SYNTHESIS AND PHASE-BEHAVIOR STUDIES OF 2 NEW CHIRAL LIQUID-CRYSTALS OF SCHIFF-BASE - THE INFLUENCE OF INTRAMOLECULAR HYDROGEN-BOND ON THE PHASE-BEHAVIOR

Two new chiral liquid crystals of schiff-base type have been synthesized. This series of compounds contain a-chloro acidic ester chain prepared from commercially available L-valine. Both of the compounds exhibit tilted smectic phases; their phase transitions were studied using DSC and polarized optical microscopy; the influence of intramolecular hydrogen bonds on the phase behavior was studied as well.

SYNTHESIS OF 2 NEW HYDROGEN-BOND INDUCED LIQUID-CRYSTALS

Two new hydrogen bond induced liquid crystals with 4-butoxy benzoic acid as the proton donor and two chiral substituted stilbazole as the proton acceptor have been synthesized. Their liquid crystal transitions were studied by DSC and optical polarized microscope, the IR spectra of the complexes show the existence of the intermolecular hydrogen bond. The results of DSC and optical polarized microscope show that one of them (4BA-VSZ) has a chiral smectic C phase.

BaF2替代BaO对钡镓锗酸盐玻璃光学性质的影响

在摩尔分数组成x(BaO),r(Ga2O),r(GeO2)为0．20，0．15,0．65的玻璃中，分别以摩尔分数0．05，0．10．0．15和0．20的BaF2替代BaO,研究了氟化物对玻璃折射率和光吸收性质的影响。结果表明，在玻璃中加入氟化物．玻璃折射率和色散降低，玻璃的紫外吸收边向短波侧迁移，而红外吸收边无明显变化。不含氟化物的氧化物玻璃中含有大量的OH基．这些OH基在2．24μm、2．97μm和4．23μm附近引起光吸收．在含氟化物的玻璃中，2．24μm的吸收峰消失，而2．97μm和4．23μm附近

Catalytic Activation of Mg-Doped GaN by Hydrogen Desorption Using Different Metal Thin Layers

The annealing of Mg-doped GaN with Pt and Mo layers has been found to effectively improve the hole concentration of such material by more than 2 times as high as those in the same material without metal. Compared with the Ni and Mo catalysts, Pt showed good activation effect for hydrogen desorption and ohmic contact to the Ni/Au electrode. Despite the weak hydrogen desorption, Mo did not diffuse into the GaNepilayer in the annealing process, thus suppressing the carrier compensation phenomenon with respect to Ni and Pt depositions, which resulted in the high activation of Mg acceptors. For the GaN activated with the Ni, Pt, and Mo layers, the blue emission became dominant, followed by a clear peak redshift and the degradation of photoluminescence signal when compared with that of GaN without metal.

Molecular imprinting of nitrophenol and hydroxybenzoic acid isomers: effect of molecular structure and acidity on imprinting

Three nitrophenol isomer-imprinted polymers were prepared under the same conditions using 4-vinylpyridine as a functional monomer. Different recognition capacities for template molecules were observed for the three polymers. Another imprinting system with stronger acidity than nitrophenol isomers, 2-hydroxybenzoic acid (salicylic acid) and 4-hydroxybenzoic acid, was imprinted using 4-vinylpyridine or acrylamide as functional monomer respectively. Both 4-hydroxybenzoic acid-imprinted polymers using the two monomers showed recognition ability for the template molecule. However, when acrylamide was chosen as functional monomer, the salicylic acid-imprinted polymer showed very weak recognition for the template molecule, whereas strong recognition ability of the resultant polymer for salicylic acid was observed with 4-vinylpyridine as functional monomer. It seems that the structure and acidity of template molecules is responsible for the difference in recognition, by influencing the formation and strength of interaction between template molecule and functional monomer during the imprinting process. An understanding of the mechanism of molecular imprinting and molecular recognition of MIPs will help to predict the selectivity of MIPs on the basis of template molecule properties. Copyright (C) 2003 John Wiley Sons, Ltd.

Tetraaqua(1,10-phenanthroline-kappa N-2,N ')cobalt(II) dinitrate: a hydrogen-bonded supramolecular network

The structure of the title compound, [Co(C12H8N2)(H2O)(4)]-(NO3)(2), consists of tetraaqua(1,10- phenanthroline)cobalt(II) cations and nitrate anions. The Co atom is located on a twofold rotation axis and is coordinated by the two N atoms of a 1,10-phenanthroline ligand and four O atoms of water molecules. The cations and anions are linked by hydrogen-bond interactions into a three-dimensional supramolecular network.

New high-dimensional networks based on polyoxometalate and crown ether building blocks

Three novel supramolecular assemblies constructed from polyoxometalate and crown ether building blocks, [(DB18C6)Na(H2O)(1.5)](2)Mo6O19.CH3CN, 1, and [{Na(DB18C6)(H2O)(2)}(3)(H2O)(2)]XMo12O40.6DMF.CH3CN (X = P, 2, and As, 3; DB18C6 = dibenzo-18-crown-6; DMF = N,N-dimethylfomamide), have been synthesized and characterized by elemental analyses, IR, UV-vis, EPR, TG, and single crystal X-ray diffraction. Compound 1 crystallizes in the tetragonal space group P4/mbm with a = 16.9701(6) Angstrom, c = 14.2676(4) Angstrom, and Z = 2. Compound 2 crystallizes in the hexagonal space group P6(3)/m with a = 15,7435(17) Angstrom, c = 30.042(7) Angstrom, gamma = 120degrees, and Z = 2. Compound 3 crystallizes in the hexagonal space group P6(3)/m with a = 15.6882(5) Angstrom, c = 29.9778(18) Angstrom, gamma = 120degrees, and Z = 2. Compound 1 exhibits an unusual three-dimensional network with one-dimensional sandglasslike channels based on the extensive weak forces between the oxygen atoms on the [Mo6O19](2-) polyoxoanions and the CH2 groups of crown ether molecules, Compounds 2 and 3 are isostructural, and both contain a novel semiopen cagelike trimeric cation [{Na(DB18C6)(H2O)(2)}(3)(H2O)(2)](3+). In their packing arrangement, an interesting 2-D "honeycomblike" "host" network is formed, in which the [XMo12O40](3-) (X = As and P) polyoxoanion "guests" resided.

1-(4-fluorophenyl)-2-{4-phenyl-5-[(1H-1,2,4-triazol-1-yl) methyl]-4H-1,2,4-triazol-3-ylsulfanyl}ethanone

The crystal structure of the title compound, C19H15FN6OS, is stabilized by a weak intermolecular C-(HN)-N-... hydrogen-bond interaction.

Forced Dissociation of Selectin-ligand Complexes Using Steered Molecular Dynamics Simulation

Selectin-ligand interactions are crucial to such biological processes as inflammatory cascade or tumor metastasis. How transient formation and dissociation of selectin-ligand bonds in blood flow are coupled to molecular conformation at atomic level, however, has not been well understood. In this study, steered molecular dynamics (SMD) simulations were used to elucidate the intramolecular and intermolecular conformational evolutions involved in forced dissociation of three selectin-ligand systems: the construct consisting of P-selectin lectin (Lec) and epidermal growth factor (EGF)-like domains (P-LE) interacting with synthesized sulfoglycopeptide or SGP-3, P-LE with sialyl Lewis X (sLeX), and E-LE with sLeX. SMD simulations were based on newly built-up force field parameters including carbohydrate units and sulfated tyrosine(s) using an analogy approach. The simulations demonstrated that the complex dissociation was coupled to the molecular extension. While the intramolecular unraveling in P-LESGP-3 system mainly resulted from the destroy of the two anti-parallel sheets of EGF domain and the breakage of hydrogen-bond cluster at the Lec-EGF interface, the intermolecular dissociation was mainly determined by separation of fucose (FUC) from Ca2+ ion in all three systems. Conformational changes during forced dissociations depended on pulling velocities and forces, as well as on how the force was applied. This work provides an insight into better understanding of conformational changes and adhesive functionality of selectin-ligand interactions under external forces.

Hybrid Qm/Mm Simulation Of The Hydration Phenomena Of Dipalmitoylphosphatidylcholine Headgroup

The polar headgroup of dipalmitoylphosphatidylcholine (DPPC) molecule both in gas phase and aqueous Solution is investigated by the hybrid quantum mechanical/molecular mechanical (QM/MM) method, in which the polar head of DPPC molecule and the bound water molecules are treated with density functional theory (DFT), while the apolar hydrocarbon chain of DPPC molecule is treated with MM method. It is demonstrated that the hybrid QM/MM method is both accurate and efficient to describe the conformations of DPPC headgroup. Folded structures of headgroup are found in gas phase calculations. In this work, both monohydration and polyhydration phenomena are investigated. In monohydration, different water association sites are studied. Both the hydration energy and the quantum properties of DPPC and water molecules are calculated at the DFT level of theory after geometry optimization. The binding force of monohydration is estimated by using the scan method. In polyhydration, more extended conformations are found and hydration energies in different polyhydration styles are estimated. (C) 2008 Elsevier Inc. All rights reserved.

魔芋葡甘聚糖结构及其应用研究

本文以葡甘聚糖为试材，运用分子模拟同仪器分析相结合的手段，预测了葡甘聚糖分子链的高级结构，分析了无机分子对其结构、性能的影响，探讨了葡甘聚糖与卡拉胶微观作用机理。 主要研究内容与结果如下： 1. 葡甘聚糖单链高级结构的预测 利用Hyperchem7.0、VM2.0分子结构计算软件采用分子动力学和分子力学的方法，以真空中葡甘聚糖单链为研究模型，研究了聚合度、取代基对动态构象的影响及影响链构象的作用力。首次提出了KGM链的动态模型，得到了以下结果：聚合度影响其链形态和稳定性，对于高聚合度的魔芋葡甘聚糖来说，其链呈现无规卷曲状态且稳定性下降，在整个动态运动过程中KGM链脱乙酰基前后都呈现无规卷曲状态，而且其伸展和卷曲的变化是周期性的，表现出了很好的柔性，说明乙酰基不是影响其链形态的主要因素，二面角能和静电作用是真空中影响单链构象的主要的键合作用力和非键合作用力，但是乙酰基对氢键作用的影响较大。 2. 无机分子对葡甘聚糖溶液体系结构性能影响的研究 利用Hyperchem7.0分子结构计算软件，采用分子动力学及红外光谱、核磁共振等技术，对无机分子对葡甘聚糖体系的影响进行分析，很好的解释了性能变化的结构原因，结合以往的研究及参考文献得出以下结论：KGM在碱性条件下由于化学作用乙酰基的脱除分子间氢键作用的加强提高了凝胶强度，分子间氢键的主要作用位点是葡萄糖 的O(6)与甘露糖的O(2)之间;硼与KGM形成的分子内和分子间配合作用及分子间作用力氢键的增强是KGM特性粘度和致密性提高的主要原因，分子间型配位反应发生在葡萄糖和甘露糖两个糖环之间的几率最大;加入尿素后，表现为宏观性能的下降，葡甘聚糖氢键网络被破坏，氢键的作用位点由甘露糖的O(2)、O（3）变为O(4)，葡萄糖的O（3）、O(6)变为O（1）、O（2）。 3. 葡甘聚糖与卡拉胶共混作用的研究 利用Hyperchem7.0分子结构计算软件运用分子动力学方法、DSC、红外光谱技术，研究了葡甘聚糖与卡拉胶的微观结构及作用过程，揭示了性能变化的结构原因和分子之间的作用位点。得出了以下结论：葡甘聚糖同卡拉胶共混后通过分子间氢键作用形成了强度高、弹性好的热可逆凝胶。其凝胶强度与单一胶相比较，凝胶特性得到了很大的改善。通过红外光谱可以发现形成复合溶胶后化学基团没有发生本质上的改变，但是氢键缔合作用增强;通过DSC分析可以发现仅出现1个吸热峰，两种生物大分子达到了相容的结果，经过分子动力学模拟表明，与单一体系比较，葡甘聚糖与卡拉胶共混时稳定性提高，分子间氢键作用力明显增强，主要的作用位点是葡甘聚糖的上甘露糖的O(2)、O(4)、O(6)、乙酰基位置及卡拉胶上糖环上的 O(6)、硫酸基。