飞秒时间分辨荧光非共线光参量放大光谱技术

时间分辨荧光光谱技术是研究激发态弛豫、能量传递以及电荷转移等光化学过程的重要且直接的工具．飞秒时间分辨荧光非共线光参量放大光谱技术是一种新发展的具有高时间分辨率、宽探测带宽、高增益的时间分辨光谱技术．本文对该技术的基本原理与工作特性、系统配置、荧光收集和会聚、数据采集模式、时问分辨光谱数据处理等进行了系统阐述．最后简单介绍了飞秒时间分辨荧光非共线光参量放大光谱技术在物理、生物和化学领域的3个典型应用,并以此展现该技术的高时间分辨率、宽光谱探测及高增益优势．     

六苄基六氦杂异伍兹烷五种氢解脱苄化合物的合成及工业制备

综述了六苄基六氮杂异伍兹烷（HBIW）五种氢解脱苄化合物的合成条件和工业制备工艺。这五种化合物是：四乙酰基二苄基六氮杂异伍兹烷（TADBIW）、四乙酰基二甲酰基六氮杂异伍兹烷（TADFIW）、四乙酰基六氮杂异伍兹烷（TAIW）、四乙酰基二乙基六氮杂异伍兹烷（TADEIW）和六乙酰基六氮杂异伍兹烷（HAIW）。其中的TADBIW系由HBIW经一次氢解合成，其它四种都系由HBIW经两次氢解合成。HBIW的这五种氢解脱苄化合物均可经硝解合成六硝基六氮杂异伍兹烷（HNIW）。另外，本文总结了HBIW及其五种氢解脱苄产物的红外、核磁和质谱数据及它们的基本性能参数。     

From titanates to TiO2 nanostructures: Controllable synthesis, growth mechanism, and applications

The design and fabrication of nanostructures based on titanium dioxide (TiO 2 ) have attracted much attention because of their low cost, non-toxicity, stability, and potential applications in industry and technology. Recently, one-dimensional (1D) structured titanates have been used as titanium source to prepare TiO 2 nanostructures with various crystalline phases, shapes, sizes, exposed facets, and hierarchical structures. Among the synthetic strategies, hydrothermal method is a facile route to controllable preparation of well-crystalline TiO 2 in one step. Herein, we review our recent progress in transferring 1D titanates into TiO 2 nanostructures through hydrothermal method, including the transformation mechanism and applications.     

The correlation timescale of the X-ray flux during the outbursts of soft X-ray transients

Recent studies of black hole and neutron star low mass X-ray binaries (LMXBs) show a positive correlation between the X-ray flux at which the low/hard(LH)-to-high/soft(HS) state transition occurs and the peak flux of the following HS state. By analyzing the data from the All Sky Monitor (ASM) onboard the Rossi X-ray Timing Explorer (RXTE), we show that the HS state flux after the source reaches its HS flux peak still correlates with the transition flux during soft X-ray transient (SXT) outbursts. By studying large outbursts or flares of GX 339-4, Aql X-1 and 4U 1705-44, we have found that the correlation holds up to 250, 40, and 50 d after the LH-to-HS state transition, respectively. These time scales correspond to the viscous time scale in a standard accretion disk around a stellar mass black hole or a neutron star at a radius of ∼10^4–5 R _g, indicating that the mass accretion rates in the accretion flow either correlate over a large range of radii at a given time or correlate over a long period of time at a given radius. If the accretion geometry is a two-flow geometry composed of a sub-Keplerian inflow or outflow and a disk flow in the LH state, the disk flow with a radius up to ∼10⁵ R _g would have contributed to the nearly instantaneous non-thermal radiation directly or indirectly, and therefore affects the time when the state transition occurs.

     

Power spectra of active galactic nuclei

The power spectral densities (PSDs) for a sample of active galactic nuclei (AGNs) are analyzed in both the frequency domain and the time domain. We find for each object that for broadband noise a character timescale-bifurcation timescale of Fourier and time-domain PSD exists in the 10³–10⁶ s range, below which the time-domain power spectrum is systematically higher than the corresponding Fourier spectrum. The relationship between bifurcation timescale, AGN mass and luminosity is studied. Compared with the fact that similar phenomena have been found for Galactic black hole candidates (GBHs) with bifurcation timescale ∼0.1 s but not for accreting neutron stars, our finding indicates that AGNs and GBHs have common intrinsic nature in rapid X-ray variability with a character time parameter scaled with their masses Supported by the Special Funds for Major State Basic Research Projects (Grant No. 2009CB824800) and the National Natural Science Foundation of China (Grant No. 10533020)     

Theoretical studies of the proton transfer behaviors in molecular complexes analogous to catalytic triad of serine protease: Toward understanding the existence and significance of the low-barrier hydrogen-bond in enzymatic catalysis

A representative acetate-(5-methylimidazole)-methanol system has been employed as a model of catalytic triad in serine protease to validate the formation processes of low-barrier H-bonds (LBHB) at the B3LYP/6-311++G** level of theory, and variable H-bonding characters from conventional ones to LBHBs have been represented along with the proceedings of proton transfer. Solvent effect is an important factor in modulation of the existence of an LBHB, where an LBHB (or a conventional H-bond) in the gas phase can be changed into a non-LBHB (an LBHB) upon solvation. The origin of the additional stabilization energy arising from the LBHB may be attributed to the H-bonding energy difference before and after proton transfer because the shared proton can freely move between the proton donor and proton acceptor. Most importantly, the order of magnitude of the stabilization energy depends on the studied systems. Furthermore, the nonexistence of LBHBs in the catalytic triad of serine proteases has been verified in a more sophisticated model treated using the ONIOM method. As a result, only the single proton transfer mechanism in the catalytic triad has been confirmed and the origin of the powerful catalytic efficiency of serine proteases should be attributed to other factors rather than the LBHB. Supported by the National Natural Science Foundation of China (Grant Nos. 20633060 & 20573063), the Natural Science Foundation of Shandong Province (Grant No. Y2007B23), the Scientific Research Foundation of Qufu Normal University (Grant Nos. Bsqd2007003 and Bsqd2007008), and the State Key Laboratory of Physical Chemistry of Solid Surfaces (Xiamen University)