Isoleucine Residues Determine Chiral Discrimination of Odorant-Binding Protein

Enzymes, receptors, and carrier proteins discriminate between enantiomers of natural and synthetic chemicals. Whereas the structural details of this phenomenon have been investigated in enzymes and receptors, much less is known for carrier proteins of hydrophobic ligands, particularly concerning the contribution of asymmetric centers in the side chains of amino acids to chirally selective binding. Working with a pig odorant-binding protein, we have found that the replacement of either one or both isoleucine residues in the binding pocket by leucines abolishes discrimination of menthol and carvone enantiomers. The results indicate that isoleucines are crucial for chiral discrimination of hydrophobic ligands, and that asymmetry in the side chain may be as important as the overall asymmetry of the protein. The results provide suggestions and guidelines for improving chiral selectivity of binding proteins and enzymes, with consequent applications in the production of enantiomerically pure drugs.     

Quantum chemical investigation of new model bent-shaped bis-azomethines for nonlinear optics applications

Abstract

Quantum-chemical calculations of the E,E-, E,Z- and Z,Z-isomers structure of model bis-azomethines by the semiempirical PM3 method and the time-dependent theory of the density functional (DFT) are performed. It is shown that a completely satisfactory agreement between the theory and experiment is achieved using the B3LYP/cc-pVDZ calculation level and the INDO/S method for calculating the absorption spectra of the new bis-azomethines. The values of polarizability, first and second hyperpolarizability of model compounds are calculated. The used approach allows to make the screening of the most promising bis-azomethines for nonlinear optics applications.     

Experimental and theoretical studies of lattice distortions caused by charged 3d impurities in II–IV semiconductors

The results of studies of photoinduced lattice vibration modes associated with charged 3d impurities (in particular, Ni) in II–IV semiconductors (ZnSe, ZnO) and solid solutions ZnSSe and ZnCdSe are presented. Experimental optical exciton-vibration spectroscopy studies revealed that the local vibration modes are coupled, which is due to strong anharmonicity of the local vibrations. Analysis of phonon replicas of the zerophonon line in the spectra allows one to elucidate the nature of the anharmonicity. Model calculations performed for ZnSe: Ni and ZnO: Ni crystals revealed that the nearest neighbor environment of a charged Ni impurity is highly distorted. A change in the charged state of Ni leads to shifts in lines of calculated and experimentally measured x-ray emission spectra and, therefore, should be taken into account.     

Synthesis of Helical and Planar Extended-Phenanthridinium Salts

The investigation of new synthetic routes towards positively charged N-heterocycles is of high importance for the further development of medicinal chemistry, functional materials, catalysis and other areas of application. For accessing acridinium dyes, we previously reported an approach based on an aryne-imine-aryne coupling followed by the subsequent oxidation of the acridane intermediates. Herein, we now present an unusual reaction outcome when phenanthryne is used as aryne component. Under optimized conditions, this two-step synthetic methodology led to the formation of a helical tetrabenzophenanthridinium derivative. Furthermore, the susceptibility of this product to photoinduced cyclodehydrogenation was observed, providing a highly fluorescent planar polycyclic aromatic hydrocarbon with a positively charged nitrogen. The photophysical and electrochemical properties of the mesityl-phenyltetrabenzophenanthridinium tetrafluoroborate were also determined.     

Integration of lateral flow and microarray technologies for multiplex immunoassay: application to the determination of drugs of abuse

We report on a lateral flow microarray that combines multi-spot immunochip technology and immunochromatography. It can serve as a tool for the simultaneous detection of multiple analytes. The test zone of the nitrocellulose support comprises a microarray spotted with up to 32 antigens that can capture labeled gold-antibodies after lateral flow. The detection limits and detectable concentration ranges of the assay were characterized. The method was applied to the determination of drugs of abuse (and their metabolites) in urine, specifically of morphine, amphetamine, methamphetamine, and benzoylecgonine. The assay format is rapid (10 min), and has both a low relative standard deviation (< 9 %) and high recoveries (95–114 %). The detection limits (2–20 ng mL^–1 for drugs of abuse) are comparable to those of conventional single-analyte strip methods.

Molecular Mechanisms of Anticancer Activity of N-Glycosides of Indolocarbazoles LCS-1208 and LCS-1269

Novel indolocarbazole derivatives named LCS were synthesized by our research group. Two of them were selected as the most active anticancer agents in vivo. We studied the mechanisms of anticancer activity in accordance with the previously described effects of indolocarbazoles. Cytotoxicity was estimated by MTT assay. We analyzed LCS-DNA interactions by circular dichroism in cholesteric liquid crystals and fluorescent indicator displacement assay. The effect on the activity of topoisomerases I and II was studied by DNA relaxation assay. Expression of interferon signaling target genes was estimated by RT-PCR. Chromatin remodeling was analyzed–the effect on histone H1 localization and reactivation of epigenetically silenced genes. LCS-induced change in the expression of a wide gene set was counted by means of PCR array. Our study revealed the cytotoxic activity of the compounds against 11 cancer cell lines and it was higher than in immortalized cells. Both compounds bind DNA; binding constants were estimated—LCS-1208 demonstrated higher affinity than LCS-1269; it was shown that LCS-1208 intercalates into DNA that is typical for rebeccamycin derivatives. LCS-1208 also inhibits topoisomerases I and IIα. Being a strong intercalator and topoisomerase inhibitor, LCS-1208 upregulates the expression of interferon-induced genes. In view of LCSs binding to DNA we analyzed their influence on chromatin stability and revealed that LCS-1269 displaces histone H1. Our analysis of chromatin remodeling also included a wide set of epigenetic experiments in which LCS-1269 demonstrated complex epigenetic activity. Finally, we revealed that the antitumor effect of the compounds is based not only on binding to DNA and chromatin remodeling but also on alternative mechanisms. Both compounds induce expression changes in genes involved in neoplastic transformation and target genes of the signaling pathways in cancer cells. Despite of being structurally similar, each compound has unique biological activities. The effects of LCS-1208 are associated with intercalation. The mechanisms of LCS-1269 include influence on higher levels such as chromatin remodeling and epigenetic effects.     

Global Bifurcations in Generic One-parameter Families on $$\mathbb{S}^2$$

In this paper we prove that generic one-parameter families of vector fields on \(\mathbb{S}^2\) in the neighborhood of the fields of classes AH, SN, HC, SC (Andronov–Hopf, saddle-node, homoclinic curve, saddle connection) are structurally stable. We provide a classification of bifurcations in these families.