The Experts below are selected from a list of 12246 Experts worldwide ranked by ideXlab platform
Klaus Merz - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis and Structure of a 2,4‐Unsubstituted cis/trans‐1,3‐Disilacyclobutane by Dehydrofluorination of a Highly Hindered Fluorosilane
European Journal of Inorganic Chemistry, 2005Co-Authors: Rudolf Pietschnig, Stefan Spirk, Ferdinand Belaj, Klaus MerzAbstract:The preparation, molecular structure, and metalation behavior of a sterically highly congested fluorosilane (tBuTipMeSiF) are described. This silane is subjected to dehydrofluorination under thermally mild conditions. A C-unsubstituted transient intermediate — either the Silene or the corresponding silenoid — is generated in a metalation/elimination sequence at low temperatures, and this intermediate dimerizes to give the corresponding 1,3-disilacyclobutane exclusively, even in the presence of a trapping agent. The significant steric hindrance in the starting fluorosilane and the final 1,3-disilacyclobutane is corroborated by their crystal structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
-
synthesis and structure of a 2 4 unsubstituted cis trans 1 3 disilacyclobutane by dehydrofluorination of a highly hindered fluorosilane
European Journal of Inorganic Chemistry, 2005Co-Authors: Rudolf Pietschnig, Stefan Spirk, Ferdinand Belaj, Klaus MerzAbstract:The preparation, molecular structure, and metalation behavior of a sterically highly congested fluorosilane (tBuTipMeSiF) are described. This silane is subjected to dehydrofluorination under thermally mild conditions. A C-unsubstituted transient intermediate — either the Silene or the corresponding silenoid — is generated in a metalation/elimination sequence at low temperatures, and this intermediate dimerizes to give the corresponding 1,3-disilacyclobutane exclusively, even in the presence of a trapping agent. The significant steric hindrance in the starting fluorosilane and the final 1,3-disilacyclobutane is corroborated by their crystal structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Lester Andrews - One of the best experts on this subject based on the ideXlab platform.
-
infrared spectra and density functional calculations for singlet ch2 six2 and triplet hc six3 and xc six3 intermediates in reactions of laser ablated silicon atoms with di tri and tetrahalomethanes
Inorganic Chemistry, 2016Co-Authors: Lester AndrewsAbstract:Reactions of laser-ablated silicon atoms with di-, tri-, and tetrahalomethanes in excess argon were investigated, and the products were identified from the matrix infrared spectra, isotopic shifts, and density functional theory energy, bond length, and frequency calculations. Dihalomethanes produce planar singlet Silenes (CH2═SiX2), and tri- and tetrahalomethanes form triplet halosilyl carbenes (HC–SiX3 and XC–SiX3). The Si-bearing molecules identified are the most stable, lowest-energy product in the reaction systems. While the C–Si bond in the Silene is a true double bond, the C–Si bond in the carbene is a shortened single bond enhanced by hyperconjugation of the two unpaired electrons on C to σ*(Si–X) orbitals, which contributes stabilization through a small amount of π-bonding and reduction of the HCSi or XCSi angles. The C–Si bond lengths in these carbenes (1.782 A for HC–SiF3) are between the single-bond length in the unobserved first insertion intermediate (1.975 A for CHF2–SiF) and the double-bond...
-
Infrared Spectra and Density Functional Calculations for Singlet CH2═SiX2 and Triplet HC–SiX3 and XC–SiX3 Intermediates in Reactions of Laser-Ablated Silicon Atoms with Di-, Tri-, and Tetrahalomethanes
Inorganic Chemistry, 2016Co-Authors: Lester AndrewsAbstract:Reactions of laser-ablated silicon atoms with di-, tri-, and tetrahalomethanes in excess argon were investigated, and the products were identified from the matrix infrared spectra, isotopic shifts, and density functional theory energy, bond length, and frequency calculations. Dihalomethanes produce planar singlet Silenes (CH2═SiX2), and tri- and tetrahalomethanes form triplet halosilyl carbenes (HC–SiX3 and XC–SiX3). The Si-bearing molecules identified are the most stable, lowest-energy product in the reaction systems. While the C–Si bond in the Silene is a true double bond, the C–Si bond in the carbene is a shortened single bond enhanced by hyperconjugation of the two unpaired electrons on C to σ*(Si–X) orbitals, which contributes stabilization through a small amount of π-bonding and reduction of the HCSi or XCSi angles. The C–Si bond lengths in these carbenes (1.782 A for HC–SiF3) are between the single-bond length in the unobserved first insertion intermediate (1.975 A for CHF2–SiF) and the double-bond...
Tatiana Giraud - One of the best experts on this subject based on the ideXlab platform.
-
Distribution and population structure of the anther smut Microbotryum Silenes-acaulis parasitizing an arctic-alpine plant
Molecular Ecology, 2016Co-Authors: Britta Bueker, Michael E Hood, Chris Eberlein, Pierre Gladieux, Angela Schaefer, Alodie Snirc, Dominic J. Bennett, Dominik Begerow, Tatiana GiraudAbstract:Cold-adapted organisms with current arctic-alpine distributions have persisted during the last glaciation in multiple ice-free refugia, leaving footprints in their population structure that contrast with temperate plants and animals. However, pathogens that live within hosts having arctic-alpine distributions have been little studied. Here, we therefore investigated the geographical range and population structure of a fungus parasitizing an arctic-alpine plant. A total of 1437 herbarium specimens of the plant Silene acaulis were examined, and the anther smut pathogen Microbotryum Silenes-acaulis was present throughout the host's geographical range. There was significantly greater incidence of anther smut disease in more northern latitudes and where the host locations were less dense, indicating a major influence of environmental factors and/or host demographic structure on the pathogen distribution. Genetic analyses with seven microsatellite markers on recent collections of 195 M. Silenes-acaulis individuals revealed three main genetic clusters, in North America, northern Europe and southern Europe, likely corresponding to differentiation in distinct refugia during the last glaciation. The lower genetic diversity in northern Europe indicates postglacial recolonization northwards from southern refugia. This study combining herbarium surveys and population genetics thus uniquely reveals the effects of climate and environmental factors on a plant pathogen species with an arctic-alpine distribution. \\textcopyright\ 2015 John Wiley \&\ Sons Ltd.
-
PERFORMANCE OF A HYBRID FUNGAL PATHOGEN ON PURE-SPECIES AND HYBRID HOST PLANTS
International Journal of Plant Sciences, 2014Co-Authors: Amanda Gibson, Guislaine Refrégier, Michael E Hood, Tatiana GiraudAbstract:Premise of research. Recent hybridization events in fungi have produced emerging pathogens characterized by novel host specificities, increased infectivity, and/or elevated severity. We investigated the potential for host shifts and increased infectivity following hybridization of fungal pathogens in the genus Microbotryum, which causes anther-smut disease on caryophyllaceous hosts. Hybrids of the closely related species Microbotryum lychnidis-dioicae (MvSl) and Microbotryum Silenes-dioicae (MvSd) are viable and fertile. Although historical genetic exchange between MvSl and MvSd is rare, there is evidence of recent hybridization of these fungal species, as well as of their plant hosts, Silene latifolia and Silene dioica. Methodology. We examined the fitness of hybrid pathogens and hosts by using F 1 hybrids of MvSl # MvSd to inoculate S. latifolia # S. dioica hybrids. Experimental inoculations of S. latifolia and hybrid hosts with pure-species and hybrid pathogens allowed assessment of the likelihood of hybrid emergence on a novel host (the hybrid plant) and of increased infectiousness of the hybrid pathogen on the pure-species host. Pivotal results. We found no evidence for pathogen hybrid inferiority, arguing against interspecific incompatibilities at small genetic distances. Instead, we found that hybrid pathogens are more infectious on pure-species hosts, while pure-species pathogens are more infectious on hybrid hosts, indicating an interaction of host and parasite genotypes. Conclusions. This finding argues against emergence of hybrid pathogens on a novel hybrid host. However, our study suggests that hybridization of pathogens and hosts in natural populations may lead to elevated disease prevalence overall, thus furthering the impact of anther-smut disease in these Silene species.
-
purifying selection after episodes of recurrent adaptive diversification in fungal pathogens
Infection Genetics and Evolution, 2013Co-Authors: Pierre Gladieux, Tatiana Giraud, Benjamin Devier, Gabriela Aguileta, Corinne CruaudAbstract:Abstract Tests of selective neutrality based on comparative and population genetic data target different time scales of selection. Investigating both time scales on the same genes has rarely been done and yet can provide insights into histories of selection. In pathogens, such a comparison can elucidate whether the same genes experience recurrent positive selection across specialization events onto novel hosts and selection in the short term, e.g. by coevolution with a current host. Here, we investigated whether the genes showing signs of positive selection (based on dN/dS ratios) between pathogens specialized on different hosts also exhibited footprints of recent positive selection. We sequenced 58 DNA fragments in the model fungal plant pathogen Microbotryum lychnidis-dioicae infecting Silene latifolia. Eleven focal genes were chosen because they showed a significant signal of positive selection in a previous study and putative functions likely involved in host–parasite interactions. In addition, 47 control genes were randomly chosen among genes showing no evidence of positive selection. We used a population genetics approach to search for signatures of recent selection, controlling for population structure and demographic history. We found footprints of purifying selection in all focal genes and of recent positive selection in two of them. Signs of purifying selection were also found at the same eleven genes in a closely related species, Microbotryum Silenes-dioicae, infecting Silene dioica. These results suggest that genes experiencing episodes of adaptive diversification during host shifts may subsequently be under strong functional constraint, although some can remain under positive selection in the short term.
-
Maintenance of Fungal Pathogen Species That Are Specialized to Different Hosts: Allopatric Divergence and Introgression through Secondary Contact
Molecular Biology and Evolution, 2010Co-Authors: P. Gladieux, E. Vercken, M. Fontaine, M. Hood, O. Jonot, A. Couloux, Tatiana GiraudAbstract:Sympatry of species that lack complete prezygotic isolation is ideal for the study of how species can be maintained in the face of potential gene flow. This is particularly important in the context of emerging diseases on new hosts because pathogen adaptation is facilitated by reduced gene flow from ancestral populations. Here, we investigated divergence and gene flow between two closely related fungal species, Microbotryum lychnidis-dioicae and M. Silenes-dioicae, causing anther-smut disease on the wide-spread plant species Silene latifolia and S. dioica, respectively. Using model-based clustering algorithms on microsatellite data from samples across Europe, we identified rare disease transmission between the host species and rare pathogen hybrids. Using a coalescent-based approach and an isolation-with-migration model, the age of divergence between the two fungal species was estimated at approximately 4.2 x 10(5) years. Levels of gene flow were low and concentrated in very recent times. In addition, gene flow appeared unidirectional from M. Silenes-dioicae to M. lychnidis-dioicae. Altogether, our findings are consistent with a scenario of recurrent introgressive hybridization but at a very low level and through secondary contact following initial divergence in allopatry. Asymmetry in the direction of gene flow mirrors previous findings on introgression between the two host plants. Our study highlights the consequences of bringing closely related pathogens into contact, which is increasing through modern global changes and favors cross-species disease transmission, hybridization, and introgression by pathogens.
Rudolf Pietschnig - One of the best experts on this subject based on the ideXlab platform.
-
Synthesis and Structure of a 2,4‐Unsubstituted cis/trans‐1,3‐Disilacyclobutane by Dehydrofluorination of a Highly Hindered Fluorosilane
European Journal of Inorganic Chemistry, 2005Co-Authors: Rudolf Pietschnig, Stefan Spirk, Ferdinand Belaj, Klaus MerzAbstract:The preparation, molecular structure, and metalation behavior of a sterically highly congested fluorosilane (tBuTipMeSiF) are described. This silane is subjected to dehydrofluorination under thermally mild conditions. A C-unsubstituted transient intermediate — either the Silene or the corresponding silenoid — is generated in a metalation/elimination sequence at low temperatures, and this intermediate dimerizes to give the corresponding 1,3-disilacyclobutane exclusively, even in the presence of a trapping agent. The significant steric hindrance in the starting fluorosilane and the final 1,3-disilacyclobutane is corroborated by their crystal structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
-
synthesis and structure of a 2 4 unsubstituted cis trans 1 3 disilacyclobutane by dehydrofluorination of a highly hindered fluorosilane
European Journal of Inorganic Chemistry, 2005Co-Authors: Rudolf Pietschnig, Stefan Spirk, Ferdinand Belaj, Klaus MerzAbstract:The preparation, molecular structure, and metalation behavior of a sterically highly congested fluorosilane (tBuTipMeSiF) are described. This silane is subjected to dehydrofluorination under thermally mild conditions. A C-unsubstituted transient intermediate — either the Silene or the corresponding silenoid — is generated in a metalation/elimination sequence at low temperatures, and this intermediate dimerizes to give the corresponding 1,3-disilacyclobutane exclusively, even in the presence of a trapping agent. The significant steric hindrance in the starting fluorosilane and the final 1,3-disilacyclobutane is corroborated by their crystal structures. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)
Verner Michelsen - One of the best experts on this subject based on the ideXlab platform.
-
Revision of the European Delia pruinosa species group (Diptera: Anthomyiidae) feeding as larvae in seed capsules of Silene L. (Caryophyllaceae)
Zootaxa, 2012Co-Authors: Verner MichelsenAbstract:The European taxon Delia pruinosa (Zetterstedt) currently treated as one species is shown to represent a complex of several closely related species all characterized by the short antennnae, enlarged proboscis with strong, black prestomal teeth and a weak tibial setation. Biologically, all members of this Delia pruinosa species group may share the larval habit of living in seed capsules of various species of Silene L. (Caryophyllaceae). The number of species recognized in both sexes is presently raized from one to four: Delia pruinosa (Zetterstedt, 1845), D. judicariae (Pokorny, 1893), D. sileni sp. nov. and D. capdellae sp. nov. It is further documented that a few more species exist within this species group, but they are so far only known from female individuals. The known distribution of the Delia pruinosa species group includes Europe and western Anatolia.
-
Revision of the European Delia pruinosa species group (Diptera: Anthomyiidae) feeding as larvae in seed capsules of Silene L. (Caryophyllaceae)
Zootaxa, 2012Co-Authors: Verner MichelsenAbstract:The European taxon Delia pruinosa (Zetterstedt) currently treated as one species is shown to represent a complex of several closely related species all characterized by the short antennnae, enlarged proboscis with strong, black prestomal teeth and a weak tibial setation. Biologically, all members of this Delia pruinosa species group may share the larval habit of living in seed capsules of various species of Silene L. (Caryophyllaceae). The number of species recognized in both sexes is presently raized from one to four: Delia pruinosa (Zetterstedt, 1845), D. judicariae (Pokorny, 1893), D. sileni sp. nov. and D. capdellae sp. nov. It is further documented that a few more species exist within this species group, but they are so far only known from female individuals. The known distribution of the Delia pruinosa species group includes Europe and western Anatolia. (Less)
