José Simões Redinha

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The structural changes occurring on erythritol as it is cooled from the melt to low temperature, and then heated up to the melting point have been investigated by differential scanning calorimetry (DSC), polarized light thermal microscopy (PLTM), X-ray powder diffraction (PXRD) and Fourier transform infrared spectroscopy (FTIR). By DSC, it was possible to(More)
The FT-IR spectra of two diastereomers of 2,3-butanediol, (R,S) and (S,S), isolated in low-temperature argon and xenon matrixes were studied, allowing the identification of two different conformers for each compound. These conformers were characterized by a +/-gauche arrangement around the O-C-C-O dihedral angle, thus enabling the establishment of a very(More)
Theoretical calculations at the MP2 level, NBO and AIM analysis, and matrix-isolation infrared spectroscopy have been used to investigate the structure of the isolated molecule of 1,4-butanediol (1,4-BDO). Sixty-five structures were found to be minima on the potential energy surface, and the three most stable forms are characterized by a folded backbone(More)
Betaxolol and its respective hydrochloride salt were studied in solution by computational calculations and infrared spectroscopy. The solution molecular conformations were taken to be the same as those exhibited by the compounds in the solid state given by X-ray diffraction and calculated after full geometry optimization by ab initio Hartree-Fock methods(More)
In this paper, the N(+)-H···N, N(+)-H···O, and O-H···O(-) charge-assisted intramolecular hydrogen bonds (CAHBs) are investigated using different theoretical approaches. Monocharged cyclohexyldiamines (CHDA), aminocyclohexanols (ACHO), and cyclohexanediols (CHDO) are used as model compounds. Geometry optimizations at the MP2/aug-cc-pVDZ level are used to(More)
The enthalpies of sublimation of erythritol and L-threitol have been determined at 298.15 K by calorimetry. The values obtained for the two diastereomers differ from one another by 17 kJ mol(-1). An interpretation of these results is based on the decomposition of this thermodynamic property in a term coming from the intermolecular interactions of the(More)
Gibbs energy, enthalpy and entropy for the reactions of ciprofloxacin and lomefloxacin with aluminium ion were determined. No significant differences were observed for Gibbs energy values for these fluorquinolones while significant differences were found for enthalpy and entropy. The highly positive values observed for the entropy give evidence for a strong(More)
Density functional theory calculations using the B3LYP functional and the 6-311++G(d,p) basis set were carried out on the isolated molecules of erythritol and L-threitol. For the meso isomer, a relatively large number of conformers have to be considered to describe the gas state structure. The lowest energy conformer is characterized by the establishment of(More)
Crystallization of pindolol from the melt was studied by differential scanning calorimetry (DSC) and polarized light thermomicroscopy (PLTM) in order to discriminate the polymorphic forms obtained by this method. The crystallization process originates one exothermic signal localized in two different well-defined temperature ranges. Fusion gives rise to(More)