Search results for "Reaction"
showing 10 items of 6134 documents
Hardening of bio-silica in sponge spicules involves an aging process after its enzymatic polycondensation: evidence for an aquaporin-mediated water a…
2011
Abstract Background Spicules, the siliceous skeletal elements of the siliceous sponges, are synthesized enzymatically via silicatein. The product formed, bio-silica, constitutes their inorganic matrix. It remained unexplored which reactions are involved in molding of the amorphous bio-silica and formation of a solid and rigid biomaterial. Methods Cell and molecular biological techniques have been applied to analyze processes resulting in the hardening of the enzymatically synthesized bio-silica. The demosponge Suberites domuncula has been used for the studies. Results Cell aggregates (primmorphs) from the sponge S . domuncula , grown in the presence of Mn-sulfate, form spicules that compris…
Spin forbidden chemical reactions of transition metal compounds. New ideas and new computational challenges.
2003
International audience; Many reactions of transition metal compounds involve a change in spin. These reactions may proceed faster, slower—or at the same rate as—otherwise equivalent processes in which spin is conserved. For example, ligand substitution in [CpMo(Cl)2(PR3)2] is faster than expected, whereas addition of dinitrogen to [Cp*Mo(Cl)(PMe3)2] is slow. Spin-forbidden oxidative addition of ethylene to [Cp*Ir(PMe3)] occurs competitively with ligand association. To explain these observations, we discuss the shape of the different potential energy surfaces (PESs) involved, and the energy of the minimum energy crossing points (MECPs) between them. This computational approach is of great he…
Synthesis, crystal structures and magnetic properties of mononuclear tris(croconate)ferrate(III) complexes
2006
Abstract A straightforward synthetic method to prepare mononuclear croconato-containing iron (III) complexes, (A)3[Fe(C5O5)3] [A = tetrabutylammonium = n-Bu4N+ (1) and tetraphenylphosphonium = PPh 4 + ( 2 ) ; C 5 O 5 2 - = croconate = dianion of 4 , 5 - dihydroxycyclopent - 4 - ene - 1 , 2 , 3 - trione ] along with their crystal structures and magnetic properties, are reported. The Fe(III) atom adopts a pseudo-octahedral geometry while magnetic susceptibility measurements, in the 2–300 K temperature range, show the occurrence of a high spin state (S = 5/2) in both complexes.
The Molecular Basis of X-Linked Spondyloepiphyseal Dysplasia Tarda
2001
The X-linked form of spondyloepiphyseal dysplasia tarda (SEDL), a radiologically distinct skeletal dysplasia affecting the vertebrae and epiphyses, is caused by mutations in the SEDL gene. To characterize the molecular basis for SEDL, we have identified the spectrum of SEDL mutations in 30 of 36 unrelated cases of X-linked SEDL ascertained from different ethnic populations. Twenty-one different disease-associated mutations now have been identified throughout the SEDL gene. These include nonsense mutations in exons 4 and 5, missense mutations in exons 4 and 6, small (2–7 bp) and large (>1 kb) deletions, insertions, and putative splicing errors, with one splicing error due to a complex deleti…
Pythium regulare sp. nov., Isolated from the Canary Islands, Its Taxonomy, Its Region of rDNA, and Comparison with Related Species
2003
Pythium regulare (CI-34) was isolated from some soil samples taken in the Canary Islands (Spain). This new species is very closely related to P. irregulare isolated from pea roots in The Netherlands by Buisman in 1927. The species of Pythium are members of the kingdom Chromista. Pythium regulare is characterized by its ornamented oogonia bearing blunt or digitate spines, and its non-sporulating type of sporangia or hyphal bodies, its aplerotic oospores, its monoclinous and diclinous antheridia that at times crowd around the oogonia. The taxonomic description of this oomycete, the PCR of the internal transcribed region (spacers ITS1, ITS2, and the gene 5.8 S) of its ribosomal nuclear DNA as …
The reaction enthalpy of hydrogen dissociation calculated with the Small System Method from simulation of molecular fluctuations.
2014
We show how we can find the enthalpy of a chemical reaction under non-ideal conditions using the Small System Method to sample molecular dynamics simulation data for fluctuating variables. This method, created with Hill's thermodynamic analysis, is used to find properties in the thermodynamic limit, such as thermodynamic correction factors, partial enthalpies, volumes, heat capacities and compressibility. The values in the thermodynamic limit at (T,V, μj) are then easily transformed into other ensembles, (T,V,Nj) and (T,P,Nj), where the last ensemble gives the partial molar properties which are of interest to chemists. The dissociation of hydrogen from molecules to atoms was used as a conve…
Rapid differentiation between livestock-associated and livestock-independent Staphylococcus aureus CC398 clades.
2013
Staphylococcus aureus clonal complex 398 (CC398) isolates cluster into two distinct phylogenetic clades based on single-nucleotide polymorphisms (SNPs) revealing a basal human clade and a more derived livestock clade. The scn and tet(M) genes are strongly associated with the human and the livestock clade, respectively, due to loss and acquisition of mobile genetic elements. We present canonical single-nucleotide polymorphism (canSNP) assays that differentiate the two major host-associated S. aureus CC398 clades and a duplex PCR assay for detection of scn and tet (M). The canSNP assays correctly placed 88 S. aureus CC398 isolates from a reference collection into the human and livestock clade…
Pyrrolomycins as potential anti-staphylococcal biofilms agents
2010
With the goal of discovering new anti-infective agents active against microbial biofilms, this investigation focused on some natural pyrrolomycins, a family of halogenated pyrrole antibiotics. In this study the anti-staphylococcal biofilm activity of pyrrolomycins C, D, F1, F2a, F2b, F3 and of the synthesized related compounds I, II, III were investigated. The susceptibility of six staphylococcal biofilms was determined by methyltiazotetrazolium staining. Most of the compounds were active at concentrations of 1.5 microg ml(-1) with significant inhibition percentages. A few of the compounds were active at the lowest screening concentration of 0.045 microg ml(-1). The population log reduction…
Unfolding dynamics of small peptides biased by constant mechanical forces
2018
We show how multi-ensemble Markov state models can be combined with constant-force equilibrium simulations. Besides obtaining the unfolding/folding rates, Markov state models allow gaining detailed insights into the folding dynamics and pathways through identifying folding intermediates and misfolded structures. For two specific peptides, we demonstrate that the end-to-end distance is an insufficient reaction coordinate. This problem is alleviated through constructing models with multiple collective variables, for which we employ the time-lagged independent component analysis requiring only minimal prior knowledge. Our results show that combining Markov state models with constant-force simu…
ANALYTICAL DETERMINATION OF INITIAL CONDITIONS LEADING TO FIRING IN NERVE FIBERS
2007
International audience; An analytical solution characterizing initial conditions leading to action potential firing in smooth nerve fibers is determined, using the bistable equation. In the first place, we present a nontrivial stationary solution wave, then, using the perturbative method, we analyze the stability of this stationary wave. We show that it corresponds to a frontier between the initiation of the travelling waves and a decay to the resting state. Eventually, this analytical approach is extended to FitzHugh-Nagumo model.