Gas-Chromatographic Study of the Polarity and Selectivity of Nematic Liquid Crystals

The sorption properties of stationary phases based on nematic p-substituted azoxybenzenes were studied. Correlations were revealed between the structural selectivity of mesogens, chemical nature of terminal substituents, capability for dispersion interactions and polarity of the sorbents, temperature gradient of the retention indices, and thermodynamic parameters of solution of xylene isomers in the sorbents.     

An error self-compensation mechanism for deposition of optical coatings with broadband optical monitoring

An error self-compensation mechanism is investigated for use during the deposition of optical coatings with broadband optical monitoring. The correlation of thickness errors caused by monitoring procedure is mathematically described. It is shown that this correlation of errors may result in the effect of selfcompensation of errors.     

Efficient refolding of a hydrophobic protein with multiple S-S bonds by on-resin immobilized metal affinity chromatography

The efficient refolding of recombinant proteins produced in the form of inclusion bodies (IBs) in Escherichia coli still is a complicated experimental problem especially for large hydrophobic highly disulfide-bonded proteins. The aim of this work was to develop highly efficient and simple refolding procedure for such a protein. The recombinant C-terminal fragment of human alpha-fetoprotein (rAFP-Cterm), which has molecular weight of 26 kDa and possesses 6 S-S bonds, was expressed in the form of IBs in E. coli. The C-terminal 7× His tag was introduced to facilitate protein purification and refolding. The refolding procedure of the immobilized protein by immobilized metal chelating chromatography (IMAC) was developed. Such hydrophobic highly disulfide-bonded proteins tend to irreversibly bind to traditionally used agarose-based matrices upon attempted refolding of the immobilized protein. Indeed, the yield of rAFP-Cterm upon its refolding by IMAC on agarose-based matrix was negligible with bulk of the protein irreversibly stacked to the resin. The key has occurred to be using IMAC based on silica matrix. This increased on-resin refolding yield of the target protein from almost 0 to 60% with purity 98%. Compared to dilution refolding of the same protein, the productivity of the developed procedure was two orders higher. There was no need for further purification or concentration of the renatured protein. The usage of silica-based matrix for the refolding of immobilized proteins by IMAC can improve and facilitate the experimental work for difficult-to-refold proteins.     

Mesomorphism of thermotropic poly(propyleneimine) dendrimers and phase equilibria in systems on their basis

The thermotropic mesomorphism of poly(propyleneimine) dendrimers of first, second, and third generations has been studied by the methods of polarization thermomicroscopy and DSC. Phase diagrams for the binary systems of dendrimers with n-amyloxy-n′-cyanobiphenyl calamite liquid crystal and hexa(pentyloxy)triphenylene discotic liquid crystal have been constructed. Measurements have been carried out over the entire concentration range at temperatures corresponding to the stable states of nematic, columnar, and isotropic phases. The effects of the chemical nature and shape of linear and cyclic mesogen molecules on the manifestation of mesomorphism in LC dendrimers are considered.     

High-performance modeling of the deposition of a silicon dioxide thin film using the LAMMPS program

Supercomputer modeling of the process of high-energy deposition (ion-beam sputtering) of thin films of silicon dioxide using the molecular dynamics (MD) approach was carried out. The deposition method based on the facilities of the LAMMPS MD program was compared with another method that is known from the literature. An analysis of the structure of the deposited film (density, radial distribution function, concentration of defects) was carried out.     

Molecular Modeling of the Binding of the Allosteric Inhibitor Optactin at a New Binding Site in Neuraminidase A from <Emphasis Type="Italic">Streptococcus pneumoniae</Emphasis>

Neuraminidase A (NanA) from the pathogenic bacteria Streptococcus pneumoniae catalyzes the cleavage of terminal sialic acid residues from oligosaccharide receptors on the surface of human respiratory epithelium cells and is considered to be the key virulence factor. The search for new regulatory ligand-binding sites in the structure of this enzyme is of fundamental interest and can reveal new targets to design drugs for treating pneumonia, meningitis, and other human infectious diseases. The low molecular weight compound optactin has been recently shown to inhibit the activity of the homologous Neuraminidase B (NanB). Furthermore, optactin binds at a separate site of the protein structure, which is topologically different from the catalytic center. The bioinformatic and structural analysis using the pocketZebra method was used to annotate a new, previously unknown site in the NanA structure. This new site is analogous to the optactin binding site in NanB and characterized by the high content of subfamily-specific positions, what indicates the importance of this site for the enzyme function. Molecular modeling was used to study optactin binding at the allosteric sites of the homologous neuraminidases NanA and NanB. Tyr250, Thr251, Lys334, Gln494, Lys499, Lys597, Thr657, and Glu658 residues were shown to stabilize the optactin molecule in the NanB structure, with water molecules playing an important role in the coordination of the ligand. Molecular modeling has shown that optactin binding by NanA is complicated due to substitutions in the subfamily-specific positions of the allosteric center. The peculiarities of the structural organization of the new NanA binding site facilitate the targeted search for complementary ligands that can selectively regulate the activity of this enzyme.