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.
Batenjany
M M
MM
Laboratory of Chemical Physics, National Institute of Diabetes, and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892.
Wang
Z Q
ZQ
Huang
C H
CH
Levin
I W
IW
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