Персона: Лебедев-Степанов, Петр Владимирович
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Studying the Dielectric Properties of the Curcubituril Cavity on the Basis of the Solvatochromic Effect of Styryl Dye upon the Formation of an Inclusion Complex
A new approach to the theoretical evaluation of the local dielectric properties of media that contain an organic dye acting as a nanoprobe is proposed. The method is checked so as to evaluate the dielectric properties of the host molecule in a supramolecular inclusion complex from the experimentally measured shift of the optical absorption spectrum of the guest molecules (dye) after the complex formation. Using the Onsager-Liptay model, the dielectric properties of the cucurbit[7]uril cavity was theoretically estimated by analyzing the experimentally measured shift of the absorption spectrum of 1-(3-ammoniopropyl)-4-[(E)-2-(3,4-dimethoxyphenyl)-ethenyl]-pyridinium dication of the dye after it forms a complex with cucurbit[7]uril in an aqueous solution. To parameterize the Onsager-Liptay equation, the positions of the absorption spectral maxima of the dye under study were experimentally measured in the following solvents with known dielectric and optical properties: methanol, ethanol, 1-propanol, 1-butanol, and water. When calculating molecular structures, dipole moments of the ground and excited states, and polarizability, the TD-DFT quantum chemical method with the CAM-B3LYP functional in the 6-311G(d,p) basis set was used within the Gamess (United States) software package. The obtained theoretical value of the effective dielectric permittivity of the cavity (about 13) is in good agreement with the published value.
Study of the 3D Structure of a Hydrogel with Gold Nanoparticles by Cryogenic Electron Microscopy
A hydrogel with gold nanoparticles stabilized in a citrate buffer is obtained by dehydration from a solution (sol-gel transition). The morphological characteristics of the hydrogel are studied using cryogenic transmission electron microscopy, in particular cryoelectron tomography. The spatial structure of the hydrogel is studied in three dimensions. The dimensional parameters of the nanoparticles and distances to nearest neighbors are determined. It is found that most of the nanoparticles are in a bound state and form clusters in the process of hydrogel formation. © 2022, Pleiades Publishing, Ltd.
Electron Emission Properties of Self-Assembling Nanodiamond‒Polymer Nanocomposite Coatings
© 2019, Pleiades Publishing, Inc.Abstract: The formation of thin-film coatings from detonation nanodiamond (DND) suspensions on atomically ordered conducting Ni–W substrates by self-assembly in an evaporating aqueous solution using the spin coating technique has been investigated. It is shown that, in the absence of a polymer matrix, the DND distribution over the substrate is nonuniform and the adhesion to the substrate is weak, which prevents obtaining a uniform and stable emission current. The use of DND–water-soluble polymer (chitosan and carrageenan polysaccharides, polyacrylic acid, and sulfonated polyaniline (SPANI)) coatings makes it possible to enhance the film adhesion to the substrate and provide a disaggregated state of nanocrystallites. The DND–SPANI coatings have demonstrated the best emission characteristics. Based on the analysis of the emission characteristics, a new model of emission center in the DND–polymer–substrate system has been proposed.
Microstructure and Rheological Behavior of Stabilized Gold Nanoparticles Hydrosol
© 2021, Pleiades Publishing, Inc.Abstract: A comprehensive analysis of an aqueous solution of gold nanoparticles with an average size of 6 nm in a citrate buffer has been carried out, with investigation of the solution rheology and structure by electron and atomic force microscopy. A deviation of the rheological behavior of hydrosol from the Newtonian properties is found even at low gold nanoparticle concentrations. The specific features of the rheological behavior of hydrosol are explained based on the transmission electron microscopy (TEM) data.
Transport and assembling microparticles via Marangoni flows in heating and cooling modes
© 2021 Elsevier B.V.The processes of the particles transfer in liquid media and the creation of structures of required configurations on substrates are of great importance in such areas as materials science, coatings, optoelectronics and biomedical researches. To control of the transfer of large ensembles of particles and dynamically transform of the particle aggregates the precise and flexible methods are strongly required. In this work, we propose a method for manipulation of microparticles in volatile liquid layers hundreds of microns thick that relies on the control of Marangoni flows by changing a sign of the temperature gradient in the liquid by the local action of the heat source and/or the heat sink. We have clearly demonstrated the applicability of the method to perform of wide range of manipulations with the particle ensembles: particles assembling in the circular patterns on a substrate when heating is applied, transfer of particles away from a heat sink when the substrate is cooled, and creation of ring-like patterns by changing the temperature gradient sign during particle assembling process. We have also studied the influence of the liquid layer thickness on the particle transfer and the size of the resulting pattern. It was found out that when heating the final pattern area on substrate decreases with the layer thickness, while the time of the pattern formation increases with the layer thickness. In the cooling mode, the final cleaned area decreases with the number of particles but the dependence on the layer thickness is ambiguous. The characteristic time decreases with an increase in the number of particles and slightly increases with the layer thickness. It was also revealed that the increase in the layer thickness makes it possible to create the multilayer dense circular assemblies of particles. The proposed method is simple for implementation, flexible and can be applied for manipulation with particles of any physicochemical properties and shapes. The method is applicable for controlling both a single microparticle and a large group of particles.
Quasi-Stationary Evaporation of a Small Liquid Droplet on a Flat Substrate: Analytical Solution in Bipolar Coordinates
Structure Visualization of 4-DASPI–Cucurbituril Supramolecular Complex to Predict the Solvatochromic Shift of Absorption Spectrum
The study of supramolecular “host-guest” complexes in solutions is of fundamental and practical significance. The structures and formation enthalpy of supramolecular complexes for the 4-DASPI dye with two cavitands (cucurbit[6]uril and cucurbit[7]uril) have been obtained by the TDDFT quantum chemistry method with a camb3lyp basis. It was shown by visualization of the structures that the size of cucurbit[6]uril is too small and doesn’t allow the dye chromophore to penetrate into the cavitand cavity while the dye stays in the ground state, but the formation of an external complex is possible. On the contrary, formation of an inclusion complex with the cucurbit[7]uril is energetically favorable, and the dye chromophore penetrates into the cavity. Visualization of the complex structure allows us to determine the chromophore position relative to the given cavitand cavity, and thus we can predict the changes in the dye spectra due to complexation. The theoretical results of the work are in good correlation with the experiment.
Parametric Broadening of the Electronic-Vibrational Spectrum of a Molecule Caused by Zero-Point Vibrations and Thermal Fluctuations of Interatomic Bonds
© 2021, Pleiades Publishing, Ltd.Abstract: The existence in the Born–Oppenheimer approximation of a fundamentally new type of broadening of the spectral line of the electronic vibrational–rotational (rovibronic) transition in a molecule, caused by zero-point vibrations and thermal fluctuations of atomic nuclei near their equilibrium positions during vibrational–rotational motion inside the molecule, is discovered. A quantitative description in the harmonic approximation is obtained to describe the shape and width of the electron transition line corresponding to this type of broadening, which is called parametric, since the energy of any rovibronic level and transition between levels depends parametrically on the current instantaneous position of nuclei, which move much more slowly than electrons. To take this effect into account, Franck-Condon diagrams with oblique (bent) levels of vibrational energy are proposed. From the point of view of the Copenhagen interpretation of quantum mechanics, the parametric broadening exists due to the difference between an open (i.e. experimentally measured) quantum system from an isolated (unobservable) one. The magnitude of this broadening is estimated on the example of the 0–0 transition in a series of polymethine dye monomers. The estimate showed that the magnitude of the parametric broadening of the indicated zero-phonon line is comparable with the broadening observed in the experiment. The existing quantum chemical methods for calculating molecular spectra do not take into account the parametric broadening. They smooth the quasi-continuum of closely spaced rovibronic transitions, approximately calculating their common envelope, but do not consider the broadening of a single transition. The creation of a theory of parametric broadening will contribute to the development of intramolecular converters of energy from nuclei to electrons and vice versa, sensing nanoprobes, and quantum radio, photoacoustic and acousto-optic, and transceiving or converting devices of molecular size.
Specific Solvation of a 4-DASPI Dye in a Water–Ethylene Glycol Binary Solvent
Abstract: The solvatochromic shifts of the maxima of the absorption spectra of a 4-DASPI dye (4-[4-(dimethylamino)styryl]-1-methylpyridinium iodide) in a water–ethylene glycol binary solvent in a range of concentrations of 0–100% are experimentally studied. The dependence of the solvatochromic shift on the macroscopic permittivity (dielectric constant) of the solution and concentration of ethylene glycol is constructed. The Onsager–Liptay model is applied for the theoretical interpretation which makes it possible to estimate the effective permittivity in the microscopic region directly adjacent to the chromophore based on the values of the measured solvatochromic shifts. It is found that the value of the permittivity in the solvate shell of this dye substantially differs from the macroscopic value of this quantity, which means that the shell is significantly enriched with ethylene glycol (specific solvation) throughout the entire range of concentrations, and the enrichment reaches a maximum approximately in the middle of the specified range. The composition of the solvate shell of the dye at different values of the concentration is discussed. © 2022, Pleiades Publishing, Ltd.