Spectroscopic measurements of the membrane surface potential

Thus pH = — log(cH,b). while cb and chb represent the concentrations of the dissociated and protonated species of the acid-hase chromophore pair, respectively. The quantity pK — F s/(RTln 10) can be considered as an apparent pK for proton binding of the chromophoric acid-base couple on the membrane surface. Eqn. 5.8 shows that the protonatiou state Cb/chb of the probe is altered if / s changes at constant pH, which results in a change in the fluorescence yield. Thus changes of fluorescence at constant bulk pH reflect chauges of aud can be utilised, therefore, to study how molecules interact with membranes. 

Estimations of thermodynamic information of the various components of the interactions (ie. binding and insertion with clearly separate kinetic rate constants) are possible which are not easily obtained by other means (Cladera O Shea 1998). One of the virtues of this approach is that virtually identical studies may be performed with living cells so direct comparisons of the interactions can be undertaken. 

---