Showing papers by "Francisco Torrens published in 1999"

Interacting induced dipoles polarization model for molecular polarizabilities. Reference molecules, amino acids and model peptides

Abstract: We outline a method for the calculation of molecular dipole ( μ ) and quadrupole ( Θ = ) moments and dipole–dipole polarizabilities ( α = ) which we have successfully applied to a series of reference molecules, amino acids and model peptides. The results for μ are in line with CPHF reference calculations. In particular, the calculated positive value of CO is in agreement with both experimental and CI calculations. The computation of ( α = ) has been performed by the interacting induced dipoles polarization model that calculates tensor effective anisotropic point polarizabilities (method of Applequist et al.). The POLAR program cannot be used as a black box. Some tests should be performed when a new molecule is calculated. The POLAR program was designed for large molecules. Although in some large molecules the POLAR program has been successfully applied to predict trends, the test with small molecules shows that we have to touch up the approximations along the formulation. The results for ( α = ) of reference molecules are shown better for the POLAR program than for the PAPID algorithm. In the former case, the POLAR-AP model is revealed superior to the POLAR-IP method. The results for the amino acids and model peptides show that, as a rule, the PAPID program produces the better results, while the POLAR program produces acceptable results and converges in all the cases. In general, POLAR-IP underestimates the molecular polarizabilities and anisotropies while POLAR-AP overestimates these properties.

Polarization by the effect of a small torsional change in the benzothiazole (A)-benzobisthiazole (B) oligomer A-B13-A

Abstract: Francisco Torrens, Jose Sanchez-Marin and Ignacio Nebot-GilDepartment of Chemistry and Biochemistry, South Dakota State University, Box 2202, Brookings,South Dakota 57007, USA, (605)-688-6260, FAX (605) 688-6364Departament de Quimica Fisica, Facultat de Quimica, Universitat de Valencia, Dr. Moliner 50,E -46100 -Burjassot (Valencia), Spain. http://www.uv.es/~anton/inicio.html. Tel. +34 96 398 3182, Fax+34 96 398 3156. Email Francisco.Torrens@uv.esReceived: 30 September 1998 / Accepted: 5 January 1999 / Published: 12 February 1999Abstract: We use a method for the calculation of the molecular dipole (µ ) and quadrupole(θ ) moments and dipole-dipole (α ), dipole-quadrupole (

Aqueous coefficient calculations for chemicals and drugs

Abstract: Aqueous functional group activity coefficients (AQUAFAC) is a group‐contribution method for estimating the aqueous coefficients. We have written a program for the calculation of these coefficients. The solubility S w of alkanes shows variation of 8 orders of magnitude. The comparison with experiment shows that AQUAFAC gives good S w estimations. For 4'‐substituted acetanilides, I‐, Br‐, nitro‐, Cl‐, F‐ and methoxy‐substituents decrease S w, while formyl‐ and amino‐substituents increase S w. For acetaminophen esters, S w decreases from the acetate to the decanoate. The S w of 29 barbiturates shows typical errors of 0.4 log S w units. For the cyclo‐alkane‐l’,5‐spirobarbituric acids, S w decreases from the cyclopropane to cyclooctane.