The energies and thermodynamic parameters of the elementary reactions involved in the gas-phase hydrolysis of silicon tetrachloride were studied using ab initio quantum chemical methods (up to ...MP4//MP2/6-311G(2d,2p)), density functional (B3LYP/6-311++G(2d,2p)), and G2(MP2) theories. The proposed mechanism of hydrolysis consists of the formation of SiCl4 - x (OH) x (x = 1−4), disiloxanes Cl4 - x (OH) x -1Si−O−SiCl4 - x (OH) x -1, chainlike and cyclic siloxane polymers −SiCl2O− n , dichlorosilanone Cl2SiO, and silicic acid (HO)2SiO. Thermodynamic parameters were estimated, and the transition states were located for all of the elementary reactions. It was demonstrated that the experimentally observed kinetic features for the high-temperature hydrolysis are well described by a regular bimolecular reaction occurring through a four-membered cyclic transition state. In contrast, the low-temperature hydrolysis reaction cannot be described by the traditionally accepted bimolecular pathway for SiCl bond hydrolysis because of high activation barrier (E a = 107.0 kJ/mol, ΔG ⧧ = 142.5 kJ/mol) nor by reactions occurring through three- or four-molecular transition states proposed earlier for reactions occurring in aqueous solution. The transition states of SiCl4 with one- and two-coordinated water molecules were located; these significantly decrease the free energy of activation ΔG ⧧ (to 121.3 and 111.5 kJ/mol, correspondingly). However, this decrease in ΔG ⧧ is not sufficient to account for the high value of the hydrolysis rate observed experimentally under low-temperature conditions.
The molecular reaction pathways of SO3 and SOCl2 reactions with one and two water molecules were studied using ab-initio and DFT quantum chemical methods (up to MP2/6-311++G(3df,3pd) and ...QCISD(T)/6-311++G(2df,2pd)) in order to describe the experimentally observed kinetic features of SO3 hydration and SOCl2 hydrolysis in the gas phase and to elucidate the reaction mechanism providing the high reaction rate. The transition state structures were located, and absolute values of kinetic rate constants were estimated for a variety of possible reaction pathways including bi- and termolecular SO and S−Cl bond hydrolysis, chlorine shift to oxygen, dissociative addition with formation of hexavalent sulfur derivative, and adjacent reactions. It was found that the termolecular mechanism of SO3 hydration proposed earlier by Morokuma and Muguruma is in good agreement with the experimental rate constants. However, none of the proposed molecular pathways of SOCl2 hydrolysis can provide the high reaction rate observed experimentally. Thus, the real hydrolysis mechanism of halogen derivatives of second-row elements in the gas phase can be sufficiently different from the regular molecular pathways, which are usually considered.
The CMD-3 detector has begun to take data at the electron-positron collider VEPP-2000 since december 2010. The collected data sample corresponds to an integrated luminosity of 60 pb−1 in the c.m. ...energy range from 0.32 up to 2 GeV and about 50pb−1 for RUN2017. The integrated luminosity was measured by counting e+e− e+e− and e+e− γγ events, allowing additional photons in the final state. Preliminary results of the luminosity measurement are presented for various energy ranges and its accuracy is estimated to be 1%.
RATIONALE:PCSKs (Proprotein convertase subtilisins/kexins) are a protease family with unknown functions in vasculature. Previously, we demonstrated PCSK6 upregulation in human atherosclerotic plaques ...associated with smooth muscle cells (SMCs), inflammation, extracellular matrix remodeling, and mitogens.
OBJECTIVE:Here, we applied a systems biology approach to gain deeper insights into the PCSK6 role in normal and diseased vessel wall.
METHODS AND RESULTS:Genetic analyses revealed association of intronic PCSK6 variant rs1531817 with maximum internal carotid intima-media thickness progression in high-cardiovascular risk subjects. This variant was linked with PCSK6 mRNA expression in healthy aortas and plaques but also with overall plaque SMA+ cell content and pericyte fraction. Increased PCSK6 expression was found in several independent human cohorts comparing atherosclerotic lesions versus healthy arteries, using transcriptomic and proteomic datasets. By immunohistochemistry, PCSK6 was localized to fibrous cap SMA+ cells and neovessels in plaques. In human, rat, and mouse intimal hyperplasia, PCSK6 was expressed by proliferating SMA+ cells and upregulated after 5 days in rat carotid balloon injury model, with positive correlation to PDGFB (platelet-derived growth factor subunit B) and MMP (matrix metalloprotease) 2/MMP14. Here, PCSK6 was shown to colocalize and cointeract with MMP2/MMP14 by in situ proximity ligation assay. Microarrays of carotid arteries from Pcsk6 versus control mice revealed suppression of contractile SMC markers, extracellular matrix remodeling enzymes, and cytokines/receptors. Pcsk6 mice showed reduced intimal hyperplasia response upon carotid ligation in vivo, accompanied by decreased MMP14 activation and impaired SMC outgrowth from aortic rings ex vivo. PCSK6 silencing in human SMCs in vitro leads to downregulation of contractile markers and increase in MMP2 expression. Conversely, PCSK6 overexpression increased PDGFBB (platelet-derived growth factor BB)-induced cell proliferation and particularly migration.
CONCLUSIONS:PCSK6 is a novel protease that induces SMC migration in response to PDGFB, mechanistically via modulation of contractile markers and MMP14 activation. This study establishes PCSK6 as a key regulator of SMC function in vascular remodeling.
The standard enthalpies, entropies, and Gibbs free energies of separate stages of the multistep hydrolysis of MX
4
molecules (M = C, Si, Ge; X = H, F, Cl) in the gas phase at 298 K were calculated by ...the G3 high-precision quantum-chemical method of calculation of thermodynamic parameters. The trends in these parameters were analyzed for each group of molecules. The calculated thermodynamic parameters make it possible to estimate the theoretical limits for the contents of water and hydrolysis products in the above high-purity carbon, silicon, and germanium derivatives.
The cross section of the process \(e^+e^-\to\pi^+\pi^-\) has been measured in the center-of-mass energy range from 0.32 to 1.2 GeV with the CMD-3 detector at the electron-positron collider VEPP-2000. ...The measurement is based on an integrated luminosity of about 88 pb\(^{-1}\), of which 62 pb\(^{-1}\) represent a complete dataset collected by CMD-3 at center-of-mass energies below 1 GeV. In the dominant region near the \(\rho\) resonance a systematic uncertainty of 0.7% was achieved. The implications of the presented results for the evaluation of the hadronic contribution to the anomalous magnetic moment of the muon are discussed.
Barrel calorimeter of the CMD-3 detector Shebalin, V. E.; Anisenkov, A. V.; Aulchenko, V. M. ...
Physics of atomic nuclei,
12/2015, Letnik:
78, Številka:
13
Journal Article
Recenzirano
The structure of the barrel calorimeter of the CMD-3 detector is presented in this work. The procedure of energy calibration of the calorimeter and the method of photon energy restoration are ...described. The distinctive feature of this barrel calorimeter is its combined structure; it is composed of two coaxial subsystems: a liquid xenon calorimeter and a crystalline CsI calorimeter. The calorimeter spatial resolution of the photon conversion point is about 2 mm, which corresponds to an angular resolution of ∼6 mrad. The energy resolution of the calorimeter is about 8% for photons with energy of 200 MeV and 4% for photons with energy of 1 GeV.
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