Mechanicochemical interaction of plant proanthocyanidins with drugs

The possibility has been studied of regulating the solubility properties of deoxypeganine by binding it with plant proanthocyanidins (katatsin, kavergal, yantapsin).Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent, fax (3712) 89 14 75. Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 226–228, March-April, 1995. Original article submitted April 14, 1994.     

Comparative theoretical study of intramolecular proton transfer in the photochemical cycles of 2-(2′-hydroxyphenyl)benzoxazole and 5,8-dimethyl-1-tetralone

We present a comparative golden rule analysis of the dynamics of the intramolecur (IM) hydrogen atom and proton transfer in the photochemical cycles of 2-(2′-hydroxyphenyl)benzoxazole (HBO) and 5,8-dimehtyl-1-tetralone (DMT). Two major effects are taken into consideration: the promoting effect of the IM vibrations which are symmetrically coupled to the reaction coordinate,and the suppressing effect resulting from the reorganization of both the molecule and solvent.

Semiempirical quantum-chemical calculations at the AM1 level were carried out to study the energy levels of all states involved in the photochemical cycles, including the effects of solvation in a polar protic solvent in the case of DMT. Two rotamers E_I and E_II for the enol form of DMT were located corresponding to different positions of the H atom in the hydroxyl group. In the group state the first is more stable both in the gas phase and in polar protic solvents such as diethyl ether—isopentane—ethanol (5:2:5 by volume). Therefore the reketonization reaction is treated as one-step tunneling from the rotamer E_I to the keto form, i.e. without the activated rotational equilibrium E_I↔E_II proposed by Grellmann and coworkers in an earlier study. The steep slope of the kinetic curve of this reaction is attributed to the additional activation energy resulting from the final reorganization of the low frequency oscillators, both intramolecular and solvent. For the dynamic calculations, the standard AM1 output (structural and force field data) was used as the input, and good agreement with the available kinetic experiments was reached for both compounds. No special reasons were found for the similarity of the kinetic curves for triplet excited-state intramolecular proton transfer in HBO and DMT.     

1, 5-Rearrangement of enol acylates of aryl 1H.-1, 2, 4-triazol-1-ylmethyl ketones

The rearrangement of enol acylates of aryl 1H-1, 2, 4-triazol-1-ylmethyl ketones at 140–150°C in acetic anhydride is studied. The migration of the acyl group to the C(5) atom of the heterocycle is found to be intramolecular. The characteristics of the original and final products are presented. X-ray structural studies of the enol acetates of 2, 4-dichlorophenyl 1H-1, 2, 4-triazol-1-ylmethyl ketone and 2, 4-dichlorophenyl 5-acetyl-1H-1, 2, 4-triazol-1-ylmethyl ketone are carried out.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 560–564, March, 1993.     

Thermodynamic properties of aqueous organic mixtures near the critical demixing: Cases of 2,6-dimethylpyridine and of 2-isobutoxyethanol

Phase diagrams, volumes and heat capacities of aqueous mixtures of 2,6-dimethylpyridine (2,6-L) and 2-isobutoxyethanol (iBE) and activities of 2,6-L in aqueous mixtures were measured in the monophasic region near the lower critical solution temperature (LCST). With 2,6-L some measurement were also made just above the LCST. From the temperature dependence of these data, partial molar relative enthalpies (2,6-L), expansibilities and the temperature derivative of heat capacities were calculated and show that iBE undergoes a microphase transition at low concentration which is not related to the phase separation. On the other hand, the properties of 2,6-L in the water-rich region at temperatures well below the LCST indicates that this solute has only a slight tendency to associate. The heat capacities of 2,6-L show an important increase near the LCST. Such changes are not observed for iBE and other alkoxyethanols and amines since these systems already exist in the form of microphases; the partial molar properties of iBE near the LCST are nearly equal to the molar values of the pure liquid, and the changes in thermodynamic properties corresponding to the macroscopic phase transition, are therefore too small to be measured by the present techniques.     

Electrochemical synthesis of π-indenyl-π-(3)-1,2-dicarbollyliron(III)

Co-electrolysis of potassium 1,2-dicarbadodecahydroundecaborate and indene in 0.1N sodium bromide solution in dimethylsulfoxide using iron electrodes afforded -indenyl--(3)-1,2-dicarbollyliron(III).Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 764–765, April, 1993.     

Stacking and discontinuous buffers in capillary zone electrophoresis

Discontinuous buffers for capillary zone electrophoresis (CZE) can be used under less rigid conditions compared to those for isotachophoresis for stacking. They can be prepared simply by modifying the sample itself, either by addition of small inorganic ions, low conductivity diluents, or both, and also by adjusting its pH, meanwhile injecting a large volume on the capillary. Zwitterionic and organic-based buffers such as triethanolamine and tris(hydroxymethyl)aminomethane (Tris) are well suited for stacking due to their low conductivity, provided the buffer is discontinuous as demonstrated here. A simple mechanism based on discontinuous buffers is described to explain many of the observed stacking types in CZE, pointing out the many similarities to transient isotachophoresis.     

Bactericidal effects of photoactivated porphyrins--an alternative approach to antimicrobial drugs

Photoactivated porphyrins display a potent cytotoxic activity towards a variety of Gram positive bacteria, mycoplasma and yeasts, but not Gram negative cells. The prerequisite for photosensitization of a microbial cell is the binding of porphyrin to the cytoplasmic membrane in a pH-dependent manner. On illumination, the membrane bound, and possibly, cytoplasmic porphyrin molecules generate singlet oxygen and radicals which sensitize biomolecules and lead to cell death. The immediate inhibition of cell growth on photodynamic treatment is accompanied by alterations in cell wall and membrane synthesis, leading to the formation of large mesosomes adjacent to the unaccomplished septa. Hemin bound to microbial cells exerts cytotoxic activity by peroxidative and oxidative reactions independent of light. Future research in the field may enhance the possibility of using porphyrin photosensitization for treatment of microbial infections. Such clinical use will be unrelated to the antibiotic resistance of the pathogen. Resistance of Gram negative bacteria to porphyrin photosensitization is the main impediment to its use as a broad spectrum antibacterial method.     

Structure of an anti-plasmin inhibitor, eckol, isolated from the brown alga Ecklonia kurome Okamura and inhibitory activities of its derivatives on plasma plasmin inhibitors

Eckol (1), a novel phlorotannin with a dibenzo-1,4-dioxin skeleton, has been isolated from the brown alga Ecklonia kurome Okamura as a potent and specific anti-plasmin inhibitor. Its structure has been elucidated based on the spectral data, in particular, by means of negative nuclear Overhauser effect (NOE), and finally established as 1-(3,5-dihydroxyphenoxy)-2,4,7,9-tetrahydroxydibenzo-1,4-dio xin by X-ray analysis. Some partially methoxylated derivatives of eckol were prepared by methylation with diazomethane and also by selective dimethylation of eckol permethylate (1b) to establish the structural requirements for inhibitory activities on alpha 2-macroglobulin and alpha 2-plasmin inhibitor, the main plasmin inhibitors in plasma.     

Embedded units in conjugated polymers

The problem of embedding of several monomeric units (benzene, thiophene, isothianaphthene) into linear oligoenes or into a polymer built up by the same units is discussed. Using a simple model Hamiltonian, we evaluate the geometry (bond lengths) and electronic structure (energy gaps) of conjugated oligomers containing up to 200 atoms. Special attention is paid to end effects. The quinoid-aromatic transition and the conjugation interruption due to embedded defects is studied in some detail.