Antimicrobial and Amyloidogenic Activity of Peptides. Can Antimicrobial Peptides Be Used against SARS-CoV-2?

At present, much attention is paid to the use of antimicrobial peptides (AMPs) of natural and artificial origin to combat pathogens. AMPs have several points that determine their biological activity. We analyzed the structural properties of AMPs, as well as described their mechanism of action and impact on pathogenic bacteria and viruses. Recently published data on the development of new AMP drugs based on a combination of molecular design and genetic engineering approaches are presented. In this article, we have focused on information on the amyloidogenic properties of AMP. This review examines AMP development strategies from the perspective of the current high prevalence of antibiotic-resistant bacteria, and the potential prospects and challenges of using AMPs against infection caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).     

Investigation of the TiCl4 reaction order in quasiliving styrene polymerization with 1-phenylethyl chloride/TiCl4/Bu2O

Summary The reaction order with respect to TiCl₄ was investigated in the quasiliving polymerization of styrene using a 1-phenylethyl chloride/TiCl₄/Bu₂O initiating system in mixture of 1,2-dichloroethane and n-hexane (55:45 v/v) at -15 °C. It was found out that the reactions order with respect to TiCl₄ was closer to 1. A mechanistic scheme to explain the kinetic behavior of quasiliving styrene polymerization in 1-phenylethyl chloride/TiCl₄/Bu₂O is proposed.     

Novel initiating system based on AlCl3 etherate for quasiliving cationic polymerization of styrene

Summary Quasiliving cationic polymerization of styrene was obtained in the system 2-phenyl-2-propano-/AlCl₃·OBu₂/Bu₂O in a mixture of 1,2-dichloroethane and n-hexane (55:45 viv) at -15 °C. The molecular weights of the polymers (M_n) increased in direct proportion to the monomer conversion. However, the experimental M_ns are essentially higher than theoretical ones, indicating that slow initiation relative to propagation takes place. The molecular weight distributions were broad (M_w/M_n2.5), probably due to the slow initiation and slow exchange between reversibly terminated and propagating species.     

Activated anionic ring-opening polymerization of ε-caprolactam with magnesium di(ε-caprolactamate) as initiator: effect of magnesium halides

The activated anionic ring-opening polymerization of ε-caprolactam initiated by 0.35 mol% of combined initiator, i.e., equimolar mixture of magnesium di(ε-caprolactamate) (CL₂Mg) with magnesium halides (MgCl₂, MgBr₂, and MgI₂) as well as of ε-caprolactam magnesium bromide (CLMgBr) in the presence of 0.35 mol% of N-acetyl-ε-caprolactam as an activator has been investigated in the temperature range 140–200 °C. It was found that the reaction rate increased while the apparent activation energy decreased in the following series: CL₂Mg/MgCl₂ < CL₂Mg/MgBr₂ ~ CLMgBr < CL₂Mg/MgI₂. In addition, the poly(ε-caprolactam)s prepared with CL₂Mg/MgX₂ (MgX₂ = MgCl₂, MgBr₂, and MgI₂) are characterized by slightly higher thermal stability than polymers obtained with CLMgBr as initiator. These observations were explained in terms of the coordination of Lewis acids (MgX₂, where X = Cl, Br, and I) with imide carbonyl of N-acyllactam end groups leading to the increase of their reactivity and stability.     

Structure of reciprocal lattice sites of a single-crystal Ni-based superalloy

Volume fractions of the ?? phase are calculated in the form of various geometrical figures depending on the ratio of the volume fraction of the ?? and ?á? phases. The ?? phase in the form of plates prevails at a 70% content of the ?á? phase, which is the most characteristic of the VZhM4 alloy after the complete heat treatment. The qualitative analysis is carried out for the arrangement of satellites in the reciprocal space of the VZhM4 single-crystal Ni-based superalloy. The lattice of the reciprocal space with the satellites caused by the stress state of ?? phase interlayers is constructed in the form of various geometrical figures. The set of experimental sections of the 3D structure of (222), (313), and (202) reciprocal lattice sites is obtained.     

Effect of some physicomechanical properties of selected ceramic materials on their abrasive resistance in the finishing of precision parts

Results of a study of the possibility of using some tungsten-free ceramic materials based on borides, oxides, and nitrides for the finishing treatment of precision parts of fuel equipment are considered. The materials were estimated with respect to the rate of removal of the metal of the part, the wear of the lap per one part, its life before regrinding, and the roughness of the surface of the part after finishing. The effect of the grain size, the ultimate bending strength, the porosity, and the hardness of the material on the service characteristics of the laps is described. It is shown that ceramic materials can be used for fabricating the functional parts of laps for finishing precision parts of fuel equipment. Translated from Ogneupory i Tekhnicheskaya Keramika, No. 4, pp. 20–24, April, 2000.     

Polymer layered silicate nanocomposites

Polymers filled with low amounts of layered silicate dispersed at nanoscale level are most promising materials characterized by a combination of chemical, physical and mechanical properties that cannot be obtained with macro‐ or microscopic dispersions of inorganic fillers. Polymer layered silicate nanocomposites can be obtained by insertion of polymer molecules in the galleries between the layers of phyllosilicate. Here, hydrated alkaline or alkaline earth metal cations are hosted which neutralize the negative charge resulting from isomorphous substitutions of Mg or Al cations within the silicate. Insertion of polymer molecules to prepare “intercalation hybrids” can be carried out by replacing the water hydration molecules in the galleries by polymers containing polar functional groups, using the so called ion‐dipole method. A more general technique involves compatibilization of the silicate by intercalation of an organic molecule, typically an organic alkylammonium salt, that replaces the cations in the interlayer galleries to form an organically modified layered silicate (OLS). The aliphatic chain of the OLS favors the intercalation of any type of polymer. Intercalated or delaminated polymer‐silicate hybrids are obtained depending on whether the stack organization of the silicate layers is preserved or is lost, with single sheets being distributed in the polymer matrix. The methods currently used for preparing polymer layered silicate (PLS) nanocomposites are: in situ polymerization, from polymer solution, or from polymer melt. Although PLS nanocomposites have been known for a long time, it is the possibility of preparing them by melt intercalation of OLS in processing that is boosting the present interest in these materials and their properties. So far PLS nanocomposites have been characterized by X‐ray diffractometry, transmission electron microscopy, differential scanning calorimetry, and NMR. Published results on PLS nanocomposites are reviewed concerning their characterization and properties with particular reference to fire retardant behavior.     

New developments in fire retardant non‐halogen aromatic phosphates

Akzo Nobel Chemicals has recently introduced on the market an aromatic oligomeric phosphate (BDP) based on Bisphenol A. This product shows higher thermal and hydrolytic stability than other aryl phosphates. It provides similar or better fire retardant performance than an oligomeric phosphate (RDP) based on resorcinol. Fire retardant formulations with BDP based on polycarbonate/ABS plastic (PC/ABS) blend, polyphenylene oxide/high impact polystyrene (PPO/HIPS) blend, and HIPS alone show similar or better physical properties than those obtained with RDP. Upon thermal decomposition of the fire retarded polymers containing BDP, phosphorus tends to accumulate in the solid residue, a result which indicates that the primary fire retardant action of BDP is likely to occur in the condensed phase.     

Effects of mutations in the calcium-binding sites of recoverin on its calcium affinity: evidence for successive filling of the calcium binding sites

A molecule of the photoreceptor Ca²⁺-binding protein recoverincontains four potential EF-hand Ca²⁺-binding sites, of whichonly two, the second and the third, are capable of binding calciumions. We have studied the effects of substitutions in the second,third and fourth EF-hand sites of recoverin on its Ca²⁺-bindingproperties and some other characteristics, using intrinsic fluorescence,circular dichroism spectroscopy and differential scanning microcalorimetry.The interaction of the two operating binding sites of wild-typerecoverin with calcium increases the protein's thermal stability,but makes the environment around the tryptophan residues moreflexible. The amino acid substitution in the EF-hand 3 (E121Q)totally abolishes the high calcium affinity of recoverin, whilethe mutation in the EF-hand 2 (E85Q) causes only a moderatedecrease in calcium binding. Based on this evidence, we suggestthat the binding of calcium ions to recoverin is a sequentialprocess with the EF-hand 3 being filled first. Estimation ofCa²⁺-binding constants according to the sequential binding schemegave the values 3.7 x 10⁶ and 3.1 x 10⁵ M^–1 for thirdand second EF-hands, respectively. The substitutions in theEF-hand 2 or 3 (or in both the sites simultaneously) do notdisturb significantly either tertiary or secondary structureof the apo-protein. Amino acid substitutions, which have beendesigned to restore the calcium affinity of the EF-hand 4 (G160D,K161E, K162N, D165G and K166Q), increase the calcium capacityand affinity of recoverin but also perturb the protein structureand decrease the thermostability of its apo-form.     

Formation Energies of Antiphase Boundaries in GaAs and GaP: An ab Initio Study

Electronic and structural properties of antiphase boundaries in group III-V semiconductor compounds have been receiving increased attention due to the potential to integration of optically-active III-V heterostructures on silicon or germanium substrates. The formation energies of {110}, {111}, {112}, and {113} antiphase boundaries in GaAs and GaP were studied theoretically using a full-potential linearized augmented plane-wave density-functional approach. Results of the study reveal that the stoichiometric {110} boundaries are the most energetically favorable in both compounds. The specific formation energy γ of the remaining antiphase boundaries increases in the order of γ_{113} ≈ γ_{112} < γ_{111}, which suggests {113} and {112} as possible planes for faceting and annihilation of antiphase boundaries in GaAs and GaP.