V. I. Yuzhakov

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.

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.

Poly(Schiff's bases)–bifluorophores: Synthesis, photophysical properties, nonradiational transfer of energy of electronic excitation

A method of the synthesis of a new generation of polymers with intrinsic fluorescence-poly(Shiffs bases)-bifluorophores-was developed. These polymers contain two different fluorophores in each unit of the main polymer chain. One of the fluorescent fragments is a donor of electron excitation energy and the second one is an acceptor. The photophysical properties of poly(Shiffs bases)-bifluorophores were investigated. It was shown that in poly(Shiffs bases)-bifluorophores nonradiation energy transfer along the polymer chain in the solid and liquid solutions of polymers takes place. The influence of the disposition of fluorophores in the polymer chain and the distance between them on nonradiation energy transfer were investigated. It was shown that the maximum nonradiation energy transfer is realized in polymers-bifluorophores with a statistical distribution of the fluorophore fragment in the polymer chain. The influence of the distance between a donor and an acceptor of the electron excitation energy on the nonradiation energy transfer was investigated. It was established that nonradiation energy transfer is not observed if the distance between a donor and an acceptor of energy exceeds 10 nm.

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 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.

Excitation energy transfer in covalently bonded porphyrin heterodimers

We describe the photophysical properties of heterodimers that are formed by the free base 2-(2-carboxyvinyl)-5,10,15,20-tetraphenylporphyrin and the zinc complex of 5-(p-aminophenyl)-10,15,20-triphenylporphyrin and that are covalently bonded by the amide link. These dimers differ in the configuration of the double bond in the spacer group. We determine fluorescence quantum yields of heterodimers and their porphyrin components. The energy transfer rate constants have been estimated from the measured fluorescence lifetimes and fluorescence excitation spectra and, also, they have been calculated from the steady-state absorption and fluorescence spectra according to the Förster theory. We have found that the efficiency of the intramolecular energy transfer in heterodimers is 0.97–0.99, and the energy migration rate constants have been found to be (1.82–4.49) × 1010 s−1. The results of our investigation show that synthesized heterodimers can be used as efficient light-harvesting elements in solar energy conversion devices.

Poly(Schiff's bases)-bifluorophores : Synthesis, photophysical properties, non-radiative energy transfer of electronic excitation

Abstract The method of synthesis of unsymmetrical azomethynes-bifluorophores where one of the fluorescent fragments is a donor of electron excitation energy and the second one is an acceptor was worked out. Photophysical properties of azomethynes-bifluorophores were investigated. It was shown that in these compounds non-radiative energy transfer takes place. It was established that quantum-chemical semiempirical method AM 1 may be used for the calculation of spatial structure of amines-fluorophores.

Absorption and fluorescence of hydrophobic components of dissolved organic matter in several Karelian lakes with stratified structures

Hydrophobic components of cromophoric dissolved organic matter (CDOM) extracted from water samples and sediments taken in several relic basins located on Karelian shoreline of the White Sea were analyzed using spectroscopic techniques. Those water reservoirs exist at various stages of isolation from the White Sea and represent complex stratified systems of fresh and marine water layers not completely mixing trough the year. Basins separating from the White Sea are the unique natural objects for investigations of properties CDOM, its transformation in the process of turning the marine ecosystem into freshwater environment. CDOM occurring in all types of natural water represents a significant reservoir of organic carbon and plays a key role in the carbon cycle on the Earth. However, aquatic CDOM and nonliving organic matter in sediments from relic separating basins still have not been studied. The target of this work was to study absorption and fluorescence spectra of hydrophobic components of aquatic CDOM from different water depth and sediments in several separated basins of the Kandalaksha Gulf of the White Sea located near the N.A. Pertsov White Sea Biological Station.