Highly stereoselective synthesis of vicinal diols by stannous chloride-mediated addition of hydroxyallylic stannanes to aldehydes

A new protocol for the synthesis of vicinal diols was accomplished by the reaction of unprotected α-hydroxymethylmetals, as hydroxymethyl anion equivalents, with aldehydes. The treatment of hydroxyallylic stannanes, which were prepared from α,β-unsaturated aldehydes and Bu₃SnLi in situ, with various aldehydes gave but-3-en-1,2-diols in the presence of SnCl₂. The stereochemistry of the diol and olefin moieties demonstrated syn- and E-selectivities, respectively. We propose the following reaction mechanism; transmetalation of a hydroxyallylic stannane with SnCl₂ gives a rearranged allylic tin(II) species that undergoes aldehyde addition via a cyclic transition state. The strict interaction between the unprotected hydroxy moiety and the tin(II) center accounts for the selectivity.     

Synthesis, crystal growth and characterization of a metal-organic nonlinear optical tri-allylthiourea mercury chloride single crystals

Metal-organic nonlinear optical material tri-allylthiourea mercury chloride single crystal was grown using low temperature solution growth method. The growth parameters such as pH and temperature were optimized for getting colorless single crystals. The X-ray rocking curve measurement shows that the grown crystal was free from internal structural grain boundaries. The structural, spectral, optical and thermal properties of the grown specimen were studied using various characterization techniques. The defects present in the grown crystals were studied with chemical etching analysis. The results show that the grown crystals are suitable candidates for nonlinear optical applications.     

Growth and characterization of an organic NLO material ammonium malate

Second harmonic generation organic material, ammonium malate (AM), has been synthesized and grown as quality single crystals by the slow evaporation technique. As-grown crystals were characterized by X-ray powder diffraction (XRPD) and Fourier transforms – nuclear magnetic resonance (FT-NMR). The optical band gap was estimated for AM crystal using UV–vis study. Measuring transmittance of AM permitted the calculation of the refractive index n; the extinction coefficient K and both the real ε_r and imaginary ε_i components of the dielectric permittivity as functions of photon energy. Density functional theory at the HF/3-21 G (d, p) level has been used to calculate the first-order hyperpolarizability of AM. The second harmonic conversion efficiency of AM was determined using Kurtz powder technique; it was observed to be greater than that of KDP. The mechanical anisotropy property of the grown crystals was studied using Vickers microhardness tester at different planes. The photoluminescence study is also analyzed. The growth features were analyzed by wet chemical etching studies. The factor group analysis was carried out for AM which predicts that there are 132 vibrational optical modes.     

The role of potassium tellurite as tellurium source in mercaptoacetic acid-capped CdTe nanoparticles

Water-soluble CdTe nanoparticles were synthesized in aqueous solution with the assistance of mercaptoacetic acid (MAA) molecules by wet chemical route and microwave-assisted method. A series of cadmium telluride (CdTe) nanoparticles capped with a bifunctional molecule, which contains both thiols and carboxylic acid groups were prepared using different pH values and using potassium tellurite as tellurium source. Thiol-capped nanocrystals of CdTe can be isolated as powders using 2-propanol. The synthesized thiol-capped CdTe were characterized with EDAX, TEM, Raman, FT–IR, UV–Visible absorption, fluorescence spectroscopy and X-ray diffraction (XRD) for the particle size determination and to understand their optical properties. The particles crystallize predominantly in cubic phase with narrow photoluminescence emission. Potassium tellurite as source of tellurium improves the photoluminescence efficiency and also avoids the cumbersome processes associated with H₂Te or NaHTe sources.     

Numerical predictions of noise due to subsonic jets from nozzles with and without chevrons

Numerical simulations of round, compressible, turbulent jets using the Shear Stress Transport (SST k-ω) model have been carried out. The three-dimensional calculations have been done on a tetrahedral mesh with 0.9 million cells. Two jets, one cold and hot, have been simulated. The Mach number for both the cases is 0.75. Overall sound pressure levels (SPL) at far-field observer locations have been calculated using Ffowcs Williams-Hawkings equation. The numerical predictions have been compared with experimental results available in the literature. Axial and radial variation of the mean axial velocity, axial variation of , radial variation of and overall SPL levels are compared. The potential core length is predicted well, but the predicted centerline velocity decay is faster than the measured value. The URANS calculations are not able to predict the absolute values for the overall SPL, but predict the trends reasonably well. The calculations predict the trends and absolute values of the variations of the spectral amplitude well for the aft receivers, but not for the forward receivers. Effect of chevrons on the noise from the jet is also investigated for cold and hot jets. In each case, two chevron taper angles, namely, 0° and 5° are considered. The latter nozzle produces the most significant modification to the baseline spectra and is less effective at high frequencies in abating the noise. The present calculations predict a reduction in the overall SPL for the chevron nozzle with 0° taper angle and a slight increase for chevron nozzle with 5° taper angle, for both cold and hot jets.     

Thermal and optical properties of Er-doped oxyfluorotellurite glasses

Er³⁺-doped oxyfluorotellurite glasses with four different concentrations of Er³⁺ ions have been prepared and investigated their thermal, optical absorption, excitation and luminescence properties. From the DSC spectra, glass transition and onset of crystallization temperatures have been found. Judd-Ofelt intensity parameters have been derived from the absorption spectrum and are in turn used to calculate radiative properties for the important luminescent levels of Er³⁺ ions. The calculated radiative properties are comparable to experimental values. The glasses show intense green and weak red emission under normal excitation with 451 nm. The decrease in emission intensities and lifetimes of the ⁴S_3/2 level with concentration of Er³⁺ ions has been explained as due to energy transfer processes between Er³⁺ ions. The stimulated emission cross-sections and quantum efficiencies of the green and infrared emissions have been determined. The results indicate that the glasses may be suitable for use as a laser medium in making solid-state green laser by normal pumping route and as laser medium and optical amplifier in the 1.5 μm region.     

Optical absorption, fluorescence and decay properties of Pr-doped PbO-H3BO3-TiO2-AlF3 glasses

Spectroscopic and laser properties of PbO-H₃BO₃-TiO₂-AlF₃ glasses doped with 0.1, 0.5, 1.0 and 2.0 mol% of Pr₆O₁₁ have been studied. Optical absorption spectra were recorded in the UV-vis-NIR regions and the observed absorption bands were assigned to different electronic transitions from ³H₄ ground state of 4f² configuration. The three phenomenological Judd-Ofelt (J-O) parameters Ω_t (t=2, 4, 6) were determined from the measured oscillator strengths by including as well as excluding the ³H₄→³P₂ hypersensitive transition in J-O analysis. The emission characteristics such as stimulated emission cross-sections (σ_e), measured branching ratios (β_m), measured lifetimes (τ_m), quantum efficiencies (η) and gain parameters (σ_e×τ_m) have been evaluated for the principal intermanifold transitions of Pr³⁺ from the ³P₀ and ¹D₂ states to the lower lying manifolds in the visible region. From the emission and decay measurements, the effect of Pr³⁺ ion concentration on the quenching of the ¹D₂ measured lifetimes has been discussed.     

基于氨基酸的Cu(Ⅱ)-色氨酸MOF催化剂上环氧化物与CO_2环加成反应（英文）

由天然的/生物单元(氨基酸)构成的金属有机框架材料(MOFs)具有自然属性和丰富的酸/碱位和官能团,因而可用于CO_2化学中.本文报道了氨基酸系含铜MOF(CuTrp,Trp=L-色氨酸)的催化效率.以甲醇为溶剂,在室温采用直接混合法合成了CuTrp催化剂,该方法具有很高的能量效率.采用X射线衍射、红外光谱、热重分析、电感耦合等离子体发射光谱法、扫描电镜和BET分析等手段对该催化剂进行了表征.采用环氧化物与CO_2环加成制备环状碳酸酯反应评价了CuTrp催化剂活性.结果表明,在无溶剂条件下,CuTrp催化剂可与四丁基溴化铵助催化剂发生协同作用.通过条件实验确定了优化的反应条件,并基于该实验结果和前期的密度泛函理论计算结果提出了反应机理.另外,CuTrp催化剂在水中也表现出令人满意的稳定性,可重复使用三次以上而活性无明显下降.     

Four cocrystals of thymine with phenolic coformers: influence of the coformer on hydrogen bonding

Cocrystals are molecular solids composed of at least two types of neutral chemical species held together by noncovalent forces. Crystallization of thymine [systematic name: 5‐methylpyrimidine‐2,4(1H,3H)‐dione] with four phenolic coformers resulted in cocrystal formation, viz. catechol (benzene‐1,2‐diol) giving thymine–catechol (1/1), C₅H₆N₂O₂·C₆H₆O₂, (I), resorcinol (benzene‐1,3‐diol) giving thymine–resorcinol (2/1), 2C₅H₆N₂O₂·C₆H₆O₂, (II), hydroquinone (benzene‐1,4‐diol) giving thymine–hydroquinone (2/1), 2C₅H₆N₂O₂·C₆H₆O₂, (III), and pyrogallol (benzene‐1,2,3‐triol) giving thymine–pyrogallol (1/2), C₅H₆N₂O₂·2C₆H₆O₃, (IV). The resorcinol molecule in (II) occupies a twofold axis, while the hydroquinone molecule in (III) is situated on a centre of inversion. Thymine–thymine base pairing is common across all four structures, albeit with different patterns. In (I)–(III), the base pair is propagated into an infinite one‐dimensional ribbon, whereas it exists as a discrete dimeric unit in (IV). In (I)–(III), the two donor N atoms and one carbonyl acceptor O atom of thymine are involved in thymine–thymine base pairing and the remaining carbonyl O atom is hydrogen bonded to the coformer. In contrast, in (IV), just one donor N atom and one acceptor O atom are involved in base pairing, and the remaining donor N atom and acceptor O atom of thymine form hydrogen bonds to the coformer molecules. Thus, the utilization of the donor and acceptor atoms of thymine in the hydrogen bonding is influenced by the coformers.     

Structural characterization,photophysical and BSA binding interaction studies of 4,4′-bis(benzimidazolyl)-2,2′-bipyridine

The title compound is synthesized from the precursors 1,2-diaminobenzene and 2,2′-bipyridine-4,4′-dicarboxylic acid (dcbpy) and characterized using ESI-Mass, ¹H NMR, FT-IR and single crystal X-ray analysis. We are the first to report the crystal structure of the 4,4′-bis(benzimidazolyl)-2,2′-bipyridine (bimbpy) ligand. The photophysical properties of the compound in dimethyl sulfoxide and in the aqueous medium are studied. The interaction studies of bimbpy with bovine serum albumin (BSA) were performed with the fluorescence technique and it strongly binds with BSA.