Search results for "Figuration"
showing 10 items of 615 documents
Polyketide Derivatives from Mangrove Derived Endophytic Fungus Pseudopestalotiopsis theae
2020
Chemical investigation of secondary metabolites from the endophytic fungus Pseudopestalotiopsis theae led to the isolation of eighteen new polyketide derivatives, pestalotheols I&ndash
The unique structure of complete lipopolysaccharide isolated from semi-rough Plesiomonas shigelloides O37 (strain CNCTC 39/89) containing (2S)-O-(4-o…
2013
The complete structure of semi-rough lipopolysaccharide (SR-LPS) of Plesiomonas shigelloides CNCTC 39/89 (serotype O37) has been investigated by (1)H and (13)C NMR spectroscopy, matrix-assisted laser-desorption/ionization time-of-flight MS, and chemical methods. The following structure of the single unit of the O-antigen has been established: [formula see text] in which α-D-Lenp is (2S)-O-(4-oxopentanoic acid)-α-D-Glcp residue which has not been found in nature. The absolute configuration of oxopentanoic acid moiety in α-d-Lenose residue was determined by NOESY experiment combined with molecular modeling (MM2 force field). The decasaccharide core is substituted at C-4 of the β-D-Glcp residu…
Theory of CaL2,3-edge XAS using a novel multichannel multiple-scattering method
2003
A new method for calculating X-ray absorption spectroscopy (XAS) at the L2,3 edges of Ca and transition metals is presented. It is based on the multichannel multiple-scattering theory by Natoli et al. [Phys. Rev. B, (1990), 42, 1944-1968] combined with the eigen-channel R-matrix formalism. Atomic multiplet-like effects, owing to the Coulomb interaction of photoelectrons and the 2p hole, are taken into account through a configuration interaction ansatz for the final-state wavefunction. The various multiplet states lead to a set of channels for the photoelectron wavefunction, which is calculated in multiple-scattering theory. The method is applied to Ca, an important element for biological ap…
A linear Fe-O-Fe unit in bis(dibenzyldimethylammonium) mu-oxo-bis[tribromoferrate(III)].
2006
The title compound, (C 16 H 20 )N) 2 [Fe 2 Br 6 O], crystallizes with one dibenzyldimethylammonium cation and one half of a μ-oxo-bis[tribromoferrate(III)] anion in the asymmetric unit. The bridging oxo group is situated on an inversion centre, resulting in a linear conformation for the Fe-O-Fe unit. The iron(III) cations have tetrahedral geometry, with bond angles in the range 106.8 (1)-112.2 (1)°. The ion pairs are held together by Coulombic forces and C-H···Br hydrogen bonds. Each Br - anion forms one hydrogen bond. No C-H···O hydrogen bonds are found between the O atom in the Fe-O-Fe unit and surrounding counter-cations, consistent with the linear configuration of the Fe-O-Fe unit.
Three-Dimensional Classification of Lower Third Molars and Their Relationship to the Mandibular Canal.
2021
PURPOSE To develop a novel classification making full use of radiographic three-dimensional (3D) information to describe the position, geometric configuration of a mandibular third molar (M3M) and its spatial relation to neighboring structures such as the mandibular canal (MC). The classification presented in this study helps to establish a common language and serves as a framework for further studies, for example, on 3D parameters influencing prognosis of the M3M and level of difficulty associated with its removal. MATERIAL AND METHODS A total of 8 parameters were included in the classification including position, the cranio-caudal height, the number of roots of the M3M as well as its spat…
Electromagnetic properties of low-lying states in neutron-deficient Hg isotopes: Coulomb excitation of Hg-182, Hg-184, Hg-186 and Hg-188
2019
The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass 182-188 Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of $ 0^{+}_{1,2}$01,2+, $ 2^{+}_{1,2}$21,2+and $ 4^{+}_{1}$41+states was observed in all nuclei under study. Reduced E2 matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate…
Hydrolase–like catalysis and structural resolution of natural products by a metal–organic framework
2020
[EN] The exact chemical structure of non-crystallising natural products is still one of the main challenges in Natural Sciences. Despite tremendous advances in total synthesis, the absolute structural determination of a myriad of natural products with very sensitive chemical functionalities remains undone. Here, we show that a metal-organic framework (MOF) with alcohol-containing arms and adsorbed water, enables selective hydrolysis of glycosyl bonds, supramolecular order with the so-formed chiral fragments and absolute determination of the organic structure by single-crystal X-ray crystallography in a single operation. This combined strategy based on a biomimetic, cheap, robust and multigr…
Measurement of the first ionization potential of lawrencium (element 103)
2015
Lawrencium, with atomic number 103, has an isotope with a half-life of 27 seconds; even so, its first ionization potential has now been measured on an atom-at-a-time scale and agrees well with state-of-the-art theoretical calculations that include relativistic effects. The most dramatic modern revision of Mendeleev's periodic table of elements came in 1944 when Glenn T. Seaborg placed a new series of elements, the actinides (atomic numbers 89–103), below the lanthanides. In this issue of Nature, Yuichiro Nagame and colleagues report the first measurement of one of the basic atomic properties of element 103 (lawrencium), namely its first ionization potential. Lawrencium is only accessible vi…
New potent antibacterials against Gram-positive multiresistant pathogens: effects of side chain modification and chirality in linezolid-like 1,2,4-ox…
2014
The effects of side chain modification and chirality in linezolid-like 1,2,4-oxadiazoles have been studied to design new potent antibacterials against Gram-positive multidrug-resistant pathogens. The adopted strategy involved a molecular modelling approach, the synthesis and biological evaluation of new designed compounds, enantiomers separation and absolute configuration assignment. Experimental determination of the antibacterial activity of the designed (S)-1-((3-(4-(3-methyl-1,2,4-oxadiazol-5- yl)phenyl)-oxazolidin-2-one-5-yl)methyl)-3-methylthiourea and (S)-1-((3-(3-fluoro-4-(3-methyl-1,2,4- oxadiazol-5-yl)phenyl)-oxazolidin-2-one-5-yl)methyl)-3-methylthiourea against multidrug resistan…
Visitor arrivals forecasts amid COVID-19: A perspective from the Africa team
2021
Abstract COVID-19 disrupted international tourism worldwide, subsequently presenting forecasters with a challenging conundrum. In this competition, we predict international arrivals for 20 destinations in two phases: (i) Ex post forecasts pre-COVID; (ii) Ex ante forecasts during and after the pandemic up to end 2021. Our results show that univariate combined with cross-sectional hierarchical forecasting techniques (THieF-ETS) outperform multivariate models pre-COVID. Scenarios were developed based on judgemental adjustment of the THieF-ETS baseline forecasts. Analysts provided a regional view on the most likely path to normal, based on country-specific regulations, macroeconomic conditions,…