New sensitive fluorophores for selective DNA detection

4,7-Disubstituted benzothiadiazoles containing 1-arylethynyl and 4-methoxyphenyl groups are selective photoluminescent "light up" probes to duplex DNA with unprecedented sensibility in both spectrophotometric and spectrofluorimetric measurements.     

Electronic interactions and their influence on the conformational stability of trans-2-halocyclopentanol

Conformational preferences and electronic interactions of trans-2-fluorocyclopentanol (1), trans-2-chlorocyclopentanol (2), and trans-2-bromocyclopentanol (3) were analyzed using experimental and theoretical (3)J(HH) coupling constants, theoretical calculations, and natural bond orbital (NBO) analysis. The conformational equilibria of compounds 1-3 can be represented by their diaxial and diequatorial conformers as supported by theoretical calculations. From (3)J(HH) coupling constant values, it can be found that the diequatorial conformer is present in the equilibrium as 55% for compound 1 and as 60% for compounds 2 and 3. This behavior is in agreement with orbital interaction analyses obtained from NBO.     

Interaction of meso-tetrakis (4-sulfonatophenyl) porphyrin with cationic CTAC micelles investigated by small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR)

Small angle X-ray scattering (SAXS) and electron paramagnetic resonance (EPR) have been used to investigate the interaction of the water-soluble meso-tetrakis (4-sulfonatophenyl) porphyrin (TPPS(4)) with cationic cethyltrimethylammonium chloride (CTAC) micelles. To evaluate if the porphyrin protonation state affects its interaction with the micelle, both SAXS and EPR measurements were performed at pH 4.0 and 9.0. The best-fit SAXS curves were obtained assuming for CTAC micelle a prolate ellipsoidal shape in the absence and upon incorporation of 2-10 mM TPPS(4). SAXS results show that the presence of porphyrin impacts on micellar hydrophobic core, leading to a micellar reassembling into smaller micelles. Lineshapes of EPR spectra of 5- and 16-doxyl stearic acids (5- and 16-DSA, respectively) bound to 100 mM CTAC micelles exhibited slight changes as a function of porphyrin concentration. Spectral simulations revealed an increase of mobility restriction for both spin probes, especially at higher porphyrin concentration, where a small reduction of environment polarity was also observed for 16-DSA. The spin labels monitored only slight differences between pH 4.0 and 9.0, in agreement with the SAXS results.     

Nanoscale conformational ordering in polyanilines investigated by SAXS and AFM

Understanding the adsorption mechanisms in nanostructured polymer films has become crucial for their use in technological applications, since film properties vary considerably with the experimental conditions utilized for film fabrication. In this paper, we employ small-angle X-ray scattering (SAXS) to investigate solutions of polyanilines and correlate the chain conformations with morphological features of the nanostructured films obtained with atomic force microscopy (AFM). It is shown that aggregates formed already in solution affect the film morphology; in particular, at early stages of adsorption film morphology appears entirely governed by the chain conformation in solution and adsorption of aggregates. We also use SAXS data for modeling poly(o-ethoxyaniline) (POEA) particle shape through an ab initio procedure based on simulated annealing using the dummy atom model (DAM), which is then compared to the morphological features of POEA films fabricated with distinct pHs and doping acids. Interestingly, when the derivative POEA is doped with p-toluene sulfonic acid (TSA), the resulting films exhibit a fibrillar morphology-seen with atomic force microscopy and transmission electron microscopy-that is consistent with the cylindrical shape inferred from the SAXS data. This is in contrast with the globular morphology observed for POEA films doped with other acids.     

Generalized canonical osp(1,2) quantization

A possibility of constructing a generalized canonical quantization for arbitrary dynamical systems with first-class constrains is considered based on the invariance principle of the osp(1,2) global supersymmetry. Tomsk State Pedagogical University, Russia; Departamento de Fisica, ICE, Universidade Federal de Juize de Fora, Brazil. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 3–6, October, 1999.     

Biosensor for phenol based on the direct electron transfer blocking of peroxidase immobilising on silica–titanium

Horseradish peroxidase (HRP) was immobilised on silica gel modified with titanium oxide. This material was employed to prepare modified carbon paste electrode. The direct electron transfer of the hydrogen peroxide reduction by HRP was blocked when immobilised on silica–titanium. This biosensor presented a very sensitive response for phenol (1 μmol l⁻¹) at an applied potential of 0 mV vs SCE. The best condition was achieved in phosphate buffer pH 6.8, ratio of hydrogen peroxide/phenol higher than 0.35. The biosensor showed a linear response range between 10 and 50 μmol l⁻¹ of phenol, adjusted by the equation j=−32.8+16.3 [phenol], for n=5 with a correlation coefficient of 0.9995. The response time of the biosensor was about 3 s.     

Alternative Entropy Measures and Generalized Khinchin–Shannon Inequalities

The Khinchin–Shannon generalized inequalities for entropy measures in Information Theory, are a paradigm which can be used to test the Synergy of the distributions of probabilities of occurrence in physical systems. The rich algebraic structure associated with the introduction of escort probabilities seems to be essential for deriving these inequalities for the two-parameter Sharma–Mittal set of entropy measures. We also emphasize the derivation of these inequalities for the special cases of one-parameter Havrda–Charvat’s, Rényi’s and Landsberg–Vedral’s entropy measures.     

Micellization study and adsorption properties of an ionic surfactant synthesized from hydrogenated cardanol in air–water and in air–brine interfaces

A sulfonate (2,4-sodium dissulfonate-5-n-pentadecylphenol) was synthesized from hydrogenated cardanol and the micellization study was carried out using temperature and electrolyte concentration as variables. The adsorption parameters were obtained using surface tension data by the Frumkin adsorption model and the Simplex Nelder–Mead method. Values of critical micelle concentration (cmc) and surface excess (Γ) were obtained in three different temperatures (303 K, 313 K, and 323 K) and two electrolyte concentrations (NaCl solution—0.1 M and 0.25 M). It was verified that cmc decreased with increasing electrolyte concentration and temperature. The Gibbs free energy showed that the micellization process was spontaneous for all studied systems and temperatures, and also that the presence of several CH₂ groups was significant for micelle formation.     

Studies on the Eschenmoser coupling reaction and insights on its mechanism. Application in the synthesis of Norallosedamine and other alkaloids

The conditions of the Eschenmoser coupling reaction were studied. The formation of the α-thioiminium ion was achieved faster in the presence of an additive (NaI) and dry chloroform as the preferred solvent. The developed conditions were used for the second part of the reaction (the sulfur extrusion itself). The present protocol avoids the formation of byproducts, which were previously described as a major drawback to be overcome. Electrospray ionization tandem mass spectrometry was used to characterize some aspects (intermediates) of the first step of the reaction mechanism. Some reduction conditions were properly tested and the selected conditions were applied to the synthesis of the natural alkaloid Norallosedamine and other derivatives.