一种新型二茂铁丁酸混配合物的合成及晶体结构

以二茂铁基丁酸(Fb)、4,4′-联吡啶(bpy)以及Zn(AC)2.2H2O为原料合成了一个新的混配合物Zn(Fb)2(bpy)2。X-射线单晶衍射分析表明,该化合物是一个四配体六配位单核配合物,并以氢键另连接两个二茂铁分子。     

Synthesis, structure, and reactivity of an iron(V) nitride

Despite being implicated as important intermediates, iron(V) compounds have proven very challenging to isolate and characterize. Here, we report the preparation of the iron(V) nitrido complex, [PhB((t)BuIm)(3)Fe(V)≡N]BAr(F24) (PhB((t)BuIm)(3)(-) = phenyltris(3-tert-butylimidazol-2-ylidene)borato, BAr(F24) = B(3,5-(CF(3))(2)C(6)H(3))(4)(-)), by one electron oxidation of the iron(IV) nitrido precursor. Single-crystal x-ray diffraction of the iron(V) complex reveals a four-coordinate metal ion with a terminal nitrido ligand. M??bauer and electron paramagnetic resonance spectroscopic characterization, supported by electronic structure calculations, provide evidence for a d(3) iron(V) metal center in a low spin (S = 1/2) electron configuration. Low-temperature reaction of the iron(V) nitrido complex with water under reducing conditions leads to high yields of ammonia with concomitant formation of an iron(II) species.     

Interface structure and atomic bonding characteristics in silicon nitride ceramics

Direct atomic resolution images have been obtained that illustrate how a range of rare-earth atoms bond to the interface between the intergranular phase and the matrix grains in an advanced silicon nitride ceramic. It has been found that each rare-earth atom bonds to the interface at a different location, depending on atom size, electronic configuration, and the presence of oxygen at the interface. This is the key factor to understanding the origin of the mechanical properties in these ceramics and will enable precise tailoring in the future to critically improve the materials' performance in wide-ranging applications.     

The molecular structure of a DNA-triostin A complex

The molecular structure of triostin A, a cyclic octadepsipeptide antibiotic, has been solved complexed to a DNA double helical fragment with the sequence CGTACG (C, cytosine; G, guanine; T, thymine; A, adenine). The two planar quinoxaline rings of triostin A bis intercalate on the minor groove of the DNA double helix surrounding the CG base pairs at either end. The alanine residues form hydrogen bonds to the guanines. Base stacking in the DNA is perturbed, and the major binding interaction involves a large number of van der Waals contacts between the peptides and the nucleic acid. The adenine residues in the center are in the syn conformation and are paired to thymine through Hoogsteen base pairing.     

The structure of a complex of recombinant hirudin and human alpha-thrombin

The crystallographic structure of a recombinant hirudin-thrombin complex has been solved at 2.3 angstrom (A) resolution. Hirudin consists of an NH2-terminal globular domain and a long (39 A) COOH-terminal extended domain. Residues Ile1 to Tyr3 of hirudin form a parallel beta-strand with Ser214 to Glu217 of thrombin with the nitrogen atom of Ile1 making a hydrogen bond with Ser195 O gamma atom of the catalytic site, but the specificity pocket of thrombin is not involved in the interaction. The COOH-terminal segment makes numerous electrostatic interactions with an anion-binding exosite of thrombin, whereas the last five residues are in a helical loop that forms many hydrophobic contacts. In all, 27 of the 65 residues of hirudin have contacts less than 4.0 A with thrombin (10 ion pairs and 23 hydrogen bonds). Such abundant interactions may account for the high affinity and specificity of hirudin.     

Crystal structure of serotonin picrate, a donor-acceptor complex

The crystal structure of the red picric acid salt of serotonin was determined by x-ray diffraction methods. The structure consists of parallel hydroxyindole and picrate planes which are intimately stacked with an interplanar separation of 3.3 to 3.4 angstroms. The stacking interaction appears to be of the donor-acceptor (charge-transfer) type, involving specific contacts between picrate nitro groups and atoms of the hydroxyindole moieties. Similar interactions might mediate biological processes involving serotonin.     

Synthesis and structure of sila-adamantane

An organosilicon cage compound containing the sila-adamantane structural unit, which is the building block of crystalline silicon, was synthesized by the Lewis acid-catalyzed rearrangement reaction of a structural isomer.     

The gramicidin pore: crystal structure of a cesium complex

Gramicidin, a linear polypeptide composed of hydrophobic amino acids with alternating L- and D- configurations, forms transmembrane ion channels. The crystal structure of a gramicidin-cesium complex has been determined at 2.0 angstrom resolution. In this structure, gramicidin forms a 26 angstrom long tube comprised of two polypeptide chains arranged as antiparallel beta strands that are wrapped into a left-handed helical coil with 6.4 residues per turn. The polypeptide backbone forms the interior of the hydrophilic, solvent-filled pore and the side chains form a hydrophobic and relatively regular surface on the outside of the pore. This example of a crystal structure of a solvent-filled ion pore provides a basis for understanding the physical nature of ion translocation.     

A terminal Pleistocene child cremation and residential structure from eastern Beringia

The dearth of human remains and residential sites has constrained inquiry into Beringian lifeways at the transition of the late Pleistocene-early Holocene. We report on human skeletal remains and a residential structure from central Alaska dated to ~11,500 calendar years ago. The remains are from a ~3-year-old child who was cremated in a pit within a semisubterranean house. The burial-cremation and house have exceptional integrity and preservation and exhibit similarities and differences to both Siberian Upper Paleolithic and North American Paleoindian features.     

Crystal and molecular structure of a double complex of manganese with phthalocyanato and pyridine ligands

A crystalline solid, formed by oxidation of phthalocyanatomanganese(II) in pyridine, has been identified as phthalocyanatopyridinemanganese(III)-micro-oxo-phthalocyanatopyridinemanganese(III)dipyridinate(C(74)H(42)Mn(2)N(18)O2C(5)H(5)N) byx-ray diffraction methods. This novel molecule consists of two manganese complexes joined by an essentially linear Mn-O-Mn bridge. Its structure may have some relation to oxidation processes in biological systems.     

Crystal structure of cobra-venom phospholipase A2 in a complex with a transition-state analogue

The crystal structure of a complex between a phosphonate transition-state analogue and the phospholipase A2 (PLA2) from Naja naja atra venom has been solved and refined to a resolution of 2.0 angstroms. The identical stereochemistry of the two complexes that comprise the crystal's asymmetric unit indicates both the manner in which the transition state is stabilized and how the hydrophobic fatty acyl chains of the substrate are accommodated by the enzyme during interfacial catalysis. The critical features that suggest the chemistry of binding and catalysis are the same as those seen in the crystal structure of a similar complex formed with the evolutionarily distant bee-venom PLA2.     

Crystal structure of bee-venom phospholipase A2 in a complex with a transition-state analogue

The 2.0 angstroms crystal structure of a complex containing bee-venom phospholipase A2 (PLA2) and a phosphonate transition-state analogue was solved by multiple isomorphous replacement. The electron-density map is sufficiently detailed to visualize the proximal sugars of the enzyme's N-linked carbohydrate and a single molecule of the transition-state analogue bound ot its active center. Although bee-venom PLA2 does not belong to the large homologous Class I/II family that encompasses most other well-studied PLA2s, there is segmental sequence similarity and conservation of many functional substructures. Comparison of the bee-venom enzyme with other phospholipase structures provides compelling evidence for a common catalytic mechanism.     

X-ray structure of the EmrE multidrug transporter in complex with a substrate

EmrE is a prototype of the Small Multidrug Resistance family of efflux transporters and actively expels positively charged hydrophobic drugs across the inner membrane of Escherichia coli. Here, we report the x-ray crystal structure, at 3.7 angstrom resolution, of one conformational state of the EmrE transporter in complex with a translocation substrate, tetraphenylphosphonium. Two EmrE polypeptides form a homodimeric transporter that binds substrate at the dimerization interface. The two subunits have opposite orientations in the membrane and adopt slightly different folds, forming an asymmetric antiparallel dimer. This unusual architecture likely confers unidirectionality to transport by creating an asymmetric substrate translocation pathway. On the basis of available structural data, we propose a model for the proton-dependent drug efflux mechanism of EmrE.     

Reductive cyclotrimerization of carbon monoxide to the deltate dianion by an organometallic uranium complex

Despite the long history of the Fischer-Tropsch reaction, carbon monoxide has proven remarkably resistant to selective homologation under mild conditions. Here, we find that an organouranium(III) complex induces efficient reductive trimerization of carbon monoxide at room temperature and pressure. The result is a triangular, cyclic C3O(2-)3, or deltate, dianion held between two uranium(IV) units. The bonding within the C3O(2-)3 unit and its coordination to the two U centers have been analyzed by x-ray diffraction and density functional theory computational studies, which show a stabilizing C-C agostic interaction between the C3 core and one U center. Solution nuclear magnetic resonance studies reveal a rapid equilibration of the deltate unit between the U centers.     

Crystal structure of a shark single-domain antibody V region in complex with lysozyme

Cartilaginous fish are the phylogenetically oldest living organisms known to possess components of the vertebrate adaptive immune system. Key to their immune response are heavy-chain, homodimeric immunoglobulins called new antigen receptors (IgNARs), in which the variable (V) domains recognize antigens with only a single immunoglobulin domain, akin to camelid heavy-chain V domains. The 1.45 angstrom resolution crystal structure of the type I IgNAR V domain in complex with hen egg-white lysozyme (HEL) reveals a minimal antigen-binding domain that contains only two of the three conventional complementarity-determining regions but still binds HEL with nanomolar affinity by means of a binding interface comparable in size to conventional antibodies.     

内蒙古草盲蝽复合组昆虫群落结构及区系

为摸清草盲蝽复合组昆虫在内蒙古地区的群落结构组成和地理分布特点,于2006—2012年,采用网捕法对内蒙古草盲蝽复合组昆虫进行野外调查,根据已有标本并结合相关资料对内蒙古草盲蝽复合组昆虫进行了较系统的研究。结果表明,内蒙古草盲蝽复合组昆虫已定名标本5属21种,其中草盲蝽属、后丽盲蝽属为优势类群。内蒙古草盲蝽复合组昆虫在世界动物地理区划组成上以古北界分布占优势(52.38%),古北界+东洋界跨区分布的次之(28.58%)。内蒙古草盲蝽复合组昆虫在中国动物地理区划组成上以蒙新区种类为主体(23.82%),且蒙新区、华北区和东北区的草盲蝽复合组昆虫亲缘关系较为密切。在内蒙古植被带中,草盲蝽复合组分布于典型草原带的物种最多,有19种,占总种数的90.48%,其中,仅分布在草原带的物种有9种,占物种总数的42.86%,由此可看出,草盲蝽复合组昆虫是对草原生境较为适应的类群。     

Rana pipiens complex: mating call structure and taxonomy

Geographic variability in call structure indicates that four largely allopatric populations of leopard frogs are present in the central United States. These forms appear to maintain their distinctness in narrow zones of sympatry, and most adult males can be separated morphologically. It is suggested that the four forms represent distinct species and that the idea of gradual clinal variability in one wide-ranging species is wrong.