七-O-乙酰基-β-乳糖异硫氰酸酯的合成、表征及电化学研究

本文合成了并培养出了七-O-乙酰基—β—乳糖异硫氰酸酯的单晶，用X射线衍射分析了其晶体结构。结果表明，晶体为正交晶系，P2₁2₁2₁空间群，a＝1．23282(7)，b＝1．80012(10)，c＝1.85230(10) nm，α＝β＝γ＝90°，V＝4．1107(4) nm³，Z＝4。电化学实验观测到单链DNA和双链DNA对该化合物的峰电流均有明显降低作用，表明化合物与DNA发生了静电作用。     

XPS and XAES analysis of copper,arsenic and sulfur chemical state in enargites

Enargite, a copper arsenic sulfide with the formula Cu₃AsS₄ is of environmental concern due to its potential to release toxic arsenic species. The oxidation and dissolution of enargite are governed by the composition and chemical state of the outermost surface layer. Qualitative and quantitative analysis of the enargite surface can be initially obtained on the basis of X‐ray photoelectron spectroscopy (XPS) binding energy and intensity data. However, a more precise determination of the chemical state of the principal elements of enargite (copper, arsenic and sulfur) in the altered surface layer and in the bulk of the mineral requires a combined analysis based on XPS photoelectron lines and the corresponding X‐ray excited Auger lines. On the basis of results obtained on natural and synthetic enargite samples and on standards of sulfides and oxides, the Auger parameter α′ of different compounds was calculated and the Wagner chemical state plots were drawn for arsenic, copper and sulfur. Arsenic in enargite is found to be in a chemical environment similar to that of arsenides or elemental arsenic, whereas copper in enargite is in a chemical state that corresponds to copper sulfide, Cu₂S, for all samples irrespective of surface treatment (natural or freshly cleaved). Only sulfur changed from a chemical state similar to that of copper or iron sulfide in freshly cleaved samples to another state in natural enargite in the as‐received state. Thus, it is the sulfur atom at the surface of enargite that is most susceptible to changes in the enargite surface state and composition. A more detailed interpretation of this behavior, based on differences in the initial and final state effects, is proposed here. The concept of Auger parameter and chemical state plot, used here for the first time for investigating enargite, has proved to be a method to unambiguously assign the chemical state of the principal elements copper, arsenic and sulfur in these minerals. Copyright © 2006 John Wiley & Sons, Ltd.     

X-ray structure and circular dichroism of pure rotamers of bis[guanosine-5'-monophosphate(-1)](N,N,N',N'-tetramethylcyclohexyl-1,2-diamine)platinum(II) complexes that have R,R and S,S configurations at the asymmetric diamine

The use of a sterically hindered diamine ligand (Me(4)DACH) has allowed for the first time, the isolation and characterization, both in the solid state (X-ray crystallography) and in solution (circular dichroism), of pure DeltaHT rotamers of [Pt(Me(4)dach)(5'-GMP)(2)] (compounds 1 and 2 for R,R and S,S configurations of the Me(4)DACH ligand, respectively). Comparison of the CD spectra obtained for each rotamer, which differ only in the chirality of the Me(4)DACH ligand (R,R or S,S) or in the chirality of the HT conformation (Delta or Lambda), allowed us to conclude that, in the 200-350 nm range, the contributions to the overall CD spectrum that stem from diamine chirality and diamine-induced chirality of platinum d--d transitions or from sugar chirality are negligible relative to the exciton chiral coupling that occurs for pi-pi* transitions of the cis guanines. Accurate molecular structures of 1.10 D(2)O and 2.14 D(2)O (conventional crystallographic agreement indexes R(1) convergent to 2.07 % and 2.18 %, respectively) revealed that the crystallized rotamers have a DeltaHT conformation that is in agreement with all previously reported X-ray structures of [Pt(diamine)(nucleos(t)ide)(2)] complexes. This conformation allows the 5'-phosphate to be located in proximity to the Me(4)DACH ligand so that (P)O...HC(N) hydrogen-bond interactions exists in both complexes. For both structures, the canting of the guanine planes on the coordination plane is right-handed (R; canting angle (Phi) of 80.9 degrees and 73.2 degrees, respectively); this indicates that the canting direction is driven by the HT conformation chirality (Delta for both compounds) and not by the chirality of the carrier ligand (different for the two compounds). Density functional theory analysis of the conformational space as a function of Phi indicated a good agreement between the computed and experimental structures. The increase in energy for Phi values below 65 degrees and 55 degrees (for 1 and 2, respectively) is mainly due to the short intramolecular contacts between C(8)H and the cis N-Me groups on the same side of the platinum coordination plane.     

Synthesis of Lanthanide Coordination Polymers with Benzophenone-4,4′-dicarboxylate： Effect of Lanthanide Contraction on Structures

Four lanthanide coordination polymers with benzophenone‐4,4′‐dicarboxylic acid (H₂bpndc) and 1,10‐phenanthroline (phen), [Ln₂(bpndc)₃(phen)] (Ln=La (1), Pr (2) and Tb (3)), [Yb(bpndc)₁₅(phen)].05H₂O (4) were obtained through solvothermal synthesis. The crystallographic data show that 1, 2, and 3 are isostructural, the Ln(III) ions in 1, 2 and 3 are all eight‐ and ten‐coordinated, respectively, and thus the Ln(III) ions are connected by bpndc ligands, resulting in an interpenetrating 3D structure. While in 4, the Yb(III) ions are eight‐coordinated and connected by bpndc ligands into a 3D structure with 1D rhombic channels, which result from the effect of lanthanide contraction from La(III) to Yb(III) ions, and the bpndc ligands in 1, 2, 3, and 4 display three types of coordination modes.     

南桐煤镜质组非晶结构的X射线衍射研究

本文对经典煤核结构模型评述后，提出了多元非晶煤结构概念。用Ｘ射线衍射方法研究了南桐煤镜质组的原子径各分布，论证了煤大分子中同时存在芳香结构单元和脂环结构单元，它们对Ｘ射线射射强度均有贡献，非晶煤结构的有序性不在于１ｎｍ。     

双（1,2—丙二胺）合铜的TCNQ盐的合成与光谱研究

合成了导电性ＴＣＮＱ盐Ｃｕ（ｐｎ）２（ＴＣＮＱ）ｎ（ｎ＝２和３，ｐｎ＝１，２－丙二胺，ＴＣＮＱ＝７，７，８，８－四氰基对苯二醌二甲烷）。红外光谱、电子光谱和Ｘ－光电子能谱研究表明ＴＣＮＱ盐中存在ＴＣＮＱ°和ＴＣＮＱ－，ＴＣＮＱ°与ＴＣＮＱ－之间发生了部分电子转移，致使铜呈混合价态。它们的粉末室温电导率为１．１×１０－５～２．４×１０－６ｏｈｍ－１ｃｍ－１。     

Enzyme inhibitors as chemical tools to study enzyme catalysis: rational design, synthesis, and applications

Carefully designed molecules that are intimately related to the reaction mechanism of enzymes are often highly selective and potent inhibitors that serve as extremely useful chemical probes for understanding the reaction mechanism and structure of enzymes. This article describes the design, synthesis, and applications of specific inhibitors of two mechanistically distinct groups of enzymes, ATP-dependent amide ligases and Ser- and Thr-hydrolases. Our strategy is based on the premise that stable analogues of the transition state (transition-state analogues) are highly potent inhibitors that serve as good mechanistic probes, and that a key structure of a good inhibitor of one enzyme is also utilized for the inhibitors of other enzymes that share the same chemistry in their catalyzed reactions, irrespective of the degree of structural similarity and evolutionary link between the enzymes. According to these principles, we designed and synthesized a series of phosphinate- and sulfoximine-based transition-state analogue inhibitors of glutathione synthetase, gamma-glutamylcysteine synthetase and asparagine synthetase. For the second group of enzymes, we synthesized a gamma-monofluorophosphono glutamate analogue for mechanism-based affinity labeling of gamma-glutamyltranspeptidase and fluorescent phosphonic acid esters for the active-site titration of lipase. These inhibitors were used successfully as ligands for detailed kinetic analyses, X-ray crystallography, and mass analysis of the enzymes to identify the key amino acid residues responsible for catalysis and substrate recognition in the transition state.     

Taking snapshots of photoexcited molecules in disordered media by using pulsed synchrotron X-rays

Photoexcited molecules are quintessential reactants in photochemistry. Structures of these photoexcited molecules in disordered media in which a majority of photochemical reactions take place remained elusive for decades owing to a lack of suitable X-ray sources, despite their importance in understanding fundamental aspects in photochemistry. As new pulsed X-ray sources become available, short-lived excited-state molecular structures in disordered media can now be captured by using laser-pulse pump, X-ray pulse-probe techniques of third-generation synchrotron sources with time resolutions of 30-100 ps, as demonstrated by examples in this review. These studies provide unprecedented information on structural origins of molecular properties in the excited states. By using other ultrafast X-ray facilities that will be completed in the near future, time-resolution for the excited-state structure measurements should reach the femtosecond time scales, which will make "molecular movies" of bond breaking or formation, and vibrational relaxation, a reality.     

Time‐Resolved Synchrotron Radiation Excited Optical Luminescence: Light‐Emission Properties of Silicon‐Based Nanostructures

The recent advances in the study of light emission from matter induced by synchrotron radiation: X‐ray excited optical luminescence (XEOL) in the energy domain and time‐resolved X‐ray excited optical luminescence (TRXEOL) are described. The development of these element (absorption edge) selective, synchrotron X‐ray photons in, optical photons out techniques with time gating coincide with advances in third‐generation, insertion device based, synchrotron light sources. Electron bunches circulating in a storage ring emit very bright, widely energy tunable, short light pulses (<100 ps), which are used as the excitation source for investigation of light‐emitting materials. Luminescence from silicon nanostructures (porous silicon, silicon nanowires, and Si–CdSe heterostructures) is used to illustrate the applicability of these techniques and their great potential in future applications.     

A Novel Octahedral Hexasilver(I) Cluster: Ag_6[SSCN(n-C_4H_9)_2]_6

ＣｏｍｐｏｕｎｄｓｆｏｒｍｅｄｆｒｏｍＣｕ ,ＡｇａｎｄＡｕｗｉｔｈｄｉｔｈｉｏ ｌａｔｅｌｉｇａｎｄｓ ,ｓｕｃｈａｓｔｈｅｄｉａｌｋｙｌｄｉｔｈｉｏｃａｒｂａｍａｔｅ (ＤＴＣ) ,ｍｅｒｃａｐｔｏｔｈｉａｚｏｌｉｎｅ (ＨＭＴ)ａｎｄｄｉａｌｋｙｌｄｉｔｈｉｏｐｈｏｓｐｈａｔｅｓ(ＤＤＰ) ,ｈａｖｅｐｌａｙｅｄａｎｉｍｐｏｒｔａｎｔｒｏｌｅｉｎｔｅｃｈｎｏｌｏｇｙ .1Ｃｕ(Ｉ) Ｓｃｌｕｓｔｅｒｓａｌｓｏｈａｖｅｂｅｅｎｉｍｐｌｉｃａｔｅｄｉｎｂｉｏｌｏｇｙａｓａｎ ｔｉ ｏｘｉｄａｎｔｓ .2Ｔｈｅｃｕｂａｎ…