Computational Assessment of the Three-Dimensional Configuration of Dissolved Organic Matter Chromophores and Influence on Absorption Spectra

The three-dimensional configuration of dissolved organic matter (DOM) is an important factor in determining the role of DOM in natural and engineered systems, yet there is still considerable uncertainty regarding the formation and potential stability of molecular aggregates within DOM. In this paper...

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Bibliographic Details
Published in:Environmental science & technology 2020-12, Vol.54 (24), p.15904-15913
Main Authors: Vialykh, Elena A, McKay, Garrett, Rosario-Ortiz, Fernando L
Format: Article
Language:English
Subjects:
Absorption spectra
Aggregates
Chromophores
Computer applications
Configurations
Contaminants in Aquatic and Terrestrial Environments
Density functional theory
Dissolved organic matter
Mass Spectrometry
Mass spectroscopy
Molecular dynamics
Molecular Dynamics Simulation
MTBE
Optical properties
Organic Chemicals
Organic solvents
Solvents
Tetrahydrofuran
Water
Water Pollutants, Chemical - analysis
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Summary:The three-dimensional configuration of dissolved organic matter (DOM) is an important factor in determining the role of DOM in natural and engineered systems, yet there is still considerable uncertainty regarding the formation and potential stability of molecular aggregates within DOM. In this paper, we describe a computational assessment of the three-dimensional configuration of DOM. Specifically, we were interested in evaluating the hypothesis that DOM forms thermodynamically stable molecular aggregates that as a result were potentially shielded from water solvent molecules. Molecular dynamics simulations of DOM model compounds carefully selected based on ultrahigh-resolution mass spectrometry data revealed that, while DOM does indeed form molecular aggregates, the large majority of molecules (especially, O-atom bearing molecules) are solvent accessible. Additionally, these computations revealed that molecular aggregates are weak and dissociate when placed in organic solvents (tetrahydrofuran, methyl tert-butyl ether). Time-dependent density functional theory calculations demonstrated long-wavelength absorbance for both model DOM chromophores and their molecular aggregates. This study has important implications for determining the origin of DOM optical properties and for enhancing our collective understanding of DOM three-dimensional structures.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.0c05860