The MM3 force field for amides,polypeptides and proteins

The potential functions for simple amides, several peptides and a small protein have been worked out for the MM3 force field. Structures and energies were fit as previously with MM2, but additionally, we fit the vibrational spectra of the simple amides (average rms error over four compounds, 34 cm^?1), and examined more carefully electrostatic interactions, including charge-charge and charge-dipole interactions. The parameters were obtained and tested by examining four simple amides, five electrostatic model complexes, two dipeptides, six crystalline cyclic peptides, and the protein Crambin. The average root-mean-square deviation from the X-ray structures for the six cyclic peptide crystals was only 0.10 Å for the nonhydrogen atomic positions, and 0.011 Å, 1.0°, and 4.9° for bond lengths, bond angles, and torsional angles, respectively. The parameter set was then further tested by minimizing the high resolution crystal structure of the hydrophobic protein Crambin. The resultant root-mean-square deviations for the non-hydrogen atomic data, in the presence of the crystal lattice, are 0.22 Å, 0.023 Å, 2.0°, and 6.4° for coordinates, bond lengths, bond angles, and torsional angles, respectively.     

Hydrothermal synthesis and characterization of [(UO2)2F8(H2O)2Zn2(4,4'-bpy)2].(4,4'-bpy), a mixed-metal uranyl aquofluoride with a pillared layer structure

A mixed-metal uranyl aquofluoride, [(UO2)2F8(H2O)2Zn2(4,4'-bpy)2].(4,4'-bpy), has been synthesized under hydrothermal conditions and has been structurally characterized by single-crystal X-ray diffraction, infrared spectroscopy, thermogravimetric analysis, emission spectroscopy, and solid-state NMR spectroscopy. It is one of the few uranium fluoride-organic framework solids in which an organic molecule is directly incorporated into the extended structure of the metal fluoride and is the first example of mixed-metal uranium oxyfluoride incorporating an organic ligand. The structure consists of neutral layers of edge- and corner-sharing uranium-centered pentagonal bipyramids and zinc-centered octahedra, which are linked through 4,4'-bpy ligands into a 3-D framework. The 1H MAS NMR spectrum is in support of the conclusion that the occluded 4,4'-bpy molecules in the structural channels are not protonated. Crystal data: monoclinic, space group P2(1)/c, a = 9.4630(5) A, b = 22.384(1) A, c = 16.7534(8) A, beta = 91.899(2) degrees , V = 3546.7(4) A(3) and Z = 4.     

Synthesis,crystal structure,and solid state NMR spectroscopy of NH(4)[(V(2)O(3))(2)(4,4'-bpy)(2)(H(2)PO(4))(PO(4))(2)].0.5H(2)O,a mixed-valence vanadium(IV,V) phosphate with a pillared layer structure

A mixed-valence vanadium phosphate, NH(4)[(V(2)O(3))(2)(4,4'-bpy)(2)(H(2)PO(4))(PO(4))(2)].0.5H(2)O, has been synthesized under hydrothermal conditions and structurally characterized by single-crystal X-ray diffraction. It crystallizes in the monoclinic space group C2/c (No. 15) with a = 12.6354(8) A, b = 9.9786(6) A, c = 23.369(1) A, beta = 92.713(1) degrees, and Z = 4 with R(1) = 0.0389. The structure consists of dimers of edge-sharing vanadium(IV,V) octahedra that are connected by corner-sharing phosphate tetrahedra to form layers in the ab-plane, which are further linked through 4,4'-bipyridine pillars to generate a 3-D framework. Magnetic susceptibility confirms the valence of the vanadium atoms. The (31)P MAS NMR spectrum shows a resonance centered at 80 ppm with a shoulder at ca. 83 ppm in an intensity ratio close to 1:2, which correspond to two distinct P sites. The observed large downfield (31)P NMR shifts can be ascribed to magnetic exchange coupling involving phosphorus atoms. The unpaired electron spin density at the phosphorus nucleus was determined from variable-temperature (31)P NMR spectra. The (1)H MAS NMR spectrum was fitted to six components in accordance with the structure as determined from X-ray diffraction.     

Synthesis and characterization of two-dimensional fluorinated metal phosphates incorporating 2,2′-bipyridine ligands: M2F2(2,2′-bpy)(HPO4)2(H2O) (M=Fe, Ga)

Two fluorinated metal phosphates, M₂F₂(2,2′-bpy)(HPO₄)₂(H₂O) (M=Fe, Ga), have been synthesized under hydrothermal conditions and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility. The two compounds are isostructural and crystallize in the triclinic space group , a=7.6595(8)Å, b=10.101(1)Å, c=11.260(1)Å, α=107.555(2)°, β=105.174(2)°, γ=98.975(2)°, V=775.1(2)ų and Z=2 for the Fe compound, and a=7.5816(6)Å, b=9.9943(7)Å, c=11.1742(8)Å, α=107.333(1)°, β=105.014(1)°, γ=99.261(1)° and V=754.2(2)ų for the Ga compound. They are the first fluorinated metal phosphates which incorporate 2,2′-bipyridine ligands. The structure consists of edge-sharing octahedral dimers with the composition Fe₂F₄(H₂O)₂O₄ and discrete FeN₂O₄ octahedra, which are linked into two-dimensional sheets through corner-sharing phosphate tetrahedra. The 2,2′-bpy ligands bind in a bidentate fashion to the metal atoms and project into interlamellar region. The layers are extended into a three-dimensional supramolecular array via π-π stacking interactions of the 2,2′-bpy ligands. Magnetic susceptibility of the iron compound confirms the presence of Fe^III.     

温度与应变率对钽流动应力的影响

 研究了温度在-100～400 ℃、应变率在10^-5～10³ s^-1范围内温度和应变率的变化对钽的流动应力的影响。结果表明,钽的流动应力对温度和应变率的变化相当敏感。同时还就两种本构模型对钽的温度效应与应变率效应的不同处理方法作了比较,指出Zerilli-Armstrong模型能更好地描述温度与应变率对钽流动应力的影响。     

冲击波作用下CHBr3/NaCl界面热弛豫特性研究

非透明材料冲击温度测量是通过对界面光辐射历史的观察实现的 ,因此对界面光辐射历史的研究是非透明材料冲击温度测量的基础。但由于冲击阻抗的失配导致界面上出现波的反射而引起温度的变化与界面热流动产生的温度变化交杂在一起 ,以及过程的瞬时性 ,使得对这一过程的实验研究显得非常困难。设计了一种界面波阻抗近似相同的特殊实验装置 ,用光辐射测量技术研究了在冲击压缩下CHBr3/NaCl界面的热弛豫过程。实验结果和理论分析表明CHBr3/NaCl界面的热弛豫时间在纳秒量级 ,与Grover等人的理论预估一致。     

Li_3N在生成BN反应中的作用

研究了常压高温下Li3N在B4 C与含氮化合物生成BN反应中的作用。实验结果表明 ,在 950℃高温下 ,B4 C与Si3N4 反应不生成hBN ,B4 C与NH4 Cl反应只生成少量hBN。在该两种原料中加入Li3N后 ,反应产物中hBN的生成量都明显增多。但Li3N本身没有与B4 C生成hBN的反应。由此推断 ,Li3N在上述B4 C与含氮化合物生成hBN的反应中表现出了催化作用。此外 ,在以hBN为原料 ,以Li3N为催化剂合成出cBN的温度压力区域内 ,对B4 C Si3N4 Li3N体系所做的高温高压实验没有合成出hBN或cBN。还讨论了在低压条件下原位合成cBN的探索实验中 ,应如何选择硼源和氮源的问题     

Aristolochic Acids as a Defensive Substance for the Aristolochiaceous Plant‐Feeding Swallowtail Butterfly,Pachliopta aristolochiae interpositus

The chemical constituents isolated from every stage of the Taiwanese swallowtail butterfly, Pachliopta aristolochiae interpositus, were studied and compared with the constituents of the insect feeding plant, A. cucurbitifolia. Two aristolochic acid derivatives ( 1 and 4 ) and three aristolactam analogues ( 5, 6 , and 7 ) were isolated from the larval osmeterial fluid and larvae of the insect. In addition, four purines ( 2, 3, 13 , and 14 ), one indole alkaloid ( 11 ), one steroid ( 10 ), two benzenoids ( 8 and 9 ) and allantoin ( 12 ) were also isolated from the insect. Among these compounds, aristolochic acid ‐I (AA‐I, 1 ) was detected in all life stages of the insect, especially in the larval osmeterial fluid. The studies confirm that the toxic AAs are used as larval feeding stimulants and deterrent allomones against birds.     

Enhanced Performance of Benzothieno[3,2‐b]thiophene (BTT)‐Based Bottom‐Contact Thin‐Film Transistors

Three new benzothieno[3,2‐b]thiophene ( BTT ; 1 ) derivatives, which were end‐functionalized with phenyl ( BTT‐P ; 2 ), benzothiophenyl ( BTT‐BT ; 3 ), and benzothieno[3,2‐b]thiophenyl groups ( BBTT ; 4 ; dimer of 1 ), were synthesized and characterized in organic thin‐film transistors (OTFTs). A new and improved synthetic method for BTT s was developed, which enabled the efficient realization of new BTT ‐based semiconductors. The crystal structure of BBTT was determined by single‐crystal X‐ray diffraction. Within this family, BBTT , which had the largest conjugation of the BTT derivatives in this study, exhibited the highest p‐channel characteristic, with a carrier mobility as high as 0.22 cm² V^?1 s^?1 and a current on/off ratio of 1×10⁷, as well as good ambient stability for bottom‐contact/bottom‐gate OTFT devices. The device characteristics were correlated with the film morphologies and microstructures of the corresponding compounds.