S.V. Patsaeva

Raman and IR spectroscopy research on hydrogen bonding in water–ethanol systems

Vibrational spectroscopy provides invaluable information about hydrogen bonding in aqueous solutions. To study changes in H-bonding due to increase of ethanol concentration in water, we perform research on water–ethanol binary mixtures with various mixing ratios using a combination of Raman scattering and IR absorption techniques. We study Raman spectra from 200 to 4000 cm−1 excited at 488 nm and IR spectra from 500 and 4000 cm−1 for solutions with different ethanol concentrations from pure water to pure ethanol. Using the intensity ratio of OH stretching band taken at 3200 and 3420 cm−1 for Raman spectra and at 3240 and 3360 cm−1 for IR spectra we evaluate the strength of H-bonding. Maximal strength of H-bonding in water–ethanol mixture corresponds to ethanol concentration 15–20% w/w. We explain it by the presence of transient ethanol hydrates similar in composition to gaseous clathrates with stoichiometric water/ethanol ratio 5:1. Further weakening of H-bonding with ethanol concentration is caused by the formation of chain aggregates from ethanol/water molecules. In addition, we apply other approaches, such as multivariate curve resolution-alternating least squares analysis, decomposition of water Raman stretching band, and comparison of water Raman stretching band in ethanol solutions to that of gas clathrates to support this hypothesis.

Decomposition of water Raman stretching band with a combination of optimization methods

In this study, an investigation of the behaviour of stretching bands of CH and OH groups of water–ethanol solutions at alcohol concentrations ranging from 0 to 96% by volume has been performed. A new approach to decomposition of the wide structureless water Raman band into spectral components based on modern mathematical methods of solution of inverse multi-parameter problems–combination of Genetic Algorithm and the method of Generalized Reduced Gradient–has been demonstrated. Application of this approach to decomposition of Raman stretching bands of water–ethanol solutions allowed obtaining new interesting results practically without a priori information. The behaviour of resolved spectral components of Raman stretching OH band in binary mixture with rising ethanol concentration is in a good agreement with the concept of clathrate-like structure of water–ethanol solutions. The results presented in this paper confirm existence of essential structural rearrangement in water–ethanol solutions at ethanol concentrations 20–30% by volume.

The study of coastal meromictic water basins in the Kandalaksha Gulf of the White Sea by spectral and physicochemical methods

Research is initiated to study water samples from stratified water basins in the Kandalaksha Gulf of the White Sea at different stages of their separation from the sea. The objects of research are lakes Elovoe and Nizhnee Ershovskoe located close to the Nikolai Pertsov White Sea Biological Station. Depth profiles of physico-chemical characteristics such as temperature, salinity, pH and dissolved oxygen were measured. Brightly colored green water layers were found in both lakes. Concentrations of photosynthetic organisms were estimated using absorption and fluorescence spectra of water samples from various depths.

Spectral Characterization of Fungal Metabolites in Aqueous Medium with Humus Substances

The work is targeted to confirm participation of microscopic fungi in transformation of humus substances in aquatic environments. The research is focused on the spectroscopic study of the collection of fungal strains with different pigmentation of mycelium. Spectral properties of fungal metabolites were measured and compared to that of natural aquatic nonliving organic matter and commercial humus substances in aqueous solutions. The experiments revealed that the effect of microscopic fungi growing in the culture medium with added humate appeared as changes in the humic-type fluorescence: its characteristics became more similar to that of nonliving organic matter in natural waters than to original humate preparation. The experiments demonstrated degradation of coal-originated humate due to microbial activity into compounds of smaller molecular size and increased heterogeneity. We resume that transformation of humus substances by fungal cultures can be monitored and characterized using spectral measurements.

Fluorescence of Nanoparticles of Organic Matter Dissolved in Natural Water

The fluorescence of nanoparticles of dissolved organic matter under 270-, 310-, and 355-nm excitation is studied for different molecular fractions. The fluorescence quantum yield of the colloidal (molecules of size 5–200 nm) and low-molecular-weight (molecules smaller than 5 nm) fractions are obtained. It is shown that the spectral position of the fluorescence peak depends on both the size of the molecules and the excitation wavelength.

Fluorescence of bean leaves grown under low-light conditions

The patterns of changes of the spectral shapes of the fluorescence of bean leaves have been identified under low-light conditions of plant cultivation and decrease in chlorophyll concentration in the leaves. Under these experimental conditions, the ratio of peak intensities of fluorescence in the red spectral region, ω = F740/F760, which was recorded after the end of the induction period, was proportional to the chlorophyll content per 1 g of the wet weight of a leaf.

Fluorescence of dissolved organic matter as a marker for distribution of desalinated waters in the Kara Sea and bays of Novaya Zemlya archipelago

The optical properties and distribution of dissolved organic matter in the surface waters of the Kara Sea and bays of Novaya Zemlya archipelago were studied during the 63th cruise of the R/V Akademik Mstislav Keldysh. The fluorescence of dissolved organic matter has been studied over wide excitation (230–550 nm) and emission (240–650 nm) wavelength ranges. Based on the results of fluorescence measurements, we propose a simple technique for estimating the relative content of humic compounds entering the Kara Sea shelf region with Ob and Yenisei river runoff. We have found that the blue shift parameters of the DOM fluorescence are Δ270–310 = 28 ± 2 nm and Δ355–310 = 29 ± 2 nm. The highest contents of humic compounds in surface waters were measured on the transect across the desalinated layer of the Kara Sea, near the continental slope on the transect along the St. Anna Trough, and in the area of Sedova, Oga and Tsivol’ki bays. Traces of labile terrigenous organic matter were found in the region of the Voronin Trough, in the bays of the Severny Island of Novaya Zemlya, as well as in some freshwater reservoirs and ice samples of the archipelago. We established a conservative distribution of dissolved organic matter, whose content in water varied from 1.25 to 8.55 mg/L.

Depth profiles of spectral and hydrological characteristics of water and their relation to abundances of green sulfur bacteria in the stratified lakes of the White Sea

We analyze the results received from two expeditions performed in August-September 2013, August-September 2014 and February 2015 in the Kandalaksha Bay of the White Sea. Depth profiles of hydrological characteristics and optical properties of water were recorded for five marine lakes being on different stages of isolation from the White Sea. Those relic lakes demonstrate a tendency to meromixis and are characterized by apparent stratification of the water bodies from the brackish top layer to the bottom salt water. Maximal concentrations of anoxygenic phototrophs (green sulfur bacteria) were found at depths close to the redox interface in all the studied lakes. To discriminate differently pigmented groups of microorganisms the fluorescence emission spectra of bacteriochlorophylls from the living cells were used. We puzzle out the data on light spectrum propagation through the water body in each lake using optical properties of water (attenuation spectra) in the UV, visible and NIR ranges, as well as direct measurements of the total irradiances at various depths. The changes in optical characteristics of water in the stratified reservoirs due to cromophoric dissolved organic matter (CDOM) and microbial pigments affect the light intensity and its spectral distribution at each water layer thus influencing the living conditions for differently pigmented phototrophic microorganisms and determining the composition of microbial community.

Quantification of two forms of green sulfur bacteria in their natural habitat using bacteriochlorophyll fluorescence spectra

Detection of phototropic organisms in their natural habitat using optical instruments operating under water is urgently needed for many tasks of ecological monitoring. While fluorescence methods are widely applied nowadays to detect and characterize phytoplankton communities, the techniques for detection and recognition of anoxygenic phototrophs are considered challenging. Differentiation of the forms of anoxygenic green sulfur bacteria in natural water using spectral techniques remains problematic. Green sulfur bacteria could be found in two forms, green-colored (containing BChl d in pigment compound) and brown-colored (containing BChl e), have the special ecological niche in such reservoirs. Separate determination of these microorganisms by spectral methods is complicated because of similarity of spectral characteristics of their pigments. We describe the novel technique of quantification of two forms of green sulfur bacteria directly in water using bacteriochlorophyll fluorescence without pigment extraction. This technique is noninvasive and could be applied in remote mode in the water bodies with restricted water circulation to determine simultaneously concentrations of two forms of green sulfur bacteria in their natural habitat.

Fluorescence and Raman Spectroscopy Study of Humic Acids in Iron Chloride Solutions and Magnetite/HA Nanoparticles

Spectral properties of water-dispersible sorbent produced from humic acids (HA) extracted from brown coal and magneto-active nanoparticles were measured for the samples of different magnetite/HA ratio and the way of their preparation. The influence of iron (III) ions on spectral properties of HA in aqueous solution was investigated using Stern-Volmer plots describing HA fluorescence quenching. The Stern-Volmer dependences were found to be linear at concentration of iron (III) ions smaller 20 μmol/L and nonlinear at higher concentrations.