Preparation of a series of N-alkyl-3-boronopyridinium halides and study of their stability in the presence of hydrogen peroxide

A simple and efficient protocol for the preparation of a series of N-alkyl-3-boronopyridinium salts is described which requires exposure of 3-pyridineboronic acid neopentylglycol ester and corresponding alkyle halide to microwave irradiation followed by boronic ester hydrolysis. The technique employed drastically reduces the reaction time and prevents thermal degradation and the formation of side products. Water solutions of the obtained boronopyridinium salts are shown to be stable at room temperature in wide pH range as well as in the presence of hydrogen peroxide at pH 10.0 for 72 h.      

Characteristics of light scattering by normal and modified areas of skin tissue

Results from numerical calculations and experimental studies of the optical backscattering coefficients and changes in the polarization characteristics of normal and modified (birthmark, scar) skin tissue structures are presented. It is shown that determining the Mueller matrix is an effective way of detecting changes in the structure of skin tissue in vivo which reflects changes in the depolarization of light by an object for different polarization parameters of the incident (probe) radiation. The depolarization of light is found to be symmetric for normal areas of skin and antisymmetric for skin tissue with a modified structure. It is proposed that the polarization characteristics of scattered radiation be used in detecting damaged areas of skin tissue.     

Fluid pressure penetration for advanced FEA of metal-to-metal seals

This numerical study investigates the behaviour of the contact faces in the metal-to-metal seal of a typical pressure relief valve in the commercial FE-package ANSYS. The valve geometry is simplified to an axisymmetric problem, which comprises a simple representative geometry consisting of only three components. A cylindrical nozzle, which has a valve seat on top, contacts with a disk, which is preloaded by a compressed linear spring. Analysis considerations include the effects of the Fluid Pressure Penetration (FPP) across the valve seat which exists at two different scales. In-service observations show that there is certain limited fluid leakage through the valve seat at operational pressures about 90% of the set pressure, which is caused by the fluid penetrating into surface asperities at the microscale. At the macroscale, non-linear FE-analysis using the FPP technique available in ANSYS revealed that there is also a limited amount of fluid penetrating into gap, which is caused primarily by the global plastic deformation of the valve seat. Accurate prediction of the fluid pressure profile over the valve seat is addressed in this study by considering the FPP interaction on both scales. The shape of this pressure profile introduces an additional component of the spring force, which needs to be considered to provide a reliable sealing. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Polarization of near-forward-scattered light from particulate substrates illuminated at near-grazing angles

Laboratory photopolarimetric measurements of light scattered by substrates consisting of semitransparent particles with sizes significantly larger than the wavelength show a polarization shoulder at small scattering angles near θ=10-30° in addition to the Brewster maximum positioned near θ=50°. With ray-tracing simulations, we find that the shoulder appears to be related to light passing through particles in the upper layers of the substrates. We study the dependence on particle absorption and packing density of particulate substrates. The studies show that the shoulder weakens with increased absorption and packing density.     

Detection of dust grains vibrations with a laser heterodyne receiver of scattered light

We present the results of measurement of grains vibrations under external action in gas and liquid with a laser heterodyne receiver of scattered radiation. For investigation of dynamic characteristics of particles we made the laser heterodyne receiver with sensitivity about 2×10⁻¹⁷ W/Hz and source of probing with radiation power 1 mW. In our pilot experiments, measurement of vibration amplitude of nanoparticles in gas (cigarette smoke) and microparticles in fluid (toothpaste in water) was made. We measured values of vibration amplitudes about 20–30 nm.     

Discrete dipole approximation simulations of light reflection from flat non-transparent particles with rough surfaces

We study light reflection from flat particles with rough surfaces and fractal statistics of topography. Discrete dipole approximation method is used to solve the problem of light scattering. Refractive indices corresponding to a metal and a transient material with conductive properties are taken. The sizes of particles are much larger than the wavelength of incident light and the roughness scales are larger, comparable to and smaller than the wavelength. The influence of the fractal dimension parameter and the amplitude of heights of random topography on reflectance and on the angular profile of the specular reflection peak is considered. Our calculations demonstrate that topography amplitude is very important for reflectance and fractal dimension is responsible for the angular dispersion of the specular reflection peak.     

Effective dichroism in forward scattering by inhomogeneous birefringent medium

The Mueller matrix model for inhomogeneous medium characterized by simultaneous linear and circular birefringence for single scattering in the forward direction is derived. We find that the presence of inhomogeneity results in the occurrence of new polarization effects. In particular, forward scattering by inhomogeneous birefringent medium exhibits linear and circular dichroism. We show that in the case of weak depolarization (when Cloude's entropy is less than 0.5), the initial parameters for linear and circular birefringence can be obtained from deterministic Mueller matrix associated with the largest eigenvalue of Cloude's coherency matrix. Sample calculations are given for quartz.     

Designing a New Class of Bases for Nucleic Acid Quadruplexes and Quadruplex‐Active Ligands

A new class of quadruplex nucleobases, derived from 3‐deazaguanine, has been designed for various applications as smart quadruplex ligands as well as quadruplex‐based aptamers, receptors, and sensors. An efficient strategy for modifying the guanine quadruplex core has been developed and tested by using quantum chemistry methods. Several potential guanine derivatives modified at the 3‐ or 8‐position or both are analyzed, and the results compared to reference systems containing natural guanine. Analysis of the formation energies (BLYP‐D3(BJ)/def2‐TZVPP level of theory, in combination with the COSMO model for water) in model systems consisting of two and three stacked tetrads with Na⁺/K⁺ ion(s) inside the internal channel indicates that the formation of structures with 3‐halo‐3‐deazaguanine bases leads to a substantial gain in energy, as compared to the corresponding reference guanine complexes. The results cast light on changes in the noncovalent interactions (hydrogen bonding, stacking, and ion coordination) in a quadruplex stem upon modification of the guanine core. In particular, the enhanced stability of the modified quadruplexes was shown to originate mainly from increased π–π stacking. Our study suggests the 3‐halo‐3‐deazaguanine skeleton as a potential building unit for quadruplex systems and smart G‐quadruplex ligands.     

Recovery of the Complete Mueller Matrix of an Arbitrary Object in the Method of Three Input Polarizations

The problem of the recovery of the complete Mueller matrix of an arbitrary object by additionally measuring the matrix elements whose values are not determined in base measuring cycles of the method of three input polarizations is considered. We suggest a number of methods for recovering the complete matrix of dependent and independent recovery and for carrying out two base measuring cycles of the method of three input polarizations. A comparative analysis of the accuracy characteristics of the proposed methods has been performed.     

Photochromism in p-methylbenzoylthioacetone and related β-thioxoketones

Irradiation of p-methylbenzoylthioacetone with UV or visible light brings about spectral changes characteristic for the photochromic behavior of β-thioxoketones. The nature of the initial species and of the photochromic product can be assigned based on spectral studies of the electronic and IR spectra in rare gas matrices combined with quantum chemical calculations. Additional arguments for the vibrational assignments are provided by using polarized light to induce the phototransformation, and by subsequent measurements of linear dichroism on partially aligned samples. Comparison with the results previously obtained for three related molecules: thioacetylacetone, p-methyl(thiobenzoyl)acetone, and monothiodibenzoylmethane reveals a common pattern of the photochromic reaction. In all four molecules, the initial species corresponds to an intramolecularly hydrogen-bonded enolic molecular structure, and the main photochromic product to an “open”, nonchelated enethiolic counterpart. On the basis of a computational TD-DFT study of ground and excited electronic states, possible mechanisms of the photochromic transformation are discussed.