Magnetic properties of superconducting FeSe in the normal state.

A detailed magnetization study for the novel FeSe superconductor is carried out to investigate the behavior of the intrinsic magnetic susceptibility χ in the normal state with temperature and under hydrostatic pressure. The temperature dependences of χ and its anisotropy Δχ = χ([parallel]) - χ([perpendicular]) are measured for FeSe single crystals in the temperature range 4.2-300 K, and a substantial growth of susceptibility with temperature is revealed.

Interactions of oligomers of organic polyethers with histidine amino acid.

Rationale: Knowledge on noncovalent intermolecular interactions of organic polyethers with amino acids is essential to gain a better understanding on how polymers assemble in organic nanoparticles which are promising for drug delivery and cryoprotection. The main objective of the present study was to determine how polyethers assemble around ionizable amino acids such as histidine.

Methods: Electrospray mass spectrometry was applied to probe the interactions in model systems consisting of polyethylene glycol PEG-400 or oxyethylated glycerol OEG-5 and amino acid histidine hydrochloride.

DNA conformational equilibrium in the presence of Zn2+ ions in neutral and alkaline solutions.

Effect of Zn(2+) ions on DNA transition from B-form to a metallized form (m-DNA) in Tris and tetraborate buffers at pH 8.5 has been studied by visible and differential UV-spectroscopy and by thermal denaturation. The results have been compared to those obtained at pH 6.

Pressure effects on the magnetic susceptibility of FeTe(x)(x approximately 1.0).

The magnetic susceptibility χ of FeTe(x) compounds (x approximately 1.0) was studied under hydrostatic pressure up to 2 kbar at fixed temperatures of 55, 78 and 300 K. Measurements were taken both for polycrystalline and single crystalline samples.

Peculiarities of homooligonucleotides wrapping around carbon nanotubes: molecular dynamics modeling.

Spontaneous adsorption of homooligonucleotides dC(25), dT(25), dG(25), and dA(25) on the surface of the carbon nanotube (16,0) has been simulated by the molecular dynamics method. It was demonstrated that the rate of pyrimidine oligonucleotide wrapping around the nanotube is higher than that of purine ones which do not form a complete pitch even after the maximum simulation time (50 ns). This behavior can be explained by a stronger self-stacking between the purines than pyrimidines, which prevents the reorientation of the polymer required for the acquisition of a more energetically favored conformation on the nanotube.

Chemical potential of the low-dimensional multisubband Fermi gas.

In this paper, the chemical potential of two-dimensional (2D) and quasi-one-dimensional (Q1D) multisubband charged Fermi gases is evaluated. We start with a rather general formula for the thermodynamic potential of an ideal quantum statistical system with arbitrary occupation-number to calculate, as a particular case, the chemical potential of the multisubband 2D Fermi gas described by a quadratic energy spectrum. The chemical potential is also studied in the case of a low-dimensional Fermi gas in the presence of a quantizing magnetic field.

Evidence for sensory effects of a 1D organic conductor under gas exposure.

This work describes the gas-sensitive properties of a one-dimensional organic conductor before and after exposure to carbon monoxide and human breath. A sensitive material, an anion-radical salt of tetracyanoquinodimethane, has been investigated by infrared spectroscopy and electrical resistivity measurements. Drastic spectral and electrical changes are found after gas exposure showing that the compound interacts strongly with human breath, carbon monoxide, and ammonia.

Observation of poly(ethylene glycol) clusters with the chlorine anion in the gas phase under electrospray conditions.

It is demonstrated herein that poly(ethylene glycol) (PEG) oligomers can form stable complexes with the chlorine anion in the gas phase as evidenced by results from electrospray ionization mass spectrometry (ESI-MS) and molecular dynamics simulation. While the formation of crown-ether-like structures by acyclic polyethers in their complexes with alkali metal cations coordinated by the ether oxygen atoms has been extensively studied, the possibility of forming 'inversed' quasi-cyclic structures able to bind a monoatomic anion has not been proved till now. We have observed the formation of stable gas-phase complexes of oligomers of PEG-400 with the Cl(-) anion experimentally by ESI-MS for the first time.

Divalent metal ion effect on helix-coil transition of high molecular weight DNA in neutral and alkaline solutions.

Effect of Mg(2+), Ca(2+), Ni(2+) and Cd(2+) ions on parameters of DNA helix-coil transition in sodium cacodylate (pH 6.5), Tris (pH 8.5) and sodium tetraborate (pH 9.

Electronic and molecular structure of M-DNA fragments.

To study M-DNA molecular structure (such DNA with transition metal ions placed between the nucleic bases is able to conduct the electric current) and its conductivity mechanisms, we carried out ab initio quantum-mechanical calculations of electronic and spatial structures, thermodynamic characteristics of adenine-thymine (АТ) and guanine-cytosine (GC) base pair complexes with Zn(2+) and Ni(2+). To take into account the influence of the alkaline environment, calculations for these complexes were also carried out with hydroxyl and two water molecules. Computations were performed at MP2 level of theory using 6-31+G* basis set.

Characteristic crossing point (T(*)≈2.7 K) in specific heat curves of samples RuSr(2)Gd(1.5)Ce(0.5)Cu(2)O(10-δ) taken for different values of magnetic field.

Magnetic properties of polycrystalline samples of RuSr(2)(Gd(1.5)Ce(0.5))Cu(2)O(10-δ), as-prepared (by solid-state reaction) and annealed (12 h at 845 °C) in pure oxygen at different pressure (30, 62 and 78 atm) are presented.

Current driven tri-stable resistance states in magnetic point contacts.

Point contacts between normal and ferromagnetic metals are investigated using magnetoresistance and transport spectroscopy measurements combined with micromagnetic simulations. Pronounced hysteresis in the point contact resistance versus both bias current and external magnetic field are observed. It is found that such hysteretic resistance can exhibit, in addition to bi-stable resistance states found in ordinary spin valves, tri-stable resistance states with a middle resistance level.

Raman spectroscopy study and first-principles calculations of the interaction between nucleic acid bases and carbon nanotubes.

In this work, we have used Raman spectroscopy and quantum chemical methods (MP2 and DFT) to study the interactions between nucleic acid bases (NABs) and single-walled carbon nanotubes (SWCNT). We found that the appearance of the interaction between the nanotubes and the NABs is accompanied by a spectral shift of the high-frequency component of the SWCNT G band in the Raman spectrum to a lower frequency region. The value of this shift varies from 0.

Adsorption of poly(rA) on the carbon nanotube surface and its hybridization with poly(rU).

Adsorption of poly(rA) on a single-walled carbon nanotube surface in aqueous suspension and the subsequent hybridization of this polymer with free poly(rU) is studied. A comparison of the temperature dependence of the absorbance of free poly(rA) and poly(rA) adsorbed on the nanotube surface [poly(rA)(NT)] at nu(max)= 38,500 cm(-1) shows that the thermostability of the adsorbed polymer is higher. Molecular dynamics simulations demonstrate that more than half of the adenines are not stacked on the tube surface and some of them undergo self-stacking.

Sensitivity of redox reactions of dyes to variations of conditions created in mass spectrometric experiments.

Redox behaviour of four imidazophenazine dye derivatives under mass spectrometric conditions of matrix-assisted laser desorption/ionization (MALDI), laser desorption/ionization (LDI) from metal and graphite surface, electrospray, low temperature secondary ion mass spectrometry (LT SIMS) and fast atom bombardment (FAB) was studied and distinctions in the reduction-dependent spectral patterns were analyzed from the point of view of different quantities of protons and electrons available for reduction in different techniques. The reduction products [M + 2H](+*), [M + 3H](+) and M(-*), [M + H](-) were observed in the positive and negative ion modes, respectively, which permitted to suggest independent occurrence of reduction and protonation/deprotonation processes. LDI from graphite substrate was the only technique that allowed us to obtain abundant negative ions of all dye derivatives.

Fluorescent studies on cooperative binding of cationic pheophorbide-a derivative to polyphosphate.

The cooperative binding of a novel water-soluble cationic derivative of pheophorbide-a (CatPheo-a) to inorganic polyphosphate (PPS) in buffered aqueous solutions was studied by means of polarized fluorescence spectroscopy in a wide range of molar phosphate-to-dye ratios (P/D). Under low P/D values, CatPheo-a forms extended stacking associates on the PPS matrix, while under high P/D the dye binds to PPS in the dimer form. The CatPheo-a self-association is accompanied by 40-fold dye fluorescence quenching and a substantial increase in the fluorescence polarization degree.

SWNT-DNA and SWNT-polyC hybrids: AFM study and computer modeling.

Hybrids of carbon single-walled nanotubes (SWNT) with fragmented single or double-stranded DNA (fss- or fds-DNA) or polyC were studied by Atom Force Microscopy (AFM) and computer modeling. It was found that fragments of the polymer wrap in several layers around the nanotube, forming a strand-like spindle. In contrast to the fss-DNA, the fds-DNA also forms compact structures near the tube surface due to the formation of self-assembly structures consisting of a few DNA fragments.

The signature of subsurface Kondo impurities in the local tunnel current.

The conductance of a tunnel point contact in a scanning tunneling microscope-like geometry having a single defect placed below the surface is investigated theoretically. The effect of multiple electron scattering by the defect after reflections by the metal surface is taken into account. In the approximation of s-wave scattering the dependence of the conductance on the applied voltage and the position of the defect is obtained.

Breakup of a multisoliton state of the linearly damped nonlinear Schrödinger equation.

We address the breakup (splitting) of multisoliton solutions of the nonlinear Schrödinger equation (NLSE), occurring due to linear loss. Two different approaches are used for the study of the splitting process. The first one is based on the direct numerical solution of the linearly damped NLSE and the subsequent analysis of the eigenvalue drift for the associated Zakharov-Shabat spectral problem.

Polymorphism of 4-bromobenzophenone.

A combination of single-crystal and powder X-ray diffractometry was used to study the structure of two polymorphs of 4-bromobenzophenone over the temperature range from 100 to 300 K. One of the polymorphs of the title compound was known previously and its structure has been determined at room temperature [Ebbinghaus et al. (1997).

Surface spin-valve effect.

We report an observation of spin-valve-like hysteresis within a few atomic layers at a ferromagnetic interface. We use phonon spectroscopy of nanometer-sized point contacts as an in situ probe to study the mechanism of the effect. Distinctive energy phonon peaks for contacts with dissimilar nonmagnetic outer electrodes allow localizing the observed spin switching to the top or bottom interfaces for nanometer thin ferromagnetic layers.

Thermodynamic analysis of conformational transitions in oligonucleotide complexes in presence of Na(+) and Mg(2+) ions, using "staggering zipper" model.

Curves of transitions in double (2-->1 transition) and triple (3-->2 transition) complexes of oligonucleotides dA(N1)with dT(N2) in solutions with Na(+) and Mg(2+) are calculated for the case of oligomer lengths from 10 to 500 nucleotides in the wide range of ion concentrations. The calculated curves of transitions and their differential analogs reflect rather exactly the position and form of experimental curves and describe dependences of transition temperatures on the length of molecules, their concentration, and ionic conditions. Values of the nucleation parameter beta for the systems studied are determined by comparison of the calculated and experimental data obtained in a number of works.

Spectroscopy of phonons and spin torques in magnetic point contacts.

Phonon spectroscopy is used to investigate the mechanism of current-induced spin torques in nonmagnetic/ferromagnetic (N/F) point contacts. Magnetization excitations observed in the magneto-conductance of the point contacts are pronounced for diffusive and thermal contacts, where the electrons experience significant scattering in the contact region. We find no magnetic excitations in highly ballistic contacts.

Evaluation of the reduction of imidazophenazine dye derivatives under fast-atom-bombardment mass-spectrometric conditions.

Satellite [M + 2](+*) and [M + 3](+) peaks accompanying the common peak of the protonated molecule [M + H](+) that are known to indicate the occurrence of a reduction process were observed in the fast atom bombardment (FAB) mass spectra of imidazophenazine dye derivatives in glycerol matrix. The distribution of the abundances in the [M + nH](+) peak group varied noticeably for different derivatives. This indicated different levels of the reduction depending on the different structure variations of the studied molecules.

Ultrasoft x-ray Bremsstrahlung isochromatic spectra from 300-2000 eV electrons on Ar and Kr.

For the first time the bremsstrahlung effect was studied experimentally in the spectral region of 6.5-10 nm with 300-2000 eV electron scattering on Ar and Kr atoms. The isochromatic curves displayed maxima at electron energies of approximately = 0.