The effect of sonication on glass electrodes

This communication describes observations made on the disturbing effect of ultrasound on the functioning of glass electrodes. It was observed that the signal of glass electrodes drops significantly, with as much as several pH units, if sonication is applied to the sample solution. The effect was studied for a variety of electrolyte solutions and for several glass electrode makes, and was always found to be reversible and reproducible. The quality and the concentration of the electrolyte, as well as the ultrasonic power applied were seen to strongly influence the magnitude of the effect. These findings suggests that (i) if a glass electrode is being used to follow chemical reactions in sonicated solutions, irradiation should be intermitted for the time of measurements, and (ii) the phenomenon may provide an alternative method for sensing ultrasound or mapping ultrasound energy distribution.     

Vertex-linked ZnO2S2 tetrahedra in the oxysulfide BaZnOS: a new coordination environment for zinc in a condensed solid

The wide-band-gap semiconductor BaZnOS adopts a high-symmetry modification of the SrZnO2 structure type and contains layers of vertex-linked ZnO2S2 tetrahedra, which represent a novel coordination environment for zinc in the solid state. BaZnOS: orthorhombic, space group Cmcm; a = 3.9619(2) angstroms, b = 12.8541(7) angstroms, c = 6.1175(4) angstroms, Z = 4. Diffuse-reflectance spectroscopy measurements reveal a direct band gap of 3.9(3) eV, consistent with the white color and the results of band structure calculations. The band gap is larger than those observed in ZnO and ZnS, consistent with the more ionic nature of BaZnOS. Attempts to dope this compound electronically have so far not proved possible.     

Modeling rate-controlling solvent effects. The pericyclic meisenheimer rearrangement of N-propargylmorpholine N-oxide

The activation parameters of the pericyclic Meisenheimer rearrangement and a competitive rearrangement of N-propargylmorpholine N-oxide were determined by experimental and computational methods. A number of aprotic and protic solvents of different polarities and hydrogen bond-forming abilities and the roles of electron-pair acceptor additives were investigated. The reaction kinetics were followed by means of NMR. In protic solvents, isotope-labeling experiments revealed a novel inverse secondary kinetic isotope effect (k(H)/k(D) about 0.8) for the rate-determining cyclization step, probably occurring because of a C(sp) --> C(sp(2)) change in hybridization at the reaction center. In molecular computations at the B3LYP/6-31++G(d,p) level of theory, implicit, explicit, and joint explicit-implicit solvent models were used. The explicit-implicit model and molecular dynamic simulations gave the most accurate results. The components of the rate-controlling solvent effect are discussed, and general equations are proposed for accurate prediction of the solvent-dependent activation parameters.     

The first ternary tin(II) nitride: NaSnN

NaSnN with the non-centrosymmetric layered structure type of KSnAs and featuring the new layered Zintl ion [SnN]- is the first example of a ternary nitride containing Sn-N bonds, and the first example of a nitride containing formally divalent tin.     

AnL 1 counting problem in ergodic theory

We give a negative solution to the following counting problem for measure preserving transformations. Forf∈L ₊ ¹ (μ), is it true that sup _n (N _n (f)(x)/n) <∞, μ a.e., where N _n (f)(x)=≠{k:f(T ^k x)/k >1/ n}? One of the consequences is the nonvalidity of J. Bourgain’s Return Time Theorem for pairs of (L ¹ ,L ¹ ) functions.     

Invariant Shen connections and geodesic orbit spaces

Summary The geodesic graph of Riemannian spaces all geodesics of which are orbits of 1-parameter isometry groups was constructed by J. Szenthe in 1976 and it became a basic tool for studying such spaces, called g.o.\ spaces. This infinitesimal structure corresponds to the reductive complement <InlineEquation ID=IE"1"><EquationSource Format="TEX"><![CDATA[<InlineEquation ID=IE"2"><EquationSource Format="TEX"><![CDATA[$]]></EquationSource></InlineEquation>]]></EquationSource></InlineEquation>\mathfrak m$ in the case of naturally reductive spaces. The systematic study of Riemannian g.o. spaces was started by O. Kowalski and L.~Vanhecke in 1991, when they introduced the most important definitions, classified the low-dimensional examples and described the basic constructions of this theory. The aim of this paper is to investigate a connection theoretical analogue of the concept of the geodesic graph.     

Increasing the solubility characteristics of fenofibrate with cyclodextrin

The incidence of genetic lipoprotein disorders, or hyperlipoproteinaemia, is currently increasing. Examinations were carried out on the hyperlipoproteinaemic drug fenofibrate and various cyclodextrin derivatives were applied to increase the solubility of this drug. Numerous products with several compositions (drug: CD mole ratio=2:1, 1:1, 1:2 or 1:3) were studied and three preparation methods (powder mixing, kneading and precipitation) were used. In vitro drug liberation and membrane diffusion examinations revealed compositions suitable for the preparation of a capsule dosage form (1:2 and 1:3 physical mixtures).Dedicated to Dr. Béla Selmeczi, university professor, with the best wishes for his 65th birthday.