Modulation of Optical Properties of Dissolved Humic Substances by their Molecular Complexity^†

Abstract

In this study, we show that several UV-Vis absorbance, steady-state and time-resolved fluorescence parameters of a series of dissolved humic substances (DHS) from different sources (e.g. terrestrial fulvic and humic acids, and humic acid-like molecules extracted from composted and vermicomposted wastes) correlate with the molar absorptivity at 280 nm per mole of organic carbon (ε(280)), which in turn is proportional to the molecular complexity (e.g. molecular size, aromaticity and oxidation degree) of the DHS. Both absorbance and fluorescence spectral responses were sensitive to the molecular complexity associated with the maturation degree of the DHS. Depending on the DHS, different emitting responses by excitation at the UVA (340 nm) and VIS (460 nm) regions of the absorption spectra were observed. The results were explained in terms of the extent of intramolecular electronic interactions between electron donor groups, such as polyhydroxylated aromatics and indoles, and more oxidized acceptor groups (e.g. quinones or other oxidized aromatics) as the molecular complexity of the DHS increased.

Interactions between protein-like and humic-like components in dissolved organic matter revealed by fluorescence quenching

“…In addition, Wang and Zhang recently reported that presence of energy transfer from polycyclic aromatic hydrocarbons to FDOM occurs because of the significant overlap between the emission spectra of polycyclic aromatic hydrocarbons and absorbance spectra of FDOM (Wang and Zhang, 2014). In fact, the humic substances themselves can also present intermolecular energy transfer between their electron donor groups (e.g., indoles, polyhydroxylated aromatics) and acceptor groups (e.g., oxidized aromatics and quinones) (Boyle et al, 2009;Del Vecchio and Blough, 2004); and the extent of the intermolecular energy transfer seemed to increase with increasing molecular complexity of the humic substances (Mignone et al, 2012).…”

“…Rayleigh light scattering was eliminated using a 290 nm emission cutoff filter. Prior to measuring, highly concentrated samples were diluted with Milli-Q water to achieve absorbance values of less than 0.1 cm À1 at 254 nm, which meets the requirement for eliminating inner-filter effects during fluorescence measurements (Miller et al, 2010). According to the manufacturer's suggested protocols, the spectrophotometer was corrected for excitation and emission.…”

Characterization and sources of colored dissolved organic matter in a coral reef ecosystem subject to ultramafic erosion pressure (New Caledonia, Southwest Pacific)

“…Indeed, the latter can potentially form supramolecular assemblies based on intramolecular energy transfer requiring small donor to acceptor distances (Jørgensen et al, 2011;Cuss and Guéguen, 2015;Wang et al, 2015). Moreover, the increasing molecular complexity of humic substances increases the intermolecular energy transfer with other fluorescent components like tyrosine-like compound (Mignone et al, 2012).…”

DOM-mediated membrane retention of fluoroquinolone as revealed by fluorescence quenching properties

“…DOM can also bind with trace contaminants 19, 51 and heavy metals 32 by forming molecular aggregates, altering the behavior, mobility and transport of these compounds. Nevertheless, the intermolecular energy transfer depends on the molecular complexity of the humic substance 52 . For example, the humic-like and protein-like components are expected to have different capacities to bind with trace contaminants or heavy metals.…”