Codings of graphs with binary edge labels

LetG(V,E) be a graph. A mappingf:E{0,1} ^m is called a (binary) coding ofG, if the induced mapping , assigns different vectors to the vertices. For the Boolean sum,f is called aB-code, and for the mod 2 sum anM-code. Letm _B (G) resp.m _M (G) be the smallest lengthm for whichB-codes resp.M-codes are possible. Trivially,m _B (G),m _M (G) log₂|V|. Improving results of Z. Tuza we showm _B (G)log₂|V| + 1,m _M (G)log₂|V|+4.     

Characterization of SiC-platelets

Three fractions of SiC platelets were characterized using polarizing microscopy, X-ray diffraction, high resolution Auger electron spectroscopy (AES), electron spectroscopy for chemical analysis (ESCA) and scanning electron microscopy with energy dispersive analysis (SEM/EDX). The chemical analysis of the three fractions is given. The determination of the SiC polytypes (4H, 6H, 15R, 3C) was done and has been correlated with the chemical analysis. The results of the X-ray diffraction investigations confirm the polarizing microscopy observations. Using microanalytical techniques important conclusions about the impurity elements (e.g. B, Al, Fe) and their local distribution could be drawn. Most of them were found to be present on the outermost surfaces of the platelets. Some conclusions concerning the processing of the platelets are suggested.Dedicated to Professor Günther Tölg on the occasion of his 60th birthday     

Resonance-enhanced multiphoton ionization (REMPI) spectroscopy of photolytically generated hot CF radicals

In this paper, we investigate the rotationally resolved spectra of hot CF radicals generated after IR multiphoton dissociation (IRMPD) of CFCl₃ or CF₂Cl₂ and subsequent UV photodissociation. It is shown that these conditions are advantageous for the spectroscopy of transitions involving high rotational quantum numbers and hot bands. Thus molecular constants of CF for the first vibrationally excited state of the electronic ground state (A_v=77.1 cm⁻¹, B_v=1.389 cm⁻¹, D_v=6.570×10⁻⁶ cm⁻¹) are determined for the first time or are calculated more accurately. The spectroscopic method used was resonance-enhanced multiphoton ionization (REMPI) spectroscopy.     

Investigations into the Pd-catalysed cross-coupling of phenylacetylene with aryl chlorides: simple one-pot procedure and the effect of ZnCl2 co-catalysis

[PdCl(C6H3(OPPri2)2-2,6)] 1 catalyses the coupling of electron-rich, electron-neutral and electron-deficient aryl chlorides with phenylacetylene in the presence of ZnCl2 as cocatalyst to give the products in modest to excellent yields.     

Analysis of free and esterified sterols in vegetable oil methyl esters by capillary GC

The introduction of quality standards for vegetable oil methyl esters is gaining in importance due to their increased use as diesel fuel substitutes and as technical products. Free and esterified sterols, the main constituents of the unsaponifiable matter in vegetable oils, are recovered in vegetable oil methyl esters and may influence the technical properties of vegetable oil methyl ester products. A rapid gas chromatographic method for the qualitative and quantitative determination of free and esterified sterols in vegetable oil methyl esters has therefore been developed. The concentration of the free sterols as well as their qualitative and quantitative composition and the concentration of the sterol esters have been determined in rape seed oil methyl ester samples by GC–FID. Prior to analysis, the free sterols were silylated with N,O-bis(trimethylsilyl)trifluoroacetamide with 1% of trimethylchlorosilane; betulinol was used as an internal standard. Calibration was performed by analysis of standard solutions containing β-sitosterol, cholesteryl stearate, and betulinol. The reproducibility of the quantitative results has been evaluated by repeated injections of the same test solution and by repeated complete analysis of the same sample.     

Octahedral (cis-cyclam)iron(III) complexes with O,N-coordinated o-iminosemiquinonate(1-) pi radicals and o-imidophenolate(2-) anions

Three octahedral complexes containing a (cis-cyclam)iron(III) moiety and an O,N-coordinated o-iminobenzosemiquinonate pi radical anion have been synthesized and characterized by X-ray crystallography at 100 K: [Fe(cis-cyclam)(L(1-3)(ISQ))](PF(6))(2) (1-3), where (L(1-3)(ISQ)) represents the monoanionic pi radicals derived from one-electron oxidations of the respective dianion of o-imidophenolate(2-), L(1), 2-imido-4,6-di-tert-butylphenolate(2-), L(2), and N-phenyl-2-imido-4,6-di-tert-butylphenolate(2-), L(3). Compounds 1-3 possess an S(t) = 0 ground state, which is attained via strong intramolecular antiferromagnetic exchange coupling between a low-spin central ferric ion (S(Fe) = 1/2) and an o-imino-benzosemiquinonate(1-) pi radical (S(rad) = 1/2). Zero-field M?ssbauer spectra of 1-3 at 80 K confirm the low-spin ferric electron configuration: isomer shift delta = 0.26 mm s(-1) and quadrupole splitting DeltaE(Q) = 1.96 mm s(-1) for 1, 0.28 and 1.93 for 2, and 0.33 and 1.88 for 3. All three complexes undergo a reversible, one-electron reduction of the coordinated o-imino-benzosemiquinonate ligand, yielding an [Fe(III)(cis-cyclam)(L(1-3)(IP))](+) monocation. The monocations of 1 and 2 display very similar rhombic signals in the X-band EPR spectra (g = 2.15, 2.12, and 1.97), indicative of low-spin ferric species. In contast, the monocation of 3 contains a high-spin ferric center (S(Fe) = 5/2) as is deduced from its M?ssbauer and EPR spectra.     

The rhodium complex of a tris(bipyridine) ligand—Its electrochemical behaviour and function as mediator for the regeneration of NADH from NAD+

The tris-bipyridine ligand3a and its stoichiometric Rh³⁺ complex have been prepared. Cyclovoltammograms of the complex at pH 7.4 using a glassy carbon disk electrode reveal a strong reduction peak at –620 mV and two weak reduction peaks at more negative voltage. The reduction potential of the new complex is shifted by 300 mV to more positive values as compared to [Rh(bipy)₃]³⁺. There is no reversible reoxidation peak of the Rh(I) complex formed due to the decomplexation of one of the three bipyridine units in the course of the transition Rh(III)Rh(I). The Rh(III) complex of3a was also studied with respect to its function as a possible redox mediator for the electrochemical regeneration of NADH from NAD⁺. The preparative electrolysis of the Rh³⁺ complex of3a in the presence of NAD⁺ yields a selective formation of NADH, whereas NAD dimers were not detected. On the other hand, a significant acceleration of this reaction compared to [Rh(bipy)₃]³⁺ was not observed.     

Polycarboxyhydrazides with ferrocenylene groups in the main chain

Polycarboxyhydrazides essentially of the type \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} [{\rm C}_{10} {\rm H}_8 {\rm Fe}\hbox{---}{\rm CONHNHCO}\rlap{--}]_n $\end{document} are synthesized by low-temperature solution condensation of 1,1′-di(chlorocarbonyl) ferrocene with hydrazine or 1, 1′-ferrocenedicarboxyhydrazide and hexamethylphosphoramide as solvent. In an analogous manner the polycondensation of 1, 1′-di(chlorocarbonyl)ferrocene with oxalyldihydrazide leads to polyhydrazides essentially possessing the structure \documentclass{article}\pagestyle{empty}\begin{document}$ \rlap{--} [{\rm C}_{10} {\rm H}_8 {\rm Fe}\hbox{---}{\rm CONHNHCO}\hbox{---}{\rm CONHNHCO}\rlap{--}]_n $\end{document}. Both polymer types exhibit inherent viscosities (0.08–0.19 dl./g.) considerably lower than reported for analogous aliphatic or benzene-aromatic polyhydrazides. This behavior points to premature chain termination via heterobridging imide groups as a result of the welldocumented tendency of appropriately substituted ferrocene compounds to undergo intramolecular cyclization. In addition, elemental analytical and spectroscopic evidence, coupled with the failure of both polymer types to undergo cyclodehydration to the corresponding 1,3,4-oxadiazole polymers upon heat treatment, suggests some structural irregularities in the aliphatic connecting segments arising from ferrocenoylation of secondary amino groups with resultant branching. With the polyhydrazide prepared from 1, 1′-di(chlorocarbonyl)ferrocene and 1, 1′-ferrocenedicarboxyhydrazide it is shown spectroscopically that treatment with alkali results in conversation of the nonconjugated hydrazide structure of the connecting segments into the polyconjugated tautomeric enol form comprising azine groups.