Abstract: The pEC₅₀ activities of 91 organic chemicals which are toxic to chlorella vulgaris have been modeled using physicochemical and topological parameters. It was observed that excellent results are obtained in multiparametric regression upon introduction of indicator parameters. The results are discussed using various statistical parameters. The multiple linear regression method was applied to select the descriptors. Our results have shown that six parametric model containing zero and second order connectivity, a physicochemical parameter, also the logarithm of  the Octanol/water partition coefficient (logKow) and finally, the energy of the lowest unoccupied molecular orbital (Elumo) along with indicator parameter play a dominating role in modeling toxicity (pEC₅₀) . The six parametric model were found to be the best which gives a variance of more than 92% (R²=0.9241). The predictive powers of the models were also discussed by using the method of cross-validation. Our results are comparatively better than the result obtained by Zhong–Sheng Yi and Li–Tang Qin.

Keywords: QSAR, Topological indices, Physicochemical parameters, chlorella vulgaris ,Acute toxicity, Regression analysis.