Relating natural organic matter conformation, metal complexation, and photophysics

• Published in: Canadian journal of chemistry Vol. 99; no. 10; pp. 787 - 794
• Main Authors: Stirchak, Laura, Donaldson, D. James
• Format: Journal Article
• Language: English
• Published: 1840 Woodward Drive, Suite 1, Ottawa, ON K2C 0P7 NRC Research Press 01.10.2021; Canadian Science Publishing NRC Research Press
• Subjects: Aluminum; Analysis; anisotropie de fluorescence; Anisotropy; Chemical analysis; Complexation; complexation métal-matière organique dissoute (MOD); Coordination compounds; Copper; Environmental aspects; Ferric ions; Fluorescence; fluorescence anisotropy; Fresh water; Marine environment; Metal complexes; Metal concentrations; Metal ions; metal-DOM complexation; NOM photophysics; Organic compounds; Organic matter; photophysique de la matière organique naturelle (MON); Properties; Sea-water; Seawater; Water analysis; United States
• ISSN: 0008-4042; 1480-3291
• DOI: 10.1139/cjc-2021-0018

We investigated the relationship between changes in fluorescence intensity and in fluorescence anisotropy for Suwannee River Natural Organic Matter (SRNOM) due to the formation of NOM-metal complexes with divalent and trivalent metals commonly present in both fresh water and sea water environments. We chose metal ions whose complexes give rise to both fluorescence quenching (Fe 3+ , Cu 2+ ) and fluorescence enhancement (Al 3+ , Mg 2+ ). Stern–Volmer type analyses quantified the changes in the SRNOM fluorescence as a function of metal concentration. All metals display strong complexation with SRNOM, associated with their effect on fluorescence. Experiments with Fe 3+ further show strong effects due to NOM aggregation at all but the lowest metal concentrations studied here. There was little to no change in the conformation of SRNOM as inferred from fluorescence anisotropy caused by increasing metal concentration. These results suggest that there is no correlation between photophysical changes and conformational changes in NOM associated with complexation by the metal ions.