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This research used electronic theory to model the biotransformation of 17α-ethinylestradiol (EE(2)) under aerobic conditions in mixed culture. The methodology involved determining the Frontier Electron Density (FED) for EE(2) and various metabolites, as well as invoking well-established degradation rules to predict transformation pathways. We show that measured EE(2) metabolites are in good agreement with what is expected based on FED-based modeling. Initiating reactions occur at Ring A, producing metabolites that have been experimentally detected. When OH-EE(2) and 6AH-EE(2) are transformed, Ring A is cleaved before Ring B. The metabolites involved in these pathways have different estrogenic potentials, as implied by our analysis of the log P values and the hydrogen bonding characteristics. The OH-EE(2) and 6AH-EE(2) transformation pathways also show redox-induced electron rearrangement (RIER), where oxidation reactions lead to the reduction of carbon units present along the bond axis. Sulfo-EE(2) appears to be difficult to biotransform. These findings clarify theoretical and practical aspects of EE(2) biotransformation.

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This research investigated the biological transformation of trimethoprim (TMP). Partial TMP removal was observed in the presence of ammonia and toluene, and increasing the solids retention time from 20 days to 60 days improved TMP removal in both the nitrifying and heterotrophic bioreactors. Two TMP-related metabolites were identified, the first (5-(3,4,5-trimethoxybenzyl) pyrimidine-2,4-diamine, 5-hydroxyl) showing that a hydroxylation reaction took place, and the second (5-(1-carboxyl, 1-methoxy, 5-methoxy 1-,4-pentene) pyrimidine-2,4-diamine, 5-hydroxyl) showing that the trimethoxybenzyl ring was cleaved. This research is the first that we are aware of to report these two TMP-related byproducts. TMP metabolites show that initiating reactions take place where the electron density is highest, and that these initiating reactions shift the electron density of TMP, likely affecting the course of transformation.