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

Theoretical Study of the Molecules in Solution and Phospholipid Bilayers

Using Molecular Dynamics simulations and Quantum Mechanical calculations, we study the behavior of molecules with biophysical and pharmacological interest in solution and in phospholipid bilayer.FAPESPCNPqINCT-FCxCAPESNBioNet / CAPE

Theoretical Study of the Effect of Phospholipid Bilayer in the Electronic Properties of Molecules with Biophysical Interest.

Solvent effects are of essential importance in many different aspects of\ud physics, chemistry, biology and material sciences. The developments of\ud quantum chemistry methods originally devised for studying isolated\ud molecules have been extended to study the properties of atoms and\ud molecules interacting with the environment. This led to the continuum\ud methods that treat the solvent by means of average macroscopic\ud constants, such as the dielectric constants. Very successful in different\ud applications these continuum methods lack the consideration of the\ud microscopic details and the necessary statistic representation of the\ud thermodynamic molecular system. The natural extension has been to\ud incorporate some molecular mechanics methods to generate solutesolvent\ud structures and couple this with the quantum mechanical\ud methods to obtain the solvent effects in the solute properties.FAPESPCNPqCAPESINCT-FC

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

Analyzing the n→π* Electronic Transition of Formaldehyde in Water. \ud A Sequential Monte Carlo/Time-Dependent Density Functional Theory

The n→π* absorption transition of formaldehyde in water is analyzed using combined and sequential classical Monte Carlo (MC) simulations and quantum mechanics (QM) calculations. MC simulations generate the liquid solute-solvent structures for subsequent QM calculations. Using time-dependent density functional theory in a localized set of gaussian basis functions (TD-DFT/6-311++G(d,p)) calculations are made on statistically relevant configurations to obtain the average solvatochromic shift. All results presented here use the electrostatic embedding of the solvent. The statistically converged average result obtained of 2300 cm-1 is compared to previous theoretical results available. Analysis is made of the effective dipole moment of the hydrogen-bonded shell and how it could be held responsible for the polarization of the solvent molecules in the outer solvation shells.A transição eletrônica n→π* do formaldeído em água é analisada usando-se um procedimento combinado e seqüencial de Monte Carlo (MC) clássico e mecânica quântica (MQ). MC é usado para gerar configurações do líquido para uso posterior em cálculos de MQ. Usando-se a representação espectral da teoria do funcional da densidade com uma base de funções gaussianas localizadas (TD-DFT/6-311++G(d,p)) cálculos são realizados em configurações estatisticamente descorrelacionadas para se obter o deslocamento solvatocrômico. Todos os resultados são obtidos usando-se uma representação onde o solvente é tratado como um campo eletrostático. O resultado médio obtido de 2300 cm-1 é comparado com resultados teóricos anteriores. Análise é feita do valor do momento de dipolo efetivo da camada associada com as ligações de hidrogênio e como ela pode influenciar as camadas de solvatação mais externas