Anastasia V. Kharcheva

Molecular Oligogermanes and Related Compounds: Structure, Optical and Semiconductor Properties

The optical (UV/Vis absorbance, fluorescence in the solid state and in solution) and semiconducting properties of a number of di- and trigermanes as well as related silicon- and tin-containing germanes, 1-6 ((p-Tol)3 GeGeMe3 (1), Ph3 SnGe(SiMe3 )3 (2), (C6 F5 )3 GeGePh3 (3), (p-Tol)3 GeSiMe2 SiMe3 (4), (p-Tol)3 GeGeMe2 Ge(p-Tol)3 (5), (p-Tol)3 GeSiMe2 SiMe2 Ge(p-Tol)3 (6)) were investigated. Molecular structures of 5 and 6 were studied by X-ray diffraction analysis. All compounds displayed luminescence properties. In addition, a band gap (of about 3.3 eV) was measured for compounds 1-6 showing that those molecules display semiconductor properties.

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.

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 intensities ratio F685/F740 for maple leaves during seasonal color changes and with fungal infection

The work is devoted to the spectral measurements of maple leaves. Fresh green leaves of maple were investigated in spring and summer, healthy leaves and leaves affected by fungal diseases - during the fall color change. F685/F740 parameter values for healthy and diseased maple leaves were found, as well as the change of this parameter during the growing season. The concentration of chlorophylls a and b and carotenoids in ethanol extracts of maple leaves with different pigmentation were calculated by absorption spectroscopy and the ratio of Chl a / Chl b was found.

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.

Spectroscopic Study of Green Sulfur Bacteria in Stratified Water Bodies of the Kandalaksha Gulf of the White Sea

Optical characteristics of water in stratified lakes of the White Sea are of particular interest in connection with the observation of thin colored layers resulting from massive development of anoxygenic phototrophic bacteria around the chemocline. While optical properties of chlorophyll are widely used in remote sensing, spectral characteristics of bacteriochlorophylls (BChl) for natural microbial communities have been little studied. In this work, spectral study of green sulfur bacteria of four water bodies of the Kandalaksha Gulf of the White Sea was carried out. Absorption and fluorescence spectra were measured for water samples taken in March 2017 from different depths and compared with spectra of monocultures isolated from the same water bodies earlier. It has been shown that the BChl fluorescence in the living cells of green sulfur bacteria has two overlapping emission bands: in the region of 740–770 nm (BChl d and e) and at 815 nm (BChl a). The wavelength of the maximum of the first band depends on the ratio of the concentrations of green- and brown-colored forms of bacteria containing different types of BChl. A new method for separating the contributions of two types of bacteria is proposed, based on the deconvolution of the BChl fluorescence spectrum into three bands whose parameters are determined from the spectra of monocultures. The BChl content at various water depths has been estimated and the percentage ratio of different types of phototrophic bacteria has been determined.

CCDC 1505509: Experimental Crystal Structure Determination

Related Article: Kirill V. Zaitsev, Kevin Lam, Zhaisan Zhanabil, Yerlan Suleimen, Anastasia V. Kharcheva, Viktor A. Tafeenko, Yuri F. Oprunenko, Oleg Kh. Poleshchuk, Elmira Kh. Lermontova, and Andrei V. Churakov|2017|Organometallics|36|298|doi:10.1021/acs.organomet.6b00767

Luminescent solutions and powders of new samarium complexes with N,N',O,O'-chelating ligands

Imaging techniques in biology and medicine are crucial tools to obtain information on structural and functional properties of living cells and organisms. To fulfill the requirements associated with application of these techniques it appears necessary to design markers with specific characteristics. Luminescent complexes of trivalent lanthanide ions with chelating ligands are of increasing importance in biomedical applications because of their millisecond luminescence lifetime, narrow emission band, high signal-to-noise ratio and minimal photodamage to biological samples. In order to extend the available emission wavelength range the luminescent samarium chelates are highly desirable. In this study the ligands with diamides of 2,2’-bipyridin-6,6’-dicarboxylic acid were used to improve photophysical characteristics of samarium complexes. We report the luminescence characteristics of samarium complexes with novel ligands. All complexes exhibited the characteristic emission of Sm (III) ion with the lines at 565, 597, 605, 645 and 654 nm, the intensity strongly depended on the ligand. Absorption and luminescence excitation spectra of Sm (III) complexes showed main peaks in the UV range demonstrating lanthanide coordination to the ligand. The absolute lumenescence quantum yield was measured for solutions in acetonitrile with excitation at 350 nm. The largest luminescence quantum yield was found for the samarium complex Bipy 6MePy Sm (3%) being much higher that for samarium complexes reported in the literature earlier. These results prove as well that samarium chelates are potential markers for multiparametric imaging techniques.

Luminescent solutions and films of new europium complexes with chelating ligands

The development of new complexes of rare earth elements (REE) with chelating organic ligands opens up the possibility of purposeful alteration in the composition and structure of the complexes, and therefore tuning their optical properties. New ligands possessing two pyridine rings in their structure were synthesized to improve coordination properties and photophysical characteristics of REE compounds. Complexes of trivalent europium with novel chelating ligands were investigated using luminescence and absorption spectroscopy, as well as atomic force microscopy. Luminescence properties of new compounds were studied both for solutions and films deposited on the solid support. All complexes exhibit the characteristic red luminescence of Eu (III) ion with the absolute lumenescence quantum yield in polar acetonitrile solution varying from 0.21 to 1.45 % and emission lifetime ranged from 0.1 to 1 ms. Excitation spectra of Eu coordination complexes correspond with absorption bands of chelating ligand. The energy levels of the triplet state of the new ligands were determined from the phosphorescence at 77 K of the corresponding Gd (III) complexes. The morphology of films of europium complexes with different substituents in the organic ligands was investigated by atomic force microscopy (AFM). It strongly depends both on the type of substituent in the organic ligand, and the rotation speed of the spin-coater. New europium complexes with chelating ligands containing additional pyridine fragments represent outstanding candidates for phosphors with improved luminescence properties.