Carmen Topala

Poly(ethylene glycol)/β-cyclodextrin covalent gel networks: host matrices for studying radical processes in plant extract–riboflavin systems following UV irradiation

Finding new, biocompatible matrices that allow us to model the generation of free radicals is of utmost importance for balancing the harmful and beneficial effects of the latter. In this respect, we report here the simultaneous encapsulation of the radical source and the antioxidant agent in a polyethylene glycol/β-cyclodextrin (PEG/β-CD) covalent gel network. We used electron paramagnetic resonance spectroscopy to evaluate the scavenging action of plant extracts (purple loosestrife, comfrey, milfoil, horsetail, thyme, carob, green coffee) embedded in PEG/β-CD gels. Free radicals were generated in situ by UV irradiation of riboflavin co-embedded in the gels. Prior to this, the extracts were characterized in what concerns their antioxidant activity, and their major polyphenolic constituents were quantified by liquid chromatography-electrospray ionization-tandem mass spectrometry. Purple loosestrife showed the highest antioxidant capacity, followed by comfrey and milfoil. Using the 5,5-dimethyl-1-pyrroline N-oxide spin trap, we have demonstrated that the gel-embedded extracts effectively scavenge the reactive carbon-centered free radicals generated in gel. The PEG/β-CD gels have been shown to be a valuable alternative matrix for the encapsulation of plant active principles having antioxidant activity. Moreover, co-encapsulation of the radical source transforms these gels into a controlled environment in which free radical processes can be tailored.

THERMALLY STIMULATED DEPOLARIZATION CURRENTS IN A NEW CHOLESTERIC LIQUID CRYSTAL

The phase transitions in cholesteryl-beta-chloropropionate were studied by using thermally stimulated depolarization current (TSDC) methods. Optical transmission studies were performed over the whole temperature range. From the experimental data, useful information with reference to the conduction mechanism was obtained. The TSDC spectra displayed a peak at the solid-cholesteric phase transition temperature. Using the plots obtained when different depolarization fields were applied, the activation energies and the relaxation time were determined.

Cholesteryl derivatives with sulfonyl moiety

Cholesteryl carbamates were prepared by reactions of cholesterylchloroformate with phenylsulfonylanilines, in the presence of pyridine as acid acceptor. Two other cholesteryl carbonates with a heterocyclic moiety were prepared in order to evaluate the effect of variation of the terminal group on the substituted cholesteryl system. The thermodynamic properties of cholesteryl derivatives were characterized by DSC and the texture of the mesophases have been determined with a hot stage equipped polarizing microscope. The relative thermal stabilities and the variation on the mesomorphic characteristics also have been studied.

Inclusion complexes of steroidal heterocyclic compounds with cyclodextrins in aqueous solution and in the solid state

The complex formation of five steroidal heterocyclic compounds (1-5) with β-cyclodextrin and hydroxypropyl-β-cyclodextrin was investigated in aqueous solution and in solid state in order to find the strenght of interaction. The complex formation of these steroidic compounds with CDs in aqueous solution was studied by solubility analysis and ultraviolet absorption methods. For the study of solid state interaction, solid complexes were prepared by the solvent evaporation method and complexes obtained were analysed by thermal analysis. Also, synthesis, NMR and IR data of the new steroidic compounds 1,2, and 3are presented.