QSAR Studies Of S-triazine Herbicides

S—triazine herbicides is one of the presently widely used herbicides in the world. Yet, this kind of herbicides have some disadvantages such as too long periods of residue effect in soil, causing sensitive plants drop in production having soil leaching, easily polluting ground water and water on the earth' s surface. People are likely to be poisoned indirectly after eating these water plants remaining these chemical compounds inside.The purpose of this research is to establish the models of Quantitative Structure —activity relationships by using various methods of quantum chemistry, molecular mechanics and statistical analysis etc. we explore the relation between structure and activity , structure and toxicity from electronic structure and three—dimensional conformation in order to provide theoretical foundations for predicting the activity and toxicity of these chemical compounds, researching into mechanism of action and choosing safener. The main conclusions are as follows:1. For QSAR research, the TSTA geometry conformations that were calculated by MNDO, PM3, AM1, RHF/STO-3G, RHF/3 —21G, RHF/6—31G, respectively have been discussed. The geometry optimized conformations of RHF/6—31G and AM1 are the best. With IR spectrum of four kinds of herbicides and ab initio GIAO method at RHF/6—31G level for Simazine have been used to theoretically predict 1H— NMR and 13C—NMR chemical shifts for conformations that have been optimized by MNDO, PM3, AM1, RHF/STO - 3G, RHF/3 - 21G, RHF/6 - 31G, respectively. The results show that the calculated δ 1H—NMR and δ 13C—NMR for the geometry conformation optimized by RHF/6—31G are most accurate in comparison conformation optimized by RHF/6—31G are most accurate in comparison with experimentally observed data. AM1 is also better. Considering the optimizing time and the necessity of research which studying the relation between structure and activity of the S — triazine molecules. We adopted RHF/6 —31G for optimization in order to conduct deep accurate theoretic researches. However, while researching into the relation between structure and toxicity of such kind of chemical compounds, we attach more importance to the relative value than absolute value of quantum chemistry parameter we adopted AM1.