Evolutionary Development and Structural Diversity of Natural Antimicrobial Peptides,Peptidometics, and Cationic Amphiphiles Based on Amino Acids

Russian Journal of General Chemistry - The review article traces the main trends of the synthetic approach to the solution of the problem of overcoming the resistance of pathogenic bacterial...     

Influence of the counterion size on swelling and collapse of polyelectrolyte gel

A theory that predicts the effect of the counterion size on the swelling and collapse of a weakly charged polyelectrolyte gel was developed. In addition to excluded-volume interactions between monomer units of the gel, the theory involves the counterion-monomer unit and counterion-counterion interactions in terms of the virial approximation. The character of interactions between different units in the system varies from repulsion to attraction depending on the type of solvent, counterion, and dielectric permittivity of the solvent. For solvents with a low permittivity, the effect of condensation of counterions resulting in the formation of ion pairs is taken into account.     

Negative normal restitution coefficient found in simulation of nanocluster collisions

The oblique impacts of nanoclusters are studied theoretically and by means of molecular dynamics. In simulations we explore two models--Lennard-Jones clusters and particles with covalently bonded atoms. In contrast with the case of macroscopic bodies, the standard definition of the normal restitution coefficient yields for this coefficient negative values for oblique collisions of nanoclusters. We explain this effect and propose a proper definition of the restitution coefficient which is always positive. We develop a theory of an oblique impact based on a continuum model of particles. A surprisingly good agreement between the macroscopic theory and simulations leads to the conclusion that macroscopic concepts of elasticity, bulk viscosity, and surface tension remain valid for nanoparticles of a few hundred atoms.     

Cooling kinetics of a granular gas of viscoelastic particles

The evolution of a granular gas of viscoelastic particles in the homogeneous cooling state is studied. The velocity distribution function of granular particles and the time dependence of the mean kinetic energy of particles (granular temperature) are found. The noticeable deviation of the distribution function from the Maxwell distribution and its non-monotonous evolution are established. The perturbation theory with respect to the small dispersion parameter is elaborated and the analytical expressions for the asymptotic time dependence of the velocity distribution function and the granular gas temperature are derived.     

Granular gas of viscoelastic particles in a homogeneous cooling state

Kinetic properties of a granular gas of viscoelastic particles in a homogeneous cooling state are studied analytically and numerically. We employ the most recent expression for the velocity-dependent restitution coefficient for colliding viscoelastic particles, which allows us to describe systems with large inelasticity. In contrast to previous studies, the third coefficient a₃ of the Sonine polynomials expansion of the velocity distribution function is taken into account. We observe a complicated evolution of this coefficient. Moreover, we find that a₃ is always of the same order of magnitude as the leading second Sonine coefficient a₂; this contradicts the existing hypothesis that the subsequent Sonine coefficients a₂,a₃…, are of an ascending order of a small parameter, characterizing particles inelasticity. We analyze evolution of the high-energy tail of the velocity distribution function. In particular, we study the time dependence of the tail amplitude and of the threshold velocity, which demarcates the main part of the velocity distribution and the high-energy part. We also study evolution of the self-diffusion coefficient D and explore the impact of the third Sonine coefficient on the self-diffusion. Our analytical predictions for the third Sonine coefficient, threshold velocity and the self-diffusion coefficient are in a good agreement with the numerical finding.     

Brownian motion in granular gases of viscoelastic particles

A theory is developed of Brownian motion in granular gases (systems of many macroscopic particles undergoing inelastic collisions), where the energy loss in inelastic collisions is determined by a restitution coefficient ɛ. Whereas previous studies used a simplified model with ɛ = const, the present analysis takes into account the dependence of the restitution coefficient on relative impact velocity. The granular temperature and the Brownian diffusion coefficient are calculated for a granular gas in the homogeneous cooling state and a gas driven by a thermostat force, and their variation with grain mass and size and the restitution coefficient is analyzed. Both equipartition principle and fluctuation-dissipation relations are found to break down. One manifestation of this behavior is a new phenomenon of “relative heating” of Brownian particles at the expense of cooling of the ambient granular gas.     

Synthesis of Amphiphilic Peptidomimetics Based on the Aliphatic Derivatives of Natural Amino Acids

Abstract—The paper describes the production of a number of lipoamino acid derivatives based on L-serine, L-ornithine, and L-lysine with potential antibacterial activity. The designed synthesis schemes are distinguished by the simplicity and versatility of the approach used. This allows us to use them to obtain a series of samples in preparative quantities required to perform the subsequent physico-chemical and biochemical studies.     

“Exclusion Zone” Formation in Mixtures of Ethanol and Water

Brownian particles suspended in water or other polar liquids are pushed out of the region next to hydrophilic polymers, leaving a microsphere-free region known as the “exclusion zone” (EZ). This study aimed to test the hypothesis that the dilution of ethanol in water may influence EZ formation. EZs were created in aqueous media using Nafion tubes as EZ-nucleating surfaces. To define the outer edge of the EZ, carboxylate microspheres, 1 µm diameter, were used. Dynamic movement of microspheres away from Nafion surface was registered in mixtures of ethanol and water, the ethanol concentration varying from 0 to 95%. We found that mixtures with the highest concentrations of ethanol generally produced the smallest EZs and the slowest EZ buildup. However, an unexpected result was the presence of an extremum corresponding to ~10% ethanol. At this concentration, the EZ is larger than in either pure water or almost pure ethanol.     

On the occasion of the 100th birthday of Nikola $$\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\smile}$}}{l}$$ Alekseevich Brilliantov

Memorial Data

On the occasion of the 100th birthday of Nikola $\overset{\lower0.5em\hbox{$\overset{\lower0.5em\hbox{ Alekseevich Brilliantov