A novel carbon/chitosan paste electrode for electrochemical detection of normetanephrine in the urine

Normetanephrine is a marker for pheochromocytoma, a rare catecholamine-secreting and neuroendocrine tumor, that arises from sympathetic and parasympathetic paraganglia. In this work, a novel carbon/chitosan electrode paste was used for sensitive voltammetric determination of normetanephrine and dopamine in the presence of ascorbic acid and uric acid. The modified electrode has shown an increase in the effective area of up to 68%, well-separated oxidation peaks, and an excellent electrocatalytic activity. The electrochemical response characteristics were investigated by cyclic and differential pulse voltammetry. Interestingly, high sensitivity and selectivity in the linear range of normetanephrine, dopamine, ascorbic acid, and uric acid concentrations were observed. The present method was applied in the urine sample and satisfactory results were obtained showing that this electrode is very suitable in pharmaceutical and clinical preparations.     

Substituent effects in the transannular cyclizations of germacranes. Synthesis of 6-epi-costunolide and five natural steiractinolides

The occurrence and orientation of substituents in the 10-membered ring characteristic of germacranes is determinant in the stereochemical outcome of the acid-promoted transannular cyclization of these metabolites. An explanation of the synthesis of eudesmanolides and guaianolides produced by the Umbelliferae family of plants is advanced. The syntheses of the natural products 6-epi-costunolide and five steiractinolides are reported.     

Biodegradable Materials from Agro-Based By-Products

Summary: A new biodegradable thermoplastic material based on a wheat flour by-product has been developed. The influence of various additives (glycerol, silica) and fibers (flax, cotton, hemp) on the mechanical properties of the material has been investigated. The development of expanded materials is also presented.     

Production of oligocellouronates by biodegradation of oxidized cellulose

The biodegradation of β-(1,4)-polyglucuronic acids from cellulose acetate oxidation utilizing the TEMPO/NaBr/NaOCl system was investigated using a glucuronan lyase isolated from Trichoderma strain GL2. Products of the β-elimination mechanism catalyzed by this enzyme were then purified by size-exclusion chromatography and characterized by ESI-Q/TOF-mass spectrometry and ¹H-NMR spectroscopy. The analyses prove the complete biodegradation of this category of cellulose derivates and open the way to the large-scale production of oligouronides.     

Stabilization in neutral bicyclic sulfoxide compounds

Density Functional Theory (DFT) calculations at the B3LYP/6‐31+G* level have been performed on 5‐thiabicyclo[2.1.1]hex‐2‐ene S‐oxide derivatives. The geometrical and electronic properties of the compounds have been analyzed in order to explain the favored stability of the exo configuration. Isodesmic reactions at the Gaussian‐G2 theory yielded the exo conformer as the most stable one. Moreover, the NMR chemical shift parameters (GIAO method) together with the Atoms in Molecules theory reveal an stabilization of the S atom with the double bond for the exo configuration, in agreement with the experimental results. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 322–327, 2000