The Effects of Charged Amino Acid Side-Chain Length on Diagonal Cross-Strand Interactions between Carboxylate- and Ammonium-Containing Residues in a β-Hairpin

The β-sheet is one of the common protein secondary structures, and the aberrant aggregation of β-sheets is implicated in various neurodegenerative diseases. Cross-strand interactions are an important determinant of β-sheet stability. Accordingly, both diagonal and lateral cross-strand interactions have been studied. Surprisingly, diagonal cross-strand ion-pairing interactions have yet to be investigated. Herein, we present a systematic study on the effects of charged amino acid side-chain length on a diagonal ion-pairing interaction between carboxylate- and ammonium-containing residues in a β-hairpin. To this end, 2D-NMR was used to investigate the conformation of the peptides. The fraction folded population and the folding free energy were derived from the chemical shift data. The fraction folded population for these peptides with potential diagonal ion pairs was mostly lower compared to the corresponding peptide with a potential lateral ion pair. The diagonal ion-pairing interaction energy was derived using double mutant cycle analysis. The Asp2-Dab9 (Asp: one methylene; Dab: two methylenes) interaction was the most stabilizing (−0.79 ± 0.14 kcal/mol), most likely representing an optimal balance between the entropic penalty to enable the ion-pairing interaction and the number of side-chain conformations that can accommodate the interaction. These results should be useful for designing β-sheet containing molecular entities for various applications.     

方波激发非接触式电导检测器信噪比的影响因素研究

研制了用于毛细管电泳的方波激发非接触式电导检测器(CCD)并详细考查了对检测器信噪比影响较大的几个重要因素,包括激发频率和运算放大器、基线分压电路和A/D转换器、数字低通滤波;以及常见缓冲体系2-(N-吗啡啉)-乙磺酸/组氨酸(MES/His)体系中电解质浓度,添加剂十六烷基三甲基溴化铵(CTAB)对金属离子的检出信号的影响。所得的结果对于该类检测器的设计和优化具有参考价值。     

稀土钐离子可见荧光量子产率的精确测试与计算

采用积分球配以CCD光谱测试系统,在蓝色半导体发光二极管激发下,对Sm3 掺杂的低声子能量、高折射率铋碲酸盐玻璃的荧光光谱进行测试。实现了荧光发射特性绝对评价为目的的绝对光谱功率分布测定,为发光与激光材料荧光发射特性的精确测量与表征提供了一种准确方法。荧光测试系统由直径为25.4cm的积分球配以CCD探测器组成,通过标准卤素灯定标,辅助卤素灯校正积分球内环境变化,解析出样品的绝对光谱功率分布,并进一步计算出光量子数分布,求得荧光量子产率等荧光特征参量。测试与计算结果表明,对应可见区Sm3 四个特征发射峰,总荧光量子产率为7.55%。     

膜载体酶标记dip-stick快速检测西维因的痕量残留

利用直接竞争酶联免疫吸附分析技术研发了一种快速、灵敏的膜载体酶标记dip-stick农残西维因检测方法。该方法以带正电尼龙膜(Millipore)为固相载体,将西维因抗体包被于膜上,包被有抗体的膜插入含有西维因和西维因酶标抗原的混合液中竞争反应10 min后直接目视判断分析结果。该方法的整个检测过程只需15 min,对西维因的检出限可达到10μg.L-1,且稳定性较好。通过与高效液相色谱法(HPLC)比较,验证了该检测方法的有效性,可作为品质控制和快速定性检测的一种有效工具。     

Eu3+掺杂硼酸盐玻璃的光谱性质研究

测试了不同浓度掺杂下Eu^3＋离子在硼酸盐玻璃的吸收光谱、激发光谱与发射光谱,根据荧光光谱计算了各样品的强度参数力2与／24,分析了Eu^3＋离子掺杂浓度对其发光强度的影响．研究结果表明：在Eu^3＋离子高掺杂浓度时,会发生浓度猝灭效应,但由于Eu^3＋激活离子之间能量传递几率很小,使得Eu^3＋离子猝灭浓度较高。     

Tropaeolin OO as a Chemical Sensor for a Trace Amount of Pd(II) Ions Determination

The selective determination of metals in waste solutions is a very important aspect of the industry and environmental protection. Knowledge of the contents and composition of the waste can contribute to design an efficient process separation and recovery of valuable metals. The problematic issue is primarily the correct determination of metals with similar properties such as palladium and platinum. Thus this paper focuses on the development of a selective method that enables Pd(II) determination in the presence of Pt(IV) ions using the azo-dye tropaeolin OO (TR). For this purpose, the process of the metalorganic complex formation and Pd(II) ions determination were studied by using UV–Vis spectrophotometry under different conditions: solvents (water and B-R buffer), pH (2.09–6.09), temperature (20–60 °C), anions and cations concentrations. The formed metalorganic complex between Pd and tropaeolin OO allows for distinguishing Pd(II) ions from both platinum complexes, i.e. Pt(II), Pt(IV). Moreover, the proposed method can be applied to solutions containing both chloride and chlorate ions. The obtained characteristic spectrum with two maxima allows the determination of palladium even in the presence of other cations (Na, K, Mg, Zn, Co, Ni, Al) and changed concentrations of Pt(IV) ions. Furthermore, the developed spectrophotometric method for the Pd(II) ions determination using tropaeolin OO is characterized by high selectivity towards palladium ions.     

荧光光谱法研究锌(Ⅱ)存在下诺氟沙星与牛血清白蛋白的结合作用

在模拟生理条件下,用荧光光谱法研究了诺氟沙星对牛血清白蛋白以及锌(Ⅱ)对诺氟沙星和牛血清白蛋白荧光光谱特性的影响。实验结果表明,诺氟沙星和锌(Ⅱ)都可以使牛血清白蛋白的荧光强度发生猝灭。根据荧光猝灭双倒数图计算诺氟沙星和牛血清白蛋白之间的结合常数为6.80×105,结合位点数为1.21。由此可见,诺氟沙星和牛血清白蛋白之间有很强的结合作用,这为诺氟沙星在体内被蛋白质储存和转运提供了条件。并且在锌(Ⅱ)存在下,诺氟沙星与牛血清白蛋白的结合作用有所增强。荧光猝灭双倒数图计算的结果表明,诺氟沙星和牛血清白蛋白之间的结合常数和结合位点数均随锌(Ⅱ)浓度的增大而增大。通过对锌(Ⅱ)、诺氟沙星和牛血清白蛋白的结合反应的研究,进一步探讨了诺氟沙星、锌(Ⅱ)在生物体内与蛋白质相互作用的机理。     

Charge state effect on the K-shell ionization of iron by xenon ions near the Bohr velocity

Fe K-shell ionization cross sections induced by 2.4–6.0 MeV Xe20+are measured and compared with different binaryencounter-approximation(BEA)models.The results indicate that the BEA model corrected both by the Coulomb repulsion and by the effective nuclear charge(Zeff)agrees well with the experimental data.Comparison of Fe K-shell X-ray emission induced by 5 MeV xenon ions with different initial charge states(20+,22+,26+,30+)verifies the applicability of the effective nuclear charge(Zeff)correction for the BEA model.It is found that Zeffcorrection is reasonable to describe direct ionization induced by xenon ions with no initial M-shell vacancies.However,when the M shell is opened,the Zeffcorrected BEA model is unable to explain the inner-shell ionization,and the electron transfer by molecular-orbital promotion should be considered.     

Copper (50 MeV) and Oxygen (84 MeV) Ion Irradiation Probed Thermal,Structural and Optical Behavior of Polyethylene Terephthalate

Polyethylene terephthalate (PET) films of 50?μm thickness were exposed to swift-heavy 50?MeV copper and 84?MeV oxygen ions, with fluence varying from 1?×?10¹¹ to 1?×?10¹³ ions cm^?2. Differential scanning calorimetry (DSC), X-ray diffraction (XRD) and Fourier-transform infrared (FTIR) and UV-visible spectroscopic techniques were used to characterize the irradiated samples. The XRD and DSC analysis indicated the loss of crystallinity during/after the irradiation. The FTIR spectra revealed the formation of alkyne end groups, C═C groups and structural deformation with increase of ion fluence. Considerable reduction in the value of the optical bandgap was inferred from the study of the UV-visible absorption curves.     

电磁场中带电粒子在非对易相空间的能级

非对易空间效应是出现在弦的尺度下的一种物理效应。 首先扼要介绍了非对易相空间中的量子力学代数、 Moyal Weyl乘法和广义Bopp变换, 然后讨论了电磁场中带电粒子的Hamiltonian算符, 最后给出了其在非对易相空间中的能级情况。