Inductive and resonance effects of substituents adjust the microalgal biodegradation of toxical phenolic compounds.

The type and the position of the substituent in the phenolic ring, the bond dissociation energy and the exogenously supplied carbon source as well as the inductive and resonance effect phenomena of the substituents adjust the biodegradability of the phenolic compounds. The comparative biodegradation study of mono-nitrophenols (electron acceptors) and mono-methylphenols (electron donors) revealed that it is a completely photoregulated process. The closer the donor group (OH(-)) of the phenolic ring is to the acceptor group (NO(2)(-)), the higher the biodegradation values are (2-nitrophenol>3-nitrophenol>4-nitrophenol); the further the donor group (OH(-)) of the phenolic compound is from the second donor group (CH(3)(+)), the higher the biodegradation values are (2-methylphenol<3-methylphenol<4-methylphenol). However, there are compounds without a specific role of acceptor or donor such as mono-iodophenols, where a type of counteraction between the inductive and resonance effect determines the behavior of the substituent. This fact combined with the presence of the hydroxyl group in the phenolic ring gave the observed stabilization in the biodegradation results of mono-iodophenols (2-iodophenol approximately 3-iodophenol approximately 4-iodophenol).