AROMATIC AMINO ACIDS AND ULTRAVIOLET INDUCED PHOTO-ELECTRIC EFFECTS IN BILAYER MEMBRANES

Abstract— Ultraviolet light flashes induced voltage transients across bilayer lipid membranes when aromatic amino acids were adsorbed to one side of the membrane. These photo-effects varied with the chromophore structure, the aqueous solution salt concentration, pH and oxygen partial pressure. These photo-effects are attributed to the migration of electrically charged photochemical intermediates in the membrane, and provide a new method for studying the effects of UV light on membranes.     

4+3] versus [4+2] mechanisms in the dimerization of 2-boryl-1,3-butadienes. A theoretical and experimental study

The thermal dimerization of 2-boryl-1,3-butadienes and the scope of this reaction to prepare six-membered rings difficult to synthesize by other methodologies have been studied. In addition, the nature of this dimerization has been studied theoretically. It has been found that the reaction coordinate associated with the formation of the cycloadduct of lowest energy has significant [4+3] character. This behavior is caused by the favorable carbon-carbon overlap and the large values of the corresponding resonance integrals. However, beyond the transition structure, the [4+2] pathway becomes the preferred one thus leading to the exclusive formation of the [4+2] cycloadduct. Aside from this effect, donating groups at the boryl moiety favor the [4+2] mechanism.     

Synthesis,crystal structure determination and pharmacological activity of 7,8,3′,4′-tetramethoxyisoflavone

7 The8,3′,4′-tetramethoxyisoflavone 2 was synthesized and its structure confirmed by X-ray crystallographic analysis. Pharmacological screening was carried out with this compound in order to assess its pharmacological profile. Isoflavone 2 possessed antiinflamatory activity in the carrageenan oedema test, with a dose-effect relationship comparable to that of hydroxylated flavonoids. It is noteworthy that 2 is one of the few isoflavones efficient as antiinflammatory with complete alkylation of hydroxyl groups.     

Phosphorous in organic chemistry. Part II: A new method of preparing N-N′ disubstituted aryl ureas using phenyl N′-phenylphosphoramidoazidate reagent.

N-N′ Disubstituted ureas were obtained from carboxylic acids, amines and phenyl N-phenylphosphoramidoazidate in good yields. This procedure constitutes an adequate modified Curtius reaction.     

Theoretical study on the mechanism of the [2+1] thermal cycloaddition between alkenes and stable singlet (phosphino)(silyl)carbenes

The mechanism and the origins of the stereocontrol observed in the reaction between differently substituted alkenes and stable (phosphino)(silyl)carbenes giving cyclopropanes have been studied computationally. These cyclopropanation reactions proceed via asynchronous concerted mechanisms involving early transition structures with a significant charge transfer from the carbene to the alkene moiety. The geometric features of these transition structures preclude a significant overlap between the orbitals required for secondary orbital interactions between the reactants. The stereoselectivity observed experimentally stems from favorable electrostatic and steric interactions between the reactants leading to the stereoisomers in which the phosphanyl and carbonyl or aryl groups are cis to each other.