Professor José Acioli e a Física na Universidade de Brasília

Discurso do Professor Sylvio Canuto por ocasiãoo da entrega do tÌtulo de Professor Emérito (Post Mortem) da Universidade de Brasília ao Professor José de Lima Acioli, em 08 de setembro de 2008

Dynamics of endo- vs. exo-complexation and electronic absorption of calix[4]arene-Ar2

AbstractThe dynamics of the calix[4]arene cone conformer (cax[4]) and calix[4]arene-Ar2 complexes (cax[4]-Ar2) at three temperatures (T=20, 100, and 200K) was investigated through Born–Oppenheimer molecular dynamics (BOMD). Thermal effects on the endo- vs. exo-complexation dynamics, the vibrational dynamics of the homodromic OH bond array, and the electronic absorption spectra are investigated. In comparison with results for the electronic spectra of gas-phase optimized structures, thermal effects on the electronic absorption spectra lead to a red-shift and broadening of the low energy excitation maxima

A Theoretical Study of the Core-lonized States of NF

Abstract Ab i n i t i o s p i n -U n r e s t r i c t e d Hartree-Fock c a l c u l a t i o n s a r e performed f o r the t r a n s i t i o n energles and v i b r a t i o n a l c o u p l i n g p a rameters associated t o t h e core ionized s t a t e s o f NF. The v i b r a t l o n a 1 e x c i t a t i o n i s discussed. Important aspects r e l a t e d t o t h e ESCA b a n d shapes and v i b r a t i o n a l e x c i t a t i o n a r e p r e d i c t e d b u t a r e n o t q u a n t i t a ti v e l y described a t t h i s leve1 o f approximation

A theoretical study of the characterization and the absorption spectrum of Mg: Tetracycline complexes in aqueous environment.

The complex formed by the tetracycline (TC) molecule with the Mg ion is able to prevent the replication of the genetic material in the bacterial ribosome, making an excellent antibiotic. In general, the absorption and emission spectra of TC are very sensitive to the host ions and the pH of the solvent that the set is immersed. However, the theoretical absorption spectrum available in the literature is scarce and limited to simple models that do not consider the fluctuations of the liquid. Our aim is to obtain the electronic absorption spectrum of TC and the complex Mg:TC in the ratio 1:1 and 2:1. Moreover, we analyze the changes in intensity and shifts of the bands in the systems listed. We performed the simulation using the classical Monte Carlo technique with the Lennard-Jones plus Coulomb potential applied to each atom of the both TC molecule and the Mg:TC complexes in water. The electronic absorption spectrum was obtained from the time-dependent density functional theory using different solvent models. In general, we obtained a good qualitative description of the spectra when compared with the experimental results. The Mg atom shifts the first band by 4 nm in our models, in excellent agreement to the experimental result of 4 nm. The second absorption band is found here to be useful for the characterization of the position where the ion attaches to the TC

Explicit solvent effects on the visible absorption spectrum of a photosynthetic pigment: Chlorophyll-c2 in methanol

AbstractThe explicit solvent effects on the light absorption properties of a photosynthetic pigment are analyzed from a combined study using Monte Carlo simulation and quantum mechanical Density-Functional Theory calculations. The case considered is chlorophyll-c2 in methanol and excellent results are obtained for both position and intensities in the entire visible region. Explicit solvent molecules are essential for describing the absorption spectrum. Analysis is also made of the coordination of the Mg atom, the influence of solute–solvent hydrogen bonds, the existence and location of dark states for internal conversion mechanisms and the adequacy of the four-state model for classifying the transitions

Isotropic and anisotropic NMR chemical shifts in liquid water: a sequential QM/MM study

We present a sequential QM/MM study of the gas-liquid chemical shifts of water. Extensive quantum chemical calculations using density functional theory have been performed for structures of liquid water generated by Monte Carlo and Molecular Dynamic simulations. The dependence of the chemical shifts on the empirical potential used in the simulations, on the cluster size and on the functional chosen for the quantum chemical calculations were analyzed. The results after correcting for basis set superposition errors are in good agreement with the experimental data, showing that a simple empirical potential associated to an appropriate functional is able to describe the chemical shifts. All results presented here are statistically converged

Solvent Effects in Chemical Processes. Water-Assisted Proton Transfer Reaction of Pterin in Aqueous Environment

"Heike Schünke, Sven Schoen und Robert Knull vom Schleswiger Landesarchiv haben an der Einsturzstelle in der Severinstraße geholfen." Quelle: Schleswiger Nachrichte