The diffusion of protons at the immediate vicinity of (less than 10 A from) a phospholipid membrane is studied by the application of the laser-induced proton pulse. A light-sensitive proton emitter (8-hydroxypyrene-1,3,6-trisulfonate) was trapped exclusively in the hydration layers of multilamellar vesicles made of egg phosphatidylcholine, and the protons were dissociated by a synchronizing laser pulse. The recombination of the proton with pyranin anion was monitored by time-resolved spectroscopy and analyzed by a diffusion-controlled formalism. The measured diffusion coefficient is only slightly smaller than the diffusion coefficient of proton in bulk water. Modulating the width of the hydration layer by external pressure had a direct effect on the diffusibility of the proton: the narrower the hydration layer, the slower is the diffusion of protons.
|Number of pages||5|
|State||Published - 1 Apr 1989|
- D(2) and D(3),two- and three-dimensional diffusion coefficients
- PC, phosphatidylcholine
- [ϕO-(2)], two-dimensional concentration of ϕO-in units of mol/cm2
- ϕOH and ϕO-acidic and alkaline forms of the proton emitter
- ϕOH* and ϕO*-, first electronically excited states of the respective forms of proton emitter