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Breaking Symmetry (breaking + symmetry)
Selected AbstractsChemInform Abstract: Breaking Symmetry: Spontaneous Resolution of a PolyoxometalateCHEMINFORM, Issue 8 2008Yu Hou 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] Breaking Symmetry: Spontaneous Resolution of a PolyoxometalateCHEMISTRY - A EUROPEAN JOURNAL, Issue 34 2007Yu Hou Abstract A chiral polyoxometalate [Hf(PW11O39)2]10, (1) has been prepared and structurally characterized. It crystallizes in the chiral space group P21212, as a conglomerate of two enantiomerically pure crystals in the absence of any chiral source. The absolute configuration of 1 was determined from the Flack parameter by X-ray crystallography. The structure of 1 comprises two lacunary [PW11O39]7, units, each functioning as a tetra-dentate ligand sandwiching an 8-coordinate HfIV centre in a distorted square antiprismatic geometry. Optically active crystals of both enantiomers were spectroscopically distinguishable by means of solid state circular dichroism spectroscopy. This hafnium-substituted polyoxometalate (POM), 1, shows that spontaneous chiral resolution, a rare phenomenon, can be operable in POM systems. [source] Breaking symmetry in protein dimers: Designs and functionsPROTEIN SCIENCE, Issue 1 2006Jerry H. Brown Abstract Symmetry, and in particular point group symmetry, is generally the rule for the global arrangement between subunits in homodimeric and other oligomeric proteins. The structures of fragments of tropomyosin and bovine fibrinogen are recently published examples, however, of asymmetric interactions between chemically identical chains. Their departures from strict twofold symmetry are based on simple and generalizable chemical designs, but were not anticipated prior to their structure determinations. The current review aims to improve our understanding of the structural principles and functional consequences of asymmetric interactions in proteins. Here, a survey of >100 diverse homodimers has focused on the structures immediately adjacent to the twofold axis. Five regular frameworks in ,-helical coiled coils and antiparallel ,-sheets accommodate many of the twofold symmetric axes. On the basis of these frameworks, certain sequence motifs can break symmetry in geometrically defined manners. In antiparallel ,-sheets, these asymmetries include register slips between strands of repeating residues and the adoption of different side-chain rotamers to avoid steric clashes of bulky residues. In parallel coiled coils, an axial stagger between the ,-helices is produced by clusters of core alanines. Such simple designs lead to a basic understanding of the functions of diverse proteins. These functions include regulation of muscle contraction by tropomyosin, blood clot formation by fibrin, half-of-site reactivity of caspase-9, and adaptive protein recognition in the matrix metalloproteinase MMP9. Moreover, asymmetry between chemically identical subunits, by producing multiple equally stable conformations, leads to unique dynamic and self-assembly properties. [source] Breaking symmetry: a clinical overview of left-right patterningCLINICAL GENETICS, Issue 6 2004K Maclean It is increasingly recognized that mutations in genes and pathways critical for left-right (L-R) patterning are involved in common isolated congenital malformations such as congenital heart disease, biliary tract anomalies, renal polycystic disease, and malrotation of the intestine, indicating that disorders of L-R development are far more common than a 1 in 10,000 incidence of heterotaxia might suggest. Understanding L-R patterning disorders requires knowledge of molecular biology, embryology, pediatrics, and internal medicine and is relevant to day-to-day clinical genetics practice. We have reviewed data from mammalian (human and mouse) L-R patterning disorders to provide a clinically oriented perspective that might afford the clinician or researcher additional insights into this diagnostically challenging area. [source] | ||||||||||