Separação de espectros simulados e de luminescência total através do método generalizado de anulação do posto (GRAM)

A multivariate curve resolution method, "GENERALIZED RANK ANNIHILATION METHOD (GRAM)", is discussed and tested with simulated and experimental data. The analysis of simulated data provides general guidelines concerning the condition for uniqueness of a solution for a given problem. The second-order emission-excitation spectra of human and animal dental calculus deposits were used as an experimental data to estimate the performance of the above method. Three porphyrinic spectral profiles, for both human and cat, were obtained by the use of GRAM.

Líquido iônico [bmim.PF6] como solvente: um meio conveniente para estudos por fotólise por pulso de laser

The spectroscopic behavior of thioxanthone and benzil (diphenylethanedione or dibenzoyl) in the ionic liquid [bmim.PF6] has been investigated employing the laser flash photolysis technique. Triplet-triplet absorption spectra for these carbonyl compounds in [bmim.PF6] are similar to those observed in organic solvents. The triplet lifetime for thioxanthone in desogygenated samples is very long (71 μs), whereas in oxygen-saturated solution is 500 ns, which indicates the low oxygen solubility in this solvent. For benzil, lifetimes of 10 μs in [bmim.PF6] and 3.8 μs in acetonitrile were obtained. The decay for triplet thioxanthone and benzil follows a clear first order kinetics in [bmim.PF6], from which one can conclude that triplet-triplet annihilation is not an important decay process in this solvent.

Luz: um raro produto de reação

The production of visible light by chemical reactions constitutes interesting and fascinating phenomena and several reaction mechanisms are discussed to rationalize excited state formation. Most efficient chemiluminescence reactions are thought to involve one or more electron transfer steps and chemiexcitation is believed to occur by radical annihilation. A brief introduction to the general principles of light production and the main known chemiexcitation mechanisms will be given here. Subsequently, recent results on the mechanistic elucidation of efficient chemiluminescence systems, as the peroxyoxalate reaction, the induced decomposition of phenoxy-substituted 1,2-dioxetanes and the catalyzed decomposition of new a-peroxylactones will be discussed.

Protein dynamics: hydration and cavities

The temperature-pressure behavior of proteins seems to be unique among the biological macromolecules. Thermodynamic as well as kinetic data show the typical elliptical stability diagram. This may be extended by assuming that the unfolded state gives rise to volume and enthalpy-driven liquid-liquid transitions. A molecular interpretation follows from the temperature and the pressure dependence of the hydration and cavities. We suggest that positron annihilation spectroscopy can provide additional quantitative evidence for the contributions of cavities to the dynamics of proteins. Only mature amyloid fibrils that form from unfolded proteins are very resistant to pressure treatment.