Differences in photochemistry between seawater and freshwater for two natural organic matter samples

Abstract

NOM displays different photochemistry in seawater than in freshwater due to its complexation with Mg2+.

Relating natural organic matter conformation, metal complexation, and photophysics

“…Further studies using complimentary techniques are needed to validate these findings, given the limitations of this study. It has been shown previously that NOM reactivity, via the formation of singlet oxygen, decreases in the presence of metals, 56,68,92 so the results of this study show that this decrease is not due to conformational changes affecting the ability of ground state oxygen to quench the excited triplet. We also showed that the analysis performed in this study, although very simplified, is applicable to both fluorescence quenching and enhancement interactions.…”

“…Many metals can quench NOM fluorescence, especially via formation of nonfluorescent NOM-metal complexes. 19,29,30,[47][48][49][50][51][52] By contrast, some metals, such as Ca 2+ , Al 3+ , and Mg 2+ , enhance the fluorescence of NOM; 22,26,[53][54][55][56] this is also thought to be due to the formation of complexes that may enhance the rigidity of NOM. 51,57,58 In general, complexation with metals is thought to change the conformation of NOM.…”

“…53 These changes in the conformation of NOM due to metal complexation have been suggested as the reason why the formation kinetics of photochemically produced reactive intermediates (PPRI) change in the presence of metal ions. 56,68,69 Fluorescence anisotropy has previously been used to look at how the conformation of NOM changes due to the addition of metals, as well as changes to the pH and ionic strength. 53,56,67,70 Fluorescence anisotropy measurements use polarized light to excite a fluorophore and interrogate the polarization state of emitted light, from which the relative speed of molecular rotation can be extracted.…”

“…56,68,69 Fluorescence anisotropy has previously been used to look at how the conformation of NOM changes due to the addition of metals, as well as changes to the pH and ionic strength. 53,56,67,70 Fluorescence anisotropy measurements use polarized light to excite a fluorophore and interrogate the polarization state of emitted light, from which the relative speed of molecular rotation can be extracted. From such measurements, changes in the molecular conformation that give rise to a change in the rotational tumbling period are inferred.…”

Formation of Toxic Unsaturated Multifunctional and Organosulfur Compounds From the Photosensitized Processing of Fluorene and DMSO at the Air‐Water Interface

“…The presence of sea salts (NaCl, NaBr, and NaI) can eventually influence the photochemical process of FL/DMSO at the sea surface (Grossman et al, ; Stirchak et al, ). Ongoing studies in our lab are focused on the influence of sea salts on photochemical degradation of FL/DMSO, and the results will be published elsewhere.…”