All-fiber holmium distributed feedback laser at 2.07 µm.

In this Letter, we present the results on fabrication and investigation of a holmium (Ho) distributed fiber laser based on a π-phase-shifted FBG inscribed in a heavily Ho-doped fiber by IR femtosecond laser pulses. Single-polarization and single-transverse mode operation regimes were observed with a linewidth of the order of 10 kHz and output power up to 53 mW at 2.07 µm. Lasing regimes are compared for room and cryogenic (77 K) temperatures of the laser cavity. To the best of our knowledge, this is the first realization of such type of fiber laser based on holmium active medium.

[Modeling and theoretical analysis of ring specific mimicry in view of isomerism within medicinal promising oligomers of "DIVEMA"]. / Raschetno-teoreticheskii analiz izomerizatsonnoi tsiklomimikrii lekarstvenno-perspektivnykh oligomerov "DIVÉMA" v protsesse ikh svobodno-radikal'nogo sinteza.

The furan or pyran related hetero cycles play basic role in structural units of nucleic acids (NA) and polysaccharides (PS), significantly predetermining their functional specifics. Some of such properties, in great relevancy for medicine, can be imitated through mimicry of polymers synthetic. Particularly, a formation of similar cycloisomeric chains is possible in process of free-radical cyclocopolymerization of divinyl ether (DVE) and maleic anhydride (MA). The products yielded (DVEMA) of general formula [DVE(MA)-alt-MA]n become precursors for a broad family of water-soluble derivatives capable of wide spectrum of bioactivity, including induction of interferon, immune-stimulated and direct antiviral protection. In this connection, the knowledge: what is content of different heterocyclic isomers in backbone of the preparations and what their partial contributions in promotion of the certain bioactivities observed, are in great importance. Available experimental data (NMR, IR, etc.), controversial for interpretations, didn't elucidate a required estimation of the DVEMA isomerism. The current work represents an independent exploration of the problem via quantum chemistry-based analysis of kinetic (activation barriers) and thermodynamic (enthalpies) priorities in competition between variable isomerism within the chain synthesis. The system is considered in maximal range of hypothetically allowable variations of two levels for double regioselective bifurcations: there are four competitive ways, each of which involves a sequence of four type elementary reactions for a diverse-isomeric formation of chain units. A genesis of six chiral centers (62 stereoisomers permitted) per every of the four part ways was accounted in view for up to 256 isomeric variations in total. The required time-minimized but precisely accurate computations were conducted via B3LYP/6-31G(d), M06-2X/6-311+G(d), M06-2X/6-31+G(2df,p) techniques, which were preselected through model test-systems. As a result, the mechanisms, crucial points and factors for the process-permitted regulation of isomeric content of DVEMA were studied in details. The narrow enough set of most probable enantiomers within highly competitive 5-exo- and 6-endo- ring closing sub-ways was revealed. The results obtained are very actual for an adequate modeling (docking / molecular dynamics) of DVEMA derivatives in their interactions with biopolymer targets, in search for purposed advancement of current background in design and synthesis of highly effective agents for combined antiviral protection (against HIV, flu, herpes, and other infections).

The structural diversity of C-rich DNA aggregates: unusual self-assembly of beetle-like nanostructures.

We studied the ability of oligonucleotides CnT25 (n = 2, 5, 7, 9, 12, 25) to form an intermolecular i-motif using circular dichroism, ultra-violet spectroscopy, nuclear magnetic resonance, high-resolution atomic force microscopy, high-performance liquid chromatography, and molecular dynamics simulations. The arrangement of single-stranded oligonucleotides in multimer i-motifs was very unusual: C-tracts of different oligonucleotides followed each other consecutively in order to fold into a closed intermolecular i-motif core with minimal loops (one cytidine in a loop spanning over a minor groove, three cytidines in a loop over a major groove); intact T-tracts protruded from predefined loci allowing visualization of beetle-like nanostructures by atomic force microscopy. The same structures were formed from analogous biotinylated oligonucleotides demonstrating one of the potential applications of such structures as carriers of multiple functional groups. Our findings open up possibilities for the rational design of pH-sensitive DNA aggregates and evaluation of the efficiency of their assembly.

EVOLUTIONARY DYNAMICS OF STRUCTURAL AND FUNCTIONAL DOMAINS OF INFLUENZA A VIRUS NS1 PROTEIN.

Influenza A virus (IAV) NS1 protein is one of the key viral factors responsible for virus-host interactions. NS1 counteracts host antiviral defense, participates in the processing and export of cellular mRNAs, regulates the activity of viral RNA polymerase and the expression of viral genes, and influences the cellular signaling systems. Multiple NS1 functions are carried out due to the interactions with cellular factors, the number of which exceeds one hundred. It is noteworthy that only two segments of IAV genome - NS and NP - did not undergo reassortment and evolved in the course of genetic drift, beginning with the pandemic of 1918 to the present. This fact may indicate the importance of NS1 and its numerous interactions with cellular factors in the interspecific adaptation of the virus. The review presents data on the evolution of the human IAV NS1 protein and analysis of the amino acid substitutions in the main structural and functional domains of NS1 protein during evolution.

[Ebola hemorrhagic fever: Properties of the pathogen and development of vaccines and chemotherapeutic agents].

Ebola hemorrhagic fever (EHF) epidemic currently ongoing in West Africa is not the first among numerous epidemics in the continent. Yet it seems to be the worst EHF epidemic outbreak caused by Ebola virus Zaire since 1976 as regards its extremely large scale and rapid spread in the population. Experiments to study the agent have continued for more than 20 years. The EHF virus has a relatively simple genome with seven genes and additional reading frame resulting from RNA editing. While being of a relatively low genetic capacity, the virus can be ranked as a standard for pathogenicity with the ability to evade the host immune response in uttermost perfection. The EHF virus has similarities with retroviruses, but belongs to (-)RNA viruses of a nonretroviral origin. Genetic elements of the virus, NIRV, were detected in animal and human genomes. EHF virus glycoprotein (GP) is a class I fusion protein and shows more similarities than distinctions in tertiary structure with SIV and HIV gp41 proteins and even influenza virus hemagglutinin. EHF is an unusual infectious disease, and studying the molecular basis of its pathogenesis may contribute to new findings in therapy of severe conditions leading to a fatal outcome.

Ebola hemorrhagic fever: Properties of the pathogen and development of vaccines and chemotherapeutic agents.

Ebola hemorrhagic fever (EHF) epidemic currently ongoing in West Africa is not the first among numerous epidemics in the continent. Yet it seems to be the worst EHF epidemic outbreak caused by Ebola virus Zaire since 1976 as regards its extremely large scale and rapid spread in the population. Experiments to study the agent have continued for more than 20 years. The EHF virus has a relatively simple genome with seven genes and additional reading frame resulting from RNA editing. While being of a relatively low genetic capacity, the virus can be ranked as a standard for pathogenicity with the ability to evade the host immune response in uttermost perfection. The EHF virus has similarities with retroviruses, but belongs to (-)RNA viruses of a nonretroviral origin. Genetic elements of the virus, NIRV, were detected in animal and human genomes. EHF virus glycoprotein (GP) is a class I fusion protein and shows more similarities than distinctions in tertiary structure with SIV and HIV gp41 proteins and even influenza virus hemagglutinin. EHF is an unusual infectious disease, and studying the molecular basis of its pathogenesis may contribute to new findings in therapy of severe conditions leading to a fatal outcome.