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Rare Example (rare + example)
Selected AbstractsSynthesis and Properties of Organometallic PtII and PtIV Complexes with Acyclic Selenoether and Telluroether Ligands and Selenoether MacrocyclesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006William Levason Abstract The first series of planar dimethyl(selenoether)PtII complexes, [PtMe2L] [L = MeSe(CH2)nSeMe (n = 2 or 3), o -C6H4(CH2SeMe)2, [8]aneSe2 (1,5-diselenacyclooctane), or [16]aneSe4 (1,5,9,13-tetraselenacyclohexadecane)], have been obtained by treatment of [PtMe2(SMe2)2] with L in Et2O solution and characterised by VT 1H, 13C{1H}, 77Se{1H} and 195Pt{1H} NMR spectroscopy, electrospray MS and microanalysis. The corresponding dimethyl(telluroether)PtII complexes do not form under similar reaction conditions. The distorted octahedral [PtMe3I(L)] [L = o -C6H4(CH2SeMe)2, [8]aneSe2, [16]aneSe4 or MeC(CH2SeMe)3] form as stable complexes in good yield from reaction of PtMe3I with L in refluxing CHCl3 and have been characterised similarly. These all show bidentate selenoether coordination, with fast pyramidal inversion occurring at room temperature. The distorted octahedral coordination environment at PtIV is also confirmed from a crystal structure of [PtMe3I{o -C6H4(CH2SeMe)2}]. Rare examples of (telluroether)PtIV complexes, [PtMe3I{o -C6H4(CH2TeMe)2}] and the dinuclear [Me3Pt(,2 -I)2(,2 -MeTeCH2TeMe)PtMe3], have also been prepared and characterised similarly (and also by 125Te{1H} NMR spectroscopy). The [8]aneSe2 and [16]aneSe4 species are the first examples of alkyl PtII or PtIV complexes with (macro)cyclic selenoether coordination. Halide abstraction (TlPF6) from [PtMe3I(,2 -[16]aneSe4)] affords [PtMe3(,3 -[16]aneSe4)]PF6; a rare example of a cationic PtIV selenoether. The (diselenoether)PtII complexes undergo oxidative addition of MeI to yield the corresponding PtIV species [PtMe3I(diselenoether)]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] The evolution of arthropod limbsBIOLOGICAL REVIEWS, Issue 2 2004Geoff A. Boxshall ABSTRACT Limb morphology across the arthropods is reviewed using external morphological and internal anatomical data from both recent and fossil arthropods. Evolutionary trends in limb structure are identified primarily by reference to the more rigorous of the many existing phylogenetic schemes, but no major new phylogenetic inferences are presented. Tagmosis patterns are not considered, although the origins and patterns of heteronomy within the postantennulary limb series are analysed. The phenomenon of annulation is examined and two basic types of annuli are recognised: terminal and intercalary. The annulation of the apical segment of a limb results in the formation of terminal flagella, and is typical of primarily sensory appendages such as insect and malacostracan antennules and maxillary palps of some hexapods. Intercalary annulation, arising by subdivision of existing subterminal segments, is common, particularly in the tarsal region of arthropodan walking limbs. Differentiating between segments and annuli is discussed and is recognised as a limiting factor in the interpretation of fossils, which usually lack information on intrinsic musculature, and in the construction of groundplans. Rare examples of secondary segmentation, where the criteria for distinguishing between segments and annuli fail, are also highlighted. The basic crown-group arthropodan limb is identified as tripartite, comprising protopodite, telopodite and exopodite, and the basic segmentation patterns of each of these parts are hypothesised. Possible criteria are discussed that can be used for establishing the boundary between protopodite and telopodite in limbs that are uniramous through loss of the exopodite. The subdivision of the protopodite, which is typical of the postantennulary limbs of mandibulates, is examined. The difficulties resulting from the partial or complete failure of expression of articulations within the mandibulate protopodite and subsequent incorporation of partial proto-podal segments into the body wall, are also discussed. The development and homology between the various exites, including gills, on the postantennulary limbs of arthropods are considered in some detail, and the question of the possible homology between crustacean gills and insect wings is critically addressed. The hypothesis that there are only two basic limb types in arthropods, antennules and postantennulary limbs, is proposed and its apparent contradiction by the transformation of antennules into walking limbs by homeotic mutation is discussed with respect to the appropriate level of serial homology between these limbs. [source] Novel, Sensitive Voltammetric Methods for Titanium Determination Using Chromotropic Acid and Azo-Compounds as Complexing AgentsELECTROANALYSIS, Issue 12 2003Marcin Gawrys Abstract Voltammetric behavior of titanium(IV) complexes with chromotropic acid, its azo-derivatives: 2-(4-sulfophenylazo)-1,8-dihydroxy-3,6-naphthalenedisulfonic acid (SPANDS), chromotrope 2B, sulfonazo III and other azo-compounds: calmagite, tropeoline O and kalces was investigated at a hanging mercury drop electrode. These complexes strongly adsorb onto the electrode, thus can be determined by an adsorptive stripping voltammetry (optimal pH about 6). At pH about 3 reduction current enhancement for Ti-kalces complex was observed in the presence of chlorate ions. It is a rare example of a catalytic process with azo-compound as a complexing agent. Signal for Fe-calmagite complex reduction was also observed. Influence of foreign ions and the optimal conditions for titanium determination are described in detail. Additionally, a connection between obtained results and a structure of titanium complexes is discussed. [source] Lady Russell, Elizabeth I, and Female Political Alliances through PerformanceENGLISH LITERARY RENAISSANCE, Issue 2 2009Elizabeth Zeman Kolkovich The entertainment at Bisham Abbey in 1592 offers a rare example of female authorship and performance in a sixteenth-century dramatic text. Lady Elizabeth (Cooke Hoby) Russell wrote and staged this entertainment for Elizabeth I during a royal progress, and her two teenaged daughters performed speaking roles. The Bisham performance challenges assumptions about women's limitations, endorses a militant Protestant foreign policy, and revises conventions of Elizabethan progress entertainments to claim the genre as an appropriate arena for aristocratic women's political negotiations. In successful auditions to be maids of honor, the young Russell women urge the Queen to surround herself with capable female servants who can better assist her in religious and gender battles than her flawed male advisors. As they propose themselves as loyal alternatives to self-serving male courtiers, these young performers adopt elements of the Queen's image, revealing that they claim authority to engage in court performance and promote political agendas from her example. (E.Z.K.) [source] Ba6Si6N10O2(CN2) , A Nitridosilicate with a NPO-Zeolite Structure Type Containing Carbodiimide IonsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2009Sandro Pagano Abstract A new precursor approach leading to NPO-zeolite analogous nitridosilicates with cavities containing carbodiimide ions is presented. The reaction of amorphous "Si(CN2)2" and barium in liquid sodium afforded Ba6Si6N10O2(CN2) as yellow crystals. The structure is a rare example of the NPO-zeolite framework type and the first nitridosilicate incorporating carbodiimide ions. The partially ordered integration of carbodiimide moieties in the channels leads to the formation of a superstructure (P, no. 174, a = 16.255(2), c = 5.4690(11) Å, Z = 3, R1 = 0.0299, 2139 data, 100 parameters) and merohedral twinning. A comprehensive structure solution is presented, taking all possible ordering variants and twin laws into account.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Mechanism of Hydride Abstraction by Cyclopentadienone-Ligated Carbonylmetal Complexes (M = Ru, Fe)EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2009Megan K. Thorson Abstract Cyclopentadienone-ligated ruthenium complexes, such as Shvo's catalyst, are known to oxidize reversibly alcohols to the corresponding carbonyl compounds. The mechanism of this reaction has been the subject of some controversy, but it is generally believed to proceed through concerted transfer of proton and hydride, respectively, to the cyclopentadienone ligand and the ruthenium center. In this paper we further study the hydride transfer process as an example of a coordinatively directed hydride abstraction by adding quantitative understanding to some features of this mechanism that are not well understood. We find that an oxidant as weak as acetone can be used to re-oxidize the intermediate ruthenium hydride without catalyst re-oxidation becoming rate-limiting. Furthermore, C,H cleavage is a significantly electrophilic event, as demonstrated by a Hammett reaction parameter of , = ,0.89. We then describe how the application of our mechanistic insights obtained from the study have enabled us to extend the ligand-directed hydride abstraction strategy to include a rare example of an iron(0) oxidation catalyst.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source] Receptor versus Counterion: Capability of N,N, -Bis(2-aminobenzyl)-diazacrowns for Giving Endo- and/or Exocyclic Coordination of ZnIIEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2007Lea Vaiana Abstract The structure of ZnII complexes with receptors L1 and L2[L1 = N,N, -bis(2-aminobenzyl)-1,10-diaza-15-crown-5 and L2 = N,N, -bis(2-aminobenzyl)-4,13-diaza-18-crown-6] was studied both in the solid state and in acetonitrile solution. Both receptors form mononuclear ZnII complexes in this solvent, while no evidence for the formation of dinuclear complexes was obtained. This is in contrast with previous investigations that demonstrated the formation of dinuclear complexes of L2 with first-row transition metals such as NiII, CoII and CuII. Compounds of formula [Zn(L1)](ClO4)2 (1), [Zn(L1)](NO3)2·2CH3CN (2), [Zn(L2)](ClO4)2 (3) and [Zn(L2)(NO3)2] (4) were isolated and structurally characterised by X-ray diffraction analyses. L1 forms seven-coordinate ZnII complexes in the presence of both nitrate and perchlorate anions, as a consequence of the good fit between the macrocyclic cavity and the ionic radius of the metal ion. The ZnII ion is deeply buried into the receptor cavity and the anions are forced to remain out of the metal coordination sphere. The cation [Zn(L1)]2+ present in 1 and 2 is one of the very few examples of seven-coordinate Zn complexes. Receptor L2 provides a very rare example of a macrocyclic receptor allowing endocyclic and exocyclic coordination on the same guest cation, depending on the nature of the anion present. Thus, in 3 the ZnII ion is endocyclically coordinated, placed inside the crown hole coordinated to four donor atoms of the ligand in a distorted tetrahedral environment, whereas in 4, the presence of a strongly coordinating anion such as nitrate results in an exocyclic coordination of ZnII, which is directly bound only to the two primarily amine groups of L2 and two nitrate ligands. Spectrophotometric titrations of [Zn(L2)]2+ with tetrabutylammonium nitrate in acetonitrile solution demonstrate the stepwise formation of 1:1 and 1:2 adducts with this anion in acetonitrile solution. The [Zn(L1)]2+, [Zn(L2)]2+ and [Zn(L2)(NO3)2] systems were characterised by means of DFT calculations (B3LYP model). The calculated geometries show an excellent agreement with the experimental structures obtained from X-ray diffraction analyses. Calculated binding energies of the macrocyclic ligands to ZnII are also consistent with the experimental data.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Synthesis and Properties of Organometallic PtII and PtIV Complexes with Acyclic Selenoether and Telluroether Ligands and Selenoether MacrocyclesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 21 2006William Levason Abstract The first series of planar dimethyl(selenoether)PtII complexes, [PtMe2L] [L = MeSe(CH2)nSeMe (n = 2 or 3), o -C6H4(CH2SeMe)2, [8]aneSe2 (1,5-diselenacyclooctane), or [16]aneSe4 (1,5,9,13-tetraselenacyclohexadecane)], have been obtained by treatment of [PtMe2(SMe2)2] with L in Et2O solution and characterised by VT 1H, 13C{1H}, 77Se{1H} and 195Pt{1H} NMR spectroscopy, electrospray MS and microanalysis. The corresponding dimethyl(telluroether)PtII complexes do not form under similar reaction conditions. The distorted octahedral [PtMe3I(L)] [L = o -C6H4(CH2SeMe)2, [8]aneSe2, [16]aneSe4 or MeC(CH2SeMe)3] form as stable complexes in good yield from reaction of PtMe3I with L in refluxing CHCl3 and have been characterised similarly. These all show bidentate selenoether coordination, with fast pyramidal inversion occurring at room temperature. The distorted octahedral coordination environment at PtIV is also confirmed from a crystal structure of [PtMe3I{o -C6H4(CH2SeMe)2}]. Rare examples of (telluroether)PtIV complexes, [PtMe3I{o -C6H4(CH2TeMe)2}] and the dinuclear [Me3Pt(,2 -I)2(,2 -MeTeCH2TeMe)PtMe3], have also been prepared and characterised similarly (and also by 125Te{1H} NMR spectroscopy). The [8]aneSe2 and [16]aneSe4 species are the first examples of alkyl PtII or PtIV complexes with (macro)cyclic selenoether coordination. Halide abstraction (TlPF6) from [PtMe3I(,2 -[16]aneSe4)] affords [PtMe3(,3 -[16]aneSe4)]PF6; a rare example of a cationic PtIV selenoether. The (diselenoether)PtII complexes undergo oxidative addition of MeI to yield the corresponding PtIV species [PtMe3I(diselenoether)]. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Lithium and Potassium Amides of Sterically Demanding AminopyridinesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2004Natalie M. Scott Abstract The reaction of Grignard compounds of 1-bromo-2,4,6-diisopropylbenzene (1) or 1-bromo-2,6-dimethylbenzene (2), formed in situ, with 2,6-dibromopyridine in the presence of a catalytic amount of [(dme)NiBr2] (dme = 1,2-dimethoxyethane) and tricyclohexylphosphane (1:2 ratio) leads to the corresponding monoarylated bromopyridines. These bromopyridines undergo Pd-catalysed aryl amination (Buchwald,Hartwig amination) with 2,6-diisopropylaniline giving rise to (2,6-diisopropylphenyl)[6-(2,4,6-triisopropylphenyl)pyridin-2-yl]amine (Ap*H) and (2,6-diisopropylphenyl)[6-(2,6-dimethylphenyl)pyridin-2-yl]amine (Ap,H) (Ap = aminopyridinate). Deprotonation of Ap*H in diethyl ether using BuLi results (after workup in hexane) in a colourless crystalline material. X-ray structural analysis reveals it to be a monomeric three-coordinate lithium aminopyridinate. In toluene solution, an equilibrium between [(Ap*Li)2] (in excess at room temperature) and [Ap*Li(OEt2)] (prominent at low temperature) is observed. Reaction of Ap,H with BuLi in diethyl ether gives rise to [Ap*LiAp*Li(OEt2)]. Deprotonation of Ap*H and Ap,H using KH leads to [Ap*K]n and [Ap,K],, respectively. [Ap,K], is a rare example of a crystalline organometallic polymer, as determined by X-ray analysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] RECENT ECOLOGICAL DIVERGENCE DESPITE MIGRATION IN SOCKEYE SALMON (ONCORHYNCHUS NERKA)EVOLUTION, Issue 6 2010Scott A. Pavey Ecological divergence may result when populations experience different selection regimes, but there is considerable discussion about the role of migration at the beginning stages of divergence before reproductive isolating mechanisms have evolved. However, detection of past migration is difficult in current populations and tools to differentiate genetic similarities due to migration versus recent common ancestry are only recently available. Using past volcanic eruption times as a framework, we combine morphological analyses of traits important to reproduction with a coalescent-based genetic analysis of two proximate sockeye salmon (Oncorhynchus nerka) populations. We find that this is the most recent (,500 years, 100 generations) natural ecological divergence recorded in a fish species, and report that this divergence is occurring despite migration. Although studies of fish divergence following the retreat of glaciers (10,000,15,000 years ago) have contributed extensively to our understanding of speciation, the Aniakchak system of sockeye salmon provides a rare example of the initial stages of ecological divergence following natural colonization. Our results show that even in the face of continued migration, populations may diverge in the absence of a physical barrier. [source] ,Agree with the king': Henry VII, Edmund Dudley and the strange case of Thomas SunnyffHISTORICAL RESEARCH, Issue 205 2006Mark R. Horowitz Although Richard Empson and Edmund Dudley were executed in 1510 in part for their rabid prosecution of written bonds, their activities at the time were only quietly recognized as part of a royal policy encouraged by Henry VII (1485,1509). Yet there has been little investigation into how these ministers went about mulcting the populace, beyond the vituperative reports of the London chronicles. The case of Thomas Sunnyff, which has not been analyzed or placed in the context of such activity, is a rare example of how Empson, Dudley and their minions went about their business. Using City, local and national documentation, the article uncovers what happened, why and how it reflected royal policy. [source] Persistent sciatic vessels associated with an arteriovenous malformationJOURNAL OF ANATOMY, Issue 3 2001ZELIHA KURTO The sciatic artery is the major arterial supply to the lower limb bud at an early embryological stage. It primarily originates from the dorsal root of the umbilical artery. After the 22 mm embryological stage, the sciatic artery involutes and the femoral artery system develops as the major inflow source to the lower limb. In the adult, remnants of the sciatic artery persist as the proximal portion of the inferior gluteal artery, the popliteal and peroneal arteries (Williams et al. 1989). It is suggested that either failure in development of the femoral system or failure in regression of the sciatic artery results in persistence of this artery (Arey, 1965). We report a rare example of persistent sciatic artery (PSA) accompanied by arterio-arterial and arteriovenous anastomoses. [source] Habitat structure mediates predation risk for sedentary prey: experimental tests of alternative hypothesesJOURNAL OF ANIMAL ECOLOGY, Issue 3 2009Anna D. Chalfoun Summary 1Predation is an important and ubiquitous selective force that can shape habitat preferences of prey species, but tests of alternative mechanistic hypotheses of habitat influences on predation risk are lacking. 2We studied predation risk at nest sites of a passerine bird and tested two hypotheses based on theories of predator foraging behaviour. The total-foliage hypothesis predicts that predation will decline in areas of greater overall vegetation density by impeding cues for detection by predators. The potential-prey-site hypothesis predicts that predation decreases where predators must search more unoccupied potential nest sites. 3Both observational data and results from a habitat manipulation provided clear support for the potential-prey-site hypothesis and rejection of the total-foliage hypothesis. Birds chose nest patches containing both greater total foliage and potential nest site density (which were correlated in their abundance) than at random sites, yet only potential nest site density significantly influenced nest predation risk. 4Our results therefore provided a clear and rare example of adaptive nest site selection that would have been missed had structural complexity or total vegetation density been considered alone. 5Our results also demonstrated that interactions between predator foraging success and habitat structure can be more complex than simple impedance or occlusion by vegetation. [source] Reproductive isolation between chromosomal races of the house mouse Mus musculus domesticus in a parapatric contact area revealed by an analysis of multiple unlinked lociJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 2 2008P. FRANCHINI Abstract The house mouse, Mus musculus domesticus, exhibits a high level of chromosomal polymorphism because of the occurrence and fast fixation of Robertsonian fusions between telocentric chromosomes. For this reason, it has been considered a classical speciation model to analyse the role of the chromosomal changes in reproductive isolation. In this study, we analysed a parapatric contact area between two metacentric races in central Italy, the Cittaducale race (CD: 2n = 22) and the Ancarano race (ACR: 2n = 24), to estimate gene flow at the boundary. Hybrids between these two races show high levels of structural heterozygosity and are expected to be highly infertile. A sample of 88 mice from 14 sites was used. The mice were genotyped by means of eight microsatellite loci mapped in four different autosomal arms. The results show clear genetic differentiation between the CD and ACR races, as revealed by differences in allele frequencies, factorial correspondence analysis and indexes of genetic population (e.g. FST and RST) along the contact zone. The genetic differentiation between the races was further highlighted by assignation and clustering analyses, in which all the individuals were correctly assigned by their genotypes to the source chromosomal race. This result is particularly interesting in view of the absence of any geographical or ecological barrier in the parapatric contact zone, which occurs within a village. In these conditions, the observed genetic separation suggests an absence of gene flow between the races. The CD,ACR contact area is a rare example of a final stage of speciation between chromosomal races of rodents because of their chromosomal incompatibility. [source] Biochemical aspects of the neuroprotective mechanism of PTEN-induced kinase-1 (PINK1)JOURNAL OF NEUROCHEMISTRY, Issue 1 2008Ryan D. Mills Abstract Mutations in PTEN-induced kinase 1 (PINK1) gene cause PARK6 familial Parkinsonism. To decipher the role of PINK1 in pathogenesis of Parkinson's disease (PD), researchers need to identify protein substrates of PINK1 kinase activity that govern neuronal survival, and establish whether aberrant regulation and inactivation of PINK1 contribute to both familial Parkinsonism and idiopathic PD. These studies should take into account the several unique structural and functional features of PINK1. First PINK1 is a rare example of a protein kinase with a predicted mitochondrial-targeting sequence and a possible resident mitochondrial function. Second, bioinformatic analysis reveals unique insert regions within the kinase domain that are potentially involved in regulation of kinase activity, substrate selectivity and stability of PINK1. Third, the C-terminal region contains functional motifs governing kinase activity and substrate selectivity. Fourth, accumulating evidence suggests that PINK1 interacts with other signaling proteins implicated in PD pathogenesis and mitochondrial dysfunction. The most prominent examples are the E3 ubiquitin ligase Parkin, the mitochondrial protease high temperature requirement serine protease 2 and the mitochondrial chaperone tumor necrosis factor receptor-associated protein 1. How PINK1 may regulate these proteins to maintain neuronal survival is unclear. This review describes the unique structural features of PINK1 and their possible roles in governing mitochondrial import, processing, kinase activity, substrate selectivity and stability of PINK1. Based upon the findings of previous studies of PINK1 function in cell lines and animal models, we propose a model on the neuroprotective mechanism of PINK1. This model may serve as a conceptual framework for future investigation into the molecular basis of PD pathogenesis. [source] Intermolecular , -dimer of oxoverdazyl radicals with long-distance multicenter (2e/8c) bonding via nitrogen atomsJOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 5 2010Sergiy V. Rosokha Abstract The 1,5-dimethyl-6-oxoverdazyl radical's solid-state structure shows distinct , -dimeric units with close interplanar separations (3.10,Å) between the head-over-tail cofacial moieties and several interatomic contacts shorter than the sums of the van der Waals radii. Evaluations of the frontier orbitals of monomeric oxoverdazyl and its , -dimer reveal that interaction of the radical SOMOs (concentrated on the nitrogen atoms) leads to the formation of the supramolecular orbital involving four equivalent bonding (N,N) segments between two oxoverdazyl moieties. As such, this , -dimer represents a rare example of nitrogen-based multicenter (2e/8c) long-distance bonding and emphasizes the universal character of this phenomenon in organic (ion-) radical systems. Copyright © 2009 John Wiley & Sons, Ltd. [source] The Sirente crater field, ItalyMETEORITICS & PLANETARY SCIENCE, Issue 11 2002Jens ORMö They are located in the Sirente plain within the mountains of the Abruzzo region, central Italy. The craters are distributed in a field 450 m long and 400 m wide. This field consists of ,17 smaller craters close to a larger main crater. The main crater is located in the southern end of the crater field and is 140 m long and 115 m wide, measured rim-to-rim. It has a well-developed, saddle-shaped rim that rises at a maximum 2.2 m above the surrounding plain. Radiocarbon dating of the target surface preserved below the rim gave a calibrated age of formation at about a.d. 412 (1650 ± 40 radiocarbon years b.p.). This young age is consistent with the apparent little modification of the rim. The morphology of the main crater and its relation to a crater field strongly points to its origin by impact from a projectile that broke up during its passage through the atmosphere. Quartz is very rare in the target and no planar deformation features have been found so far. The rim material and the upper 4 m of the main crater infill are impregnated with ferric oxides, which gives a more reddish colour compared to the other sediments of the plain. Rusty crusts with high Fe and Mn content occur in the rim material, but have not been found in the plain's sediments. Some of these crusts can be separated by magnet, and have sporadic micron-sized Ni-rich granules. The main crater is in the size range of the craters with explosive dispersion of the projectile and has many features comparable to both large experimental and meteoritic impact craters formed in loose sediments. We suggest that this crater represents a rare example of well-preserved, small impact crater formed in unconsolidated target materials. [source] Nature versus nurture in two highly enantioselective esterases from Bacillus cereus and Thermoanaerobacter tengcongensisMICROBIAL BIOTECHNOLOGY, Issue 1 2010Stephan Grosse Summary There is an increasing need for the use of biocatalysis to obtain enantiopure compounds as chiral building blocks for drug synthesis such as antibiotics. The principal findings of this study are: (i) the complete sequenced genomes of Bacillus cereus ATCC 14579 and Thermoanaerobacter tengcongensis MB4 contain a hitherto undescribed enantioselective and alkaliphilic esterase (BcEST and TtEST respectively) that is specific for the production of (R)-2-benzyloxy-propionic acid ethyl ester, a key intermediate in the synthesis of levofloxacin, a potent antibiotic; and (ii) directed evolution targeted for increased thermostability of BcEST produced two improved variants, but in either case the 3,5°C increase in the apparent melting temperature (Tm) of the mutants over the native BcEST that has a Tm of 50°C was outperformed by TtEST, a naturally occurring homologue with a Tm of 65°C. Protein modelling of BcEST mapped the S148C and K272R mutations at protein surface and the I88T and Q110L mutations at more buried locations. This work expands the repertoire of characterized members of the ,/,-fold hydrolase superfamily. Further, it shows that genome mining is an economical option for new biocatalyst discovery and we provide a rare example of a naturally occurring thermostable biocatalyst that outperforms experimentally evolved homologues that carry out the same hydrolysis. [source] Ecological, morphological and genetic divergence of sympatric North Atlantic killer whale populationsMOLECULAR ECOLOGY, Issue 24 2009ANDREW D. FOOTE Abstract Ecological divergence has a central role in speciation and is therefore an important source of biodiversity. Studying the micro-evolutionary processes of ecological diversification at its early stages provides an opportunity for investigating the causative mechanisms and ecological conditions promoting divergence. Here we use morphological traits, nitrogen stable isotope ratios and tooth wear to characterize two disparate types of North Atlantic killer whale. We find a highly specialist type, which reaches up to 8.5 m in length and a generalist type which reaches up to 6.6 m in length. There is a single fixed genetic difference in the mtDNA control region between these types, indicating integrity of groupings and a shallow divergence. Phylogenetic analysis indicates this divergence is independent of similar ecological divergences in the Pacific and Antarctic. Niche-width in the generalist type is more strongly influenced by between-individual variation rather than within-individual variation in the composition of the diet. This first step to divergent specialization on different ecological resources provides a rare example of the ecological conditions at the early stages of adaptive radiation. [source] Extensive intraspecific polymorphism detected by SSCP at the nuclear C- mos gene in the endemic Iberian lizard Lacerta schreiberiMOLECULAR ECOLOGY, Issue 3 2006RAQUEL GODINHO Abstract C- mos is a highly conserved intronless gene that has proved useful in the analysis of ancient phylogenetic relationships within vertebrates. We selected the Iberian endemic Schreiber's green lizard (Lacerta schreiberi) that persisted in allopatric refugia since the late Pliocene to investigate the utility of the C- mos nuclear gene for intraspecific phylogeographic studies. Our combination of DNA sequencing with the high resolving power of single-strand conformational polymorphism (SSCP) effectively discriminated four common alleles showing strong population structuring (FST = 0.46). In addition, reconstruction of allele phylogenetic relationships further improved our understanding of C- mos spatial patterns of variation and allowed a comparison with previously described mitochondrial DNA data. Finally, limited sequencing of an extended C- mos fragment in six additional Lacerta species showed extensive polymorphism, to our knowledge representing a rare example of variation in a highly conserved nuclear gene. [source] Genetic variation in the Desert Springsnail (Tryonia porrecta): implications for reproductive mode and dispersalMOLECULAR ECOLOGY, Issue 6 2005R. HERSHLER Abstract Allozymes and mitochondrial cytochrome c oxidase subunit I (mtCOI) sequences were analysed to determine whether populations of the western North American gastropod Tryonia porrecta (from California, Nevada, Utah, and northwest Mexico) are strongly differentiated in accordance with traditional interpretation of regional fauna as ancient relicts inhabiting isolated fragments of late Tertiary palaeodrainages. These data were also used to assess whether this species, for which males have not been recorded, is a rare example of a molluscan parthenogen. Both data sets strongly supported monophyly of T. porrecta populations. Five of the nine sampled populations consisted of a single monoallelic allozyme genotype while the others contained two to 10 distinct genotypes. Allozymic data for genetically diverse Utah populations provided evidence of clonal and sexual reproduction. mtCOI haplotypes of T. porrecta formed two subgroups which differed by 1.99,2.60%. The common haplotype was found in seven populations with rare haplotypes observed in single populations. Based on these results and an available mtCOI molecular clock for related hydrobiid snails, T. porrecta is interpreted as a primarily parthenogenetic species that undergoes occasional sexual reproduction and has accumulated substantial diversity following its mid-Pliocene to mid-Pleistocene origin. Our results also suggest that the distribution of present-day populations of these gill-breathing snails did not result from fragmentation of an ancient, well-integrated drainage but instead reflects overland colonization of habitats which only recently became available following desiccation of late Quaternary pluvial lakes. [source] ECHA J0843.3,7905: Discovery of an ,old' classical T Tauri star in the , Chamaeleontis clusterMONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY, Issue 2 2002Warrick A. Lawson A limited-area survey of the , Chamaeleontis cluster has identified two new late-type members. The more significant of these is ECHA (=IRAS , a slowly rotating M2 classical T Tauri (CTT) star with a spectrum dominated by Balmer emission. At a distance of 97 pc and cluster age of ,9 Myr, the star is a nearby rare example of an ,old' CTT star and promises to be a rewarding laboratory for the study of disc structure and evolution in pre-main sequence (PMS) stars. The other new member is the M4 weak-lined T Tauri (WTT) star ECHA , which is the lowest mass primary known in the cluster. [source] Malignant peripheral nerve sheath tumor arising in benign ancient schwannoma: A case report with an immunohistochemical studyPATHOLOGY INTERNATIONAL, Issue 2 2000Yoshiki Mikami A rare example of malignant transformation in an ancient schwannoma arisng in the right side of the neck of a 51-year-old man without any clinical manifestations suggesting neurofibromatosis is described. The tumor, approximately 4 cm at its largest dimension, was well circumscribed and had a direct connection with the sympathetic nerve. Microscopically, the central portion of the tumor showed features of ancient schwannoma characterized by extensive hyalinization with cystic degeneration, scattered spindle cells with hyperchromatic and tapered nuclei, and some symplastic changes. However, predominantly in the outer portion, a proliferation of spindle-shaped cells with enlarged nuclei was present. The nuclei of these cells showed irregular contours, coarse granular chromatin texture, and conspicuous nucleoli. Mitotic figures and small necrotic foci with scattered apoptotic bodies were also seen. Immunohistochemically, S-100 protein was almost negative in areas consisting of overtly atypical cells where the mitotic index evaluated with MIB-1 antibody was 30.5%. In contrast, S-100-positive bland spindle cells were scattered in an extensively hyalinized area with a labeling index less than 3%. P53 protein was strongly positive in atypical spindle cells. Although it is a very uncommon event, definite nuclear atypia, frequent mitotic figures, and the existence of small necrotic foci should be recognized as indicating a diagnosis of malignant degeneration of benign schwannoma. Immunohistochemistry would be useful as an ancillary technique in such a setting. [source] The OD interpretation of the crystal structure of kettnerite CaBiOFCO3ACTA CRYSTALLOGRAPHICA SECTION A, Issue 6 2009í Hybler The mineral kettnerite, CaBi(OFCO3), is a rare example of an order,disorder (OD) structure with a quadratic net. The lattice parameters of the simplest possible 1O polytype are a = 5.3641,(1), b = 5.3641,(1), c = 13.5771,(2),Å, and the space group is Pbaa. There are three kinds of OD layers, identical to structure-building layers. Two of them are non-polar: the Bi,O and Ca,F at z = 0 and z = 1/2, respectively, with the layer-group symmetry C2/m2/m(4/a,b)21/m21/m. The third kind of OD layer of CO3 groups (located between the Bi,O and Ca,F layers) is polar, with alternating sense of polarity. The layer group is Pba(4)mm. Triangular CO3 groups are parallel to (110) or () planes with one O atom oriented towards the Bi,O layer and the remaining two O atoms oriented towards the Ca,F layer. The orientations of CO3 groups alternate along the [110] and [] directions. As a result, each group parallel to (110) is surrounded by four nearest neighbors parallel to () and vice versa. These positions can be interchanged by an (a + b)/2 shift or by ,/2 rotation; thus stacking of the layer onto adjacent ones is ambiguous. Instead of OD layers, the polytypes are generated by stacking of OD packets, comprising the whole CO3 layers and adjacent halves of the Bi,O and Ca,F layers. They are polar, with alternating sense of polarity; the layer group is Pba(4)mm. Stacking sequences are expressed by ball-and-stick models, with the aid of symbolic figures, and by sequences of orientational characters. There are two maximum-degree-of-order (MDO) polytypes, 1O (really found and described, see lattice parameters and space group above) and 2O, with doubled c parameter and space group Ibca (not yet found). The derivation of the MDO generating operations of both polytypes is presented in this paper. The stacking rule also allows another, non-MDO, polytype with doubled c, i.e. the 2Q polytype, space group P42bc (tetragonal, not yet found). Various kinds of domains can exist: (i) out-of-step domains shifted by (a + b)/2, (ii) twin domains rotated by ,/2 around local tetrads of odd or even packets, and (iii) upside-down domains in the polar 2Q polytype. Stacking sequences of 16 possible domains of the polytypes mentioned above are listed. Also 60 domains of four distinct six-packet polytypes are theoretically possible. [source] Rapid mixing of Gibbs sampling on graphs that are sparse on averageRANDOM STRUCTURES AND ALGORITHMS, Issue 2 2009Elchanan Mossel Abstract Gibbs sampling also known as Glauber dynamics is a popular technique for sampling high dimensional distributions defined on graphs. Of special interest is the behavior of Gibbs sampling on the Erd,s-Rényi random graph G(n,d/n), where each edge is chosen independently with probability d/n and d is fixed. While the average degree in G(n,d/n) is d(1 - o(1)), it contains many nodes of degree of order log n/log log n. The existence of nodes of almost logarithmic degrees implies that for many natural distributions defined on G(n,p) such as uniform coloring (with a constant number of colors) or the Ising model at any fixed inverse temperature ,, the mixing time of Gibbs sampling is at least n1+,(1/log log n). Recall that the Ising model with inverse temperature , defined on a graph G = (V,E) is the distribution over {±}Vgiven by . High degree nodes pose a technical challenge in proving polynomial time mixing of the dynamics for many models including the Ising model and coloring. Almost all known sufficient conditions in terms of , or number of colors needed for rapid mixing of Gibbs samplers are stated in terms of the maximum degree of the underlying graph. In this work, we show that for every d < , and the Ising model defined on G (n, d/n), there exists a ,d > 0, such that for all , < ,d with probability going to 1 as n ,,, the mixing time of the dynamics on G (n, d/n) is polynomial in n. Our results are the first polynomial time mixing results proven for a natural model on G (n, d/n) for d > 1 where the parameters of the model do not depend on n. They also provide a rare example where one can prove a polynomial time mixing of Gibbs sampler in a situation where the actual mixing time is slower than npolylog(n). Our proof exploits in novel ways the local tree like structure of Erd,s-Rényi random graphs, comparison and block dynamics arguments and a recent result of Weitz. Our results extend to much more general families of graphs which are sparse in some average sense and to much more general interactions. In particular, they apply to any graph for which every vertex v of the graph has a neighborhood N(v) of radius O(log n) in which the induced sub-graph is a tree union at most O(log n) edges and where for each simple path in N(v) the sum of the vertex degrees along the path is O(log n). Moreover, our result apply also in the case of arbitrary external fields and provide the first FPRAS for sampling the Ising distribution in this case. We finally present a non Markov Chain algorithm for sampling the distribution which is effective for a wider range of parameters. In particular, for G(n, d/n) it applies for all external fields and , < ,d, where d tanh(,d) = 1 is the critical point for decay of correlation for the Ising model on G(n, d/n). © 2009 Wiley Periodicals, Inc. Random Struct. Alg., 2009 [source] Guidelines and the adoption of ,lipid rescue' therapy for local anaesthetic toxicityANAESTHESIA, Issue 2 2009J. Picard Summary Gathering evidence from animal experiments, an editorial in this journal and published human case reports culminated in the Association of Anaesthetists of Great Britain and Ireland recommending in August 2007 that lipid emulsion be immediately available to all patients given potentially cardiotoxic doses of local anaesthetic drugs. This development offered an opportunity to track the adoption of an innovation by anaesthetists in the UK and to gauge the effects of guidelines. Two surveys, each of 66 NHS hospitals delivering acute care within London and its penumbra, examined the adoption of lipid emulsion therapy. After the publication of the editorial in autumn 2006, the spread of ,lipid rescue' was rapid. The timing of the adoption and the impetus for innovation varied substantially between the sampled hospitals. When the formal guidelines were published, approximately half of the hospitals surveyed did not have lipid rescue. Of those that subsequently adopted it, half attributed their decision to the guidelines. At the end of 2007, there remained a small number of hospitals that had yet to adopt lipid rescue. Lipid rescue's adoption by anaesthetists in the UK offers a rare example of swift uptake of an innovation. National guidelines accelerated the adoption of innovation by some hospitals. [source] A new three-dimensional cobalt(II) coordination polymer with a 4-connected CdSO4 -like topologyACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Zhan-Lin Xu The title cobalt(II) coordination polymer, poly[[diaquacobalt(II)]-,4 -3,3,-(p -phenylene)diacrylato], [Co(C12H8O4)(H2O)2]n, was obtained by reaction of Co(NO3)2·6H2O and 3,3,-(p -phenylene)diacrylic acid (H2L) under hydrothermal conditions. Each CoII cation sits on a centre of inversion and is hexacoordinated by six O-atom donors in an octahedral geometry. The CoII centres are connected by four centrosymmetric L2, anions, resulting in a three-dimensional framework structure. The coordinated water molecules and carboxylate O atoms form hydrogen-bond interactions, stabilizing the structure of the three-dimensional framework. Topologically, the framework represents a rare example of the three-dimensional 4-connected CdSO4 network type. The metal cations and the organic ligand both show in-plane coordination with respect to the extended structure. [source] Bis(1,3,4-trimethylpyridinium) tetrachloridocuprate(II) and bis(1,3,4-trimethylpyridinium) tetrabromidocuprate(II): an examination of the A2CuX4Fdd2 structure typeACTA CRYSTALLOGRAPHICA SECTION C, Issue 8 2009Marcus R. Bond The title bis(1,3,4-trimethylpyridinium) tetrahalidocuprate(II) structures, (C8H12N)2[CuCl4], (I), and (C8H12N)2[CuBr4], (II), respectively, consist of flattened [CuX4]2, tetrahedral complex anions and planar 1,3,4-trimethylpyridinium cations. Chloride compound (I) is a rare example of an A2CuCl4 structure with an elongated unit cell in the polar space group Fdd2. The [CuCl4]2, anions have twofold rotational symmetry and are arranged in distorted hexagonal close-packed (hcp) layers, which are interleaved with layers of cations, each in a four-layer repeat sequence, to generate the elongated axis. The organic cations stack along [101] or [10] in alternating layers. The methyl groups meta on the cation ring and the larger of the trans Cl,Cu,Cl angles both face the same direction along the polar axis and are the most prominent features determining the polarity of the structure. Bromide compound (II) crystallizes in a centrosymmetric structure with a similar layer structure but with only a two-layer repeat sequence. Here, symmetry-inequivalent cations are segregated into alternating layers with cations, forming hcp layers of inversion-related cation pairs in one layer and parallel stacks of cations in the other. The change in space group when the larger Br, ion is present suggests that the 1,3,4-trimethylpyridinium ion has a minimal size to allow the Fdd2 A2CuX4 structure type. [source] cis -Dichloridobis{dimethyl[3-(9-phosphabicyclo[3.3.1]non-9-yl)propyl]amine-,P}platinum(II)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 4 2009Peter N. Bungu The title compound, [PtCl2(C13H26NP)2], is a rare example of a sterically bulky ligand adopting a cis geometry in a square-planar complex. It crystallizes on a twofold rotation axis which bisects the Pt centre and the P,Pt,P, and Cl,Pt,Cl, angles. The ligand exhibits a random packing disorder in the N,N -dimethylpropylamine substituent, with the two orientations refining to occupancies of 0.404,(15) and 0.596,(15). Weak intermolecular interactions between a Cl and a H atom of the ligand of a neighbouring molecule result in extended chains along the a axis. The effective cone angle for the dimethyl[3-(9-phosphabicyclo[3.3.1]non-9-yl)propyl]amine (Phoban[3.3.1]-C3NMe2) ligand was determined as being in the range 160,181°, depending on the choice of atoms used in the calculations. [source] Tetra-,-chloro-1:2,4Cl;1:3,4Cl -bis(4,4,-dimethyl-2,2,-bipyridine)-2,2N,3,2N -lithium(I)dipalladium(II) tetrakis(pentafluorophenyl)borate dichloromethane 1.196-solvateACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2003Han Shen In the crystal structure of the title compound, [LiPd2Cl4(C12H12N2)2](C24F20B)·1.196CD2Cl2 or [{(Me2bipy)PdCl2}2(,-Li)]+·B(C6F5)4,·1.196CD2Cl2 (Me2bipy is 4,4,-dimethyl-2,2,-bipyridine), an Li+ cation is stabilized by complexation with two (Me2bipy)PdCl2 units through weak Li,Cl interactions. This compound is thus a rare example of a complex that exhibits an arrested Cl, abstraction. [source] | |||||||||||||||||||||||||