Versatile access to C-4-substituted 2-amino-1,3-azoles from hydropyridines in oxidative conditions

[Chemical reaction: see text] Various substituted 2-aminotetrahydroazolopyridines and 2-aminohexahydroazolopyridines have been prepared by bromine-mediated addition of protected guanidine or urea to hydropyridine derivatives. The pH-dependent regioselective cleavage of the resulting aminal function led to the 2-aminoazole products III. The yields of the bicycles of type II, and their conversion into azoles III depends on the electronic properties of the substituents on the nitrogen of the tetrahydopyridine.     

Nitroso group transfer in s-nitrosocysteine: evidence of a new decomposition pathway for nitrosothiols

The rate of S-nitrosocysteine decomposition in a pH range between 0.7 < pH < 13 exhibits first- and second-order dependence on total cysteine concentration. The second-order term is only observed for pH values between 6.9 < pH < 12. Both first- and second-order terms show a complex dependence on the acidity of the medium. They increase with increasing pH, reaching a maximum value around pH = 8 and then decrease with further increase in pH. An analysis of the reaction products reveals the absence of nitrite ion and ammonia. No evidence of catalysis by copper ions is observed. These results suggest the existence of a new decomposition pathway for S-nitrosocysteine, which proceeds via an intramolecular nitroso group transfer producing a primary N-nitrosamine that decomposes rapidly to give the corresponding diazonium salt. The nitroso group transfer reaction occurs intermolecularly for the decomposition pathway exhibiting a quadratic dependence on cysteine concentration. Both nitroso group transfer pathways are subject to acid catalysis by cysteine. Kinetic results indicate that the extent of S...NO bond cleavage in the transition state is ahead of protonation of the AH...S sulfur atom. The results obtained show the existence of a new decomposition pathway for the S-nitrosocysteine where NO is not released, and hence, it has a significant biological impact due to the potential use of nitrosothiols as NO donors.     

Shape-complementarity in the recognition of tricarboxylic acids by a [3+3] polyazacyclophane receptor

[structure: see text] The interaction of a macrocycle containing three trans-(1R,2R)-diaminocyclohexane units connected by p-xylene spacers with the isomers 1,3,5-benzenetricarboxylic (1,3,5-BTC), 1,2,4-benzenetricarboxylic (1,2,4-BTC), and 1,2,3-benzenetricarboxylic (1,2,3-BTC) acids and their relevant anions is studied by means of potentiometric and NMR analysis. The interaction is highest for the isomer 1,3,5-BTC, which perfectly fits within the macrocyclic cavity of the host species. The studies have been extended to the triacid 1,3,5-benzenetriacetic observing in this case the effect of a size mismatch between host and guest species.     

Oxidation process induced by 2-mercaptopyrimidine at a mercury electrode

The oxidation process induced by 2-mercaptopyrimidine (RSH) at a hanging mercury drop electrode was studied in aqueous media by normal and cyclic voltammetry. The results indicate the formation of a weakly adsorbed HgSR complex according to the reaction Hg+RSH-->HgSR+e(-)+H+. When the surface excess of HgSR is high, a two-dimensional condensation takes place if the potential is positive enough, as proved by phase-sensitive ac and cyclic voltammetry.     

Electrochemical evidences of morphological transformation in ordered mesoporous titanium oxide thin films

We provide the first electrochemical evidence of permeability changes in continuous mesoporous TiO2 thin film electrodes induced by nanocrystallisation.     

Design, self-assembly, and photophysical properties of pentameric metallomacrocycles: [M5(N-hexyl[1,2-bis(2,2':6',2''-terpyridin-4-yl)]carbazole)5][M = Fe(II), Ru(II), and Zn(II)

A novel family of metallopentacycles was constructed by the facile self-assembly of a bis(terpyridine)-carbazole monomer utilizing terpyridine-metal(II)-terpyridine connectivity; its photophysical properties were investigated.     

The application of NIR Raman spectroscopy in the assessment of serum thyroid-stimulating hormone in rats

Serum blood samples of euthyroid and thyroidectomized rats treated with thyrotropin-releasing hormone (TRH) were analyzed on aluminum substrates using the near-infrared Raman spectroscopy (830 nm). Spectra of thyroid-stimulating hormone (TSH), TRH and prolactin standards were obtained. Differences between Raman spectra profiles of control and Tx + TRH samples groups were found. These differences were confirmed by the linear discriminant analysis (LDA), which presents a good classification between groups. It is supposed that these differences are produced by the increment of TSH in the thyroidectomized rats.     

Microbial hydroxylation of sclareol by Rhizopus stolonifer

Incubation of sclareol with Rhizopus stolonifer affords in high yield a mixture of triols with 18-hydroxy-sclareol as the main component.