Xymedon conjugate with biogenic acids. Antioxidant properties of a conjugate of Xymedon with <Emphasis Type="SmallCaps">l</Emphasis>-ascorbic acid

Antiradical activity and antioxidant properties of a conjugate of Xymedon with l-ascorbic acid were studied. In contrast to Xymedon, a conjugate of Xymedon with l-ascorbic acid was found to react with free radicals. Pro-oxidant activity of the conjugate of Xymedon with l-ascorbic acid in a chemiluminescence system is weaker as compared to individual l-ascorbic acid. This is the evidence of the increase in the stability of ascorbic acid upon conjugation with a molecule of Xymedon. Conjugate of Xymedon with l-ascorbic acid facilitates the decrease in the concentration of a lipid peroxidation product (malondialdehyde) and the activity of superoxide dismutase in liver and serum of laboratory animals exposed to intoxication with a known hepatotropic toxin CCl₄. This observation shows the contribution of the antioxidant action to the hepatoprotective effect of the studied Xymedon derivative.     

Reactivity of rhenium(V) oxo Schiff base complexes with phosphine ligands: rearrangement and reduction reactions

The symmetric rhenium(V) oxo Schiff base complexes trans-[ReO(OH2)(acac2en)]Cl and trans-[ReOCl(acac2pn)], where acac2en and acac2pn are the tetradentate Schiff base ligands N,N'-ethylenebis(acetylacetone) diimine and N,N'-propylenebis(acetylacetone) diimine, respectively, were reacted with monodentate phosphine ligands to yield one of two unique cationic phosphine complexes depending on the ligand backbone length (en vs pn) and the identity of the phosphine ligand. Reduction of the Re(V) oxo core to Re(III) resulted on reaction of trans-[ReO(OH2)(acac2en)]Cl with triphenylphosphine or diethylphenylphosphine to yield a single reduced, disubstituted product of the general type trans-[Re(III)(PR3)2(acac2en)]+. Rather unexpectedly, a similar reaction with the stronger reducing agent triethylphosphine yielded the intramolecularly rearranged, asymmetric cis-[Re(V)O(PEt3)(acac2en)]+ complex. Reactions of trans-[Re(V)O(acac2pn)Cl] with the same phosphine ligands yielded only the rearranged asymmetric cis-[Re(V)O(PR3)(acac2pn)]+ complexes in quantitative yield. The compounds were characterized using standard spectroscopic methods, elemental analyses, cyclic voltammetry, and single-crystal X-ray diffraction. The crystallographic data for the structures reported are as follows: trans-[Re(III)(PPh3)2(acac2en)]PF6 (H48C48N2O2P2Re.PF6), 1, triclinic (P), a = 18.8261(12) A, b = 16.2517(10) A, c = 15.4556(10) A, alpha = 95.522(1) degrees , beta = 97.130(1) degrees , gamma = 91.350(1) degrees , V = 4667.4(5) A(3), Z = 4; trans-[Re(III)(PEt2Ph)2(acac2en)]PF6 (H48C32N2O2P2Re.PF6), 2, orthorhombic (Pccn), a = 10.4753(6) A, b =18.4315(10) A, c = 18.9245(11) A, V = 3653.9(4) A3, Z = 4; cis-[Re(V)O(PEt3)(acac2en)]PF6 (H33C18N2O3PRe.1.25PF6, 3, monoclinic (C2/c), a = 39.8194(15) A, b = 13.6187(5) A, c = 20.1777(8) A, beta = 107.7730(10) degrees , V = 10419.9(7) A3, Z = 16; cis-[Re(V)O(PPh3)(acac2pn)]PF6 (H35C31N2O3PRe.PF6), 4, triclinic (P), a = 10.3094(10) A, b =12.1196(12) A, c = 14.8146(15) A, alpha = 105.939(2) degrees , beta = 105.383(2) degrees , gamma = 93.525(2) degrees , V = 1698.0(3) A3, Z = 2; cis-[Re(V)O(PEt2Ph)(acac2pn)]PF6 (H35C23N2O3PRe.PF6), 5, monoclinic (P2(1)/n), a = 18.1183(18) A, b = 11.580(1) A, c = 28.519(3) A, beta = 101.861(2) degrees , V = 5855.9(10) A(3), Z = 4.     

On distributions of random variables chosen at random

The existence of typical distributions for random variables chosen at random from a finite-dimensional random variable vector space of high dimension is established. Possible typical distributions are described, and conditions for the typical distribution to be standard Gaussian are given. Bibliography: 2 titles. Translated fromZapiski Nauchnykh Seminarov POMI, Vol. 216, 1994, pp. 153–160. Translated by the author.     

3-Color bipartite Ramsey number of cycles and paths

The -color bipartite Ramsey number of a bipartite graph is the least integer for which every -edge-colored complete bipartite graph contains a monochromatic copy of . The study of bipartite Ramsey numbers was initiated, over 40 years ago, by Faudree and Schelp and, independently, by Gyárfás and Lehel, who determined the 2-color Ramsey number of paths. In this paper we determine asymptotically the 3-color bipartite Ramsey number of paths and (even) cycles.     

Optical design of a freeform TIR lens for LED streetlight

Secondary optics is a critical component determining the output efficiency and light distribution of the LED streetlight. A good roadway illumination requires the LED streetlight have a rectangular light pattern just cover the roadway and without excess spill light creeping into yards and shining into windows of neighbor residents. The adoption of the unsymmetrical freeform optics with different light distributions along X and Y directions is necessary. The whole LED streetlight can be constructed if only mounts these LED modules on the planar PCB plate. The mechanism, thermal management, and the power control electronics of the LED streetlight become very simple. In this paper, an optical design approach of a freeform TIR (total internal reflection) lens for the LED streetlight is investigated. With these freeform lenses, high output efficiency, even light distribution, and batwing far field beam angle distribution can be achieved.     

Minors in Expanding Graphs

We propose a unifying framework for studying extremal problems related to graph minors. This framework relates the existence of a large minor in a given graph to its expansion properties. We then apply the developed framework to several extremal problems and prove in particular that: (a) Every -free graph G with average degree r ( are constants) contains a minor with average degree , for some constant ; (b) Every C_2k-free graph G with average degree r (k ≥ 2 is a constant) contains a minor with average degree , for some constant c = c(k) > 0. We also derive explicit lower bounds on the minor density in random, pseudo-random and expanding graphs. Received: March 2008, Accepted: May 2008     

Analysis of the quadrupole mass filter with quadrupole excitation by the envelope equation method

The method of the envelope equation has been developed to describe the stability of the motion of ions in a quadrupole mass filter in the presence of periodic excitations of the feeding voltage. Dynamic equations that describe the variations in the envelope of ion vibrations in the vicinity of the vertex of the first common stability region have been obtained and reduced to the form of the Mathieu equations. The splitting of the stability diagram of the motion of ions into stability islands due to excitation has been described. The results of the approximate theory have been confirmed by an exact analysis of the stability diagram for rational values of the relative excitation frequency. The boundaries of the applicability domain for the developed theory limited by first-order resonances have been determined.