Semiempirical Studies of Inner-Core Energy Levels. Part 7. ESCA Shifts of Germanium in Molecular Systems

Shifts of the 3p213 ene;.·gy levels of germanium in different chemical moieties were studied by using the semiempirical SCC-MO method. The calculations were performed within the framework of the electrostatic potential method in the point-charge approximation. Relaxation energies were explicitly taken into account by employing the equivalent core and transition potential methods. It was found out that the relaxation energy plays a decisive role in determining shifts along the series GeH4--+ Ge(CHak The results obtained by the equivalent core and transition potential methods are similar being in the same time in good agreement with experiment. Performance of various semiempirical schemes in evaluating ESCA shifts is briefly discussed

Point-charge Description of some Molecular Properties

The notion of formal atomic charges in molecules is probably the most debated issue in quantum chemistry. Although atomic charge can not be rigorously defined in a unique way, conclusive evidence is given here which shows that it provides semiquantitative information about a number of molecular properties in a very simple and transparent way. In particular, the calculations of ESCA chemical shifts, diamagnetic shielding of nuclei and diamagnetic part of the molecular magnetic susceptibility are well described and thoroughly discussed. Finally, a relation between the effective atomic charges and total molecular SCF energies is illustrated by numerical examples. The point-charge description of the mentioned molecular properties is particularly useful if it is employed within the framework of semiempirical theories .because the computational costs are then negligible. The most successful semiempirical scheme in this respect seems to be the SCC- MO (self-consistent charge MO) method

Point-charge Description of some Molecular Properties

The notion of formal atomic charges in molecules is probably the most debated issue in quantum chemistry. Although atomic charge can not be rigorously defined in a unique way, conclusive evidence is given here which shows that it provides semiquantitative information about a number of molecular properties in a very simple and transparent way. In particular, the calculations of ESCA chemical shifts, diamagnetic shielding of nuclei and diamagnetic part of the molecular magnetic susceptibility are well described and thoroughly discussed. Finally, a relation between the effective atomic charges and total molecular SCF energies is illustrated by numerical examples. The point-charge description of the mentioned molecular properties is particularly useful if it is employed within the framework of semiempirical theories .because the computational costs are then negligible. The most successful semiempirical scheme in this respect seems to be the SCC- MO (self-consistent charge MO) method

Model Description of Some Molecular Properties by the Modified-Atom-in-Molecule (MAM) Approach

Conclusive evidence is presented whlch shows that the concept of modified atoms in molecule (MAM) is a viable model for a good description of numerous molecular properties. Atomic modification . can be decomposed to isotropic and anisotropic components. The isotropic change caused by molecular formation is given by the electric monopoles of atoms. It is a consequence of the charge drift accompanying chemical bonding. Atomic monopoles reproduce diamagneticshielding of the nuclei rJAd, diamagnetic susceptibility xd and ESCA shifts with an intriguing success. The atomic monopole model is easily extended to include higher local multipoles (i. e. anisotropic contribution), thus yielding satisfactory total molecular multipoles and extramolecular electrostatic potentials. Salient directional properties of covalent bonds are well described by the use of polarized atomic orbitals. It was shown that hybridization is the underlying concept which explains interrelations between steric features and local bond properties. Hybridization rationalizes in a natural and simple way the electron pair (Lewis) bond which is one of the corner stones of chemistry being particularly important for the first row atoms. It was concluded that the high information content of hybrid AOs can be ascribed to the fact that they conform to the local symmetry of the immediate molecular environment. Thus the HAOs are local wavefunctions of the zeroth order which describe atomic angular distortions. Although atoms can not be uniquely defined within molecules, the MAM model has high interpretative power yielding reasonable results. Special attention deserves a picture of charged atoms immersed in the »sea« of mixed electron density, because it is free of any arbitrariness in the slicing of molecular volume of partitioning of overlap charge. Finally, the definition of pseudo-observables is given. It was concluded that atomic monopoles and hybridization indices are pseudo-observables par exceHence. A.pparently there is colour, apparently sweetness, apparently bitterness; actuaUy there are only atoms and the void. Democritus, 420 B. C

Model Description of Some Molecular Properties by the Modified-Atom-in-Molecule (MAM) Approach

Conclusive evidence is presented whlch shows that the concept of modified atoms in molecule (MAM) is a viable model for a good description of numerous molecular properties. Atomic modification . can be decomposed to isotropic and anisotropic components. The isotropic change caused by molecular formation is given by the electric monopoles of atoms. It is a consequence of the charge drift accompanying chemical bonding. Atomic monopoles reproduce diamagneticshielding of the nuclei rJAd, diamagnetic susceptibility xd and ESCA shifts with an intriguing success. The atomic monopole model is easily extended to include higher local multipoles (i. e. anisotropic contribution), thus yielding satisfactory total molecular multipoles and extramolecular electrostatic potentials. Salient directional properties of covalent bonds are well described by the use of polarized atomic orbitals. It was shown that hybridization is the underlying concept which explains interrelations between steric features and local bond properties. Hybridization rationalizes in a natural and simple way the electron pair (Lewis) bond which is one of the corner stones of chemistry being particularly important for the first row atoms. It was concluded that the high information content of hybrid AOs can be ascribed to the fact that they conform to the local symmetry of the immediate molecular environment. Thus the HAOs are local wavefunctions of the zeroth order which describe atomic angular distortions. Although atoms can not be uniquely defined within molecules, the MAM model has high interpretative power yielding reasonable results. Special attention deserves a picture of charged atoms immersed in the »sea« of mixed electron density, because it is free of any arbitrariness in the slicing of molecular volume of partitioning of overlap charge. Finally, the definition of pseudo-observables is given. It was concluded that atomic monopoles and hybridization indices are pseudo-observables par exceHence. A.pparently there is colour, apparently sweetness, apparently bitterness; actuaUy there are only atoms and the void. Democritus, 420 B. C

Semiempirical versus ab Initio Calculations of Molecular Properties. I. Diamagnetic Susceptibilities and Quadrupole Moments in Some Medium Size Molecules

The self-consistent charge molecular orbital (SCC-MO) method was applied to a number of medium size molecules involving atoms exhibiting large differences in electronegativity and possessing one or more lone pairs. The quality of the wave functions thus obtained was applied to a number of medium size molecules involving atoms calculated by a rigorous treatment of the operators x2, y2, and z2• The SCC quadrupole moments can be favourably compared with the ab initio results of Snyder and Basch obtained by the use of a Gaussian double zeta basis set. The present results provide additional justification of the sec method, which has apparent advantages over the methods based on the ZDO approximation. Some difficulties encountered in the treatment of pi-electrons are discussed and suggestions for their remedy are given. The second moments calculated by the application of a simple additivity formula (Z. B. Maksic and J. E. Bloor, Chem. Phys. Lett., 13 (1972) 571; J. Phys. Chem., 77 (1973) 1520) and the related diamagnetic susceptibilities are in very good agreement with the ab initio values

Search for π0→νμνˉμ\pi^0 \to \nu_{\mu}\bar\nu_{\mu} Decay in LSND

We observe a net beam-excess of $8.7 \pm 6.3$ (stat) $\pm 2.4$ (syst) events, above 160 MeV, resulting from the charged-current reaction of $\nu_{\mu}$ and/or $\bar\nu_{\mu}$ on C and H in the LSND detector. No beam related muon background is expected in this energy regime. Within an analysis framework of $\pi^0 \to \nu_{\mu}\bar\nu_{\mu}$, we set a direct upper limit for this branching ratio of $\Gamma(\pi^0 \to \nu_\mu \bar\nu_\mu) / \Gamma(\pi^0 \to all) < 1.6 \times 10^{-6}$ at 90% confidence level.Comment: 4 pages, 4 figure

Rethinking “democratic backsliding” in Central and Eastern Europe – looking beyond Hungary and Poland

This essay introduces contributions to a special issue of East European Politics on “Rethinking democratic backsliding in Central and Eastern Europe”, which seeks to expand the study of democratic regression in CEE beyond the paradigmatic cases of Hungary and Poland. Reviewing these contributions, we identify several directions for research: 1) the need to critique “democratic backsliding”, not simply as a label, but also as an assumed regional trend; 2) a need to better integrate the role of illiberal socio-economic structures such as oligarchical structures or corrupt networks; and 3) a need to (re-)examine the trade-offs between democratic stability and democratic quality. We also note how insights developed researching post-communist regions such as Western Balkans or the post-Soviet space could usefully inform work on CEE backsliding. We conclude by calling for the study of CEE democracy to become more genuinely interdisciplinary, moving beyond some narrowly institutionalist comparative political science assumptions

Susceptibility of hamsters to clostridium difficile isolates of differing toxinotype

Clostridium difficile is the most commonly associated cause of antibiotic associated disease (AAD), which caused ~21,000 cases of AAD in 2011 in the U.K. alone. The golden Syrian hamster model of CDI is an acute model displaying many of the clinical features of C. difficile disease. Using this model we characterised three clinical strains of C. difficile, all differing in toxinotype; CD1342 (PaLoc negative), M68 (toxinotype VIII) and BI-7 (toxinotype III). The naturally occurring non-toxic strain colonised all hamsters within 1-day post challenge (d.p.c.) with high-levels of spores being shed in the faeces of animals that appeared well throughout the entire experiment. However, some changes including increased neutrophil influx and unclotted red blood cells were observed at early time points despite the fact that the known C. difficile toxins (TcdA, TcdB and CDT) are absent from the genome. In contrast, hamsters challenged with strain M68 resulted in a 45% mortality rate, with those that survived challenge remaining highly colonised. It is currently unclear why some hamsters survive infection, as bacterial and toxin levels and histology scores were similar to those culled at a similar time-point. Hamsters challenged with strain BI-7 resulted in a rapid fatal infection in 100% of the hamsters approximately 26 hr post challenge. Severe caecal pathology, including transmural neutrophil infiltrates and extensive submucosal damage correlated with high levels of toxin measured in gut filtrates ex vivo. These data describes the infection kinetics and disease outcomes of 3 clinical C. difficile isolates differing in toxin carriage and provides additional insights to the role of each toxin in disease progression