Humic amino acid contents

There are no accurate determinations of the overall contributions of peptide components to the compositions of HS and of SOM. The difficulties arise from the problems of separating these from other components of the SOM mixtures. Use of DMSO + 1% 12M HC1 and XAD-8 resin [(poly)methylmethacrylate] technology enabled Appelqvist et al. (1996) to decrease the amino acid content of a HA by 23%, and the decrease was uniform for the different amino acid groupings. This still left considerable amounts of peptide material in association with the HAs. Some may well have been in association with the humic matrix, and some may have been covalently linked to the humic core through, for example, the formation of Schiff... 

FIGURE 7. Vertical changes in humic substances and their carbohydrate and amino acid contents in Lake Haruna sediments (Ishiwatari, 1975 Yamamoto, 1983 Uzaki, unpublished). 

The chemical character of dissolved humic substances in estuaries also reflects its mixed origin, with a number of parameters exhibiting values intermediate between the riverine and oceanic endmembers. These properties include UV-visible absorptivities, C/N ratios, total acidity, molecular weight (Preston, 1979), amino acid content (Fox, 1981), and perhaps C/ C... 

Humic acido from ooilo and ligniteo have been examined by ERR spectrometry. All samples showed a stable free organic radical content of about 1018 spins per gram. When these samples were converted to their sodium salts, a marked increase in radical content occurred. This was interpreted to indicate that a quinhydrone moiety exists in the humic acid macromolecule. Synthetic humic acid, prepared by oxidizing catechol in the presence of amino acids, also showed similar ERR spectra, as did selected quinhydrone model compounds. The radical moiety appeared to be stable to severe oxidation and hydrolytic conditions. Reduction in basic media caused an initial decrease in radical species continued reduction generated new radical species. A proposed model for humic acid based on a hydroxyquinone structure is proposed. 

Clay size layer silicates also have the ability to catalyze the polycondensation of phenolic compounds and amino acids. Wang et al. (1985) examined the catalytic effect of Ca-illite on the formation of N-containing humic polymers in systems containing various phenolic compounds and amino acids. The yields and N contents... 

Some intriguing variations in the nature of the humate ligands have also recently come to light. Studies of metal fixation in sedimentary organic matter recently deposited in the form of algal mats have been carried out. " The material was originally derived from cyanobacteria and the humic substances are characterized by a very low aromatic content balanced by the incorporation of large amounts of carbohydrates and amino acids. Similarities between cation coordination... 

Nitrogen content in aquatic humic materials usually ranges from 0.5 to 2%, although in seawater DOM it has been reported to be as high as 6.5% (Thurman and Malcolm, 1989). Little is known about the nature of the combined nitrogenous structural types that are present, although hydrolytic studies have revealed some bound amino acids (Lytle and Perdue, 1981 Thurman and Malcolm, 1989). 

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