Application of QSAR to biodegradation of linear alkylbenzene sulphonate (LAS) isomers and homologues.

An approach of initially testing various structure descriptors on a trial and error basis, followed by mechanistic hypothesis and simple mathematical modelling to refine the choice of descriptor, is applied to develop a quantitative structure-activity relationship (QSAR) correlating initial biodegradation relative rate constants with carbon number and substitution position for (4-sulphophenyl)-substituted alkanes (linear alkyl benzene sulphonates, LAS). The relative rate constants are found to be linearly correlated with a composite descriptor, [(0.5 + L-1)-12 + (0.5 + S-1)-12]1/2 where L and S are the carbon numbers of the longer and shorter chains, respectively, counting from the (4-sulphophenyl) substitution position.