The diffusion of L(+)-ascorbic acid across DPPC vesicle membranes.

The transmembrane diffusion of L(+)-ascorbic acid has been studied by means of 1H-n.m.r. spectroscopy using small unilamellar DPPC vesicles as a model system. It is shown that the electro-neutral form of L(+)-ascorbic acid diffuses faster across the membranes than the anionic form by about two orders of magnitude. The diffusion is influenced by a molecular interaction between L(+)-ascorbate and the membrane surface and depends also on the fluidity of the membrane. The calculated permeation coefficients of neutral L(+)-ascorbic acid are between 6 x 10(-10) and 3 x 10(-8) cm s-1 (35-52 degrees C).