Ti8C12+-Metallo-Carbohedrenes: A New Class of Molecular Clusters?

During the course of studying the dehydrogenation reactions of hydrocarbons by titanium atoms, ions, and clusters, an exceptionally stable and abundant cluster which contains 8 titaniums and 12 carbons was discovered. "Titration" reactions with ND(3) reveal the uptake of eight molecules, pointing to the fact that the titanium atoms are at exposed positions of similar coordination. A dodecahedral structure of T(h) point group symmetry is proposed to account for the unusual stability of this molecular cluster. The Ti(8)C(12)(+) dodecahedron has 12 pentagonal rings and each of the rings is formed by two titanium and three carbon atoms, where each titanium is bound to three carbons. Based on the model, it is expected that neutral Ti(8)C(12) would be a stable metallo-carbododecahedral molecule and may comprise one member of a new class of molecules, namely metallo-carbohedrenes.     

The structure of the c60 molecule: x-ray crystal structure determination of a twin at 110 k

Single-crystal x-ray diffraction methods were used to determine the crystal and molecular structure of C(60) buckminsterfullerene. At 110 kelvin C(60) is cubic, apparent Laue symmetry m3m, but it exhibits noncrystallographic systematic extinctions indicative of a twin in which I(hkl) and I(khl) are superimposed. In fact, C(60) crystallizes with four molecules in space group [See equation in the PDF file] of the cubic system (Laue symmetry m3) with lattice constant a = 14.052(5) angstroms (A) at 110 kelvin. The twin components are equal. A given component, which has crystallographically imposed symmetry [See equation in the PDF file] displays an ordered structure of a truncated icosahedron. The five independent C=C bonds that join C(6) rings average 1.355(9) A; the ten independent C-C bonds that join C(6) and C(5) rings average 1.467(21) A. The mean atom-to-atom diameter of the C(60) molecule is 7.065(3) A. The molecules are very tightly packed in the crystal structure, with intermolecular C...C distances as short as 3.131(7) A.     

Synthesis and Single-Crystal X-ray Structure of a Highly Symmetrical C60 Derivative, C60Br24

C(60) and liquid bromine react to form C(60)Br(24), a crystalline compound isolated as a bromine solvate, C(60)Br(24)(Br(2))(x), The x-ray crystal structure defines a new pattern of addition to the carbon skeleton that imparts a rare high symmetry. The parent C(60) framework is recognizable in C(60)Br(24), but sp(3) carbons at sites of bromination distort the surface, affecting conformations of all of the hexagonal and pentagonal rings. Twenty-four bromine atoms envelop the carbon core, shielding the 18 remaining double bonds from addition. At 150 degrees to 200 degrees C there is effectively quantitative reversion of C(60)Br(24) to C(60) and Br(2).     

Design, activity, and 2.8 A crystal structure of a C2 symmetric inhibitor complexed to HIV-1 protease

A two-fold (C2) symmetric inhibitor of the protease of human immunodeficiency virus type-1 (HIV-1) has been designed on the basis of the three-dimensional symmetry of the enzyme active site. The symmetric molecule inhibited both protease activity and acute HIV-1 infection in vitro, was at least 10,000-fold more potent against HIV-1 protease than against related enzymes, and appeared to be stable to degradative enzymes. The 2.8 angstrom crystal structure of the inhibitor-enzyme complex demonstrated that the inhibitor binds to the enzyme in a highly symmetric fashion.     

Structural evidence for common ancestry of the nuclear pore complex and vesicle coats

Nuclear pore complexes (NPCs) facilitate nucleocytoplasmic transport. These massive assemblies comprise an eightfold symmetric scaffold of architectural proteins and central-channel phenylalanine-glycine-repeat proteins forming the transport barrier. We determined the nucleoporin 85 (Nup85)*Seh1 structure, a module in the heptameric Nup84 complex, at 3.5 angstroms resolution. Structural, biochemical, and genetic analyses position the Nup84 complex in two peripheral NPC rings. We establish a conserved tripartite element, the ancestral coatomer element ACE1, that reoccurs in several nucleoporins and vesicle coat proteins, providing structural evidence of coevolution from a common ancestor. We identified interactions that define the organization of the Nup84 complex on the basis of comparison with vesicle coats and confirmed the sites by mutagenesis. We propose that the NPC scaffold, like vesicle coats, is composed of polygons with vertices and edges forming a membrane-proximal lattice that provides docking sites for additional nucleoporins.     

Flip-flopping fractional flux quanta

The d-wave pairing symmetry in high-critical temperature superconductors makes it possible to realize superconducting rings with built-in pi phase shifts. Such rings have a twofold degenerate ground state that is characterized by the spontaneous generation of fractional magnetic flux quanta with either up or down polarity. We have incorporated pi phase-biased superconducting rings in a logic circuit, a flip-flop, in which the fractional flux polarity is controllably toggled by applying single flux quantum pulses at the input channel. The integration of p rings into conventional rapid single flux quantum logic as natural two-state devices should alleviate the need for bias current lines, improve device symmetry, and enhance the operation margins.     

How a DNA polymerase clamp loader opens a sliding clamp

Processive chromosomal replication relies on sliding DNA clamps, which are loaded onto DNA by pentameric clamp loader complexes belonging to the AAA+ family of adenosine triphosphatases (ATPases). We present structures for the ATP-bound state of the clamp loader complex from bacteriophage T4, bound to an open clamp and primer-template DNA. The clamp loader traps a spiral conformation of the open clamp so that both the loader and the clamp match the helical symmetry of DNA. One structure reveals that ATP has been hydrolyzed in one subunit and suggests that clamp closure and ejection of the loader involves disruption of the ATP-dependent match in symmetry. The structures explain how synergy among the loader, the clamp, and DNA can trigger ATP hydrolysis and release of the closed clamp on DNA.     

Motoneuron morphology and synaptic contacts: determination by intracellular dye injection

The structure and dendritic connections of an identified crustacean motoneuron were analyzed by intracellular injection of dye. Some processes of the neuron end in the ganglionic neuropil, but most terminate on axons which pass through the ganglion in specific, identifiable tracts. The former processes are ipsilateral to the soma, while the latter, as well as their connections, display bilateral symmetry. Structural and functional evidence suggests that the demonstrated contacts are synaptic junctions, and that the approach can therefore be used to study patterns of synaptic organization in complex neural networks.     

Territorial strategies in ants

Several features in social insects, particularly in ants, make the behavioral organization of territoriality considerably more complex than that of solitary animals. The establishment and maintenance of territories are based on a division of labor and a complex communication system. The analyses of territorial strategies in ants comprise the study of the design and spatiotemporal structure of the territory, as well as the social mechanisms through which the insect society pursues its territorial strategy. The geometric and behavioral organization of the absolute territories of the African weaver ants (Oecophylla longinoda) and harvester ants (Pogonomyrmex), and of the "spatiotemporal territories" of honey ants (Myrmecocystus mimicus) are described, and simple cost-benefit models are developed to illustrate the economic defensibility of each type of territory.     

Cartwheel architecture of Trichonympha basal body

Centrioles and basal bodies are essential for the formation of cilia, flagella, and centrosomes. They exhibit a characteristic ninefold symmetry imparted by a cartwheel thought to contain rings of SAS-6 proteins. We used cryoelectron tomography to investigate the architecture of the exceptionally long cartwheel of the flagellate Trichonympha. We found that the cartwheel is a stack of central rings that exhibit a vertical periodicity of 8.5 nanometers and is able to accommodate nine SAS-6 homodimers. The spokes that emanate from two such rings associate into a layer, with a vertical periodicity of 17 nanometers on the cartwheel margin. Thus, by using the power of biodiversity, we unveiled the architecture of the cartwheel at the root of the ninefold symmetry of centrioles and basal bodies.     

Bond lengths in free molecules of buckminsterfullerene, c60, from gas-phase electron diffraction

Electron diffraction patterns of the fullerene C(60) in the gaseous state have been obtained by volatilizing it from a newly designed oven-nozzle at 730 degrees C. The many peaks of the experimental radial distribution curve calculated from the scattered intensity are completely consistent with icosahedral symmetry for the free molecule. On the basis of this symmetry assumption, least-squares refinement of a model incorporating all possible interatomic distances led to the values r(g)(C(1)-C(2)) = 1.458(6) angstroms (A) for the thermal average bond length within the five-member ring (that is, for the bond fusing five- and six-member rings) and r(g)(C(1)-C(6)) = 1.401(10) A for that connecting five-member rings (the bond fusing six-member rings). The weighted average of the two bond lengths and the difference between them are the values 1.439(2) A and 0.057(6) A, respectively. The diameter of the icosahedral sphere is 7.113(10) A. The uncertainties in parentheses are estimated 2sigma values.     

Ability of the c-mos product to associate with and phosphorylate tubulin.

The mos proto-oncogene product, pp39mos, is a protein kinase and has been equated with cytostatic factor (CSF), an activity in unfertilized eggs that is thought to be responsible for the arrest of meiosis at metaphase II. The biochemical properties and potential substrates of pp39mos were examined in unfertilized eggs and in transformed cells in order to study how the protein functions both as CSF and in transformation. The pp39mos protein associated with polymers under conditions that favor tubulin oligomerization and was present in an approximately 500-kilodalton "core" complex under conditions that favor depolymerization. beta-Tubulin was preferentially coprecipitated in pp39mos immunoprecipitates and was the major phosphorylated product in a pp39mos-dependent immune complex kinase assay. Immunofluorescence analysis of NIH 3T3 cells transformed with Xenopus c-mos showed that pp39mos colocalizes with tubulin in the spindle during metaphase and in the midbody and asters during telophase. Disruption of microtubules with nocodazole affected tubulin and pp39mos organization in the same way. It therefore appears that pp39mos is a tubulin-associated protein kinase and may thus participate in the modification of microtubules and contribute to the formation of the spindle. This activity expressed during interphase in somatic cells may be responsible for the transforming activity of pp39mos.     

土著菌田间扩繁技术对烟叶质量的影响

[目的]研究土著菌田间扩繁技术对烟叶质量的影响,探讨进一步降低化肥施用量的可行性。[方法]于2016年在费县试验田以NC102为研究材料,设置T1、T2、CK(对照)3个处理,研究不同处理对农艺性状、经济性状、烟叶外观质量和感官质量的影响。[结果]施用土著菌处理的烟株长势良好,在农艺性状方面,有效叶数较多,抗病性能较高,叶面积较大,组织结构好,田间整齐度较高;在经济性状方面,T2处理最优,产量、均价、产值等各项经济指标均最高,其次是T1处理,CK组各项指标均最低;原烟外观质量方面,2个土著菌处理烟株烤后烟呈橘黄色,烟叶油分有,组织结构疏松,优于CK组;在感官质量方面,2个土著菌处理香气质稍提升、杂气减轻、刺激性降低,余味有所改善,整体感官质量提升,优于CK组。[结论]土著菌田间扩繁技术对于提高烟叶质量具有显著的影响。     

Structure of the rotor ring of F-Type Na+-ATPase from Ilyobacter tartaricus

In the crystal structure of the membrane-embedded rotor ring of the sodium ion-translocating adenosine 5'-triphosphate (ATP) synthase of Ilyobacter tartaricus at 2.4 angstrom resolution, 11 c subunits are assembled into an hourglass-shaped cylinder with 11-fold symmetry. Sodium ions are bound in a locked conformation close to the outer surface of the cylinder near the middle of the membrane. The structure supports an ion-translocation mechanism in the intact ATP synthase in which the binding site converts from the locked conformation into one that opens toward subunit a as the rotor ring moves through the subunit a/c interface.     

Topologically linked protein rings in the bacteriophage HK97 capsid

The crystal structure of the double-stranded DNA bacteriophage HK97 mature empty capsid was determined at 3.6 angstrom resolution. The 660 angstrom diameter icosahedral particle contains 420 subunits with a new fold. The final capsid maturation step is an autocatalytic reaction that creates 420 isopeptide bonds between proteins. Each subunit is joined to two of its neighbors by ligation of the side-chain lysine 169 to asparagine 356. This generates 12 pentameric and 60 hexameric rings of covalently joined subunits that loop through each other, creating protein chainmail: topologically linked protein catenanes arranged with icosahedral symmetry. Catenanes have not been previously observed in proteins and provide a stabilization mechanism for the very thin HK97 capsid.     

Graphite polyhedral crystals

Polyhedral nano- and microstructures with shapes of faceted needles, rods, rings, barrels, and double-tipped pyramids, which we call graphite polyhedral crystals (GPCs), have been discovered. They were found in pores of glassy carbon. They have nanotube cores and graphite faces, and they can exhibit unusual sevenfold, ninefold, or more complex axial symmetry. Although some are giant radially extended nanotubes, Raman spectroscopy and transmission electron microscopy suggest GPCs have a degree of perfection higher than in multiwall nanotubes of similar size. The crystals are up to 1 micrometer in cross section and 5 micrometers in length, and they can probably be grown in much larger sizes. Preliminary results suggest a high electrical conductivity, strength, and chemical stability of GPC.     

Planet Within a Planet: Rotation of the Inner Core of Earth

The time dependence of the orientation of Earth's inner core relative to the mantle was determined using a recently discovered 10-degree tilt in the axis of symmetry of the inner core's seismic-velocity anisotropy. Two methods of analyzing travel-time variations for rays traversing the inner core, on the basis of 29 years of data from the International Seismological Centre (1964-1992), reveal that the inner core appears to rotate about 3 degrees per year faster than the mantle. An anomalous variation in inner-core orientation from 1969 to 1973 coincides in time with a sudden change ("jerk") in the geomagnetic field.     

槭树绵粉蚧雄性生殖器官和精子超微结构观察

槭树绵粉蚧是我国北方林木的一种重要害虫。本文详细描述了其雄性生殖器官和精子的超微结构。每精子束有精子 1 3～1 8根 ,平均 1 6根。精子内的微管 52～ 54个 ,平均 53个 ,在无核区呈 3圈完全同心圆排列 ,有核区呈 2 圈不完全同心圆排列。     

Metallo-Carbohedrenes [M8C12+ (M = V, Zr, Hf, and Ti)]: A Class of Stable Molecular Cluster Ions

Findings of magic peaks corresponding to M(8)C(12)(+) (M = V, Zr, and Hf) formed from reactions of the respective metals with various small hydrocarbons, in conjunction with recent findings for the titanium system, establish metallo-carbohedrenes as a stable general class of molecular cluster ions. A dodecahedral structure of T(h) point symmetry accounts for the stability of these ionic clusters.     

Structure and specificity of a class II MHC alloreactive gamma delta T cell receptor heterodimer

Two distinct CD3-associated T cell receptors (TCR alpha beta and TCR gamma delta) are expressed in a mutually exclusive fashion on separate subsets of T lymphocytes. While the specificity of the TCR alpha beta repertoire for major histocompatibility complex (MHC) antigens is well established, the diversity of expressed gamma delta receptors and the ligands they recognize are less well understood. An alloreactive CD3+CD4-CD8- T cell line specific for murine class II MHC (Ia) antigens encoded in the I-E subregion of the H-2 gene complex was identified, and the primary structure of its gamma delta receptor heterodimer was characterized. In contrast to a TCR alpha beta-expressing alloreactive T cell line selected for similar specificity, the TCR gamma delta line displayed broad cross-reactivity for multiple distinct I-E-encoded allogeneic Ia molecules.