- © The Mineralogical Society Of America
Organic molecules are found everywhere and play an important role in almost all biogeochemical processes occurring on the surface of the Earth (Aiken et al. 1985; Thurman 1985; Schwartzenbach et al. 1993; Senesi and Miano 1994). They are found in soluble and insoluble phases, coatings on mineral and colloidal particles, and in gas phase molecules in soils, sediments and aquatic systems. The activities of macro- and micro-fauna and flora release organic molecules of various sizes and composition. Photochemical reactions in the atmosphere also add certain small chain molecules to the organic carbon content in the environment. Significant compositional variations occur in natural organic molecules, which include small chain carboxylic acids, alcohols and amino acids; and polymeric, polyfunctional and polydisperse macromolecules such as humic and fulvic acids. The behavior of small chain molecules and their influence on different geochemical reactions is well understood. However, understanding of the chemistry of biopolymers and their role in different biogeochemical processes in the environment is poor, which may be attributed to the unavailability of instrumentation to examine the chemistry of natural organic molecules in their pristine state.
Two important properties that dictate the behavior of natural organic molecules and biopolymers in the environment are: functional group chemistry and (macro)molecular structure (Schnitzer 1991). Evaluation of these two properties is complicated by the compositional and structural heterogeneity of the naturally occurring organic molecules, and their ability to form intramolecular and intermolecular H-bonds, which further modify their structure and chemical reactivity. These two properties are interrelated and one influences the other. The chemical composition of natural waters (pH, ionic composition and concentration, redox conditions) and soil and sediment particle surface chemistry (composition, coordination environment, number of reactive groups) also modify their behavior. It is not well understood how each of these environmental variables influences the …