The crystal structures of 204 polybromides and bromine solvates were extracted from the Cambridge Structural Database and the Inorganic Crystal Structures Database. The electron density distribution was theoretically obtained for 18 selected compounds and topological analysis of the electron density by means of the R. Bader atoms in molecules (AIM) theory was performed. For the 18 compounds, the topology of networks formed by Br–Br and Br⋯Br interactions was revealed only within the AIM approach and compared with that found by means of the Voronoi tessellation. Satisfactory correlation between the description of Br⋯Br bonding within the AIM and the Voronoi approaches was found. The effect of cation size, presence of C–Br bonds and bromine content on the dimensionality of the network was studied for 204 solids using the Voronoi tessellation. The Voronoi approach demonstrated good potential to reveal extended architectures based on Br⋯Br interactions that are typical for electroconductive polybromide-based materials.
The development of advanced electrochemical devices for energy conversion and storage requires fine tuning of electrode reactions, which can be accomplished by altering the electrode/solution interface structure. Particularly, in case of an alkali-salt electrolyte the electric double layer (EDL) composition can be managed by introducing organic cations (e.g. room temperature ionic liquid cations) that may possess polar fragments. To explore this approach, we develop a theoretical model predicting the efficient replacement of simple (alkali) cations with dipolar (organic) ones within the EDL. For the typical values of the molecular dipole moment ($2-4~D$) the effect manifests itself at the surface charge densities higher than 30 $\mu C/cm^2$. We show that the predicted behavior of the system is in qualitative agreement with the molecular dynamics simulation results.
In this article, I summarize my theoretical developments in the statistical field theory of salt solutions of zwitterionic and multipolar molecules. Based on the Hubbard-Stratonovich integral transformation, I represent configuration integrals of dilute salt solutions of zwitterionic and multipolar molecules in the form of functional integrals over the space-dependent fluctuating electrostatic potential. In the mean-field approximation, for both cases, I derive integro-differential self-consistent field equations for the electrostatic potential, generated by the external charges in solutions media, which generalize the classical Poisson-Boltzmann equation. Using the obtained equations, in the linear approximation, I derive for the both cases a general expression for the electrostatic potential of a point-like test ion, expressed through certain screening functions. I derive an analytical expression for the electrostatic potential of the point-like test ion in a salt zwitterionic solution, generalizing the well known Debye-Hueckel potential. In the salt-free solution case, I obtain analytical expressions for the local dielectric permittivity around the point-like test ion and its effective solvation radius. For the case of salt solutions of multipolar molecules, I find a new oscillating behavior of the electrostatic field potential of the point-like test ion at long distances, which is caused by the nonzero quadrupole moments of the multipolar molecules. I obtain a general expression for the average quadrupolar length of a multipolar solute. Using the random phase approximation (RPA), I derive general expressions for the excess free energy of bulk salt solutions of zwitterionic and multipolar molecules and analyze the limiting regimes resulting from them. I generalize the salt zwitterionic solution theory for the case when several kinds of zwitterions are dissolved in the solution. In this case, within the RPA, I obtain a general expression for the solvation energy of the test zwitterion. Finally, I demonstrate how to take a systematic account of the excluded volume correlations between multipolar molecules in addition to their electrostatic correlations. I believe that the formulated findings could be useful for the future theoretical models of the real ion-molecular solutions, such as salt solutions of micellar aggregates, metal-organic complexes, proteins, betaines, etc.
Supercapacitors based on carbon nanomaterials are attracting much attention because of their high capacitance enabled by large specific surface area. The introduction of heteroatoms such as N or O enhances the specific capacitance of these materials. However, the mechanisms that lead to the increase in the specific capacitance are not yet well-studied. In this Letter, we demonstrate an effective method for modification of the surface of carbon nanowalls (CNWs) using DC plasma in atmospheres of O2, N2, and their mixture. Processing in the plasma leads to the incorporation of ∼4 atom % nitrogen and ∼10 atom % oxygen atoms. Electrochemical measurements reveal that CNWs functionalized with oxygen groups are characterized by higher capacitance. The specific capacitance for samples with oxygen reaches 8.9 F cm−3 at a scan rate of 20 mV s−1. In contrast, the nitrogen-doped samples demonstrate a specific capacitance of 4.4 F cm−3 at the same scan rate. The mechanism of heteroatom incorporation into the carbon lattice is explained using density functional theory calculations.
The review summarizes studies of chemical and biological processes occurring in human body upon exposure to coronaviruses, in particular SARS-CoV-2. The mechanisms of viral particles penetration into the cell and their replication, impact on the immune system and oxygen transport systems are considered. The mechanisms of complications occurring as a consequence of viral infection - vasculitis, thrombosis, cytokine storm and lung fibrosis are discussed. The review also includes data on the latest research in the field of small molecule medication to counteract the virus. Molecular targets and possible vectors of exploiting them are considered. The review is written primarily for specialists who want to understand the chains of activation, replication, actions and methods of protection/inhibition of SARS-CoV-2. Due to the short period of such studies, the data on complexes of small molecule compounds and possible protein targets are not numerous, but they will be useful in search and synthesis of new potentially effective drugs.
Snake venom α-neurotoxins, invaluable pharmacological tools, bind with high affinity to distinct subtypes of nicotinic acetylcholine receptor. The combinatorial high-affinity peptide (HAP), homologous to the C-loop of α1 and α7 nAChR subunits, binds biotinylated α-bungarotoxin (αBgt) with nanomolar affinity and might be a protection against snake-bites. Since there are no data on HAP interaction with other toxins, we checked its binding of α-cobratoxin (αCtx), similar to αBgt in action on nAChRs. Using radioiodinated αBgt, we confirmed a high affinity of HAP for αBgt, the complex formation is supported by mass spectrometry and gel chromatography, but only weak binding was registered with αCtx. A combination of protein intrinsic fluorescence measurements with the principal component analysis of the spectra allowed us to measure the HAP-αBgt binding constant directly (29 nM). These methods also confirmed weak HAP interaction with αCtx (>10000 nM). We attempted to enhance it by modification of HAP structure relying on the known structures of α-neurotoxins with various targets and applying molecular dynamics. A series of HAP analogues have been synthesized, HAP[L9E] analogue being considerably more potent than HAP in αCtx binding (7000 nM). The proposed combination of experimental and computational approaches appears promising for analysis of various peptide-protein interactions.
Remote nano-magneto-mechanical actuation of magnetic nanoparticles (MNPs) by non-heating extremely low frequency magnetic field (ELF MF) is explored as a tool for non-invasive modification of bionanomaterials in pharmaceutical and medical applications. Here we study the effects of ELF MF (30-160 Hz, 8-120 kA/m) on the activity and release of a model enzyme, superoxide dismutase 1 (SOD1) immobilized by polyion coupling on dispersed MNPs aggregates coated with poly(L-lysine)-block-poly(ethylene glycol) block copolymer (s-MNPs). Such fields do not cause any considerable heating of MNPs but promote their rotating-oscillating mechanical motion that produces mechanical forces and deformations in adjacent materials. We observed the changes in the catalytic activity of immobilized SOD1 as well as its release from the s-MNPs/SOD1 polyion complex upon application of the ELF MF for 5 to 15 min. At longer exposures (25 min) the s-MNPs/SOD1 dispersion destabilizes. The bell-shaped effect of the field frequency with maximum at f = 50 Hz and saturation effect of field strength (between 30 kA/m and 120 kA/m at f = 50 Hz) are reported and explained. The findings are significant as one early indication of the nano-magneto-mechanical disruption by ELF MF of cooperative polyion complexes that are widely used for design of current functional healthcare bionanomaterials.
NaCl is one of the simplest compounds and was thought to be well-understood, and yet, unexpected complexities related to it were uncovered at high pressure and in low-dimensional states. Here, exotic hexagonal NaCl thin films on the (110) diamond surface were crystallized in the experiment following a theoretical prediction based on ab initio evolutionary algorithm USPEX. State-of-the-art calculations and experiments showed the existence of a hexagonal NaCl thin film, which is due to the strong chemical interaction of the NaCl film with the diamond substrate.
In this paper we present our study of carbamazepine solubility in supercritical carbon dioxide. We have calculated the solubility values along two isochores corresponding to the CO2 densities ρ = 1.1ρcr(CO2) and ρ = 1.3ρcr(CO2), where ρcr(CO2) is the critical density of CO2, in the temperature range from 313 to 383 K, as well as along three isotherms at T = 318, 328 and 348 K by an approach based on the classical density functional theory. The solubility values were also obtained using in situ IR spectroscopy and molecular dynamics simulations along the mentioned isochores and isotherms, respectively. Because the density functional theory only takes into account the Lennard-Jones interactions, it can be expected to underestimate the solubility values when compared to the experimental ones. However, we have shown that the data calculated within the classical density functional theory qualitatively reproduce the solubility trends obtained by IR spectroscopy and molecular dynamics simulation. Moreover, the obtained position of the upper crossover pressure is in good agreement with the experimental literature results