Department of Bioengineering and Therapeutic Sciences, University of California, San Francisco, 513 Parnassus Avenue, San Francisco, California 94143-0912, United States
The UC Berkeley-UCSF Graduate Program in Bioengineering, University of California Berkeley, Berkeley, CA 94720-1762, United States
J. Am. Chem. Soc., Article ASAP
DOI: 10.1021/ja210989h
Publication Date (Web): February 27, 2012
Copyright © 2012 American Chemical Society
Zwitterionic inverse-phosphocholine (iPC) lipids contain headgroups with an inverted charge orientation relative to phosphocholine (PC) lipids. The iPC lipid headgroup has a quaternary amine adjacent to the bilayer interface and a phosphate that extends into the aqueous phase. Neutral iPC lipids with ethylated phosphate groups (CPe) and anionic iPC lipids nonethylated phosphate groups (CP) were synthesized. The surface potential of CPe liposomes remains negative across a broad pH range and in the presence of up to 10 mM Ca2+. CP liposomes aggregate in the presence of Ca2+, but at a slower rate than other anionic lipids. Hydrolysis of CP lipids by alkaline phosphatases generates a cationic lipid. CPe liposomes release encapsulated anionic carboxyfluorescein (CF) 20 times faster than PC liposomes and release uncharged glucose twice as fast as PC liposomes. As such, iPC lipids afford a unique opportunity to investigate the biophysical and bioactivity-related ramifications of a charge inversion at the bilayer surface.
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