Function of lipid concentration

Figure 4. Half-life Ti/2of pH gradient decay in the dark as a function of lipid concentration for Mab(Phyt)2 or EPC vesicles after light-induced proton translocation by BR at 2S°C,...

Fc is the fluorescence of the dye in a lipid vesicle suspension with a lipid concentration of C F0 and Fx are the limiting dye fluorescence readings in the absence of lipid and at very high lipid concentrations, respectively. The fluorescence as a function of lipid concentration is fitted to this equation via nonlinear regression. The results of such measurements for a series of styryl dyes (10), as well as the spectral characteristics of the dyes in several solvents, are given in Table I. As expected, the membrane affinity of the dyes increases with the length of the chromophore or the number of carbons in the appended hydrocarbon chains. Also noteworthy is the striking increase in fluorescence quantum yield for the membrane-bound dyes this is probably due to the well-ordered immobile environment of the membrane, which inhibits nonradiative decay processes that require molecular motion in the excited state. 

In aqueous solution, single lipids behave as lyotropic liquid crystals, forming a variety of different phases. We can observe the micellar, lamellar, and hexagonal lyotropic phases as a function of lipid concentration, although micellar phases are less likely in a system with two flexible chains (due to their cylindrical shape see Section 3.6). Alternatively, lipids at low concentrations will tend to form bilayer shells, either multilamellar or unilamellar vesicles. These phases correspond directly to the surfactant phases that we discovered in Chapter 3. Lipid molecules are composed... 

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