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

Area of Science:

• Biochemistry
• Physical Chemistry
• Membrane Biophysics

Background:

• L-ascorbic acid (vitamin C) is essential for numerous biological processes.
• Understanding its transport across biological membranes is crucial for cellular function.
• The physicochemical properties of vitamin C influence its membrane permeability.

Purpose of the Study:

• To investigate the transmembrane diffusion of L-ascorbic acid.
• To elucidate the factors affecting vitamin C membrane transport.
• To quantify the permeation coefficients of different L-ascorbic acid forms.

Main Methods:

• Utilized 1H-n.m.r. spectroscopy.
• Employed small unilamellar dipalmitoylphosphatidylcholine (DPPC) vesicles as a model membrane system.
• Analyzed diffusion rates under varying temperature conditions.

Main Results:

• The electro-neutral form of L-ascorbic acid exhibits significantly higher membrane diffusion rates compared to the anionic form (approximately two orders of magnitude faster).
• Molecular interactions between L-ascorbate and the membrane surface were observed to influence diffusion.
• Membrane fluidity was identified as another key factor affecting L-ascorbic acid transport.
• Calculated permeation coefficients for neutral L-ascorbic acid ranged from 6 x 10(-10) to 3 x 10(-8) cm s-1 between 35-52°C.

Conclusions:

• The charge state of L-ascorbic acid critically determines its transmembrane diffusion rate.
• Membrane composition and surface interactions play a significant role in vitamin C permeability.
• The findings provide quantitative insights into the biophysical mechanisms of L-ascorbic acid transport across lipid bilayers.