On the Riemann–Hilbert problem for difference and <Emphasis Type="Italic">q</Emphasis>-difference systems

We study an analog of the classical Riemann–Hilbert problem stated for the classes of difference and q-difference systems. We generalize Birkhoff’s existence theorem.     

Thermal oxidative destruction of isomeric dipyrrolylmethanes

3,3′,4,4′-tetramethyl-5,5′-dicarboethoxydipyrrolylmethane-2,2′ and its α,β and β,β′ isomers were synthesized. The compounds were characterized by recording of their proton NMR spectra. The thermal oxidative destruction of the compounds was studied by thermogravimetry. The thermal stability of dipyrrolylmethanes was found to be primarily characterised by molecular isomerism for symmetrically substituted α,α′-and β,β′-dipyrrolylmethanes compared with α,β isomer.     

Molecular Complexes of Phthalocyanine with Organic Solvents

It was established that in crystal solvates and solutions zinc(II)tetra-tert-butylphthalocyanine formed stable molecular complexes with benzene and pyridine. The characteristics of the corresponding molecular complexes were estimated. Molecules of electron-donor and aromatic solvents do not break down the zinc(II)tetra-tert-butylphthalocyanine associates and do not facilitate intraphase polymorphic transition. A comparative analysis was carried out for the coordinative properties of zinc(II)tetra-tert-butylphthalocyanine and its structural analog, zinc(II)tetrabenzoporphyrin, with respect to pyridine in benzene solutions.     

Titration Calorimetric Investigations on the Interactions of Zn(II) Porphyrin Complexes with Pyridine in Benzene and Chloroform at 298.15 K

Titration calorimetry was used in a thermodynamic study on the interactions of pyridine with natural zinc(II) porphyrin derivatives in benzene and chloroform at 298.15 K. The ability of zinc porphyrins to coordinate to pyridine is higher in benzene than in chloroform and also depends on the molecular structure of the metalloporphyrin.This revised version was published online in November 2005 with corrections to the Cover Date.