Growth and characterization of a new nonlinear optical material: Potassium p-nitrophenolate dihydrate (NO2–C6H4–OK·2H2O) with new bonding properties

Single crystals of potassium p-nitrophenolate dihydrate (NPK·2H₂O) have been grown successfully using the isothermal solvent evaporation technique. It is a new semiorganic nonlinear optical crystal, possessing a d_eff of about 1.5 times that of lithium niobate and in which the K⁺ ions are bonded to the nitro group instead of bonding with the phenolic O⁻. Large single crystals of dimension upto 20×6×4 mm³ are harvested within a period of 60 days. The grown crystals are subjected to single crystal X-ray, FTIR and DRS-UV visible spectral, thermal and microhardness analyses. Single crystal X-ray analysis confirms the molecular formula and the structure of the crystal. FTIR spectral studies verify the functional groups present in the crystal. The DRS-UV visible spectrum proved the optical transparency of the crystal in the entire visible and near infrared region. Thermal studies reveal that the crystals are stable upto 180 °C. Microhardness measurements on the cleaved plane (1 1 0) explain the strength and slip direction in the crystal. The SHG efficiency of the crystal is examined by performing the Kurtz powder test using Nd:YAG laser.     

A convenient and efficient one pot synthesis of unsymmetrically substituted p-terphenyls via a phosphine-free double Suzuki cross-coupling protocol using 1,4-dibromo-2-nitrobenzene as the substrate

A synthetic procedure has been developed to enable the sequential regio-selective Suzuki-Miyaura cross-coupling of 1,4-dibromo-2-nitrobenzene with a variety of arylboronic acids. The first Suzuki coupling step, using a phosphine-free palladium catalyst at room temperature, gave selective coupling at the position ortho to the nitro group, opening a convenient synthetic route to unsymmetrical para-terphenyls. The bromobiaryl product was then subjected directly to the second coupling step, in situ, using preferred aryl-boronic acids to give by this one-pot batch procedure unsymmetrically substituted para-terphenyls in excellent overall isolated yields. This methodology should be particularly suited for the generation of targeted chemical libraries, as well as for the synthesis of precursors of biologically active compounds or natural products which are derived from the unsymmetrical para-terphenyl core.     

Growth,spectral, optical,and dielectric studies on novel semiorganic NLO single crystal: d-phenylglycine hydrochloride

Good quality novel semiorganic nonlinear optical single crystal of d-phenylglycine hydrochloride has been grown from the aqueous solution by low temperature solution growth method. X-ray diffraction reveals that the crystal crystallises into orthorhombic system with noncentrosymmetric space group P2₁2₁2₁. Experimental parameters are evaluated based on single-crystal XRD and the calculated values of the polarisability were compared with the values of polarisability using Clausius–Mossotti equation. The functional groups present in the grown crystal were confirmed by Fourier transform infrared spectral analysis. The ¹H and ¹³C FT–NMR has been recorded to elucidate the molecular structure. Ultraviolet–visible-near infra-red absorption studies on this crystal reveal that the minimum absorption region is around 228 nm. The optical band gap of the crystal was found to be 2.9 eV. The scanning electron microscope study has been carried out to determine the surface morphology of the grown crystal. Photoluminescence studies show that the material emits violet fluorescence. Thermal studies bring forth that the crystal is thermally stable up to 255 °C. Dielectric studies reveal that both the dielectric constant and dielectric loss decrease with the increase in frequency as like the typical semiorganic nonlinear optical crystals such as bisthiourea zinc chloride, bisthiourea cadmium chloride and l-arginine dihydrogen phosphate. Electrical conductivity measurements were carried out and the Arrhenius plot is used to determine the value of activation energy. The Kurtz powder analysis on the crystal confirms the existence of second harmonic generation properties. The SHG efficiency was found to be 1.15 times that of KDP crystal.     

Unidirectional growth,optical, mechanical and dielectric studies on a novel NLO crystal: l-Arginine 4-nitrophenolate 4-nitrophenol dihydrate

The bulk single crystal of l-arginine 4-nitrophenolate 4-nitrophenol dihydrate (LAPP), an efficient organic NLO material of size 74 mm in length, 18 mm in diameter, was grown successfully by Sankaranarayanan–Ramasamy (SR) method. Single crystal X-ray diffraction study reveals that LAPP crystallizes into monoclinic system with the space group P2₁. The unidirectional growth along the plane (1 1 0) was confirmed from the powder XRD pattern with the sharp peak having maximum intensity. Optical absorption spectrum shows that LAPP has highly transparent in the entire visible and IR region with a wide band gap of 3.9 eV for large photon absorption. Vickers micro hardness measurement was performed to know the mechanical strength of the crystal. Dielectric profile of LAPP at room temperature brings forth low value of dielectric loss and dielectric constant at higher frequencies. Photoluminescence study reveals that LAPP exhibit green emission in the wavelength region 538 nm. The SHG efficiency of the crystal is measured by Kurtz's powder test using Nd:YAG Laser.     

$\mathcal{PT}$-Symmetric Quantum Electrodynamics—$\mathcal{PT}$QED

The construction of PT\mathcal{PT}-symmetric quantum electrodynamics is reviewed. In particular, the massless version of the theory in 1+1 dimensions (the Schwinger model) is solved. Difficulties with unitarity of the S-matrix are discussed.     

The vanishing viscosity limit for some symmetric flows

The focus of this paper is on the analysis of the boundary layer and the associated vanishing viscosity limit for two classes of flows with symmetry, namely, Plane-Parallel Channel Flows and Parallel Pipe Flows. We construct explicit boundary layer correctors, which approximate the difference between the Navier–Stokes and the Euler solutions. Using properties of these correctors, we establish convergence of the Navier–Stokes solution to the Euler solution as viscosity vanishes with optimal rates of convergence. In addition, we investigate vorticity production on the boundary in the limit of vanishing viscosity. Our work significantly extends prior work in the literature.     

The Production of Threose as a Degradation Product from L-Ascorbic Acid

Abstract

In order to examine the nature of in. vivo Maillard reactions that involve L-ascorbate and proteins, rates of formation of threose from L-ascorbic acid (1), dehydro-L-ascorbic acid (2), and 2,3-diketo-L-gulonic acid (3) were measured in the presence and absence of oxygen at pH 7.0 (phosphate buffer) and at 37 °C. Threose is produced in measurable quantities from L-ascorbate only in the presence of oxygen. Compounds 2 and 3 both give rise to threose in both the presence and absence of oxygen. Compound 3 gives threose at a faster rate and in higher amounts than 1 or 2, suggesting that it is the primary source of threose in this reaction. Incubations of dehydro-L-ascorbate with N^a -acetyl-L-lysine in the presence of cyanoborohydride gave N^a -acetyl-N^e -(1-deoxy-L-threitol-l-yl)-L-lysine which was chemically synthesized (from threose and N'-acetyl-L-lysine) and unequivocally characterized. The data suggest that the Maillard reaction observed when L-ascorbic acid is incubated with protein may well arise as a result of interactions of L-threose with amino groups, and that the function of oxygen in the reaction is to convert 1 into the more reactive 2. and 3. Oxygen does not appear to be necessary for the further degradation of 2 or 3.     

Synthesis of N-heterocyclic ligands for use in affinity and mixed mode chromatography

A set of heterocyclic ligands have been synthesised for use in the preparation of mixed mode affinity chromatographic adsorbents for application in the purification of proteins, including antibodies. The ligand structures were designed to consist of a pyridinyl or related aza-heterocyclic nucleus bearing a pendant arm containing either an alkylamine, alkylthiol or hydroxyalkyl nucleophilic group to allow their facile immobilisation onto an activated support matrix. Ligand diversity was achieved by altering the length of the alkyl chain between the heterocyclic nucleus and nucleophilic group, varying the position of alkyl chain attachment to the heterocycle, and incorporating extra substituents into the pyridinyl or related aza-heterocyclic ring. This diversity in ligand structure was intended to enable key structural features of the ligand, required for efficient protein binding, to be determined. In contrast to the previously used multi-step procedures for the preparation of analogous substituted pyridine or aza-heterocyclic compounds, the synthesis routes for the ligands described here have generally utilized very mild, one-step reactions with readily available heterocyclic precursors.     

Zone trapping/merging zones in flow analysis: a novel approach for rapid assays involving relatively slow chemical reactions

A novel strategy for accomplishing zone trapping in flow analysis is proposed. The sample and the reagent solutions are simultaneously inserted into convergent carrier streams and the established zones merge together before reaching the detector, where the most concentrated portion of the entire sample zone is trapped. The main characteristics, potentialities and limitations of the strategy were critically evaluated in relation to an analogous flow system with zone stopping. When applied to the spectrophotometric determination of nitrite in river waters, the main figures of merit were maintained, exception made for the sampling frequency which was calculated as 189 h⁻¹, about 32% higher relatively to the analogous system with zone stopping. The sample inserted volume can be increased up to 1.0 mL without affecting sampling frequency and no problems with pump heating or malfunctions were noted after 8-h operation of the system. In contrast to zone stopping, only a small portion of the sample zone is halted with zone trapping, leading to these beneficial effects.     

Performance of a Halo Ion Trap Mass Analyzer with Exit Slits for Axial Ejection

The halo ion trap (IT) was modified to allow for axial ion ejection through slits machined in the ceramic electrode plates rather than ejecting ions radially to a center hole in the plates. This was done to preserve a more uniform electric field for ion analysis. An in-depth evaluation of the higher-order electric field components in the trap was also performed to improve resolution. The linear, cubic and quintic (5th order) electric field components for each electrode ring inside the IT were calculated using SIMION (SIMION version 8, Scientific Instrument Services, Ringoes, NJ, USA) simulations. The preferred electric fields with higher-order components were implemented experimentally by first calculating the potential on each electrode ring of the halo IT and then soldering appropriate capacitors between rings without changing the original trapping plate design. The performance of the halo IT was evaluated for 1% to 7% cubic electric field (A ₄/A ₂) component. A best resolution of 280 (m/Δm) for the 51-Da fragment ion of benzene was observed with 5% cubic electric field component. Confirming results were obtained using toluene, dichloromethane, and heptane as test analytes.