Comparison of proton transfers in (S2H5)+ and (O2H5)+

The energetics and electronic rearrangements associated with proton transfer between S atoms in (H2S–H–SH2)+ are calculated using ab initio molecular orbital methods and compared with similar data in the first‐row analog (H2O–H–OH2)+. The full potential energy surface of (S2H5)+, calculated as a function of the H‐bond length as well as the position of the proton, contains two equivalent minima separated by a small energy barrier, whereas the surface of (O2H5)+ contains a single minimum corresponding to a symmetric position for the central proton. In both cases the energy barrier to transfer increases as the H bond is lengthened. This rise is noticeably less steep in the case of (S2H5)+, a fact attributed to the greater ease with which a proton may be pulled a given distance from each SH2 subunit in the absence of the other. Enlargements of the proton transfer barriers also result from angular distortions of each H bond; these increases are qualitatively quite similar in the two systems. There is a great deal of resemblance also in the electronic redistribution patterns accompanying proton transfer in the two systems. However, the greater polarizability of SH2 as compared to OH2 leads to greater overall charge transfer between the subunits in (H2S–H–SH2)+ and to larger extent of spatial regions of density change

Complexes Containing CO2 and SO2. Mixed Dimers, Trimers and Tetramers

Mixed dimers, trimers and tetramers composed of SO2 and CO2 molecules are examined by ab initio calculations to identify all minimum energy structures. While AIM formalism leads to the idea of a pair of C···O bonds in the most stable heterodimer, bound by some 2 kcal mol(-1), NBO analysis describes the bonding in terms of charge transfer from O lone pairs of SO2 to the CO π* antibonding orbitals. The second minimum on the surface, just slightly less stable, is described by AIM as containing a single O···O chalcogen bond. The NBO picture is that of two transfers in opposite directions: one from a SO2 O lone pair to a π* antibond of CO2, supplemented by CO2 Olp → π*(SO). Decomposition of the interaction energies points to electrostatic attraction and dispersion as the dominant attractive components, in roughly equal measure. The various heterotrimers and tetramers generally retain the dimer structure as a starting point. Cyclic oligomers are favored over linear geometries, with a preference for complexes containing larger numbers of SO2 molecules

Strongly Bound Noncovalent (SO3)n:H2CO Complexes (n = 1, 2)

The potential energy surfaces (PES) for the SO3:H2CO and (SO3)2:H2CO complexes were thoroughly examined at the MP2/aug-cc-pVDZ computational level. Heterodimers and trimers are held together primarily by SO chalcogen bonds, supplemented by weaker CHO and/or OC bonds. The nature of the interactions is probed by a variety of means, including electrostatic potentials, AIM, NBO, energy decomposition, and electron density redistribution maps. The most stable dimer is strongly bound, with an interaction energy exceeding 10 kcal mol(-1). Trimers adopt the geometry of the most stable dimer, with an added SO3 molecule situated so as to interact with both of the original molecules. The trimers are strongly bound, with total interaction energies of more than 20 kcal mol(-1). Most such trimers show positive cooperativity, with shorter SO distances, and three-body interaction energies of nearly 3 kcal mol(-1)

Quasiparticle band structure of infinite hydrogen fluoride and hydrogen chloride chains

We study the quasiparticle band structure of isolated, infinite HF and HCl bent (zigzag) chains and examine the effect of the crystal field on the energy levels of the constituent monomers. The chains are one of the simplest but realistic models of the corresponding three-dimensional crystalline solids. To describe the isolated monomers and the chains, we set out from the Hartree-Fock approximation, harnessing the advanced Green's function methods "local molecular orbital algebraic diagrammatic construction" (ADC) scheme and "local crystal orbital ADC" (CO-ADC) in a strict second order approximation, ADC(2,2) and CO-ADC(2,2), respectively, to account for electron correlations. The configuration space of the periodic correlation calculations is found to converge rapidly only requiring nearest-neighbor contributions to be regarded. Although electron correlations cause a pronounced shift of the quasiparticle band structure of the chains with respect to the Hartree-Fock result, the bandwidth essentially remains unaltered in contrast to, e.g., covalently bound compounds.Comment: 11 pages, 6 figures, 6 tables, RevTeX4, corrected typoe

Tetrel, Chalcogen, and CH⋅⋅O Hydrogen Bonds in Complexes Pairing Carbonyl-Containing Molecules with 1, 2, and 3 Molecules of CO2

The complexes formed by H2CO, CH3CHO, and (CH3)2CO with 1, 2, and 3 molecules of CO2 are studied by ab initio calculations. Three different types of heterodimers are observed, most containing a tetrel bond to the C atom of CO2, and some supplemented by a CH⋅⋅O H-bond. One type of heterodimer is stabilized by an anti-parallel arrangement of the C=O bonds of the two molecules. The binding energies are enhanced by methyl substitution on the carbonyl, and vary between 2.4 and 3.5 kcal/mol. Natural bond orbital analysis identifies a prime source of interaction as charge transfer into the π*(CO) antibonding orbital. Heterotrimers and tetramers carry over many of the geometrical and bonding features of the binary complexes, but also introduce O⋅⋅O chalcogen bonds. These larger complexes exhibit only small amounts of cooperativity

Histomorphological analysis of the urogenital diaphragm in elderly women: a cadaver study

The objective of this study was to describe the histomorphological structure of the urogenital diaphragm in elderly women using a modern morphometric procedure. Biopsies were taken from the posterior margin of the urogenital diaphragm of 22 female cadavers (mean age, 87years) using a 60-mm punch. Hematoxylin/eosin and Goldner sections were analyzed with the Cavalieri estimator. The mean thickness of the urogenital diaphragm was 5.5mm. The main component was connective tissue. All biopsies contained smooth muscle. Eighteen biopsies contained more smooth muscle than striated muscle. In six of 22 biopsies, no striated muscle was found. The ratio of striated to smooth muscle to connective tissue was 1:2.3:13.3. Muscle fibers were dispersed in all parts of the urogenital diaphragm. The urogenital diaphragm of elderly women mainly consists of connective tissue. Smooth muscle was also found but to a lesser extent. The frequently used English term "perineal membrane” for the urogenital diaphragm is justified and well describes our findings in elderly wome

Solar spectral conversion for improving the photosynthetic activity in algae reactors

Sustainable biomass production is expected to be one of the major supporting pillars for future energy supply, as well as for renewable material provision. Algal beds represent an exciting resource for biomass/biofuel, fine chemicals and CO2 storage. Similar to other solar energy harvesting techniques, the efficiency of algal photosynthesis depends on the spectral overlap between solar irradiation and chloroplast absorption. Here we demonstrate that spectral conversion can be employed to significantly improve biomass growth and oxygen production rate in closed-cycle algae reactors. For this purpose, we adapt a photoluminescent phosphor of the type Ca 0.59Sr0.40Eu0.01S, which enables efficient conversion of the green part of the incoming spectrum into red light to better match the Qy peak of chlorophyll b. Integration of a Ca 0.59Sr0.40Eu0.01S backlight converter into a flat panel algae reactor filled with Haematococcus pluvialis as a model species results in significantly increased photosynthetic activity and algae reproduction rate

Hydrogen bonding in infinite hydrogen fluoride and hydrogen chloride chains

Hydrogen bonding in infinite HF and HCl bent (zigzag) chains is studied using the ab initio coupled-cluster singles and doubles (CCSD) correlation method. The correlation contribution to the binding energy is decomposed in terms of nonadditive many-body interactions between the monomers in the chains, the so-called energy increments. Van der Waals constants for the two-body dispersion interaction between distant monomers in the infinite chains are extracted from this decomposition. They allow a partitioning of the correlation contribution to the binding energy into short- and long-range terms. This finding affords a significant reduction in the computational effort of ab initio calculations for solids as only the short-range part requires a sophisticated treatment whereas the long-range part can be summed immediately to infinite distances.Comment: 9 pages, 4 figures, 3 tables, RevTeX4, corrected typo