MECHANISM-BASED QUANTITATIVE STRUCTURE BIODEGRADABILITY RELATIONSHIPSFOR HYDROLYTIC DEHALOGENATION OF CHLORO-ALKENE AND BROMO-ALKENE

Quantitative Structure-Biodesadability Relationships (QSBRs) have been developed for microbial hydrolytic dehalogenation of small chlorinate d and brominated alkenes. Two different reaction mechanisms, S(N)2 and S(N)2', were considered for the dehalogenation of small haloalkenes b y hydrolytic dehalogenases. Multivariate QSBRs based on quantum-chemic ally calculated descriptors were used to distinguish between these deh alogenation mechanisms. A QSBR based on atom valence and partial atomi c charge on electrophilic site, together with the energy of the lowest unoccupied molecular orbital, molecular weight and dipole moment were able to explain 92% (81% cross-validated) of the quantitative varianc e in the dehalogenation rates. This QSBR supported a S(N)2 reaction me chanism. This reaction mechanism was also confirmed by GC-MS identific ation of the reaction products for the compounds which should give dis criminating reaction products depending on mechanism. The substrate sp ecificity of hydrolytic dehalogenases for unsaturated halogenated; sub strates is discussed in the light of chemical structure and properties of the substrate molecules.