The optical properties of dissolved organic matter (DOM) are of great interest to scientists and engineers, as they are used as surrogates for both concentration and properties of this material, including being used to predict photochemical reactivity. However, there is ongoing debate in the literature regarding two competing hypotheses that could explain the observed optical properties of DOM: a) charge transfer interactions or b) superposition of individual components. In this work, computational modeling was used to ascertain the nature of the optical properties of DOM. Six models of DOM that fit to chemical characteristics of Suwannee River fulvic acid were generated. The difference in the models was the choice of molecular fragments and the molecular size of individual components. Molecular dynamic simulations were performed with three different solvents: water, methyl tert-butyl ether and tetrahydrofuran. Radius of gyration (RofG) as a parameter was used to estimate relative free energy of the models. Snapshots with RofG that corresponded to the lowest free energy were used to calculate solvent accessible surface area as well hydrophobic and hydrophilic surface area. UV-Vis spectra were calculated for the individual components that make up the different models for SRFA. In this presentation, the results of this work will be discussed, along with the implications for the study of the optical properties of DOM.

Computational assessment of the optical properties of dissolved organic matter

ACS Fall 2021

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