Search results for "Matter"
showing 10 items of 16762 documents
Substituent effects of nitro group in cyclic compounds
2020
AbstractNumerous studies on nitro group properties are associated with its high electron-withdrawing ability, by means of both resonance and inductive effect. The substituent effect of the nitro group may be well described using either traditional substituent constants or characteristics based on quantum chemistry, i.e., cSAR, SESE, and pEDA/sEDA models. Interestingly, the cSAR descriptor allows to describe the electron-attracting properties of the nitro group regardless of the position and the type of system. Analysis of classical and reverse substituent effects of the nitro group in various systems indicates strong pi-electron interactions with electron-donating substituents due to the re…
High-resolution spectroscopy of difference and combination bands of SF6 to elucidate the ν3 + ν1 − ν1 and ν3 + ν2 − ν2 hot band structures in the ν3 …
2014
The strong infrared absorption in the ν3 S–F stretching region of sulphur hexafluoride (SF6) near 948 cm−1 makes it a powerful greenhouse gas. Although its present concentration in the atmosphere is very low, it is increasing rapidly, due to industrial pollution. The ground state population of this heavy species is only 32% at room temperature and thus many hot bands are present. Consequently, a reliable remote-sensing spectroscopic detection and monitoring of this species require an accurate modelling of these hot bands. We used two experimental set-ups at the SOLEIL French synchrotron facility to record some difference and combination bands of SF6: (1) a new cryogenic multiple pass cell w…
Optical investigation of spin-crossover in cobalt(II) bis-terpy complexes
2007
Abstract The spin transition of the [Co(terpy) 2 ] 2+ complex (terpy = 2,2′:6′,2″-terpyridine) is analysed based on experimental data from optical spectroscopy and magnetic susceptibility measurements. The single crystal absorption spectrum of [Co(terpy) 2 ](ClO 4 ) 2 shows an asymmetric absorption band at 14 400 cm −1 with an intensity typical for a spin-allowed d–d transition and a temperature behaviour typical for a thermal spin transition. The single crystal absorption spectra of suggest that in this compound, the complex is essentially in the high-spin state at all temperatures. However, the increase in intensity observed in the region of the low-spin MLCT transition with increasing te…
High-spin → low-spin relaxation in the two-step spincrossover compound [Fe(pic)3]Cl2EtOH (pic = 2-picolylamine)
1998
Abstract The spin-crossover compound [Fe(pic) 3 ]Cl 2 EtOH (pic = 2-picolylamine) shows an unusual two-step spin transition. This is thought to be caused by specific nearest-neighbour interactions and short-range correlations and requires a theoretical treatment of the elastic interactions between the spin-changing molecules beyond the mean-field approximation. Such short-range correlations also influence the high-spin → low-spin relaxation following the light-induced population of the high-spin state at cryogenic temperatures, leading to characteristic deviations from the predictions of a mean-field treatment. These deviations are directly observable by comparison of the full and unperturb…
Effects of air pollution on dementia over Europe for present and future climate change scenarios.
2020
The scientific literature is scarce when referring to the influence of atmospheric pollutants on neurodegenerative diseases for present and future climate change scenarios. In this sense, this contribution evaluates the incidence of dementia (Alzheimer's disease, AD, and dementia from unspecified cause, DU) occurring in Europe associated with the exposure to air pollution (essentially NO2 and PM2.5) for the present climatic period (1991-2010) and for a future climate change scenario (RCP8.5, 2031-2050). The GEMM methodology has been applied to air pollution simulations using the chemistry/climate regional model WRF-Chem. Present population data were obtained from NASA's Center for Socioecon…
(R)-(−)-Quinuclidin-3-ol
2013
The structure of the title compound [alternatively called (R)-(−)-1-azabicyclo[2.2.2]octan-3-ol], C7H13NO, at 100 K has hexagonal (P61) symmetry. The structure shows a twist along the C—N pseudo-threefold axis. In the crystal, molecules are linkedviaO—H...N hydrogen bonds, forming infinite chains along thec-axis direction. The crystal studied was twinned by merohedry (twin law: 010, 100, 00-1; population: 0.925:0.075)
Palaeogenetics and cultural heritage. Species determination and STR-genotyping from ancient DNA in art and artefacts
2000
Abstract In recent years, a few papers have addressed the palaeogenetic analysis of cultural, historical and archaeological artefacts. We provide an overview of the individual published articles and then describe the results we had in the framework of a palaeogenetic research project involving various historical and prehistoric finds from museums, archaeological excavations, and libraries. We show that ancient DNA can be isolated from most of the various biomaterials (leather, parchment, glue, binding media, crusted organic plant remains in containers). Short pieces of degraded DNA are used, on the one hand, to determine the organic remnant’s genus/species of origin, and on the other hand, …
Hartree - Fock simulation of the Ag/MgO interface structure
1996
The atomic and electronic structure of the Ag/MgO interface are calculated using an ab initio Hartree - Fock computer code and a supercell model of a silver monolayer atop three layers of MgO substrate. The band structure, electronic density distribution and densities of states are analysed in detail for isolated and interacting slabs of a metal and MgO. The energetically most favoured adsorption position for Ag atoms is found to be above the O atoms, with the binding energy of 0.20 eV and the equilibrium Ag - O distance of 2.64 A. Neither appreciable charge transfer in the interfacial region, nor considerable population of bonds between the silver monolayer and the insulating substrate tak…
Comparative parallel characterization of particle populations with two mass spectrometric systems LAMPAS 2 and SPASS
2006
Abstract Two transportable laser mass spectrometers, Single Particle Analysis and Sizing System (SPASS) and Laser Mass Analyzer for Particles in the Airborne State (LAMPAS 2), have been applied to investigate the dependence of spectra patterns on instrumental parameters and data evaluation procedures in an inter-comparison experiment. Laboratory experiments showed the spectral response of both instruments for mineral particles before and after heterogeneous reactions. During a period of 47 h, both instruments determined size and chemical composition of several thousand single particles of an ambient particle population. Time-resolved evaluation (1-h resolution) of specific ion signals, whic…
Conformational equilibrium of chorismate. A QM/MM theoretical study combining statistical simulations and geometry optimisations in gas phase and in …
2003
We report a theoretical study on the conformational equilibrium of chorismate that precedes its rearrangement to prephenate, an important enzyme-catalyzed reaction. In first place we show that the usual classification of chorismate conformers based on the relative position of the hydroxyl and ether bridge, pseudo-diaxial and pseudo-diequatorial, is not the only relevant factor from the point of view of the a posteriori rearrangement. Here we also analyse another complementary geometrical classification based on the interatomic distance between the carbon atoms to be bounded. Using the umbrella sampling approach and this distance as distinguished internal reaction coordinate, the gas phase A…