 because of their widespread occurrence and substantial biological activity , halogenated aromatic hydrocarbons such as polychlorinated biphenyls ( pcbs ) , polychlorinated dibenzofurans ( pcdfs ) , and polychlorinated dibenzo - p - dioxins ( pcdds ) comprise one of the more important classes of contaminants in the environment . some chemicals in this 
 class cause adverse biological effects after binding to an intracellular cytosolic protein called the aryl hydrocarbon receptor ( ahr ) . 
 toxic responses such as thymic atrophy , weight loss , immunotoxicity , and acute lethality , as well as induction of cytochrome p4501a1 , have been correlated with the relative affinity of pcbs , pcdfs , and pcdds for the ahr . 
 therefore , an important step in predicting the effects of these chemicals is the estimation of their binding to the receptor . to date , however , the use of quantitative structure activity relationship ( qsar ) models to estimate binding affinity across multiple chemical classes has shown only modest success possibly due , in part , to a focus on minimum energy chemical structures as the active molecules . in this study , we evaluated the use of structural conformations other than those of minimum energy for the purpose of developing a model for ahr binding affinity that encompasses more of the halogenated aromatic chemicals known to interact with the receptor . 
 resultant qsar models were robust , showing good utility across multiple classes of halogenated aromatic compounds.imagesfigure 1 . 
 afigure 1 . 
 bfigure 1 . 
 cfigure 2.figure 3.figure 4.figure 5 . 
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