and CE–ESI–MS in metalloproteomics: challenges,developments, and limitations

Application of capillary electrophoresis (CE) as a high-resolution separation technique in metalloproteomics research is critically reviewed. The focus is on the requirements and challenges involved in coupling CE to sensitive element and molecule-specific detection techniques such as inductively coupled plasma mass spectrometry (ICP–MS) or electrospray ionisation mass spectrometry (ESI–MS). The complementary application of both detection techniques to the structural and functional characterisation of metal-binding proteins and their structural metal-binding moieties is emphasised. Beneficial aspects and limitations of mass spectrometry hyphenated to CE are discussed, on the basis of the literature published in this field over the last decade. Recent metalloproteomics applications of CE are reviewed to demonstrate its potential and limitations in modern biochemical speciation analysis and to indicate future directions of this technique.     

Bulk properties and hydration numbers of components of water–salt,water–urea,and water–urea–salt systems

With an increase in the concentration of additives, the hydration numbers of compounds decrease. Thus, in a saturated 54.6% solution, urea loses approximately 3/4 of the initial amount of water, forming an aquacomplex of the composition (NH₂)₂CO?H₂O. In a supersaturated 44% solution, the sodium chloride aquacomplex is dehydrated by 2/3, and in a supersaturated 67% solution, sodium sulfate is dehydrated by 5/6. The density of these solutions is 1.354÷1.360 g/cm³ (44% NaCl) and 1.800÷1.849 g/cm³ (67% Na₂SO₄). In a saturated urea solution, NaNO₃, NaCl, and Na₂SO₄ complexes lose 53÷55% of hydration water. It is shown that the interactions in the binary water–urea system somewhat increase the hydration number of the salts (structural hydration). The hydration water density, a structurally important characteristic, increases in the series of solutions of urea, NaNO₃, NaCl, and Na₂SO₄. In the same series of additives, the excess volume of binary water–urea and water–salt systems becomes more negative.     

Cryoscopic Studies of the Uranyl Sulfate–Water, Uranyl Nitrate–Water, and Uranyl Nitrate–Nitric Acid–Water Systems

Freezing point lowerings of aqueous solutions of uranyl sulfate in the concentration range m 0.40 mol-kg^–1 and the activity and osmotic coefficients, which were calculated using the Pitzer equations for 2:2 electrolytes, are presented. Crystallization temperatures are reported for 0 to 13 molar nitric acid and 10–150 g uranium per liter uranyl nitrate–nitric acid–water solutions.     

Design,synthesis, and characterization of fullerene–peptide–steroid covalent hybrids

The present study reports the synthesis, spectral characterization, self-assembly properties, and preliminary in vitro study of antioxidant capacity of two triple covalent hybrids consisting of fullerene C₆₀, peptide, and steroidal moiety. Previously synthesized fulleropyrrolidinic acid and pregnenolone were connected by peptide linker using a multistep DCC/DMAP and/or EDC/HOBT esterification/amidation procedure. The hybrids were characterized by comparative analysis of spectroscopic data obtained from FTIR, UV–vis, HRMS, and extensive NMR experiments (¹H, ¹³C, COSY, HSQC, and HMBC). The self-assembling properties and morphology of triads samples prepared by drop-drying method were examined by scanning electron microscopy (SEM). Preliminary in vitro antioxidant activity was studied by Ferrous ion Oxidation-Xylenol orange (FOX) method.     

Contracted polarization functions for the atoms Ca, Ga–Kr, Sr, and In–Xe

 Contracted Gaussian-type function sets are proposed for polarization functions of the atoms Ga–Kr and In–Xe. We also report polarization functions for Ca and Sr. A segmented contraction scheme is used for its compactness and computational efficiency. The contraction coefficients and orbital exponents are fully optimized to minimize the deviation from accurate atomic natural orbitals. The present polarization functions yield more than 99% of atomic correlation energies predicted by accurate natural orbitals of the same size. Received: 23 February 2001 / Accepted: 19 April 2001 / Published online: 13 June 2001     

离子色谱法测定生活饮用水中的F~–,Cl~–,SO_4~(2–)和NO_3~–

建立了电导检测–离子色谱法同时测定生活饮用水中F–,Cl–,SO42–,NO3–的方法。选择30 mmol/L Na OH溶液为淋洗液,流量为1.40 m L/min,检测器电流为106 m A。F–的线性范围为0.15~2.0 mg/L,Cl–,SO42–,NO3–的线性范围为3.00~40.0 mg/L,4种离子的线性相关系数均大于0.999 5。F–,Cl–,SO42–,NO3–的方法检出限分别为0.02,0.13,0.14,0.02 mg/L,加标回收率在95.2%~103.0%之间。对环境标准204715进行了平行测试,各阴离子测定值均在标准值的不确定度范围内,测定结果的相对标准偏差小于2%(n=6)。该方法灵敏、准确、快速,可用于生活饮用水中F–,Cl–,SO42–,NO3–的同时测定。     

Donor–acceptor perylenediimide–ferrocene conjugates: synthesis,photophysical, and electrochemical properties

Donor–acceptor, perylenediimide–ferrocene conjugates have been synthesized by Suzuki, and Sonogashira coupling reactions. The photophysical and electrochemical properties of these conjugates are discussed. It has been shown that fluorescence as well as the electron affinity of the perylenediimide can be tuned by attaching the appropriate ferrocenyl derivatives.     

Analysis of Deoxynivalenol,Nivalenol, Zearalenone in Food by LC–APCI–MS

The detection of mycotoxins is an important task for analytical analysis, as they are a source of contaminants in foods today. The very small amounts of toxic mycotoxins (zearalenone, deoxynivalenol) make it important to determine the most reliable analytical methods. There are several options for the detection of mycotoxins, LC–API–MS techniques being the most common ones. The aim of the present determination is to give an overview on the application of LC–(API)-MS in the analysis of frequently occurring and highly toxic mycotoxins, such as deoxynivalenol, nivalenol and zearalenone, in organic foods. The limits of these three toxins in foods are very low: deoxynivalenol 1,250 μg kg^?1, nivalenol 0.9 μg kg^?1 of body weight, zearalenone 100 μg kg^?1.     

Tetra-nuclear copper complex having P–N–P ligand to P–O–P ligand – synthesis,structural, and mechanistic studies

We report the synthesis and structures of three copper(I) complexes, [Cu₄(μ₃-Cl)₂(μ₂-Cl)₂{μ₂-(2,6-Me₂C₆H₃N(PPh₂)₂)}₂] (2), [Cu₄(μ₃-Cl)₂(μ₂-Cl)₂{μ₂-(Ph₂POPPh₂)}₂] (4), and [Cu₂(μ₂-Cl)₂(μ₂-PPh₂OPPh₂)(η¹-Ph₂PP(=O)Ph₂)(PPh₃)] (5), and one cobalt complex, [(CoCl₂){μ₂-2,6-Me₂C₆H₃N(PPh₂)₂}₂][CoCl₃NH₂(2,6-Me₂Ph)] (3). Tetra-nuclear copper complex 2 was prepared in good yield by the reaction of bis(diphenylphosphino)-2,6-dimethylaniline [2,6-Me₂C₆H₃N(PPh₂)₂] (1) with copper(I) chloride along with triphenylphosphine in methanol. Adding a calculated amount of water and dichloromethane mixture (1?:?10) to 2 produced a second tetra-nuclear copper(I) complex, 4, with a P–O–P backbone, along with a small amount of the unsymmetrical copper(I) complex 5. The cobalt complex 3 was obtained by reaction of 1 with cobalt(II) chloride. The solid-state structures of 2–5 were established by single-crystal X-ray diffraction analysis. In the solid state, both 2 and 4 form a tetra-nuclear copper core. In the ³¹P{¹H} NMR study, we observed the conversion of 2, with P–N–P backbone, to 4, with P–O–P backbone.     

New ciprofloxacin–dithiocarbamate–benzyl hybrids: design,synthesis, antibacterial evaluation,and molecular modeling studies

Research on Chemical Intermediates - We designed and synthesized a series of new ciprofloxacin–dithiocarbamate–benzyl hybrids 5a–n as potential antibacterial agents. All of the...     

Synthesis,characterization and electrocatalytic activity for ethanol oxidation of carbon supported Pt,Pt–Rh,Pt–SnO2 and Pt–Rh–SnO2 nanoclusters

Nanoclusters of Pt, Pt–Rh, Pt–SnO₂ and Pt–Rh–SnO₂ were successfully synthesized by polyol method and deposited on high-area carbon. HRTEM and XRD analysis revealed two phases in the ternary Pt–Rh–SnO₂/C catalyst: solid solution of Rh in Pt and SnO₂. The activity of Pt–Rh–SnO₂/C for ethanol oxidation was found to be much higher than Pt/C and Pt–Rh/C and also superior to Pt–SnO₂/C. Quasi steady-state measurements at various temperatures (30–60 °C), ethanol concentrations (0.01–1 M) and H₂SO₄ concentrations (0.02–0.5 M) showed that Pt–Rh–SnO₂/C is about 20 times more active than Pt/C in the potential range of interest for the fuel cell application.