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High Symmetry (high + symmetry)
Selected AbstractsChemInform Abstract: Theoretical Investigation of Clusters of Phosphorus and Arsenic: Fascination and Temptation of High Symmetries.CHEMINFORM, Issue 30 2008Paola Nava Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Antiaromaticity in Bare Deltahedral Silicon Clusters Satisfying Wade,s and Hirsch,s Rules: An Apparent Correlation of Antiaromaticity with High Symmetry.CHEMINFORM, Issue 16 2004R. Bruce King No abstract is available for this article. [source] D5h Cu5H5X: Pentagonal Hydrocopper Cu5H5 Containing Pentacoordinate Planar Nonmetal Centers (X = B, C, N, O)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2004Si-Dian Li Abstract Pentacoordinate planar nonmetals (PPNs) centered in perfect pentagonal hydrocopper complexes Cu5H5X (X = B, C, N, O), as determined by density functional theory methods, are presented in this communication. The results obtained in this work complete the hypercoordinate planar carbon series with high symmetries (D4h, D5h, and D6h), and may shed new insight in catalyst chemistry. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] Three-dimensional thermoelastic stresses in off-axis oriented single crystals with hexagonal symmetryCRYSTAL RESEARCH AND TECHNOLOGY, Issue 3 2007K. Böttcher Abstract A three-dimensional (3D) thermoelastic stress analysis is carried out on a single crystal with axisymmetric geometry but with a hexagonal crystallographic symmetry. The crystallographic orientation is off-axis with respect to the cylindrical coordinate system. By applying a Fourier series expansion with respect to the rotational angle , of the cylindrical coordinates, the 3D boundary value problem is reduced to a sequence of 2D ones on the meridian plane, which are solved by the finite-element method. In our example, the off-axis orientation is towards a direction of high symmetry, and therefore only four of the six stress tensor components are non-zero. In the end, the stress tensor is projected onto the slip system of the crystal. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Synchronization patterns in spaghetti-like nanoclustersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 15 2008Acep Purqon Abstract Spaghetti-like nanoclusters concern disordered shapes and irregular shape fluctuations in few correlated biological lipids. We evaluate the shape fluctuations by introducing Symmetry- S as a physical parameter for measuring symmetry degrees and detecting shape transitions. From numerical simulation of few correlated lipids of POPC and POPE at 300 K and 340 K by using molecular dynamics, we investigate the symmetry dynamics for each individual cluster by analyzing both spatiotemporal and frequency. From spatiotemporal analysis, we find several jump motions in S -dynamics and non-Gaussian distributions in S -distribution. Interestingly, the jump motions likely contribute on the existence of transitions in the non-Gaussian distributions. Additionally, even number of lipids show more symmetric than the odd number of lipids and the symmetry distributions shift at higher temperature, while, from three dimension of actual position of symmetry dynamics, they are not easy to configure high symmetry as well as showing certain patterns. From power spectra density analysis, each individual cluster shows nearly random fluctuation. Besides individual clusters, we also investigate mutual clusters. Surprisingly, although individual clusters show fluctuations randomly, mutual clusters show certain direction correlations. Moreover, they show certain patterns in delayed time analysis such as mutual fluctuations periodically occur for same number of lipids. It indicates that an existence of synchronization patterns occur in shape fluctuations of spaghetti-like nanoclusters. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2008 [source] 7Li and 13C solid-state NMR spectra of lithium cuprates,MAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2006Steffen Jost Abstract 7Li and 13C solid-state MAS NMR spectra of three lithium cuprates with known X-ray structures,lithium([12]crown-4)2 dimethyl and diphenyl cuprate (1,2) and lithium(thf)4 -[tris(trimethylsilyl) methyl]2 cuprate (3),have been measured and analysed with respect to the quadrupolar coupling constants of lithium-7, ,(7Li), and the asymmetry parameters of the quadrupolar interactions, ,(7Li), as well as the 6, 7Li and 13C chemical shifts. The ,(7Li) values of 23, 30, and 18 kHz for 1, 2 and 3, respectively, are in line with the high symmetry around the lithium nucleus in the solvent-separated structures and may be used as reference data for this structural motif. Calculations based on charges derived from ab initio 6-31 G* HF computations using the point charge model (PCM) and the program GAMESS support the experimental findings. Copyright © 2006 John Wiley & Sons, Ltd. [source] Type II dehydroquinase: molecular replacement with many copiesACTA CRYSTALLOGRAPHICA SECTION D, Issue 1 2008Kirsty Anne Stewart Type II dehydroquinase is a small (150-amino-acid) protein which in solution packs together to form a dodecamer with 23 cubic symmetry. In crystals of this protein the symmetry of the biological unit can be coincident with the crystallographic symmetry, giving rise to cubic crystal forms with a single monomer in the asymmetric unit. In crystals where this is not the case, multiple copies of the monomer are present, giving rise to significant and often confusing noncrystallographic symmetry in low-symmetry crystal systems. These different crystal forms pose a variety of challenges for solution by molecular replacement. Three examples of structure solutions, including a highly unusual triclinic crystal form with 16 dodecamers (192 monomers) in the unit cell, are described. Four commonly used molecular-replacement packages are assessed against two of these examples, one of high symmetry and the other of low symmetry; this study highlights how program performance can vary significantly depending on the given problem. In addition, the final refined structure of the 16-dodecamer triclinic crystal form is analysed and shown not to be a superlattice structure, but rather an F -centred cubic crystal with frustrated crystallographic symmetry. [source] Self-Assembled Ionophores from Isoguanosine: Diffusion NMR Spectroscopy Clarifies Cation's and Anion's Influence on Supramolecular StructureCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007Tamar Evan-Salem Abstract Cation-templated self-assembly of the lipophilic isoguanosine (isoG,1) with different monovalent cations (M+=Li+, Na+, K+, NH4+, and Cs+) was studied in solvents of different polarity by using diffusion NMR spectroscopy. Previous studies that did not use diffusion NMR techniques concluded that isoG,1 forms both pentamers (isoG,1)5,M+ and decamers (isoG,1)10,M+ in the presence of alkali-metal cations. The present diffusion NMR studies demonstrate, however, that isoG,1 does not form (isoG,1)5,M+ pentamers. In fact, the diffusion NMR data indicates that both doubly charged decamers of formula (isoG,1)10,2,M+ and singly charged decamers, (isoG,1)10,M+, are formed with lithium, sodium, potassium, and ammonium tetraphenylborate salts (LiB(Ph)4, KB(Ph)4, NaB(Ph)4 and NH4B(Ph)4), depending on the isoG,1:salt stoichiometry of the solution. In the presence of CsB(Ph)4, isoG,1 affords only the singly charged decamers (isoG,1)10,Cs+. By monitoring the diffusion coefficient of the B(Ph)4, ion in the different mixtures of solvents, we also concluded that the anion is more strongly associated to the doubly charged decamers (isoG,1)10,2,M+ than to the singly charged decamers (isoG,1)10,M+. The (isoG,1)10,2,M+ species can, however, exist in solution without the mediation of the anion. This last conclusion was supported by the finding that the doubly charged decamers (isoG,1)10,2,M+ also prevail in 1:1 CD3CN:CDCl3, a solvent mixture in which the B(Ph)4, ion does not interact significantly with the self-assembled complex. These diffusion measurements, which have provided new and improved structural information about these decameric isoG,1 assemblies, demonstrate the utility of combining diffusion NMR techniques with conventional NMR methods in seeking to characterize labile, multicomponent, supramolecular systems in solution, especially those with high symmetry. [source] | ||||||||||