Bilayer packing characteristics of mixed chain phospholipid derivatives: Raman spectroscopic and differential scanning calorimetric studies of 1-stearoyl-2-capryl-sn-glycero-3-phosphocholine (C(18):C(10)PC) and 1-stearoyl-2-capryl-sn-glycero-3-phospho-N-trimethylpropanolamine (C(18):C(10)TMPC).
Raman spectroscopy and high-sensitivity differential scanning calorimetry (DSC) were used to compare the effects of headgroup conformation on the acyl chain packing arrangements in two highly asymmetric phosphatidylcholine (PC) analogues, 1-stearoyl-2-capryl-sn-glycero-3-phosphocholine (C(18):C(10)PC) and a polar headgroup derivative of C(18):C(10)PC, 1-stearoyl-2-capryl-sn-glycero-3-phospho-N-trimethylpropanolami ne (C(18):C(10)TMPC), which contains an additional methylene group within the choline moiety; namely, -P-O-(CH2)3-N(CH3)3. The C(18):C(10)TMPC headgroup exhibits an extended trans conformation which is independent of bilayer phase. A comparison of gel phase spectral order parameters of the two lipid species indicates a mixed interdigitated state characteristic of three chains per headgroup for C(18): C(10)TMPC. A more intermolecularly ordered liquid crystalline phase is observed, however, for the C(18):C(10)TMPC bilayers. The phase transition cooperative unit size estimated for the C(18):C(10)PC bilayers (approximately 140 molecules per unit) is about 7-fold greater than that for the C(18):C(10)TMPC dispersions (approximately 20 molecules per unit). We suggest that the extended headgroup for C(18):C(10)TMPC induces a slight tilt in the gel phase packing arrangements for the acyl chains, which may persist in the partially interdigitated liquid crystalline phase bilayer. Macroscopically, tighter packed multilamellar dispersions of C(18):C(10)TMPC occur for systems prepared first in the presence of a higher ionic strength medium. The stacked bilayers may then be transferred to a lower ionic strength environment without loss of their more closely packed adjacent lamellae.
Laboratory of Chemical Physics, National Institute of Diabetes, and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
M M
MM
Batenjany
Z Q
ZQ
Wang
C H
CH
Huang
I W
IW
Levin
D002152:Calorimetry, Differential Scanning; D008051:Lipid Bilayers / Q000737:chemistry; D008968:Molecular Conformation; D010713:Phosphatidylcholines / Q000737:chemistry*; D010743:Phospholipids / Q000737:chemistry*; D013059:Spectrum Analysis, Raman
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D010743:Phospholipids; C088166:1-stearoyl-2-capryl sn-glycero-3-phospho-N-trimethylpropanolamine; C059534:1-stearoyl-2-caproyl-sn-glycero-3-phosphocholine