ИСТИНА

Phenolic acids (PA) are important products of lignin breakdown. Their interactions with minerals and oxidative enzymes lead to accumulation of aromatic compounds in soil organic matter. Little is known on cooperative sorption of PA by mineral phases under environmentally relevant concentrations and on the impact of phenoloxidases, ubiquitous at soil interfaces, on this process. In the present work the sorption of an equimolar mixture of phenolic acids by kaolinite modified with amorphous aluminium hydroxide has been studied in the presence and absence of fungal laccase in Na-acetate buffer (pH 4.5). Teflon flow-through column equipped with peristaltic pump has been used for simulation of dynamic conditions and reversed-phase HPLC for acids determination. Phenolic acids sorption was 3-4 times lower in 50 mM buffer than in 5 mM buffer, suggesting competition among PA and acetate ions for binding sites. The sorption of gallic and protocatechuic acids exceeded the sorption of p-hydroxybenzoic, vanillic, syringic, and ferulic acids by an order of magnitude. Phenolic acids competed for binding sites on kaolinite-Al(OH)x. The sorbed gallic acid displaced the other acids, which passed into solution in the following order: p-hydroxybenzoic acid > vanillic acid > syringic acid > ferulic acid > protocatechuic acid. In the presence of inactivated fungal laccase PA sorption decreased by 1.2-1.4 times suggesting that the protein reduces the number of available active sites on the mineral. Sorption of certain PA in the presence of active laccase increased and the surface of the mineral became darker, suggesting oxidation/oligomerization of PA in the presence of laccase. Results of the study show selectivity in PA sorption; potential importance of o-substituted phenols and syringyl structures in SOM formation; importance of oxidative enzymes for aromatic C sequestration in soils.