Fourier Transformed Infrared Spectroscopy, Thermogravimetric Analysis, and X-ray Diffractometry have been used to investigate the rigid, semi rigid, and soft polyurethane (PU) forms, which were developed by the Group of Analytic Chemistry and Technology of Polymers -USP -São Carlos. The -NCO/-OH ratios were 0.6, 0.5, and 0.3% for rigid, semi rigid, and soft PUs, respectively, showing that different ratios cause differences in thermal behaviors and crystalline structures of the synthesized PU resins.

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We observe for the first time a structural phase transition in the oxyborate Fe3O2BO3 which occurs along three leg ladders present in this material. X-ray diffraction shows that this transition at 283 K is associated with a new phase where atomic displacements occur in alternate directions perpendicular to the axis and within the plane of the ladders. Magnetic data show that these displacements lead to the formation of singlet pairs which dissociate close to the structural transition. Anomalies in the transport properties also occur close to 283 K showing that the structural transition is related to a charge ordering phenomenon in a low dimensional structure.

Bothropstoxin I (BthTX-I) from the venom of Bothrops jararacussu is a myotoxic phospholipase A2 (PLA2) homologue which, although catalytically inactive due to an Asp49-->Lys substitution, disrupts the integrity of lipid membranes by a Ca2+-independent mechanism. The crystal structures of two dimeric forms of BthTX-I which diffract X-rays to resolutions of 3.1 and 2.1 angstroms have been determined. The monomers in both structures are related by an almost perfect twofold axis of rotation and the dimer interfaces are defined by contacts between the N-terminal alpha-helical regions and the tips of the beta-wings of partner monomers. Significant differences in the relative orientation of the monomers in the two crystal forms results in "open" and "closed" dimer conformations. Spectroscopic investigations of BthTX-I in solution have correlated these conformational differences with changes in the intrinsic fluorescence emission of the single tryptophan residues located at the dimer interface. The possible relevance of this structural transition in the Ca2+-independent membrane damaging activity is discussed.