Xinxin Hu

Thermal and mechanical properties of BaWO4 crystal

A large single crystal of barium tungstate (BaWO4) with dimensions of 22-mmdiameter×80-mm length was grown by the Czochralski method using an iridium crucible. The melting point, molar enthalpy of fusion, and molar entropy of fusion of the crystal were determined to be 1775.10 K, 96913.80Jmol−1, and 54.60JK−1mol−1, respectively. The average linear thermal-expansion coefficients are αa=10.9526×10−6∕K, αb=10.8069×10−6∕K, and αc=35.1063×10−6∕K in the temperature range from 303.15 to 1423.15 K along the three respective crystallographic axes. The density of the crystal follows an almost linear decrease from 6.393×103 to 6.000×103kgm−3 when the temperature is increased from 303.15 to 1423.15 K. The measured specific heat are 115.56–130.96JK−1mol−1 in the temperature range of 323.15–1173.15 K. The thermal diffusion coefficient of the crystal was measured in the temperature range of 297.15–563.15 K. The calculated thermal conductivity is 2.256Wm−1K−1 along the [001] direction and 2.324Wm−1K−1 along the [100] dir...

Spectroscopic investigations on the interactions between isopropanol and trypsin at molecular level.

The toxicity of hydroxyl group of isopropanol to trypsin in aqueous solution was investigated by techniques including UV-visible absorption spectroscopy, fluorescence spectroscopy, circular dichroism (CD) spectroscopy, enzyme activity assay and molecular docking technology. The results of UV-visible absorption spectroscopy and CD spectra indicate that isopropanol could change the secondary structure of trypsin by increasing the content of α-helix and decreasing the content of β-sheet. The tertiary structure of trypsin was also changed owing to the loss of environmental asymmetry of amino acid residues. Isopropanol bound into a hydrophobic cavity on the surface of trypsin by a hydrogen bond located between the hydrogen atom on the hydroxyl of isopropanol and the oxygen atoms on SER 214 and hydrophobic interaction, as the molecular docking results showed. In addition, isopropanol could affect the function of trypsin by increasing its catalytic activity.

Optical-transition properties of the Nd3+ ion in Gd0.8La0.2VO4 crystal

Nd:Gd0.8La0.2VO4 has been investigated as a Nd-doped laser crystal belonging to the zircon structural family. The optical absorption and emission properties have been characterized for the Nd3+ ion in Nd:Gd0.8La0.2VO4 crystal. It results in a good fit when the Judd–Ofelt theory of parity-forbidden electric-dipole transitions of rare earth ions on noncentrosymmetric sites is applied to the crystal. Based on the Judd–Ofelt theory, the following spectral parameters have been obtained: the phenomenological parameters Ωt (t=2, 4, and 6), the radiative lifetime, the fluorescence branching ratios and the quantum efficiency. The stimulated emission cross section σe for the 1.06 μm transition of Nd3+ in the crystal has been determined from fluorescence measurements. In comparison with those of other laser crystals, these results indicated that Nd:Gd0.8La0.2VO4 is a promising efficient laser material.

Dependence of photochromic damage on polarization in KTiOPO4 crystals

Studies of photochromic damage induced in KTiOPO4 single crystals by 514.5 nm laser irradiation is reported. A dependence of photochromic damage on polarization was observed. Along the same propagation direction (y ¼ 901; j ¼ 23:31), the gray-track susceptibility for 8z polarization irradiation is one order magnitude lower than that for >z polarization irradiation for KTP crystal. The results clearly show that in KTiOPO4, a correlation exists between the gray-track susceptibility and the ionic electrical conductivity. Due to a high ionic electrical conductivity along the polar z-axis, the optical absorption centers will be annihilated with 8z polarization irradiation as soon as they are produced. This results in a lower gray-track susceptibility for 8z polarization irradiation. r 2002 Elsevier Science B.V. All rights reserved.

Dissection of the binding of hydrogen peroxide to trypsin using spectroscopic methods and molecular modeling.

Studies on the effects of environmental pollutants to protein in vitro has become a global attention. Hydrogen peroxide (H2O2) is used as an effective food preservative and bleacher in industrial production. The toxicity of H2O2 to trypsin was investigated by multiple spectroscopic techniques and the molecular docking method at the molecular level. The intrinsic fluorescence of trypsin was proved to be quenched in a static process based on the results of fluorescence lifetime experiment. Hydrogen bonds interaction and van der Waals forces were the main force to generate the trypsin-H2O2 complex on account of the negative ΔH(0) and ΔS(0). The binding of H2O2 changed the conformational structures and internal microenvironment of trypsin illustrated by UV-vis absorption, fluorescence, synchronous fluorescence, three-dimensional (3D) fluorescence and circular dichroism (CD) results. However, the binding site was far away from the active site of trypsin and the trypsin activity was only slightly affected by H2O2, which was further explained by molecular docking investigations.

Effects of γ-Irradiation on the Molecular Structures and Functions of Human Serum Albumin

In this paper, we use spectroscopic methods (fluorescence spectroscopy, UV absorption spectroscopy, and circular dichroism (CD) spectroscopy) to elucidate the effects of reactive oxygen species generated by γ‐irradiation on the molecular properties of human serum albumin (HSA). The results of fluorescence spectroscopy indicated that oxidation by γ‐irradiation can lead to conformational changes of HSA. Data of CD spectra suggested that with the increase of radiation dose the percentage of α‐helix in HSA has decreased. The determination of protein hydrophobicity showed that the effective hydrophobicity of HSA decreased up to 62% compared to the native HSA solution due to the exposure to the γ‐irradiation. Furthermore, small changes in the esterase‐like activity of HSA were introduced because of oxidation. The content of bityrosine increased markedly, suggesting that the oxidized HSA was aggregated. Moreover, there was no obvious change in the molecular properties of HSA with low γ‐irradiation dose. Changes happened when the irradiation dose exceeded 200 Gy.

Comparative Studies on the Discrepant Fragmentation Mechanisms of the Gly-Asp-Gly-Arg and Arg-Gly-Asp-Gly: Evidence for the Mobile Proton Model

The fragmentation mechanisms of singly protonated Gly-Asp-Gly-Arg (GDGR) and Arg-Gly-Asp-Gly (RGDG) were investigated by mass spectrometry and theoretical methods. Both protonated molecules are fragmented mainly at the Asp–Gly amide bond C-terminal to Asp, as supported by quantum chemical calculations. Charge distributions of C and N atoms (QC + QN) on the amide bonds were collected when the ionizing proton was fixed at different nitrogen atoms along the backbone for each peptide. Compared with the neutral molecules, the total charges of C and N atoms (QC + QN) for the singly charged peptides tended to be negative when the proton was located at the backbone nitrogen atoms. A relatively larger value of QC + QN corresponds to a higher trend of fragmentation, which is consistent with the experimental relative abundances data that the predominant ions are y2 for [GDGR + H]+ and b3 for [RGDG + H]+. Also, the anhydride mechanism driven by the C-terminal COOH for [RGDG + H]+ was explored by a quantum–mechanical/molecular–mechanical method. Calculations indicate that the protonated peptide can be cleaved through an unusual charge-directed pathway by forming a salt bridge at the C-termini. The formation of the anhydride linkage is much more feasible since this process needs very little energy and is exothermic, though the subsequent nucleophilic attack on the Asp carbonyl carbon is more difficult. The combined experimental and theoretical methods substantiate the mobile proton model, which opens a way to analyze quantitatively the discrepant fragmentation of dissociated peptides in peptide/protein identification.