Influence of O/S/Se Exchange on the Stability of 1,3,4-Selana(Thia/Oxa)Diazole-Palladium Complexes as Studied by Electrospray Ionization Mass Spectrometry

Abstract

The complexes of 2-phenyl-1,3,4-selena(thia/oxa)diazole with a palladium cation were studied by using electrospray ionization mass spectrometry. Palladium chloride was used as a source of palladium cations. The complexes of ligand:metal stoichiometry of 3:1 (ions [L₃+PdCl]⁺) were formed for selenadiazoles and thiadiazoles. Quantum mechanical calculations performed indicated that ligand molecules are attached to palladium cation by the N-4 atom. The fragment ions formed [L₂–H+Pd]⁺ may be regarded as organometallic species. Selenadiazoles were found more prone to form the palladium complexes than thiadiazoles. Oxadiazoles did not yield the respective palladium complexes. For comparison, the nickel cation was also included in the study but only 1:1, and less abundant 2:1 complexes were observed. Exchange of selenium into oxygen does not affect the abilities of the ligands to form nickel complexes.     

Complexation of peptides with crown ethers. Structure and thermal behaviour of ternary compounds: 18-crown-6/glycylglycine/water and 18-crown-6/L-α-alanyl-L-α-alanine/water

Abstract

X-ray structures of ternary complexes composed of small dipeptides, i.e. glycylglycine or L-α-alanyl-L-α-alanine, 18-crown-6 and water molecules are determined based on single-crystal studies. It has been concluded that both dipeptides exist in the complex as zwitterions and are bonded to the 18-crown-6 macrocycle by the -NH⁺ ₃ end group through N-H…O hydrogen bonds. The carboxylic groups at the opposite side of the peptide molecules take part in hydrogen bonding with water molecules. This scheme of water-peptide hydrogen bonding is particularly interesting in the glycylglycine compound where the water content is rather high (approximately 16 moles per mole of crown/dipeptide, 6 of which are found in the X-ray study) and may have interesting relevance with respect to the structure of gel solutions which easily form in these systems. The DSC and TGA thermograms of different hydrated forms of the complexes were obtained. Two types of water, i.e. weakly and strongly bonded, were observed upon heating of the hydrated complex. On further heating the anhydrous complexes have at least two transitions in the range 320–470 K: melting of complexes at 373–383 K and decomposition above 410 K.     

Studies on the catalysis of the reaction of organotin phenoxides with diethyl acetylenedicarboxylate

Different organotin phenoxides react at room temperature with diethyl acetylenedicarboxylate in diethyl ether, in the presence of lithium perchlorate to give a mixture of corresponding phenyl vinyl ethers and ring ethenylated phenols. Copyright © 2005 John Wiley & Sons, Ltd.     

Kinetics and mechanism of the reaction of allyl chloride with trichlorosilane catalyzed by carbon‐supported platinum

The kinetics of substrate conversions in the commercially important hydrosilylation of allyl chloride with trichlorosilane, catalyzed by active carbon‐supported platinum, as well as the yields of the main product (3‐chloropropyltrichlorosilane) and by‐products (tetrachlorosilane, propyltrichlorosilane) have been studied. On the basis of the measurements performed, the pseudo first‐order rate constants (k_obs, k₁ and k₂ from the model of competitive reactions) and activation energy (E_a = 11 kcal mol^?1 (46.2 kJ mol^?1)) were determined. The data obtained point to a non‐linear dependence of k_obs on the catalyst amount. From the kinetic relationships, the kinetic equation was deduced. All the results of kinetic, IR spectroscopic and thermogravimetric measurements, as well as the derived kinetic equation, have confirmed the general model of consecutive–competitive reaction involving the formation of a surface complex C₁ which can decompose in two directions according to the Chalk–Harrod mechanism. Copyright © 2003 John Wiley & Sons, Ltd.     

Martingales of Random Subsets of a Metric Space of Negative Curvature

We prove extension of classical convergence theorem of P. Lévy for martingales of random subsets of a metric space of negative curvature.     

Higgs boson production and weak boson structure

The influence of the QCD structure of the weak bosons on the Higgs boson production ine-p scattering is studied. The energy and Higgs boson mass dependence of the cross-section, following from the new contributions, is calculated. Work supported by the Polish State Committee for Scientifić Research (grant No. 2 P03B 081 09) and the Volkswagen-Stiftung