Electrochemical Detection of 2‐Naphthol at a Glassy Carbon Electrode Modified with Tosflex Film

In this study, a Tosflex (a perfluoro‐anion‐exchange membrane) modified glassy carbon electrode has been used to detect 2‐naphthalenol (2‐naphthol) in aqueous solutions in order to demonstrate the electroanalytical application of Tosflex. 2‐naphthol polymerizes upon electrochemical oxidation at a glassy carbon electrode; however, the current related to this oxidation is too small for analytical purpose at low concentration level. A Tosflex polymer modified glassy carbon electrode (TFGCE) was found of having capability to improve the detection limit because 2‐naphthol molecules deprotonated in basic solutions to form 2‐naphtholate anions that were accumulated to TFGCE by the anion‐exchange characteristic of Tosflex. The accumulated 2‐naphtholate anions were determined with the following differential pulse voltammetry. With 3 minutes accumulation at +0.05 V, the dependence of oxidation current versus concentration was linear from 8×10^?7 M to 1×10^?5 M with a regression coefficient of 0.999 and a detection limit of 2×10^?7 M. Unlike many other anion‐exchange polymer modified electrodes, the TFGCE is stable at highly basic condition.     

Efficient synthesis of serically constrained smmetrically alpha,alpha-disubstituted alpha-amino acids under operationally convenient conditions

Homologation of the nucleophilic glycine equivalent Ni-Gly-PABP [Ni(II) complex of glycine Schiff base with 2-[N-(alpha-picolyl)amino]benzophenone (PABP)] 2 via alkyl halide alkylations and Michael addition reactions was systematically studied as a general method for preparing symmetrically alpha,alpha-disubstituted alpha-amino acids (sym-alpha,alpha-AA). The dialkylation reactions are conducted under operationally convenient conditions without recourse to inert atmosphere, dried solvents, and low temperatures, thus enjoying key advantages of the experimental simplicity and attractive cost structure. The method has been shown to be particularly successful for the dialkylation of complex 2 with activated and nonactivated alkyl halides, including propargyl derivatives, affording a generalized and practical access to the corresponding sym-alpha,alpha-AA. This study has also shown some limitation of the method, as it cannot be extended to alpha- or beta-branched alkyl halides or Michael acceptors to be used for the dialkylation of glycine equivalent 2. High chemical yields of the dialkylated products, combined with the simplicity of the experimental procedure, render this method worth immediate use for multigram scale preparation of the sym-alpha,alpha-AA.     

Determination of Thorium and Total Rare Earths in Monazite Sand with Fluoride Electrode

A new method has been proposed to determine the total rare earths and thorium in monazite sand with fluoride electrode. The total amount of thorium and rare earths could be determined by back-titration with standard lanthanum solution in excess fluoride, and the rare earths were titrated directly with fluoride from separate sample. Fluoride electrode was used as indicator electrode. Precision and accuracy were improved by Gran's plot technique.     

Ultraviolet difference spectroscopic study on the interactions of cellulase fromTrichoderma reesei with cellodextrins

The formation of cellodextrin-cellobiohydrolase complex was studied by ultraviolet difference spectroscopy. Upon the binding of cellodextrins (G₇‐G₃), cellobiohydrolase (EC 3.2.1.91) purified fromTrichoderma reesei produced difference spectra having maxima at 289‐293 nm and 283‐286 nm. These spectra are consistent with prior observations reported for lysozyme and amylase. In this case, water soluble cellulose oligomers (i.e., cellodextrins) are shown to interact with tryptophan residue(s) on cellobiohydrolase. The difference spectral maxima observed at acidic or alkaline pH were shifted. This was accompanied by a marked decrease of binding ability of cellobiohydrolase for cellodextrins. The standard free energy change for the association of cellodextrins to the cellobiohydrolase was an order of 4 kcal/gmol. The association constant of enzyme for substrate decreases by 15‐20% as temperature increases from 20 to 48°C. At 25°C, the dissociation constants for the enzyme with respect to cellohexose and cellotriose were estimated to be 1.19 and 1.37 mM, respectively. A decrease in dissociation constants was observed with an increase in the number of glucosyl units from 3 to 6. This suggests that there may be six or more subsites in the active center of cellobiohydrolase.     

Natural Product Chemistry: From Plants to Human

Conventionally, natural product chemistry deals with the isolation, characterization, and synthesis of compounds from plants. It a broad sense, natural product chemistry may include all fields of biochemistry. Two projects are presented to illustrate the expanded definition of natural product chemistry. One deals with phosphatidylinositol (PI) and the key enzyme involved in its metabolism, PI-specific phospholipase C. The other project is on the structure-function relationship of human tumor suppressor p16.     

Stability-indicating high-performance liquid chromatographic assay method and photostability of carprofen

A rapid, sensitive, and accurate stability-indicating high-performance liquid chromatographic assay method for determining the degradation of carprofen (CPF) is developed and validated under acidic, basic, or photo-irradiated conditions. The analysis is monitored with a Cosmosil 5C18-AR column using a mobile phase of CH3CN-H2O-AcOH (50:49:1, v/v/v) at 260 nm. The developed method satisfies the system suitability criteria, peak integrity, and resolution among the parent drug and its degradation products. The results indicate that the established assay method shows good selectivity and specificity suitable for stability measurements of CPF. CPF is found to be more sensitive to exposure to light and in acidic conditions, but it is stable in a basic medium. The kinetic study of the photodegradation of CPF follows an apparent first-order reaction in a variety of solvents. The solvent effects on the rates of degradation are in the decreasing order of chloroform > dichloromethane > methanol > ethanol > 2-propanol, which is irrelevant to the dielectric constant epsilon. However, the hydrogen-donating ability of the solvents is essential to the photochemical decomposition of CPF. A plot of log k versus the Kirkwood function exhibits a linear relationship in aqueous ethanolic solutions, which implies that degradation proceeds via an ionic mechanism.     

Coking and Deactivation of H-ZSM-5 Zeolites during Ethylbenzene Disproportionation: I. Formation and Location of Coke

The mode of deactivation and coke formation in a H-ZSM-5 zeolite during ethylbenzene disproportionate has been investigated by TGA, adsorption, IR, and ¹²⁹Xe NMR techniques. The initial rate of deactivation and the total coke content are found to increase with increasing conversion level. Within the range of conversion (54-63%) covered in the present study, the location and extent of coke deposition can be divided into three distinct regions. At low coke content, coke is found to deposit on the Brønsted acid sites and resulted in a notable decrease in catalytic activity. As the amount of coke increases (≤ 7 wt%), while the catalytic activity decreases slightly, most of coke still tends to deposit within the zeolite channels. The slight decrease in catalytic activity is ascribed to steric hindrance by coke residues. When the coke content exceeds 7 wt%, while the activity remains almost constant, the deposition of coke on the external surface of the zeolite crystallites is evident. It is found that neither the pore opening nor the acid site were completely blocked off by coke residues even at the highest coke loading.     

Studies on the Preparation and Biological Activities of 3-(O-Methoxybenzyl)Sydnone Derivatives and 3-(Fluorophenyl)Sydnones

Two new sydnones; 3-(o-methoxybenzyl)sydnone(1) and 3-(o-melhoxybenzyl)-4-morpholinomethylsydnone(2) were synthesized from o-methoxybenzylamine and ethyl bromoacetat in moderate yields. 3-(o-,m-,p-Fluorophenyl)sydnones were prepared from the corresponding fluoroaniline and chloroacetic acid in higher yields with a conventional method. From the biological activity test, 1 shows significant response of coronary dilation test, collagen induced platelet aggregation inhibition, local anesthetic and moderate cardiotropic activity. In addition, 1 also leads to anticonvuls, muscle relaxation and behavior depression. But 2 only shows inhibition of collagen induced platelet aggregation and antiwrithing. 3-(p-Fluorophenyl)sydnone (5) shows significant response of coronary dilation, collagen induced platelet aggregation inhibition, moderate cardiotropic activity, antiwrithing and local anesthetic But 3-(o-Fluorophenyl)sydnone(3) and 3-(m-fluorophenyl)sydnone(4) only show coronary dilation and moderate cardiotropic activity.     

Violet light emitting diode-induced fluorescence detection combined with on-line sample concentration techniques for use in capillary electrophoresis

The first application of a violet light-emitting diode (LED) for fluorescence detection in capillary electrophoresis (CE) is described. The utility of violet LED (peak emission wavelength at 410 nm, approximately 2 mW) for fluorescence detection is demonstrated by examining reserpine and dopamine-labeled NDA (naphthalene-2,3-dicarboxaldehyde), respectively. The detection limit for reserpine was determined to be 2.5 x 10(-6) M by normal micellar electrokinetic capillary chromatography (MEKC) and this was improved to 2.0 x 10(-9) M and 2.0 x 10(-10) M when sweeping-MEKC and cation-selective exhaustive injection (CSEI)-sweep-MEKC techniques were applied, respectively. In addition, the detection limit of NDA-labeled dopamine was determined to be 6.3 x 10(-6) M by means of normal MEKC and this was improved to 3.0 x 10(-8) M when the sweeping-MEKC mode was applied.     

Effects of binder, coking and regeneration on acid properties of H-mordenite during TDP reaction

The effects of binder, coking and regeneration on the acid properties of H-mordenite zeolite during toluene disproportionation reaction (TDP) have been investigated by solid-state ³¹P-MAS-NMR of various adsorbed phosphorous probe molecules in conjunction with elemental analysis by ICP-MS technique. A series of fresh, spent and regenerated mordenite-based commercial catalysts were examined and the results were also compared with binder-free H-mordenite zeolite and unformulated γ-alumina binder. It is found that parent H-mordenite zeolite possessed only Brønsted acidity, which is responsible for the observed catalytic activity. In contrast, the γ-Al₂O₃ binder exhibited only Lewis acidity and plays a minor role during the catalytic reaction. While the amount of strong Brønsted acid sites decreased rapidly during initial coking, it reached a plateau at a total coke content of ca. 7 wt%, corresponding to ca. 80% decrease in total acidity. That the catalyst remained active even under deep coke deposition (>7 wt%) condition indicated catalytic activity may be invoked by subsequent coking taking place on the external surface rather than intracrystalline channels of the zeolite catalyst. Furthermore, upon catalyst regeneration treatment, ca. 75% of the total acidity could be effectively recovered.