Fabrication and laser-assisted modification of the Ag particles ensembles supporting quadrupole plasmon oscillations

Optical and Quantum Electronics - In this paper, a theoretical analysis of figure of merit (FOM) of a surface plasmon resonance (SPR) sensor with a buffer layer of magnesium fluoride has been...     

Light-induced multi-wavelength lasing in dye-doped chiral nematic liquid crystals due to strong pumping illumination

The influence of the pump laser beam on the lasing spectral characteristics in dye-doped cholesteric liquid crystal is investigated. Under the influence of the pump laser pulses with different repetition rates and energies, non-linear reorientation and light-induced flow reorientation of chiral nematic liquid crystals (CLC) molecules was observed. Independent of the reorientation mechanism, multi-wavelength lasing was achieved due to stepwise uncoiling of the CLC structure. Under the influence of a pump laser beam with low repetition rate, Cano–Grandjean disclination defect lines were induced which remain even after removal of the laser beam.     

Cluster analysis of molecular simulation trajectories for systems where both conformation and orientation of the sampled states are important

Clustering methods have been widely used to group together similar conformational states from molecular simulations of biomolecules in solution. For applications such as the interaction of a protein with a surface, the orientation of the protein relative to the surface is also an important clustering parameter because of its potential effect on adsorbed‐state bioactivity. This study presents cluster analysis methods that are specifically designed for systems where both molecular orientation and conformation are important, and the methods are demonstrated using test cases of adsorbed proteins for validation. Additionally, because cluster analysis can be a very subjective process, an objective procedure for identifying both the optimal number of clusters and the best clustering algorithm to be applied to analyze a given dataset is presented. The method is demonstrated for several agglomerative hierarchical clustering algorithms used in conjunction with three cluster validation techniques. © 2016 Wiley Periodicals, Inc.     

Low-temperature spectral observation of the first six-coordinate nitrosyl complexes of cobalt(II) meso-tetratolylporphyrin with trans nitrogen base ligands

Low-temperature interaction of nitrogen base ligands with layered Co(TTP)(NO) (TTP = meso-tetratolylporphyrinato dianion) as well as its toluene solution leads to the formation of the first six-coordinate species of the general formula (B)Co(TTP)(NO) (where B = piperidine and pyridine). The nu(NO) stretching bands of these species appear at lower frequencies compared with the five-coordinate nitrosyl derivative and depend on the nature of the trans axial ligand. The equilibrium constants and enthalpies of formation of these new species are determined. Fairly stable at low-temperature conditions in the solid state, they slowly dissociate the nitrogen base ligands upon warming to restore the five-coordinate nitrosyl complex Co(TTP)(NO).     

The first-principle studies of the elastic,electronic, and vibrational properties of L-alanine

The calculation in the present work is conducted with the help of CRYSTAL’17 package using PBE method, including gradient approximation and taking into account van der Waals forces as well as the B3LYP hybrid functional. Crystal structure and chemical bond, elastic properties, equation of state, structural properties under pressure, and vibrational properties are studied. The elastic constants of single crystal and polycrystalline properties are obtained; anisotropic nature of the crystal is determined. The impact of hydrostatic compression up to pressure of 7.5 GPa on the L-alanine properties is studied. The effect of taking into account the forces of intermolecular interaction on the accuracy of calculation of lattice constants and intermolecular distances is shown. The atom charges and bond overlap population in molecules are determined within the framework of the Mulliken scheme. The total and partial density of states is calculated and it is established that the transition from valence band to conduction band is performed by electrons from oxygen atoms to carbon atoms of the –COO group. The average value of the tensor component of the polarizability, permittivity, and piezoelectric stress coefficients were 40.67 Å³, 2.08, and ? 4.25 pm/V, relatively. The obtained dependence of the lattice constants demonstrated occurrence of intersection within pressure interval of about 1.8 GPa, the fact that has earlier been established experimentally. It has been shown that C–C and C–N intramolecular distances reduce with pressure increase, as for the –COO group, C1–O1 distances decrease, while C1–O2 distances increase. The mode Grüneisen parameters, obtained from ab initio calculations for the first time, revealed the increase in the vibration frequency of the –NH₃ group, while other vibration frequencies decrease with increasing pressure.

     

The spherical sector of the Calogero model as a reduced matrix model

We investigate the matrix-model origin of the spherical sector of the rational Calogero model and its constants of motion. We develop a diagrammatic technique which allows us to find explicit expressions of the constants of motion and calculate their Poisson brackets. In this way we obtain all functionally independent constants of motion to any given order in the momenta. Our technique is related to the valence-bond basis for singlet states.     

Intensity correlations in a coherently prepared Rb vapor in a magnetic field

We have studied the intensity correlations between two orthogonally linearly polarized components of a laser field propagating through a resonant atomic medium. These experiments have been performed in a rubidium atomic vapor. We observe that the correlations between the orthogonally polarized components of the laser beam are maximal in the absence of a magnetic field. The magnitude of the correlations depends on the applied magnetic field, and the magnitude first decreases and then increases with increasing magnetic field. Minimal correlations and maximal rotation angles are observed at the same magnetic fields. The width of the correlation function is directly proportional to the excited state lifetime and inversely proportional to the Rabi frequency of laser field.     

Energetics of nucleic acid stability: the effect of DeltaCP

We report high-resolution differential scanning calorimetric data on the poly(dAdT)poly(dAdT), poly(dA)poly(dT), poly(dIdC)poly(dIdC), poly(dGdC)poly(dGdC), poly(rA)poly(rU), and poly(rI)poly(rC) nucleic acid duplexes. We use these data to evaluate the melting temperatures, TM, enthalpy changes, DeltaHM, and heat capacity changes, DeltaCP, accompanying helix-to-coil transitions of each polymeric duplex studied in this work at different NaCl concentrations. In agreement with previous reports, we have found that DeltaCP exhibits a positive, nonzero value, which, on average, equals 268 +/- 33 J mol(-1) K(-1). With DeltaCP, we have calculated the transition free energies, DeltaG, enthalpies, DeltaH, and entropies, DeltaS, for the duplexes as a function of temperature. Since, DeltaG, DeltaH, and DeltaS all strongly depend on temperature, the thermodynamic comparison between DNA and/or RNA duplexes (that may differ from one another with respect to sequence, composition, conformation, etc.) is physically meaningful only if extrapolated to a common temperature. We have performed such comparative analyses to derive differential thermodynamic parameters of formation of GC versus AT, AU, and IC base pairs as well as B' versus A and B helix conformations. We have proposed some general microscopic interpretations for the observed sequence-specific and conformation-specific thermodynamic differences between the duplexes.     

High-throughput protein precipitation method with 96-well plate for determination of doxepin and nordoxepin in human plasma using LC–MS/MS

The aim of this study was to establish a high-throughput and sensitive LC–MS/MS method for the determination of doxepin and its major active metabolite nordoxepin in human plasma. It has been designed for bioequivalence study for formulations containing 25 mg of doxepin. Doxepin and nordoxepin were extracted from human plasma samples by protein precipitation with acetonitrile by using protein precipitation 96-well plates. The analyte was separated using a Phenomenex Kinetex Biphenyl column (100 × 2.1 mm, 2.6 μm) using isocratic elution with a mobile phase of 20 mM ammonium formate (30%) and acetonitrile:methanol 3:7 v:v (70%) at a flow rate of 0.5 mL/min and an injection volume of 10 μL. The detection was performed using a triple quadrupole mass spectrometer by multiple reaction monitoring mode to monitor the precursor-to-product ion transitions of m/z 280.4 → 107.0 and 283.4 → 235.0 for doxepin and doxepin-D3, respectively, and 266.3 → 106.9 and 269.3 → 235.0 for nordoxepin and nordoxepin-D3, respectively, in positive electrospray ionization mode. The total run time was 3.5 min. The method was validated over a concentration range of 50–10,000 pg/mL using a Triple Quad 4500 MS System (Sciex) for both analytes. The developed and validated method can be successfully used to study the bioequivalence/pharmacokinetics of doxepin and nordoxepin.     

Interaction of nitrogen oxides with sublimed layers of (meso-tetraphenylporphyrinato)cobalt(II); IR evidence of oxo-transfer from (nitro)porphyrinatocobalt(III) to free nitric oxide

Interaction of a low-pressure NO2 with sublimed layers of (meso-tetraphenylporphyrinato)cobalt(II) (Co(TPP)) leads to formation of 5-coordinate nitro complex Co(III)(TPP)(NO2). Upon exposure of these layers to pyridine vapors, the fast reaction with formation of 6-coordinate nitro-pyridine porphyrins (Py)Co(III)(TPP)(NO2) occurs. By means of IR spectroscopy and use of nitrogen oxide isotopomers, it is shown that an oxo-transfer reaction occurs from 5-coordinate species to free nitric oxide (NO) while the 6-coordinate complex is rather inert. It is also demonstrated that the stepwise addition of low-pressure NO2 to nitrosyl complex Co(TPP)(NO) leads to formation of the nitro complex most likely by an exchange reaction.