Differences in coating mechanism of structurally different aluminosilicates observed through the thermal analysis

Systematic modification of three structurally different minerals (zeolite, mica, and vermiculite) was carried out with the aim of determining the modification mechanism and exposing the hydrophobic surface that can be used as a sorbent for many organic compounds. Mechanism of modification with cationic surfactant depends strongly on the mineral type. In order to identify the influence of aluminosilicates structural differences on the modification process, adsorption experiments with organic matter and water vapor, supplemented with the DTA/TG analysis, were performed. The cation exchange capacity (CEC) value was 1454?>?560?>?28 meq kg^?1 for zeolite (clinoptilolite), vermiculite, and mica (muscovite), respectively. Despite its CEC value, vermiculite adsorbed three times the amount of organic matter than did clinoptilolite due to the porous structure of zeolite, which acted to limit the adsorption only on the external exchangeable cations. If the loading amount is equal to the CEC or the external cation exchange capacity for clinoptilolite (ECEC?≈?10% CEC), the monolayer will form while mineral surface will have hydrophobic character. Only one active center exists at the surface of the clinoptilolite that was identified by DTA curves with a sharp and defined peak around 300 °C and by the mass loss at the TG diagrams. Two significant and equal active centers were observed in vermiculite, one for the exchange of the surface cations and the other for the interlayer cations and H₂O molecules. Muscovite CEC is negligible, and due to the absence of any other functional groups, the modification of this mineral was impossible.     

Ordering Starlike Trees by the Totality of Their Spectral Moments

The k-th spectral moment M_k(G) of the adjacency matrix of a graph G represents the number of closed walks of length k in G. We study here the partial order ? of graphs, defined by G ? H if M_k(G) ≤ M_k(H) for all k ≥?0, and are interested in the question when is ? a linear order within a specified set of graphs? Our main result is that ? is a linear order on each set of starlike trees with constant number of vertices. Recall that a connected graph G is a starlike tree if it has a vertex u such that the components of G ? u are paths, called the branches of G. It turns out that the ? ordering of starlike trees with constant number of vertices coincides with the shortlex order of sorted sequence of their branch lengths.

     

Proton exit channels in bovine cytochrome c oxidase

Cytochrome c oxidase (CcO) is the terminal transmembrane enzyme of the respiratory electron transport chain in aerobic cells. It catalyzes the reduction of oxygen to water and utilizes the free energy of the reduction reaction for proton pumping, a process which results in a membrane electrochemical proton gradient. Although the structure of the enzyme has been solved for several organisms, the molecular mechanism of proton pumping and proton exit pathways remain unknown. In our previous work, the continuum electrostatic calculations were employed to evaluate the electrostatic potential, energies, and protonation state of bovine cytochrome c oxidase for different redox states of the enzyme. A possible mechanism of oxygen reduction and proton pumping via His291 was proposed. In this paper, using electrostatic calculations, we examine the proton exit pathways in the enzyme. By monitoring the changes of the protonation states, proton affinities, and energies of electrostatic interactions between the titratable groups in different redox states of CcO, we identified the clusters of strongly interacting residues. Using these data, we detected four possible proton exit points on the periplasmic side of the membrane (Lys171B/Asp173B, His24B/Asp25B, Asp51, and Asp300). We then were able to trace the proton exit pathways and to evaluate the energy profiles along the paths. On the basis of energetic considerations and the conservation of the residues in a protein sequence, the most likely exit pathway is one via the Lys171B/Asp173B site. The obtained results are fully consistent with our His291 model of proton pumping, and provide a rationale for the absence of proton leaking in CcO between the pumping strokes.     

Unions of dihedral groups

By the following simple formula (1) $$\forall x \exists y (x = xyy, y = xyx)$$ We characterize semigroups from the title. Considering a local property of their ?-classes we get bands and Boolean groups as extreme cases of semigroups with that property. We also provide a construction showing that ?-classes can be sufficiently complicated (at least as Abelian groups are). Then we permute right-hand sides of identities in (1) getting Boolean semigroups (x³=x) and so-called anti-inverse semigroups. Finally we show that Boolean semigroups are a proper subclass of the intersection of anti-inverse semigroups and unions of dihedral groups.     

Investigation of ionic thermocurrents in SrCl2-K crystals

Ionic thermocurrents in SrCl₂-K crystals have been investigated for the first time. Two maxima of thermally stimulated depolarization currents have been detected at T=112°K and T=210–240°K. The low-temperature maximum with a reorientation energy =0.25 eV and a frequency factor _o=7.1·10⁹ Hz is due to relaxation of impurity-vacancy dipoles. Its intensity grows linearly with the concentration of the dopand. The high-temperature maximum is due to the space charge. Its activation energy =0.46 eV coincides with the migration energy of anion vacancies associated with the potassium ions.Translated from Izvestiya Vysshikh Zavedenii, Fizika, No. 9, pp. 80–83, September, 1982.     

Hydrothermal Synthesis and Crystal Structure of AgVMO5 (M = Se,Te)

Single crystals of AgVSeO₅ and AgVTeO₅ were obtained under hydrothermal conditions at 190 °C by reacting stoichiometric amounts of AgNO₃, NaVO₃, TeO₂ and SeO₂, respectively. AgVSeO₅ crystallizes in Pbcm with a = 418.14(3) pm, b = 2007.70(6) pm, c = 521.17(2) pm, V = 437.52(2) × 10⁶ pm³ and Z = 4, as red needles. The structure consists of VO₅ square pyramids, trigonal SeO₃ pyramids and AgO₈ polyhedra, as primary building units. The VO₅ square pyramids are linked to chains running along the c‐axis, by sharing oxygen atoms in the basal plane in cis‐position. The remaining basal O atoms of the VO₅ moieties are shared with two oxygen atoms of the SeO₃ units. The resulting polyanionic strands of composition [VSeO₅]^? are interconnected by silver atoms to form a three dimensional network. AgVTeO₅ crystallizes as yellow needles in P2₁/c with a = 586.59(1) pm, b = 1137.98(2) pm, c = 680.78(1) pm, β = 102.733(1)°, V = 443.26(1) × 10⁶ pm³ and Z = 4. The structure consists of VO₄ tetrahedra, Ψ‐trigonal‐bipyramidal TeO₄ units and AgO₈ polyhedra as primary building units. The TeO₄ groups form dimers by edge sharing, which are linked through vertices to the VO₄ tetrahedra. The resulting one dimensional polyanion is extending along [101]. The structural motifs and charge distribution according to Se⁴⁺/V⁵⁺, and Te⁴⁺/V⁵⁺ respectively, seem to allow for a reshuffling of the charge distribution, thus inducing interesting physical phenomena, at elevated temperatures or pressures.     

Remarks on Q-integral complete multipartite graphs

A graph is Q-integral if the spectrum of its signless Laplacian matrix consists entirely of integers. In their study of Q-integral complete multipartite graphs, [Zhao et al., Q-integral complete r-partite graphs, Linear Algebra Appl. 438 (2013) 1067–1077] posed two questions on the existence of such graphs. We resolve these questions and present some further results characterizing particular classes of Q-integral complete multipartite graphs.