Effect of solution pH on SOPC membrane mechanics and dipole potential

PHYS 495

Yong Zhou, yzhou@bioc.rice.edu, Department of Biochemistry, Rice University, Houston, TX 77251 and Robert M. Raphael, rraphael@rice.edu, Department of Bioengineering, Rice University, MS 142, PO Box 1892, Houston, TX 77251.
Solution pH affects numerous biological processes and some biological membranes are exposed to acidic environments. We utilized micropipette aspiration of giant unilamellar vesicles (GUVs) to characterize the effect of solution pH (2 to 9) on SOPC membrane elasticity and bending stiffness. We found that the elastic compressibility modulus was unchanged between pH 3 and 9 but was reduced to 175 mN/m at pH 2, which we attribute to a pH-induced phase transition. The bending stiffness increased to 1.1x10-19 J at pH 4 and 1.3x10-19 J at pH 9. Using di-8 ANEPPS, we determined that the dipole potential of SOPC membranes increases at pH 4, but decreases at pH 9. Interestingly, the solution pH affects SOPC mechanics at the pKa's of different functional groups, and these changes correspond with alterations in the lipid dipole potential. These results demonstrate the intricate relationship between the electrical and mechanical properties of lipid membranes.

Poster Session
7:30 PM-10:00 PM, Wednesday, 13 September 2006 Moscone Center -- Hall D, Poster

8:00 PM-10:00 PM, Monday, 11 September 2006 Moscone Center -- Hall D, Sci-Mix

Division of Physical Chemistry

The 232nd ACS National Meeting, San Francisco, CA, September 10-14, 2006