Biomedical subjects

Ricardo L Longo

Publications and source records attributed to Ricardo L Longo.

3 recordsLinked to original sources

PubMed2004

AIPAR: ab initio parametrization of intermolecular potentials for computer simulations.

An unambiguous, fully ab initio and automated technique denoted AIPAR ("ab initio parametrization") implemented in the SJBR program has been proposed to yield intermolecular interaction potentials between polar molecules and water. The AIPAR procedure has been applied to several organic molecules covering a wide range of structure and functional groups, namely methanol, acetone (propanone), methanethiol (methyl mercaptan), imidazole (1,3-diazole), oxazole and furan. The AIPAR-derived sets of parameters compare well with the empirical OPLS ones, mainly when the all-atoms model is employed in the OPLS procedure. Monte Carlo simulations were performed for an aqueous solution of methanol and for an equimolar binary mixture methanol-water using the AIPAR and OPLS parameters. The thermodynamic and geometric results obtained with the parameters obtained with the AIPAR procedure compare favorably with the OPLS simulations, even for the binary mixture, demonstrating the precision, robustness and transferability of the parameters obtained with the AIPAR procedure.

Computer Simulation↗

PubMed2004

Experimental and theoretical study of the photophysics and structures of europium cryptates incorporating 3,3'-bi-isoquinoline-2,2'-dioxide.

A detailed photophysical study of [Eu within (biqO2.2.2)(CF3SO3)](CF3SO3)2. CH3CN.H2O (Eu within 1) and two other types of cryptates incorporating three 3,3'-biisoquinoline-2,2'-dioxide units has been performed. Structural crystallographic data of Eu within 1, electronic structure calculations and theoretical models were used to obtain the intramolecular energy transfer rates and the appropriate set of rate equations, which was solved numerically. Quantum yields and decay lifetimes were obtained from these results and compared to the experimental data. The role of the ligand-to-metal charge transfer (LMCT) states was ascertained. A theoretical ligand field and intensity analysis was carried out and the results agree very well with the emission spectra. The molecular structures of the lanthanide cryptates were successfully modelled by the YIII ion using the restricted Hartree-Fock (RHF) method, with the advantage of dealing with closed-shell systems. These molecular structures were used to explain the drastic differences in the photophysics of the three EuIII cryptates.

Journal Article↗

PubMed2003

Chemometric study of liquid water simulations. I. The parameters of the TIP4P model potential.

The multivariate chemometric techniques two level factorial design (TLFD) and principal component analysis (PCA) were used to investigate the TIP4P model potential behavior with respect to perturbations on all intermolecular interaction parameters. The effects of these perturbations were calculated for the enthalpy of vaporization, the density, the first maximum of the radial distribution functions of the O-H and O-O pairs, and the second maximum of the radial distribution function of the O-H pair obtained from Monte Carlo simulations of liquid water at 25 degrees C. The principal effects were quantified and rationalized in terms of the pair-wise interaction potential of the TIP4P model. They also corroborate previously published sensitivity analysis results using molecular dynamics and other model potentials. In addition, significant interaction effects between some parameters of the TIP4P model potential were observed and quantified, which hardly could be obtained without such a statistic approach. These interaction effects are very regular and systematic, and their behavior has not been encountered in other chemometric studies and cannot be rationalized in terms of the functional form of the pair-wise potential.

Journal Article↗