Biomimetic sensor for ethambutol employing ß-cyclodextrin mediated chiral copper metal organic framework and carbon nanofibers modified glassy carbon electrode.

Stereochemical configuration of the drug is responsible for racemic switch with enantiomers in presence of chiral environment for human beings. Therefore, its determination in racemic and pharmaceutical samples becomes a challenge. Addressing this issue, an enantioselective electrochemical biomimetic sensor for discrimination of isomers of ethambutol (ETB) employing square wave voltammetry (SWV) is reported for the first time. For this purpose, a chiral host, ß-Cyclodextrin based copper metal organic framework (CD-CuMOF) was synthesized and used for chelate complexation of ETB isomers (SS-ETB/RR-ETB). A glassy carbon electrode (GCE) is chemically modified using CD-CuMOF and carbon nanofibers (CNF) composite material to construct a sensor in the form of (CD-CuMOF-CNF-GCE). The behaviour of CD-CuMOF for ETB isomers on GCE is postulated to be an artificial enzyme model (AEM) as it mimics the catalytic activity similar to enzyme alcohol dehydrogenase for ETB. The biosensor exhibits excellent peak potential difference (ΔEp (SS-RR) = 108 mV) between ETB isomers using SWV showing a clear distinction in the racemic mixture. It showed a linear response in the range of 1.0 x 10-7 to 1 x 10-4 M and 5.0 x 10-7 to 2.5 x 10-4 M with low detection limit of 3.10 x 10-8 M and 8.52 x 10-8 M for RR-ETB and SS-ETB isomers respectively. The sensor was applied for the estimation of ETB isomers in racemic mixture and real samples viz., blood, urine and pharmaceutical. The CD-CuMOF is a low-cost material with higher stability than enzyme and offers an advantage for sensing and catalysis in future.

A dual metal organic framework based on copper-iron clusters integrated sulphur doped graphene as a porous material for supercapacitor with remarkable performance characteristics.

Herein, a novel bimetallic metal organic framework (MOF) using copper and iron as the metal centers with 1,3,5-tricarboxylic acid as a ligand (CuFeBTC) and its composite with sulphur doped graphene (S-GNS) have been investigated for supercapacitive performance. The synthesis of materials has been carried out using a facile wet chemical route. The physicochemical characterization of the materials employing various structural and surface techniques has been performed which confirms the successful formation of nanocomposite. The capacitive behavior of CuFeBTC, S-GNS and CuFeBTC/S-GNS has been systematically examined using 1 M Na2SO4 as an electrolyte in a three and two electrode assembly. The electrochemical studies reveal that CuFeBTC/S-GNS electrode demonstrates highest specific capacitance of 1164.3 F g-1 at 0.5 A g-1 with suffice rate capability as compared to CuFeBTC and S-GNS electrodes. Moreover, a symmetric supercapacitor is configured using the CuFeBTC/S-GNS nanocomposite electrodes which deliver remarkable energy and power output of 96.57 Wh kg-1 and 1595.12 W kg-1 at an operating voltage of 1.8 V. The as-fabricated symmetric supercapacitor displays competent energy storage retention of 50.2 Wh kg-1 even at current density of 20.0 A g-1 with high power density 26973.13 W kg-1. These deliverables epitomize the latest performance record of bimetallic MOFs based supercapacitors, suggesting that CuFeBTC/S-GNS is a promising active material for high performance electrochemical energy storage applications.

Highly sensitive and selective determination of methylergometrine maleate using carbon nanofibers/silver nanoparticles composite modified carbon paste electrode.

A highly sensitive and selective voltammetric method for determination of Methylergometrine maleate (MM) in pharmaceutical formulations, urine and blood serum samples has been developed based on enhanced electrochemical response of MM at carbon nanofibers and silver nanoparticles modified carbon paste electrode (CNF-AgNP-CPE). The electrode material was characterized by various techniques viz., X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy. The electrocatalytic response of MM at CNF-AgNP-CPE was studied by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). Under optimized conditions, the proposed sensor exhibits excellent electrochemical response towards MM. The DPV study shows greatly enhanced electrochemical signal for MM at CNF-AgNP-CPE lending high sensitivity to the proposed sensor for MM detection. The peak (Ip) current for MM is found to be rectilinear in the range 4.0×10(-8)-2.0×10(-5)M with a detection limit of 7.1×10(-9)M using DPV. The feasibility of the proposed sensor in analytical applications was investigated by conducting experiments on commercial pharmaceutical formulations, human urine and blood serum samples, which yielded satisfactory recoveries of MM. The proposed electrochemical sensor offers high sensitivity, selectivity, reproducibility and practical utility. We recommend it as an authentic and productive electrochemical sensor for successful determination of MM.

Identification of potent caspase-3 inhibitors for treatment of multi- neurodegenerative diseases using pharmacophore modeling and docking approaches.

Neurodegenerative disorders are due to excessive neuronal apoptosis and the caspase-3 plays a key role in the apoptotic pathway. The caspase-3 inhibition may be a validated therapeutic approach for neurodegenerative disorders and an interesting target for molecular modeling studies using both Ligand and structure based approaches. In view of the above we have generated the Ligand based pharmacophore model using the Discovery studio 2.0 software. In addition to this a structure based approach has been used to validate the developed pharmacophoric features to gain a deeper insight into its molecular recognition process. This validated pharmacophore and the docking model was then implemented as a query for pharmacophore based virtual screening to prioritize the probable hits for the Caspase-3. Two ligands, ZINC12405015 and ZINC12405043 were finally selected on the basis of their fit values and docking scores. This study also reveals the important amino acids viz. His-121, Ser-205, Arg-207 which were found to be playing crucial role in the binding of the selected compounds within the active site of caspase-3.

Prevalence and molecular characterisation of New Delhi metallo-ß-lactamases NDM-1, NDM-5, NDM-6 and NDM-7 in multidrug-resistant Enterobacteriaceae from India.

The growing prevalence of carbapenem resistance in Enterobacteriaceae worldwide is a major concern. New Delhi metallo-ß-lactamase (NDM)-mediated carbapenem resistance has been identified in Enterobacteriaceae from numerous countries including those of the Indian subcontinent. Currently, seven NDM ß-lactamase variants (NDM-1 to -7) have been identified. This study evaluated the detection and molecular characterisation of NDM variants in Enterobacteriaceae at a tertiary care hospital in India. A total of 464 isolates were tested; 57 (12.3%) were resistant or showed reduced susceptibility to imipenem and meropenem. All carbapenem-resistant isolates were blaNDM-positive by PCR, but 13 isolates bore variants that differed in sequence from blaNDM-1. NDM-5, NDM-6 and NDM-7 were identified in two, eight and three isolates, respectively. blaNDM variants were located on plasmids of >100kb with IncF, IncA/C and untypeable replicon types. Genes encoding the 16S rRNA methyltransferases RmtB, RmtC and ArmA as well as those for AmpC ß-lactamases were also located on the same plasmids as blaNDM in different combinations. The prevalence of NDM-5 to -7 variants was significantly higher in Escherichia coli (P=0.015) and they were more frequently isolated from the urology ward (P=0.037) than NDM-1. The mortality rate was comparable between patients infected with isolates positive for blaNDM-1 and blaNDM variants [25% (11/44) vs. 23% (3/13)]. Expression of blaNDM variants in E. coli using the same promoter showed that NDM-7 conferred higher resistance to imipenem. The diverse genotypic features of blaNDM indicate rapid evolution of NDM resulting from their wide spread in the Indian subcontinent.

Voltammetric determination of sumatriptan based on a graphene/gold nanoparticles/Nafion composite modified glassy carbon electrode.

A mixture of graphene oxide and tetrachloroauric acid was electrochemically co-reduced directly on a glassy carbon electrode (GCE) surface via cyclic voltammetry so as to form a graphene (Gr)-gold nanoparticles (AuNP) composite. This nanocomposite was then coated with nafion (NAF) film so as to form Gr/AuNP/NAF/GCE. Sumatriptan (SUM) is a drug belonging to the triptan class, used for the treatment of migraine headaches. In this work, an electrochemical method based on the adsorptive stripping differential pulse voltammetry (AdSDPV) employing Gr/AuNP/NAF/GCE has been proposed for the subnanomolar determination of SUM. Characterization of the electrode material has been carried out by UV-visible spectrophotometry, X-ray diffraction and scanning electron microscopy. Also the electrode surface has been characterized by means of cyclic voltammetry, electrochemical impedance spectroscopy, chronocoulometry. By employing Gr/AuNP/NAF/GCE at pH 7.0 phosphate buffer, a 20-fold enhancement in the AdSDPV signal was observed as compared to GCE. Under the optimized conditions, Ip (µA) was proportional to the SUM concentration in the range of 1.0×10(-6)-4.12×10(-5) M (R(2)=0.9991) and 2.14×10(-9)-1.0×10(-6) M (R(2)=0.9954) with a detection limit (3×SD/s) of 7.03×10(-10) M. The practical analytical utilities of the modified electrode were demonstrated by the determination of SUM in pharmaceutical formulations, human urine and blood serum samples. This proposed method was validated by HPLC and the results are in agreement at the 95% confidence level.

An in vitro and molecular informatics study to evaluate the antioxidative and ß-hydroxy-ß-methylglutaryl-CoA reductase inhibitory property of Ficus virens Ait.

The present study is initially intended to evaluate antioxidant and ß-hydroxy-ß-methylglutaryl-CoA reductase (HMGR) inhibitory property of Ficus virens Ait., first by in vitro analyses followed by a corroboratory molecular informatics study. Our results show that of all the sequentially extracted fraction of F. virens bark and leaves extract, F. virens bark methanol extract exhibits strong radical scavenging, antioxidant and oxidative DNA damage protective activity, which is well correlated with its total phenolic content. In addition, F. virens bark methanol extract, which is non-cytotoxic, significantly and non-covalently inhibit the HMGR activity (IC50 = 3.45 ± 0.45 µg/ml) in comparison with other extracts. The mechanistic aspect of this inhibition activity is authenticated by molecular docking study of bioactive compounds as revealed from gas chromatography-mass spectrometry data, with HMGR. The analysis for the first time indicates that quinic acid (ΔG: -8.11 kcal/mol) and paravastatin (ΔG: -8.22 kcal/mol) exhibit almost same binding energy, while other compounds also showed good binding energy, suggesting that quinic acid alone or in combination with other major bioactive compound is probably responsible for HMGR inhibitory property of the extract and plausibly can be used in in vivo system for the management, prevention, and alleviation of hypercholesterolemia as well as hypercholesterolemia-induced oxidative stress.

Simultaneous determination of L-tyrosine and caffeine based on their electrocatalytic oxidation at a 4-tert-butylcalix[6] arene-modified carbon paste electrode.

Simultaneous determination of L-tyrosine and caffeine was performed at a carbon paste electrode modified with 4-tert-butylcalix[6]arene and in situ Ni2+ ions. Surface characterization of the electrode was carried out by means of scanning electron microscopy. Electrochemical impedance diagnosis revealed that oxidation of both molecules is kinetically facile on the modified electrode. The electrochemical behavior of both molecules was studied using cyclic voltammetry, and further quantified using differential pulse voltammetry (DPV). The results revealed a high sensitivity for their simultaneous detection. DPV allowed simultaneous detection of L-tyrosine and caffeine in the range of 10(-6) to 10(-3) M, with LODs of 2.19 x 10(-7) and 4.03 x 10(-7) M, respectively. The modified electrode was used for individual determination of L-tyrosine and caffeine in various pharmaceutical formulations and simultaneous monitoring in human body fluids.

Adsorptive stripping voltammetric determination of imipramine, trimipramine and desipramine employing titanium dioxide nanoparticles and an Amberlite XAD-2 modified glassy carbon paste electrode.

An Amberlite XAD-2 (XAD2) and titanium dioxide nanoparticles (TNPs) modified glassy carbon paste electrode (XAD2-TNP-GCPE) was developed for the determination of imipramine (IMI), trimipramine (TRI) and desipramine (DES). The electrochemical behavior of these molecules was investigated employing cyclic voltammetry (CV), chronocoulometry (CC), electrochemical impedance spectroscopy (EIS) and adsorptive stripping differential pulse voltammetry (AdSDPV). After optimization of analytical conditions using a XAD2-TNP-GCPE electrode at pH 6.0 phosphate buffer (0.1 M), the peak currents were found to vary linearly with its concentration in the range of 1.30 × 10(-9) to 6.23 × 10(-6) M for IMI, 1.16 × 10(-9) to 6.87 × 10(-6) M for TRI and 1.43 × 10(-9) to 5.68 × 10(-6) M for DES. The detection limits (S/N = 3) of 3.93 × 10(-10), 3.51 × 10(-10) and 4.35 × 10(-10) M were obtained for IMI, TRI and DES respectively using AdSDPV. The prepared modified electrode showed several advantages such as a simple preparation method, high sensitivity, very low detection limits and excellent reproducibility. The proposed method was employed for the determination of IMI, TRI and DES in pharmaceutical formulations, blood serum and urine samples.

Biomimetic sensor for certain catecholamines employing copper(II) complex and silver nanoparticle modified glassy carbon paste electrode.

A dimeric Cu(II) complex [Cu(µ(2)-hep)(hep-H)](2)·2ClO(4) (1) containing bidentate (hep-H=2-(2-hydroxyethyl)pyridine) ligand was synthesized and characterized by single crystal X-ray diffraction studies. Each Cu-ion in 1 is in a distorted square pyramidal geometry. Further 1 along with silver nanoparticles (SNPs) have been used as modifier in the construction of a biomimetic sensor (1-SNP-GCPE) for determining certain catecholamines viz., dopamine (DA), levodopa (l-Dopa), epinephrine (EP) and norepinephrine (NE) using cyclic voltammetry, chronocoulometry, electrochemical impedance spectroscopy and adsorptive stripping square wave voltammetry (AdSSWV). Finally, the catalytic properties of the sensor were characterized by chronoamperometry. Employing AdSSWV, the calibration curves showed linear response ranging between 10(-6) and 10(-9)M for all the four analytes with detection limits (S/N=3) of 8.52×10(-10)M, 2.41×10(-9)M, 3.96×10(-10)M and 3.54×10(-10)M for DA, l-Dopa, EP and NE respectively. The lifetime of the biomimetic sensor was 3 months at room temperature. The prepared modified electrode shows several advantages such as simple preparation method, high sensitivity, high stability, ease of preparation and regeneration of the electrode surface by simple polishing along with excellent reproducibility. The method has been applied for the selective and precise analysis of DA, l-Dopa, EP and NE in pharmaceutical formulations, urine and blood serum samples.

Development and validation of a liquid chromatography method for the simultaneous determination of eight water-soluble vitamins in multivitamin formulations and human urine.

A simple, precise, and rapid RPLC method has been developed without incorporation of any ion-pair reagent for the simultaneous determination of vitamin C (C) and seven B-complex vitamins, viz, thiamine hydrochloride (B1), pyridoxine hydrochloride (B6), nicotinamide (B3), cyanocobalamine (B12), folic acid, riboflavin (B2), and 4-aminobenzoic acid (Bx). Separations were achieved within 12.0 min at 30 degrees C by gradient elution on an RP C18 column using a mobile phase consisting of a mixture of 15 mM ammonium formate buffer and 0.1% triethylamine adjusted to pH 4.0 with formic acid and acetonitrile. Simultaneous UV detection was performed at 275 and 360 nm. The method was validated for system suitability, LOD, LOQ, linearity, precision, accuracy, specificity, and robustness in accordance with International Conference on Harmonization guidelines. The developed method was implemented successfully for determination of the aforementioned vitamins in pharmaceutical formulations containing an individual vitamin, in their multivitamin combinations, and in human urine samples. The calibration curves for all analytes showed good linearity, with coefficients of correlation higher than 0.9998. Accuracy, intraday repeatability (n = 6), and interday repeatability (n = 7) were found to be satisfactory.

Potentiometric stripping analysis of methyl and ethyl parathion employing carbon nanoparticles and halloysite nanoclay modified carbon paste electrode.

Carbon nanoparticles (CNPs) and halloysite nanoclay (HNC) modified carbon paste electrode (HNC-CNP-CPE) was developed for the determination of methyl parathion (MP) and ethyl parathion (EP). The electrochemical behavior of these molecules was investigated employing cyclic voltammetry (CV), chronocoulometry (CC), electrochemical impedance spectroscopy (EIS) and potentiometric stripping analysis (PSA). After optimization of analytical conditions employing this electrode at pH 5.0 in acetate buffer (0.1 M), the peak currents were found to vary linearly with its concentration in the range of 1.55×10(-9) to 3.67×10(-6) M and 1.21×10(-9) to 4.92×10(-6) M for MP and EP, respectively. The detection limits (S/N=3) of 4.70×10(-10) M and 3.67×10(-10) M were obtained for MP and EP, respectively, using PSA. The prepared modified electrode showed several advantages such as simple preparation method, high sensitivity, very low detection limits and excellent reproducibility. The proposed method was employed for the determination of MP and EP in fruits, vegetables, water and soil samples.

Simultaneous voltammetric determination of acetaminophen and tramadol using Dowex50wx2 and gold nanoparticles modified glassy carbon paste electrode.

A glassy carbon paste electrode (GCPE) modified with a cation exchanger resin, Dowex50wx2 and gold nanoparticles (D50wx2-GNP-GCPE) has been developed for individual and simultaneous determination of acetaminophen (ACOP) and tramadol (TRA). The electrochemical behavior of both the molecules has been investigated employing cyclic voltammetry (CV), chronocoulometry (CC), electrochemical impedance spectroscopy (EIS) and adsorptive stripping square wave voltammetry (AdSSWV). The studies revealed that the oxidation of ACOP and TRA is facilitated at D50wx2-GNP-GCPE. Using AdSSWV, the method allowed simultaneous determination of ACOP and TRA in the linear working range of 3.34×10(-8) to 4.22×10(-5) M with detection limits of 4.71×10(-9) and 1.12×10(-8) M (S/N=3) for ACOP and TRA respectively. The prepared modified electrode shows several advantages such as simple preparation method, long-time stability, ease of preparation and regeneration of the electrode surface by simple polishing and excellent reproducibility. The high sensitivity and selectivity of D50wx2-GNP-GCPE were demonstrated by its practical application in the determination of both ACOP and TRA in pharmaceutical formulations, urine and blood serum samples.

Potentiometric stripping analysis of antimony based on carbon paste electrode modified with hexathia crown ether and rice husk.

An electrochemical method based on potentiometric stripping analysis (PSA) employing a hexathia 18C6 (HT18C6) and rice husk (RH) modified carbon paste electrode (HT18C6-RH-CPE) has been proposed for the subnanomolar determination of antimony. The characterization of the electrode surface has been carried out by means of scanning electron microscopy, cyclic voltammetry, electrochemical impedance spectroscopy and chronocoulometry. By employing HT18C6-RH-CPE, a 12-fold enhancement in the PSA signal (dt/dE) was observed as compared to plain carbon paste electrode (PCPE). Under the optimized conditions, dt/dE (sV(-1)) was proportional to the Sb(III) concentration in the range of 1.42×10(-8) to 6.89×10(-11)M (r=0.9944) with the detection limit (S/N=3) of 2.11×10(-11)M. The practical analytical utilities of the modified electrode were demonstrated by the determination of antimony in pharmaceutical formulations, human hair, sea water, urine and blood serum samples. The prepared modified electrode showed several advantages, such as simple preparation method, high sensitivity, very low detection limit and excellent reproducibility. Moreover, the results obtained for antimony analysis in commercial and real samples using HT18C6-RH-CPE and those obtained by inductively coupled plasma-atomic emission spectrometry (ICP-AES) are in agreement at the 95% confidence level.

Reversible single-crystal to single-crystal transformations in a Hg(II) derivative. 1D-polymeric chain <=>2D-networking as a function of temperature.

Reactions of HgX(2) (X = Cl(-), Br(-), l(-)) with the ligand hep-H (hep-H = 2-(2-hydroxyethyl)pyridine) in methanol at 298 K result in 1D-polymeric chains of [(X)Hg(mu-X)(2)(hep-H)](infinity), 1-3, respectively, where hep-H binds to the Hg(ii) ions in a monodentate fashion exclusively with the pyridine nitrogen donor and the suitably ortho-positioned -(CH(2))(2)OH group of hep-H remains pendant. The packing diagrams of 1-3 exhibit extensive intramolecular and intermolecular hydrogen bonding interactions leading to hydrogen bonded 2D network arrangement in each case. Though the single crystal of either 2 (X = Br) or 3 (X = I) loses crystallinity upon heating, the single crystal of 1 selectively transforms to a 2D-polymeric network, 4 on heating at 383 K for 1.5 h. The polymeric 4 consists of central dimeric [Hg(mu(3)-Cl)(hep-H)Cl](2) units, which are covalently linked with the upper and lower layers of [-(mu-Cl)(2)-Hg-(mu-Cl)(2)-Hg(mu-Cl)(2)-](n). The packing diagram of 4 reveals the presence of O-H-Cl and C-H-Cl hydrogen bonding interactions which in effect yields hydrogen bonded 3D-network. Remarkably, the single crystals of 4 convert back to the single crystals of parent 1 on standing at 298 K for three days.

Biomimetic sensor for certain phenols employing a copper(II) complex.

A new dimeric Cu(II) complex [Cu(mu(2)-hep)(hep-H)](2).2PF(6) (1) containing a bidentate (hep-H = 2-(2-hydroxyethyl)pyridine) ligand was synthesized and characterized by single crystal X-ray diffraction studies. Each Cu ion in 1 is in a distorted square pyramidal geometry. Further 1 is used as a modifier in the construction of a biomimetic sensor for determining phenols [phenol (Phe), resorcinol (Res), hydroquinone (HQ), and catechol (Cat)] in phosphate buffer by using cyclic voltammetry (CV), chronocoulometry, electrochemical impedance spectroscopy (EIS), differential pulse voltammetry (DPV), and square wave voltammetry (SWV). DPV has been proposed for trace determination of Phe and Res while SWV for HQ and Cat. The method has been applied for the selective and precise analysis of Phe in commercial injections, Res in hair coloring agents, HQ in photographic developers and cosmetics, and Cat in tea samples and guarana tablets. The calibration curves showed a linear response ranging between 10(-6) and 10(-8) M for all four of the analytes with detection limits (3sigma) of 1.04 x 10(-8), 2.31 x 10(-8), 1.54 x 10(-8), and 0.86 x 10(-8) M for Phe, Res, HQ, and Cat, respectively. The lifetime of the biomimetic sensor was 200 days at room temperature (at least 750 determinations). The catalytic properties of 1-CPE were characterized by chronoamperometry and were found to be in good agreement with Michaelis-Menten kinetics.

Single-crystal to single-crystal transformations in discrete hydrated dimeric copper complexes.

The single crystals of discrete hydrated [(OAc)Cu(mu-hep)(2)Cu(OAc)].2H(2)O (.2H(2)O) and [(OAc)Cu(mu-hep)(2) Cu(O(n)Pr)].2H(2)O (.2H(2)O) (the lattice H(2)O molecules exist as a tetrameric water cluster, hep-H = 2-(2-hydroxyethyl)pyridine), OAc(-) = acetate and O(n)Pr(-) = n-propionate) undergo single-crystal to single-crystal (SCSC) transformations to the dehydrated and , respectively, under the influence of heat. The reverse SCSC processes of /-->.2H(2)O/.2H(2)O involving the regeneration of the lattice water tetramers take place on exposure of / to water vapour. However, the blue single crystal of discrete hydrated [(O(n)Pr)Cu(mu-hep)(2)Cu(O(n)Pr)].2H(2)O (.2H(2)O), incorporating the two bulkier O(n)Pr(-) terminal bidentate ligands, irreversibly converts to the green single crystal of a unique discrete tetrameric [Cu(4)(mu(3)hep)(2)(mu-hep)(2)(mu-O(n)Pr)(2)(O(n)Pr)(2)] () with double open cubane core either by heating or by a simple vapour diffusion technique via the breaking and forming of multiple covalent bonds.

Vapor-diffusion-mediated single crystal-to-single crystal transformation of a discrete dimeric copper(II) complex to a discrete tetrameric copper(II) complex.

The symmetric dimeric complex [Cu(mu(2)-hep)(TFA)(H(2)O)](2) (1) has been synthesized from 2-(2-hydroxyethyl)pyridine (hep-H), trifluoroacetic acid (TFA-H), and copper acetate in a 95:5 (v/v) MeOH-H(2)O mixture at 298 K. Each Cu(II) ion in 1 is linked with two mu(2)-alcoholic oxygen atoms and one pyridine nitrogen atom of hep, and the other two coordination sites are occupied by the oxygen donors of TFA and H(2)O. At room temperature, the blue single crystals of 1 transform to the green single crystals of a tetrameric complex, [Cu(4)(mu(3)-hep)(2)(mu(2)-hep)(2)(mu(2)-TFA)(2)(TFA)(2)] (2), in presence of alcoholic vapor. The facile single crystal-to-single crystal (SCSC) transformation of 1 to 2 is accompanied by the removal of coordinated H(2)O molecules in 1 and concomitant formation of four new covalent bonds, two Cu-O(mu(3)-hep) and two Cu-O(mu(2)-TFA). The SCSC transformation of 1 to 2 is selective to the alcoholic vapor; the exposure of single crystals of 1 to heat or light or in vacuum has resulted in an immediate loss in crystallinity.

Development of a carbon paste electrode containing benzo-15-crown-5 for trace determination of the uranyl ion by using a voltammetric technique.

The interaction of macrocyclic compounds like crown ethers and UO2(2+) has been studied by electrochemical methods. A modified carbon paste electrode incorporating benzo-15-crown-5 (B15C5) was used to evaluate the electron transfer reaction of UO2(2+) by cyclic voltammetry, differential pulse voltammetry, and electrochemical impedance spectroscopy. Electrochemical impedance studies showed that charge transfer resistance was less for the B15C5-modified electrode than for the plain carbon paste electrode (PCPE). On the basis of these observations, a UO2(2+)-sensitive crown ether chemically modified electrode (CME) for trace analysis was fabricated and investigated in aqueous solutions. It was found that a 5% B15C5-CME for UO2(2+) showed a better voltammetric response than did the PCPE. UO2(2+) could be quantified at sub-microg/mL levels by differential pulse voltammetry with a detection limit of 0.03 microg/mL. By differential pulse adsorptive stripping voltammetry, UO2(2+) could be quantified in the working range of 0.002-0.2 microg/mL, with a detection limit of 1.1 microg/L. Simultaneous determination of UO2(2+), Pb(2+), and Cd(2+) was possible. The method was successfully applied to the determination of UO2(2+) in synthetic, as well as real, samples; the results were found to be comparable to those obtained by inductively coupled plasma-atomic emission spectroscopy.

Polarographic behavior of nicotinamide in surfactant media and its determination in cetyltrimethylammonium bromide surfactant system.

The behavior of nicotinamide has been studied by differential pulse polarography and cyclic voltammetry in the presence of certain ionic and nonionic surfactants, viz. cetyltrimethylammonium bromide (CTAB), sodium dodecylsulfate (SDS) and Triton X-100 (TX-100). The cathodic peak potential (E(p(c))) and peak current (I(p(c))) of nicotinamide were found to be remarkably dependent on the charge and concentration of the surfactant. The presence of SDS and that of TX-100 cause a shift in peak potential and a change in peak current of nicotinamide. In the presence of the cationic surfactant, CTAB, an enhancement in the sensitivity of nicotinamide was observed. A sharp peak with more than two-fold increase in current was used to determine the limit of detection and linear working range using the differential pulse polarographic technique. The present method was successfully used for the simultaneous determination of nicotinamide and pyridoxine hydrochloride, and for the determination of nicotinamide in multivitamin pharmaceutical preparations.