Quenching membranes

Our main focus in this chapter has been on the applications of the replica Ornstein-Zernike equations designed by Given and Stell [17-19] for quenched-annealed systems. This theory has been shown to yield interesting results for adsorption of a hard sphere fluid mimicking colloidal suspension, for a system of multiple permeable membranes and for a hard sphere fluid in a matrix of chain molecules. Much room remains to explore even simple quenched-annealed models either in the framework of theoretical approaches or by computer simulation. 

The statistical properties of polymer chains in a quenched random medium have been the subject of intensive investigations during the last decades, both theoretically [79-89] and experimentally [90-96], because diffusion in such media is of great relevance for chromatography, membrane separation, ultrafiltration, etc. 

The experimental principle is illustrated in Fig. 3. The interaction of the polymer with the liposomal membranes causes the perturbation of the bilayer. This perturbation follows the leakage of calcein from the liposome. Calcein in high concentration in the liposome is self-quenched, but has strong fluorescence intensity by the leak from the liposome. Therefore, the extent of the membrane interaction can be estimated quantitatively from the fluorescence spectroscopy. 

Membrane osmometry. fCapillary isotachophoresis. gFluorescence quenching. 

Montenegro, M.A. Nazareno, M.A Durantini, E.N. Borsarelli, G.D. (2002). Singlet oxygen quenching ability of carotenoids in a reverse micelle membrane mimetic system. Photochemistry and Photobiology, Vol. 75, No. 4, (April 2002), pp.353-361, ISSN 0031-8655... 

Di Mascio, R, Kaiser, S., and Sies, H., Lycopene as the most efficient biological carotenoid singlet oxygen quencher. Arch. Biochem. Biophys., 274, 532, 1989. Cantrell, A. et ah. Singlet oxygen quenching by dietary carotenoids in a model membrane environment. Arch. Biochem. Biophys., 412, 47, 2003. 

A second potential area to be explored may be biochemical encapsulation of chlorophylls to protect and prolong their stability. New techniques of encapsulation produce a milieu capable of quenching active forms of O2 (radicals and 02) that mimic the protective enviromnent of chlorophylls in the thylacoid membranes. 

Cantrell, A. et al., Singlet oxygen quenching by dietary carotenoids in a model membrane environment, Arch. Biochem. Biophys., 412, 47, 2003. 

Mooradian (1993) has studied the antioxidant properties of 14 steroids in a non-membranous system in which the fluorescence of the protein phycoerythrin was measured in the presence of a lipid peroxyl radical generator (ABAP). Oxidation of the protein produces a fluorescent species. Quenching of fluorescence by a test compound indicates antioxidant activity. Oestrone, testosterone, progesterone, androstenedione, dehydroepian-drosterone, cortisol, tetrahydrocortisone, deoxycorti-... 

Figure 7.46 Fluorescence quenching of doxorubicin by DNA [597] (a) doxorubicin in aqueous solution, quenched immediately on addition of DNA (b) doxorubicin fluorescence not affected by vesicles (c) Doxorubicin preequihbrated with vesicles, and then subjected to DNA. The fraction bound to the outer membrane leaflet is immediately quenched by the DNA. (d) Same as (c), but multilamellar vesicles used. The left arrow represents a 5-min interval and applies to the first three cases the right arrow represents 30-min interval and applies to (d) only. [Reprinted from Ronit Regev and Gera D. Eylan, Biochemical Pharmacology, vol. 54, 1997, pp. 1151-1158. With permission from Elsevier Science.]...

Horton, P., Wentworth, M., and Ruban, A. 2005. Control of the light harvesting function of chloroplast membranes The LHCII-aggregation model for non-photochemical quenching II. FEBS Lett. 579 4201 1206. 

As noted earlier, environments such as water/methanol mixtures are useful models of membrane environments. These mixed solvents lead to a reduced efficiency of 02 quenching and the quenching becomes negligible at high water concentrations. Figure 14.2 shows an example of this behavior for zeaxanthin (ZEA), as the aggregation of ZEA is increased. 

Cantrell et al. (2003) studied the quenching of 02 by several dietary carotenoids in dipalmitoyl phosphatidylcholine (DPPC) unilamellar liposomes. These workers used water soluble and lipid soluble 02 sensitizers so that a comparison of the efficiencies of quenching 02 generated within and outside the membrane model could be made. Perhaps surprisingly there was little difference in the efficiency of quenching in either situation. Typical results are presented in Table 14.3 (taken from Cantrell et al. (2003 and 2006)). 

The aggregation and the orientation of a carotenoid in the lipid bilayer may be major factors in determining the efficiency of 02 quenching, for example, ZEA may span the membrane and aggregate while P-CAR, p-CRYP, and LYC are more randomly ordered. 

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