QSPR Prediction of Retention Times of Phenylurea Herbicides by Biological Plastic Evolution

Francisco      Torrens; Gloria      Castellano

Abstract

A simple/sensitive high-performance liquid chromatographic method, with ultraviolet (UV) detection, was developed for phenylurea-herbicide analysis, which involves preconcentration using solid-phase extraction. Mobile phase was acetonitrile/water at flow-rate of 1mL·min–1 with direct UV absorbance detection at 210nm. Analyte separation studied on a C18 column was applied successfully to herbicide analysis in soft drink’s brands and tap water. Good linearity/repeatability was observed for all pesticides. Retention times increase as: metoxuron < monuron < diuron < matazachlor < linuron. They are modelled by structure–property relations. The effect of different types of features is analyzed: electronic, solvation, lipophilic and steric, etc. Formation enthalpy and molecular dipole moment are calculated with MOPAC–AM1. Most important properties are hydration free energy and dipole moment. Results are improved if competitive conformation with higher dipole moment is considered at 1.1kJ·mol–1. Plastic evolution is an evolutionary perspective conjugating the effect of acquired characters, and relations that emerge among the principles of evolutionary indeterminacy, morphologic determination and natural selection. Plastic evolution is applied to design co-ordination index Ic, which is used to characterize phenylurea herbicides and compared to molecular dipole moment for retention time. Parametres needed to calculate Ic are formation enthalpy and molecular weight/surface area. Ic improves multivariable regression equations for retention and is predictive when it is used together with dipole and hydration free energy. Correction introduced in retention is produced in the correct direction. Hierarchical quantitative structure–property relationship provided simplified properties analysis. Structural classification is based on the presence of two Cl/O/N atoms.

Keywords: Biological plastic evolution, morphologic index, co-ordination index, molecular dipole moment, solvation parametre model, hydration free energy, parametre model, hydration free energy, Phenylurea Herbicides, chromatographic method, MOPAC–AM1