Significance of Mn(IV) oxide in abiotic formation of organic nitrogen complexes in natural environments

Abstract

The high resistance of organic nitrogen complexes in soil to microbial attack is of significance to crop production, N balance of soils, geochemical and pedological processes, and environ mental quality^1–3. Several theories have been given to account for this phenomenon. An important theory indicates the stabilization of nitrogen through the formation of nitrogenous polymers during the reaction of nitrogenous substances with polyphenols^1–3. It is well known that the formation of nitrogenous polymers from nitrogenous substances and polyphenols is accelerated in the presence of phenol oxidase enzymes^1–8 and oxidants such as Ag₂O (ref. 9). However, the promoting effects of soil inorganic components on the formation of organic N complexes have received little attention. Mn(IV) oxides are common in soil¹⁰. Furthermore, the effect of Mn(IV) oxides on the oxidative polymerization of hydroquinone is much greater than that of various other inorganic components such as short-range ordered Fe(III), Al and Si oxides¹¹, primary minerals¹² and clay minerals¹³ which are commonly present in soil environments. We report here that Mn(IV) oxide (birnessite), which is common in natural environments, greatly promotes the abiotic formation of nitrogenous polymers in hydroquinone–glycine systems in the common pH range (4–8) of soils. The findings indicate that Mn(IV) oxides merit close attention in the abiotic formation of organic N complexes from nitrogenous substances and polyphenols and the subsequent turnover of N in soil and the associated emvironments.