Excitation-Dependent Fluorescence Quantum Yield for Freshwater Chromophoric Dissolved Organic Matter from Northern Russian Lakes

Abstract

Advanced fluorescence analysis within the wide range of excitation wavelengths from 230 to 510 nm accompanied with chromatography was used to study natural chromophoric dissolved organic matter (CDOM) from three freshwater Karelian lakes. The influence of excitation wavelength (λex) on fluorescence quantum yield and emission maximum position was determined. The CDOM fluorescence quantum yield has reached a minimum at λex∼270–280 nm and a maximum at λex∼340–360 nm. It was monotonously decreasing after 370 nm towards longer excitation wavelengths. Analytical reversed-phase high-performance liquid chromatography with multiwavelength fluorescence detector characterized distribution of fluorophores between hydrophilic/hydrophobic CDOM parts. This technique revealed “hidden” protein-like fluorophores for some CDOM fractions, in spite of the absence of protein-like fluorescence in the initial CDOM samples. The humic-like fluorescence was documented for all hydrophilic and hydrophobic CDOM chromatographic peaks, and its intensity was decreasing along with peaks’ hydrophobicity. On contrary, the protein-like fluorescence was found only in the hydrophobic peaks, and its intensity was increasing along with peaks’ hydrophobicity. This work provides new data on the CDOM optical properties consistent with the formation of supramolecular assemblies controlled by association of low-molecular size components. In addition, these data are very useful for understanding the CDOM function in the environment.

L-Tryptophan Aqueous Systems at Low Concentrations: Interconnection between Self-Organization, Fluorescent and Physicochemical Properties, and Action on Hydrobionts

“…Considering such systems as simple models of natural water containing DOM, the obtained results can provide new information concerning fluorescence monitoring of DOM in surface water systems. In DOM fluorescence monitoring, the spectral band λ em of 300–350 nm serves as a marker of the presence of tryptophan-like components or protein-like fractions in water [ 6 , 7 , 28 ]. The established correlation between fluorescence and nanoassociates’ parameters ( Figure 2 and Figure 8 ) indicates that this band also reflects the presence of a dispersed phase in water, formed mainly by ordered structures such as EZ-water [ 35 ], and bioorganic substances of different structures in low concentrations, as a rule, below 1 × 10 −8 mol/L.…”

“…Works [ 28 , 30 , 31 , 32 , 33 , 34 , 35 ] also show the presence of similar absorption bands in the UV spectra of natural water, diluted aqueous solutions of some BACs, and systems containing structured water (EZ-water) in contact with a hydrophilic surface. Excitation in this UV region causes fluorescence in two spectral ranges of 300–350 and 400–450 nm.…”

“…The consequences of the L -Trp presence in natural water at low concentrations are not yet established for aquatic organisms and humans. Studying the physicochemical and spectral patterns of diluted L -Trp solutions, as well as their relation to the solutions’ bioeffects, can provide conceptually new and important information regarding the unknown effects of diluted aqueous solutions and help to develop the natural water diagnostic methods, while improving the further understanding of the origin and composition of DOM [ 6 , 7 , 28 ].…”

Diluted Aqueous Dispersed Systems of 4-Aminopyridine: The Relationship of Self-Organization, Physicochemical Properties, and Influence on the Electrical Characteristics of Neurons

“…The fluorescence spectrum of the S-24 system had a different band shape with the maximum in the region of 312–325 nm. This suggests that the nature of the structures formed at high dilutions differs from the nature of domains and nanoassociates formed, as a rule, in the 1·10 −4 –1·10 −18 M range ( Sedlák, 2006 ; Sedlák and Rak, 2013 ; Elia et al, 2014 ; Ryzhkina et al, 2018a ; Ryzhkina et al, 2018b ; Patsaeva et al, 2018 ; Ryzhkina et al, 2019 ; Ryzhkina et al, 2020 ), i.e., capable of containing a certain amount of solute ( Ryzhkina et al, 2017 ).…”

“…Recently, and for the first time, it was established that the rearrangement of nanoassociates at certain low critical concentrations is accompanied not only by a significant change in physicochemical properties and bioeffects but also in the UV absorption in the 200–300 nm range ( Ryzhkina et al, 2018a ; Ryzhkina et al, 2018b ). Works ( Lobyshev et al, 1999 ; Chai et al, 2008 ; Elia et al, 2014 ; Elia et al, 2018 ; Patsaeva et al, 2018 ) have demonstrated the presence of absorption within the range of 200–350 nm in the UV spectra of natural water, aqueous solutions of BAS, and systems containing structured water in contact with a hydrophilic surface. Excitation in this region results in fluorescence within two spectral ranges: 300–350 and 400–450 nm.…”