Nataša Šegatin

Antioxidant properties of 4-vinyl derivatives of hydroxycinnamic acids.

The compounds 4-vinylphenol (4-VP), 4-vinylguaiacol (4-VG), 4-vinylsyringol (4-VS) and 4-vinylcatechol (4-VC) were prepared by thermal decarboxylation of the corresponding hydroxycinnamic acids p-coumaric, ferulic, sinapic and caffeic acid, respectively. For confirmation of the synthesised products LC-MS followed by NMR analysis was used. To evaluate their antioxidant potential, their reducing power and efficiency in scavenging the alkylperoxyl radical generated in an emulsion system, the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical and the superoxide anion radical (O2(-)) were determined. All tested 4-vinyl derivatives revealed weaker antioxidant activity in a homogeneous polar medium than the corresponding phenolic acids. In the emulsion system the activity for 4-vinyl derivatives was higher than was the activity of their corresponding phenolic acids, with 4-VG as the most active among the tested phenolic compounds.

DPPH assay of vegetable oils and model antioxidants in protic and aprotic solvents

The rate of reaction of phenolic antioxidants with DPPH depends on solvent composition. The rate constants can differ by more than two orders of magnitude for the same phenolic compound. Reactions are faster in alcohols than in ethyl acetate that is used routinely for the analysis of antioxidant potential (AOP) of nonpolar samples such as vegetable oils. Incorporation of an acid base pair into the assay solvent buffers the system against acid impurities such as free fatty acids and CO2 from the air. This is shown to increase the rate of oxidation and number of electrons of phenolic compounds exchanged with DPPH. Typically, DPPH assays are performed for predetermined time intervals at which phenolic compounds are not fully oxidized and therefore higher reaction rates result in higher values of AOP. More than twofold AOP was obtained for oleuropein, sesamol, sinapic acid, caffeic acid and protocatechuic acid in buffered alcohols than in ethyl acetate. The AOP of sesame, pumpkin seed and extra virgin olive oil is accordingly higher when determined in buffered alcohols. DPPH assays in ethyl acetate result in underestimation of AOP of unrefined vegetable oils.

BROMINATION OF ORGANIC MOLECULES WITH POLYMER-SUPPORTED BROMINE COMPLEXES

Abstract Three types of bromine complexes with various polymers bearing basic units (pyridine, piperidine and piperazine) were investigated and the role of polymer matrices on reactivity was tested by three types of organic reactions: electrophilic addition, aromatic substitution and radical substitution. Pyridine complex (1a) was most reactive in all three types of reactions, while immobilisation of bromine to polymers bearing more basic units resulted in much less reactive complexes; in the reaction with 1,1-diphenylethylene reactivity was diminished to 29% of that with (1a), when piperidine complex (1b) was used, while only 11% of that of (1a) was achieved with piperazine complex (1c) in methanol. An even greater reduction in reactivity was found in the reaction with anisole where (1b) was 9% and (1c) only 1% as reactive as (1a). Exclusive side chain bromination was observed in the reactions of bromine complexes (1a). (1b) and (1c) in carbon tetrachloride in the presence of dibenzoyl peroxide at 77°C w...

Polymers as Reagents and Catalysts. Part 28. the Effect of Polymer Catalyst Structure on the Esterification of Acids

Abstract Crosslinked sulphonated polystyrene (Dowex 20 M) and various salts of crosslinked co-poly[styrene-4-vinylpyridine] with hydrogen halides were used as solid catalysts in investigations of the conversion of acids to esters. The role of the structure of the acid (acetic acid, benzoic acid), solvent (n-octane, toluene, n-butanol) and reaction temperature in the presence of polymer supported catalyst was tested in the reaction with n-butanol. Sulphonated crosslinked polystyrene (3a) was the most active catalyst, similar activity was found with crosslinked co-poly[styrene-4-vinyl(pyridinium chloride)], while catalysts bearing a fluoride (3b) and iodide (3e) function were almost unreactive. The important role of cosolvents was also established.