Molecular Basis of the Dynamic Strength of the Sialyl Lewis X—Selectin Interaction

The selectins are Ca²⁺‐dependent cell adhesion molecules that facilitate the initial attachment of leukocytes to the vascular endothelium by binding to a carbohydrate moiety as exemplified by the tetrasaccharide, sialyl Lewis X (sLeX). An important property of the selectin‐sLeX interaction is its ability to withstand the hydrodynamic force of the blood flow. Herein, we used single‐molecule dynamic force spectroscopy (DFS) to identify the molecular determinants within sLeX that give rise to the dynamic properties of the selectin/sLeX interaction. Our atomic force microscopy (AFM) measurements revealed that the unbinding of the selectin/sLeX complexes involves overcoming at least two activation barriers. The inner barrier, which determines the dynamic response of the complex at high forces, is governed by the interaction between the Fuc residue of sLeX and a Ca²⁺ ion chelated to the lectin domain of the selectin molecule, whereas the outer activation barrier can be attributed to interactions involving the sialic acid residue of sLeX. Due to their steep inner activation barriers, the selectin‐sLeX complexes are less sensitive to high pulling forces. Hence, besides its contribution to the bond energy, the Ca²⁺ ion also grants the selectin–sLeX complexes a tensile strength that is crucial for the selectin‐mediated rolling of leukocytes.     

Observation of self-ion-molecule reactions during collisionally activated dissociation in an ion-trap mass spectrometer

This paper describes the formation of protonated molecules ([M + H]+) and adduct ions by self-ion-molecule reactions (SIMR) during collisionally activated decomposition (CAD) of methyne addition ions ([M + CH]+) produced from chemical ionization (CI) or SIMR in both an external and internal source ion-trap mass spectrometer (ITMS). The CAD results for the methyne addition ions of dopamine produced from both SIMR and dimethyl ether CI undertaken in the external and internal source ITMS were compared in order to prove the occurrence of SIMR during CAD processes. Compared with the external source ITMS, the internal source ITMS is much more easily applicable to this type of reaction owing to the large population of neutral analytes present in the trap.     

全内反射荧光成像技术及其在单分子检测中的研究进展

全内反射荧光显微镜技术是当今最灵敏的生物成像和检测方法之一,可以直接探测单个荧光分子。这种方法已成功地用于生命科学、化学、物理学等研究领域,获得了常规方法无法得到的重要信息。本文介绍了全内反射荧光显微镜的工作原理和实验技术,总结了近年来这种单分子检测方法在生命科学、化学等领域的重要应用,并对其发展前景进行了展望。     

Photophysical aspects of single-molecule detection by two-photon excitation with consideration of sequential pulsed illumination.

An important goal in single molecule fluorescence correlation spectroscopy is the theoretical simulation of the fluorescence signal stemming from individual molecules and its autocorrelation function. The simulation approaches developed up to now are based exclusively on continuous-wave (cw) illumination and consequently on cw-excitation. However, this approximation is no longer valid in the case of two-photon excitation, for which pulsed illumination is usually employed. We present a novel theoretical model for the simulation of the fluorescence signal of single molecules and its autocorrelation function with consideration of the time dependence of the excitation flux and thus of all illumination-dependent photoprocesses: two-photon excitation, induced emission and photobleaching. Further important characteristics of our approach are the consideration of the dependence of the photobleaching rate on illumination and the low intersystem-crossing rates of the studied coumarins. Moreover, using our approach, we can predict quantitatively the effect of the laser pulse width on the fluorescence signal of a molecule, that is, the contributions of the photobleaching and saturation effects, and thus we can calculate the optimal laser pulse width. The theoretical autocorrelation functions were fitted to the experimental data, and we could ascertain a good agreement between the resulting and the expected parameters. The most important parameter is the photobleaching constant sigma, the cross section of the transition Sn<--S1, which characterises the photostability of the molecules independent of the experimental conditions. Its value is 1.7 x 10(-23) cm2 for coumarin 153 and 5 x 10(-23) cm2 for coumarin 314.     

有机分子与聚电解质静电吸附成膜特性研究

选取多种有机分子及聚电解质，采用静电吸附自组装法制备了聚电解质，聚电解质、聚电解质，有机分子、有机分子，有机分子的复合薄膜，讨论了这些体系的静电吸附成膜特性及其成膜机理．     

Synthesis, Crystal Structure and Inhibition of the K562 Cell Proliferation of N＇-Tertbutylaminocarbonyl-N-2-chlorophenoxyacetylthiourea

The title compound N'-tert-butylaminocarbonyl-N-2-chlorophenoxyacetylthiou- rea has been synthesized for the first time. Complete assignments were achieved by IR, 1H NHR and single-crystal X-ray diffraction analyses. The inhibitory rate of the cellular growth of K562 cells (chronic myeloid 1eukemic cells) was measured using MTT [3-(4,5-dimethylthiazo-2-y1)-2,5-di- phenyltetra-zolium bromide] assay. The cell apoptosis was assessed by agarose gel electrophoresis to find that the title compound has antiproliferation and apoptosis inducing effects on K562 cells. In order to investigate the relationship between structure and activity of the target compound, we report its crystal structure and biological behavior in the present paper. Crystallographic data: C14H18- ClN3O3S, Mr = 343.82, orthorhombic, space group Pnma, a = 19.786(6), b = 6.789(2), c = 12.938(4) , V = 1738.0(9) 3, Z = 4, Dc = 1.314 g/cm3, F(000) = 720, μ(MoKα) = 0.354 mm-1, R = 0.0378 and wR = 0.0941. The molecule is a planar structure.     

水分子团簇分子力场方法的比较研究

采用传统水分子力场模型(SPC, TIPnP(n=3-5))和极化模型(POL3, AMOEBA, SPC-FQ, TIP4P-FQ)对水分子二聚体团簇性质进行了比较和研究. 以从头计算和实验数据为依据, 分析水分子在外场作用下体系的静电极化, 电荷转移和分子结构变化. 通过水分子二聚体结合能和各分解能量项评价极化静电势能在双分子结合能中的地位和作用, 以及各水分子力场的适用性. 通过水分子团簇多体相互作用能的计算,展示不同极化水分子力场定量计算极化能量的实际能力. 通过对力场模型结果的对比和分析, 为进一步发展极化力场模型, 并应用到其他体系提供借鉴和依据.     

过渡金属配合物催化剂及其分子设计构思的发展与相互作用

讨论了某些不对称合成和α－烯烃定向配位聚合及α－烯烃氢甲酰化的过渡金属配合物向络合催化剂的发展与催化剂分子设计构思的发展及相互促进作用，并藉以说明过渡金属配合物定向络合物催化剂的分子设计已具备向计算机辅助设计发展的科学基础。     

The crystallographic structure of the natural air-hydrate in Greenland dye-3 deep ice core

We have carried out X-ray diffraction studies on single crystals of natural air-hydrate in deep ice cores recovered at Dye-3 Greenland. Integrated intensities for 470 diffracting planes were measured by an automated four-circle diffractometer. The space group determined is cubicFd3m and the lattice constant is 17.21(3) Å. These results indicate that the crystallographic structure is the Stackelberg's structure II, in contrast to the previously anticipated structure. This finding agrees with the recent results on the synthetic air-hydrate by Davidsonet al. It was also found by difference Fourier synthesis for guest molecules that electron density in a 16-hedral cage has multiple maxima displaced from the center of the cage while that in the 12-hedron was approximately spherical.Dedicated to Dr D. W. Davidson in honor of his great contributions to the sciences of inclusion phenomena.     

Accurate electrical and spectroscopic properties ofX 1Σ+ BeO from coupled-cluster methods

Summary This paper reports a series of coupled-cluster (CC) calculations through CCSDT on the theoretically challenging ground state of the BeO molecule. Along with CC methods, quadratic configuration interaction (QCI) approximations to CC theory have been used (QCISD and QCISD(T)), which show several dramatic failings. Equilibrium electrical properties (, _xx , and _zz ) and basic spectroscopic properties (r _e, _e,D _e, and infrared intensity (I)) have been computed. Basis set and electron correlation effects are analyzed in order to arrive at accurate values of the dipole moment and polarizability, which are not known experimentally. For the dipole moment, we obtain a value of 6.25 D, with an uncertainty of about 0.1 D. For _xx and _zz , we suggest respective values of 32 and 36 atomic units (a.u.) and error bars of about 1 and 2 a.u. With extended basis sets, the spectroscopic propertiesr _e, _e, andD _e are reproduced to high accuracy, which is the first time this has been achieved for this species byab initio methods. At the highest calculation levels,I is predicted to be very small. AlthoughI has not been measured, some support for this prediction comes from a recent infrared study of BeO-rare gas complexes. The QCI methods are shown to be much more sensitive to basis set, and even with large basis sets yield values of _zz andI which differ from CC results by an order of magnitude and three orders of magnitude, respectively. These differences doubtless arise from the importance of single excitations (T ₁) for this molecule, as several terms involvingT ₁ are neglected in the QCISD approximation compared with CCSD. We also report CC calculations with Brueckner orbitals, which yield results similar to those obtained with restricted Hartree-Fock orbitals.