A DFT-based QSAR study of the toxicity of quaternary ammonium compounds on Chlorella vulgaris

The DFT-based descriptors were used to derive the quantitative structure–activity relationship (QSAR) models enabling the calculated quantum chemistry parameters to be correlated to the toxicity of quaternary ammonium compounds (QACs) on green alga Chlorella vulgaris  . DFT/B3LYP level of theory with the 6-31G(d) basis set was applied to calculate a set of quantum chemistry descriptors for 11 QACs. The partial least squares (PLS) analysis implemented in Simca-P was employed to obtain the QSAR models. The optimal PLS model with the cumulative cross-validated regression coefficient (Qcum2=0.893) and the correlation coefficient between observed values and fitted values (R = 0.975) explained 95.3% of the variance of the independent variables and 92.8% of the variance of the dependent variable. The results of this investigation show that alkyl chain lengths (CL), polarizability tense (αzz  ), the most positive net atomic charges on a hydrogen atom (qH+) and entropy (So) are the major descriptors in governing the log(1/EC50) values of the QACs.