The relationship between chemical structures and biodegradation rates （k b） of 22 polycyclic aromatic hydrocarbons （PAHs） was studied using density functional theory （DFT） and stepwise multiple linear regression analysis （SMLR） method.The equilibrium geometries and vibration frequency have been investigated at the B3LYP/6-31＋G（d,p） level by thinking Solvent effects using a selfconsistent reaction field （SCRF） based on the polarizable continuum model （PCM）.It was concluded that the biodegradation rate was closely related to its molecular structure,and there is one high correlation coefficient between the in-plane bending vibration frequency of the conjugated ring of PAHs （Freq） and k b.By means of regression analysis,the main factors affecting the biodegradation rate were obtained and the equation of quantitative structure-activity relationship （QSAR） was successfully established kb =-0.653＋0.001Freq＋0.068CQ＋0.049N1.Statistical evaluation of the developed QSAR showed that the relationships were statistically significant and the model had good predictive ability.The fact that a bending frequency is more important than the HOMO or LUMO energies in predicting k b suggests that the bending of benzene ring might play an important role in the enzymatic catalysis of the initial oxidation step.
