Screening of octanol-water partition coefficients for pharmaceuticals by pressure-assisted microemulsion electrokinetic chromatography

A rapid screening assay for the determination of octanol-water partition coefficients (log P(OW)) of pharmaceuticals was developed by using pressure-assisted microemulsion electrokinetic chromatography (MEEKC). The microemulsion system contains 50 mM sodium dodecyl sulfate, 0.87 M l-butanol, 82 mM heptane, and 50 mM borate-phosphate (2:3) at pH 10. Ten standard compounds with known log P(OW) values from -0.26 to 4.88 were used for constructing the calibration curve of log P(OW) against the MEEKC retention factor, log k. The log P(OW) values of the compounds were calculated based on the log k values measured by MEEKC and the slope and intercept of the calibration curve. For 13 literature and 32 Roche compounds, about 90% of the log P(OW) values measured by MEEKC are within 0.5 log units of the values from the literature and potentiometric titration. The throughput is about 2 samples/h using +20 kV voltage plus 5 mbar air pressure for separation. This MEEKC method is applicable for log P(OW) screening of weakly basic, weakly acidic, and neutral pharmaceuticals with log P(OW) = 0-5 and pKa < or = 10.     

Yb~(3+)∶KY(WO_4)_2晶体生长与光谱性能

采用泡生法生长Yb∶KYW晶体,通过XRD分析确认所生长的晶体为-βYb∶KYW。TG-DTA测量结果表明,晶体的熔点为1045℃,相变温度为1010℃。测得晶体红外光谱和拉曼光谱,对其峰值所属振动的归属进行了指认,并测量了晶体的吸收光谱和荧光光谱。结果表明,Yb∶KYW晶体在940,980 nm附近有很强的吸收峰,主峰980 nm处的吸收截面积为1.34×10-19cm2;该晶体在990,1010,1030 nm附近都有较强的荧光发射峰,其中最强发射峰1030 nm的发射线宽高达16 nm,有望作为可调谐激光器的增益介质。计算得其1030 nm受激发射截面积为3.1×10-20cm2。     

Interfacially Super-Assembled Benzimidazole Derivative-Based Mesoporous Silica Nanoprobe for Sensitive Copper (II) Detection and Biosensing in Living Cells

Mesoporous silica nanoparticles (MSNs) functionalized with benzimidazole-derived fluorescent molecules (DHBM) are fabricated via a feasible interfacial superassembly strategy for the highly sensitive and selective detection of Cu²⁺. DHBM-MSN exhibits an obvious quenching effect on Cu²⁺ in aqueous solutions, and the detection limit can be as low as 7.69×10⁻⁸ M. The DHBM-MSN solid-state sensor has good recyclability, and the silica framework can simultaneously improve the photostability of DHBM. Two mesoporous silica nanoparticles with different morphologies were specially designed to verify that nanocarriers with different morphologies do not affect the specific detectionability. The detection mechanism of the fluorescent probe was systematically elucidated by combining experimental results and density function theory calculations. Moreover, the detection system was successfully applied to detect Cu²⁺ in bovine serum, juice, and live cells. These results indicate that the DHBM-MSN fluorescent sensor holds great potential in practical and biomedical applications.     

Multi-Stimuli-Induced Mechanical Bending and Reversible Fluorescence Switching in a Single Organic Crystal

Fluorescent single crystals that respond to multiple external stimuli are of great interest in molecular machines, sensors, and displays. The integration of photo- or acid-induced fluorescence enhancement and bending in one organic crystal, however, has not been reported yet. Herein, we report the interesting plastic photomechanical bending and switching on of the fluorescence of an azine crystal in a single-crystal transformation, due to extended π-conjugation and molecular slippage. Moreover, the fluorescent plastic bending driven by multiple volatile acid vapors was firstly observed, and attributed to the synergistic effect of push–pull electronic structure and hydrogen bonding. The single crystal also shows high elasticity under external force. In addition, reversible fluorescence switching can be triggered by grinding and solvent fuming, as well as by the adsorption and desorption of HCl vapor. The integration of plastic, elastic bending and switch-on fluorescence into one single crystal provides a new strategy for next-generation smart materials.     

Solid-state reaction synthesis of boron carbonitride nanotubes

ZnO films were deposited by RF magnetron sputtering at the substrate temperature of 120∼420°C. XRD measurements revealed the improvement of crystalline quality and grain size of the films with substrate temperature. The dielectric function of the films was determined by fitting the experimental transmission spectra with Tauc–Lorentz (TL) model and a single Lorentzian oscillator (SLO) dispersion function in the energy range of 1∼5 eV. The optical properties of the ZnO films strongly depended on the substrate temperature. The optical band gap and the Penn gap of the ZnO films increased with the substrate temperature. The band gap of the ZnO films indicated a direct interband transition between the valence and conduction band, and the change of the in-plane film stress promoted the enhancement of the band gap. These results of the optical properties of the ZnO films might be very meaningful to the application in the window design in solar cells.     

Optimization of VI/II pressure ratio in ZnTe growth on GaAs(0 0 1) by molecular beam epitaxy

ZnTe epilayers were grown on GaAs(0 0 1) substrates by molecular beam epitaxy (MBE) at different VI/II beam equivalent pressure (BEP) ratios (R_VI/II) in a wide range of 0.96-11 with constant Zn flux. Based on in situ reflection high-energy electron diffraction (RHEED) observation, two-dimensional (2D) growth mode can be formed by increasing the R_VI/II to 2.8. The Te/Zn pressure ratios lower than 4.0 correspond to Zn-rich growth state, while the ratios over 6.4 correspond to Te-rich one. The Zn sticking coefficient at various VI/II ratios are derived by the growth rate measurement. The ZnTe epilayer grown at a R_VI/II of 6.4 displays the narrowest full-width at half-maximum (FWHM) of double-crystal X-ray rocking curve (DCXRC) for (0 0 4) reflection. Atomic force microscopy (AFM) characterization shows that the grain size enlarges drastically with the R_VI/II. The surface root-mean-square (RMS) roughness decreases firstly, attains a minimum of 1.14 nm at a R_VI/II of 4.0 and then increases at higher ratios. It is suggested that the most suitable R_VI/II be controlled between 4.0 and 6.4 in order to grow high-quality ZnTe epitaxial thin films.     

Almost periodic solutions for Lotka–Volterra systems with delays

This paper studies a general class of delayed almost periodic Lotka–Volterra system with time-varying delays and distributed delays. By using the definition of almost periodic function, the sufficient conditions for the existence and uniqueness of globally exponentially stable almost periodic solution are obtained. The conditions can be easily reduced to special cases of cooperative systems and competitive systems.     

The degree of rotation independence of conjugation of S-N bonds

The electron delocalization in pi-electron systems is frequently described qualitatively by the concept of conjugation between formal double bonds separated by a formal single bond. In carbon compounds the optimum conjugation usually requires a rather strict, geometrical condition: the exact or near coplanarity of the participating carbon atoms. However, the geometrical conditions are much less strict for third-row atoms if the bonding involves valence-shell d orbitals. In some sulfur compounds, such as N-sulfonylsulfilimines, the conjugation is almost unaffected within large ranges of bond-rotation angles, which amounts to rotation-independent conjugation. On the basis of the indications of earlier, limited studies using only minimal basis set and no geometry optimization, in the more extensive present study Density Functional Theory B3LYP calculations using 6-31G basis set provide more reliable evidence for such flexible conjugation in some sulfur compounds and give an explanation for the experimentally observed interconversion of chiral conformers of N-sulfonylsulfilimines.