Dejan Z. Marković

Copper, iron, and zinc interactions with chlorophyll in extracts of photosynthetic pigments studied by VIS spectroscopy

Interactions of copper, iron and zinc with chlorophyll, the major photosynthesis pigment, were studied by VIS spectrophotometry in extracts of photosynthetic pigments (in vitro). Copper predominantly forms Cu-Chl complexes in all studied systems (Cu-, Cu/Fe-, Cu/Zn- and Cu/Fe/Zn-incubated pigment solutions). It is not clear whether iron forms Fe-Chl complexes or produces pheophytin. It’s effect is dominant over zinc (Fe/Zn-system) but highly minor compared to Cu-effect when all three metals are present (Cu/Fe/Zn-Chl system) in the same concentrations.

Benzophenone Suppression of Quercetin Antioxidant Activity towards Lipids under UV-B Irradiation Regime: Detection by HPLC Chromatography

Quercetin, a well-known flavonoid antioxidant, has been employed to control benzophenone-sensitized peroxidation of the lipid mixture in methanol solution, induced by continuous UV-B irradiation. Surprisingly, the detected quercetin antioxidant activity was almost negligible. The presented data suggests that the reason is not in its own UV-B-induced degradation but rather in its interrelationship with benzophenone during UV-B stress. On the other side of this relationship, benzophenone anticipated sensitizing role towards lipids; that is, the initiation of lipid peroxidation has been affected as well. These results, obtained by HPLC chromatography, partly confirm but partly relativize to some extent recent results obtained with the same system by spectrophotometric method.

Investigation into the potential chemical mechanism of carotenoids pro-oxidant activity with liposomes under UV- irradiation

This study focuses on the behavior of β-carotene and lutein inside multilamellar liposomes under continuous UV-irradiation. Liposomes were obtained by thin film method and carotenoids (Crts) were incorporated by mixing method at various concentrations (0.005, 0.0075, 0.02, 0.07 and 0.5 mol%). Liposomes formation and presence of Crts inside them were confirmed by SEM microscopy and FT-IR spectroscopy, respectively. The antioxidant/prooxidant activity of Crts inside liposomes was determined by Thiobarbituric Acid – Malondialdehyde (TBA-MDA) test. Investigated Crts act more or less unexpected (as pro-oxidants) inside lipid bilayer, interacting with UV-produced lipid radicals and suffering under UV-irradiation in the same time. Their pro-oxidant activity, with liposomes and under UV-irradiation, can be explained by unstable adducts formation in reaction with peroxyl radicals, or by Crts-cation radicals formation via electron transfer mechanism. Such tentatively unexpected behavior of carotenoids should be taken into account in further carotenoids based UV-filters projections in cosmetic formulation for skin protection.

Riboflavin degradation in the presence of quercetin in methanol under continuous UV-B irradiation: the ESI–MS–UHPLC analysis

The presented work deals with continuous UV-B irradiation of riboflavin in MeOH solution, leading to its degradation under anaerobic as well as aerobic conditions (faster in the former case), which is related to riboflavin photosensitizing properties (type I photosensitizer in the first case, and type II in the other one). Addition of quercetin, a well-known antioxidant in the system causes a decrease of the (riboflavin) degradation in both cases. In anaerobic conditions it might be a consequence of quercetin antioxidant scavenging activity, while under aerobic conditions it could be related to singlet oxygen formation. The degradation dynamics—in both systems, in the presence and in the absence of quercetin—is well synchronized with dynamics formation of the two major products, lumiflavin and lumichrome.Graphical abstract

Lycopene control of benzophenone-sensitized lipid peroxidation

Lycopene antioxidant activity in the presence of two different mixtures of phospholipids in hexane solution, under continuous regime of UV-irradiation from three different ranges (UV-A, UV-B, and UV-C) has been evaluated in this work. Lycopene expected role was to control lipid peroxidation, by scavenging free radicals generated by UV-irradiation, in the presence and in the absence of selected photosensitizer, benzophenone. This work shows that lycopene undergoes to UV-induced destruction (bleaching), highly dependent on the incident photons energy input, more expressed in the presence than in the absence of benzophenone. The further increase (“excess”) of its bleaching is undoubtedly related to the further increase of its antioxidant activity in the presence of benzophenone, having the same cause: increase of (phospholipids peroxidation) chain-breaking activities.