Cleavage of 14C-labeled glycine and its polycondensation with pyrogallol as catalyzed by birnessite

Deamination as well as decarboxylation of amino acids and their polycondensation with polyphenols catalyzed by Mn(IV) oxide have been reported. However, the mechanisms of cleavage of amino acids and their polycondensation with polyphenols by soil inorganic components are not well understood. The objective of this study was, thus, to investigate the enhanced abiotic decarboxylation of carboxyl group and dealkylation of alkyl group of glycine by birnessite (δ-MnO2, 0.2-2 μm) both in the presence and absence of pyrogallol and the resultant formation of humic polycondensates in systems free of microbial activity. The degradation of 14C-labeled glycine through either carboxyl or alkyl group on the birnessite surface was demonstrated. Birnessite enhanced the dealkylation of alkyl C and especially decarboxylation of carboxyl C of glycine. Furthermore, it promoted the interaction of glycine and pyrogallol and the resulting simultaneous decarboxylation and dealkylation of glycine, ring cleavage of pyrogallol, and polycondensation. Carboxyl C and especially alkyl C of glycine were incorporated into the humic polycondensates. This study indicates that structural configuration and functionality of amino acids and polyphenols merits closer attention in understanding mechanisms of humification processes catalyzed by soil mineral colloids.