Humic acid is a remarkably diverse biopolymer with multiple chemical functionalities. Two principle models exist for the biosynthesis of HA: (1) biodegradation of lignins, and (2) in vivo plant biosynthesis. Though the first model is supported by the high degree of correlation between the HA building block and lignan structures; the second model seems more credible, now that HA has been isolated from numerous genera of live plants. Regardless of "synthetic" mechanism, HA's are versatile materials. Metal binding capacities, metal exchange rates and affinities have been well studied. These processes are crucial to biomineralization, environmental remediation, and agricultural applications of HA. In natural waters, HA adsorbs virus particles and heavy metals. HA's display both estrogenic and heparin-like activity. HA's can also be ozonated and chlorinated to produce potentially carcinogenic compounds.
HA's are photoactive. Irradiation studies show that HA's produce a large number of characteristic radical species, most of which are quinone- or catechol-based, after short exposure to UV. They are bleached by irradiation from 300 to 350 nm. Previous studies have been limited by a lack of understanding of HA structure and difficulty in obtaining homogeneous HA materials. Careful isolation of HA from soils has provided materials with consistent and highly correlated chemical properties, and therefore these materials serve as good substrates for our analyses. In this work, the chemistry of HA free radicals is evaluated by a series of experiments in which the role of radical species is critical in understanding many biological and environmental functions of HA.
© 2003-2012 by Lawrence T. Sein. All rights reserved.
Send questions to: lseinjr@hotmail.com