Self-assembly of humic acid: influence of pH and chemical composition
Abstract
Interest in enhancing the residence time of soil organic matter (SOM) through natural or engineered mechanisms as a possible means of sequestering organic carbon to mitigate the impacts of carbon-dioxide induced global warming effects has steadily increased over the last decade. Humic substances are major organic constituents of SOM and were recently shown that can self-organize or self-assemble into a composite material with different characteristics than those of the starting materials, and the organized state controls its mineralization by microorganisms. This study examines the role of pH and the relative concentration of humic-like amphiphilic (HA2) and lipid-like (L1) components in the self-assembly of the lipid-humic composite (L0). The L0, L1 and HA2 fractions were isolated using a combination of organic solvent and aqueous alkaline extractions from two humic acid samples at various pH values. HA2 and L1 isolated at low pH were mixed in various mass ratios in organic solvent in order to “reassemble” L0. The data show that the amount of L0 decreased with increasing the pH and reached a constant value from pH 6 to pH 11, and the proportion of L1 increased with the pH. Comparative measurements of the specific heat capacity as a function of temperature of the recombined L0 reveal differences when compared to the physical mixture of the HA2 and L1 depending on the ratio of the components. These differences are an indication that the recombined L0’s solid-state structure is more than just a mixture of components and is determined by specific interactions between its components.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.B41E0350C
- Keywords:
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- 0400 BIOGEOSCIENCES