The role of ascorbate in antioxidant protection of biomembranes: Interaction with vitamin E and coenzyme Q

One of the vital roles of ascorbic acid (vitamin C) is to act as an antioxidant to protect cellular components from free radical damage. Ascorbic acid has been shown to scavenge free radicals directly in the aqueous phases of cells and the circulatory system. Ascorbic acid has also been proven to protect membrane and other hydrophobic compartments from such damage by regenerating the antioxidant form of vitamin E. In addition, reduced coenzyme Q, also a resident of hydrophobic compartments, interacts with vitamin E to regenerate its antioxidant form. The mechanism of vitamin C antioxidant function, the myriad of pathologies resulting from its clinical deficiency, and the many health benefits it provides, are reviewed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44796/1/10863_2004_Article_BF00762775.pd

Assessing content of selected macro- and microelements in commercial honeys and in honeys derived directly from apiary

Miód charakteryzuje się unikatowymi właściwościami sensorycznymi i prozdrowotnymi. W skład miodu wchodzą między innymi przeciwutleniacze, enzymy, witaminy, makro- i mikroelementy, które kształtują jego aktywność biologiczną i odgrywają kluczową rolę w prawidłowym funkcjonowaniu orga- nizmu. Miody stanowią źródło potasu, magnezu, wapnia, sodu, siarki, manganu, żelaza, wanadu, chromu, fosforu, srebra, boru i miedzi. Celem pracy było określenie składu mineralnego miodów odmianowych dostępnych na polskim rynku. W badaniach użyto polskich miodów różnych odmian: akacjowego, wielo- kwiatowego, lipowego i rzepakowego. Ocenie poddano miody zakupione w supermarkecie i pochodzące bezpośrednio z pasieki. Średnia zawartość Ca, K, Na, Mg, Mn, Zn, Cu i Fe w miodach wynosiła odpo- wiednio [mg/100 g]: 7,42, 59,66, 1,57, 1,44, 0,11, 0,46, 0,02 i 0,12. Największą zawartością makro- i mikroelementów charakteryzował się miód wielokwiatowy pochodzący bezpośrednio z pasieki – 133,77 mg/100 g. Najmniejszą zawartość składników mineralnych wykazano w miodzie akacjowym zakupionym w supermarkecie – 27,23 mg/100 g. Dodatkowo przeanalizowano wpływ położenia prywat- nej pasieki w okolicach Huty Miedzi Głogów na zawartość miedzi w próbach miodów różnych odmian. Nie stwierdzono statystycznie istotnej różnicy (p ≥ 0,05) pomiędzy średnią zawartością miedzi w miodach komercyjnych i w miodach z prywatnej pasieki, co wskazuje na brak wpływu pochodzenia geograficznego na zawartość tego pierwiastk

Antioxidant and co-antioxidant activity of vitamin C. The effect of vitamin C, either alone or in the presence of vitamin E or a water-soluble vitamin E analogue, upon the peroxidation of aqueous multilamellar phospholipid liposomes

Thermally labile azo-initiators, dissolved in either the aqueous or lipid phase, have been used to generate peroxyl radicals at a known, steady rate in an aqueous dispersion of dilinoleoylphosphatidylcholine multilamellar liposomes at 37\ub0 C in order to study the antioxidant behaviour of ascorbate itself and ascorbate in combination with either \u3b1-tocopherol or a water-soluble \u3b1-tocopherol analogue (TROLOX(-)). It is found that ascorbate is an effective inhibitor of peroxidations initiated in the aqueous phase, with each ascorbate terminating 0.6 radical chains (i.e., n = 0.6), but it is a very poor inhibitor of peroxidations initiated in the lipid phase. Peroxidations initiated in the lipid-phase in the presence of either \u3b1-tocopherol or TROLOX(-) indicate that ascorbate is an excellent synergist with both phenolic antioxidants (n = 0.4). In peroxidations initiated in the aqueous phase ascorbate acts as a co-antioxidant with TROLOX(-) (n = 0.7), but the interpretation of the approximately additive effect obtained in the presence of \u3b1-tocopherol is complicated by the fact that under the experimental conditions employed \u3b1-tocopherol alone does not give a distinct, measurable inhibition period. The latter problem is shown to be due to a non-uniform distribution of the water-soluble initiator within the liposome. Other examples of the complicating effects of non-uniform distributions of reactants in kinetic studies of the autoxidation of organic substrates dispersed in water are described. \ua9 1985.Peer reviewed: YesNRC publication: Ye

EPR spectra of some \u3b1-tocopherol model compounds. Polar and conformational effects and their relation to antioxidant activities

Peer reviewed: YesNRC publication: Ye

Hydrogen abstraction by methyl radicals in glasses

An experimental and theoretical study is reported of the abstraction of hydrogen atoms by methyl radicals from organic glasses, in particular methanol and several of its deuterated analogues. Rate constants are obtained for hydrogen and deuterium transfer as a function of temperature for a distribution of trapping sites of the radical in the glass. The site dependence is investigated by an analysis of the non-exponential decay of the methyl radical concentration based on the use of Laplace transforms. With the help of a recently developed theoretical model for hydrogen tunnelling, a relationship between tunnelling rate and tunnelling distance is established on the basis of these observations. The results yield a detailed picture of the structure of the trapping sites: roughly spherical cages in which the tumbling radical is surrounded on average by eleven rotating methyl groups, with the closest of which it reacts. The model yields a quantitative description of the rate of this reaction, expressed in terms of spectroscopic, thermodynamic and quantum-chemical input parameters.Peer reviewed: YesNRC publication: Ye

Temperature and site dependence of the rate of hydrogen and deuterium abstraction by methyl radicals in methanol glasses

Rate constants are reported for hydrogen and deuterium abstraction by methyl radicals in CH3OH and CD3OD glasses in the ranges 5-89 and 77-97 K, respectively. At each temperature, they show a distribution due to a variation of radical trapping sites. The rate constants of this distribution are analyzed theoretically to yield a quantitative relation between tunneling rate and equilibrium tunneling distance.Peer reviewed: YesNRC publication: Ye

Structural interpretation of non-exponential hydrogen transfer in glassy methanol

The non-exponential time dependence of hydrogen abstraction by methyl radicals in a methanol glass is reinvestigated and explained as due to a narrow random distribution of hydrogen tunnelling distances. Possible implications for other non-exponential relaxation processes in non-crystalline materials are briefly discussed. \ua9 1985.Peer reviewed: YesNRC publication: Ye