An "average" structure proposed for soil fulvic acid aided by dept/quat ¹³C NMR pulse techniques

A soil fulvic acid was extracted from topsoil of the Okchun Basin, Republic of Korea, and purified and characterized by chemical methods (elemental analysis, number averaged molecular weight) and by ¹³C and ¹H NMR spectroscopy. An "average" structure of a soil fulvic acid has been developed by modifying one of the structural models proposed for Suwannee River fulvic acid, IHSS (International Humic Substances Society) reference sample, based on comparative chemical and NMR data. The assignment of the structural moieties was facilitated by the use of a set of ¹³C NMR subspectra of the CH_n (n = 0 to 3) groups, obtained by distortionless enhancement by polarization transfer (DEPT) pulse sequence and the quaternary-only carbon spectra (QUAT) under quantitative conditions. The nature of metal binding sites on such soil fulvic acid molecule is discussed.