Raman spectroscopic studies of the packing properties of mixed dihexadecyl- and dipalmitoylphosphatidylcholine bilayer dispersions

Abstract

X-ray diffraction studies suggest the existence of two separate gel phases for mixed dihexadecylphosphatidylcholine (DHPC)/dipalmitoylphosphatidylcholine (DPPC) bilayers [Kim, J. T., Mattai, J., & Shipley, G. G. (1987) Biochemistry 26, 6599-6603; Lohner, K., Schuster, A., Degovics, G., Müller, K., & Laggner, P. (1987) Chem. Phys. Lipids 44, 61-70]. In one gel phase the lipid chains are interdigitated, while the other gel phase exhibits the conventional bilayer form. We use Raman spectroscopy to provide a detailed molecular analysis of the intermolecular and intramolecular interactions of the DHPC and DPPC molecules within these mixed bilayers. Observation of the methylene chain C-H stretching modes of DHPC and the methylene chain C-D stretching modes of DPPC-d62 for various mixed DHPC/DPPC-d62 bilayers enables the packing characteristics and conformational order of each lipid to be monitored separately. The spectral data indicate that the packing properties of DPPC-d62 in the mixed-lipid bilayers remain relatively unchanged, while the intramolecular and intermolecular properties of DHPC change dramatically as a function of the composition of the DHPC/DPPC-d62 mixed bilayer. This is consistent with a model based upon the existence of three characteristic lipid types for the mixed-lipid system, namely, domains of pure DPPC-d62 and pure DHPC species with interface lipids or boundary regions between the bulk domains.

Packing characteristics of two-component bilayers composed of ester- and ether-linked phospholipids

“…This has been accomplished by studying the properties of two-component, fully hydrated multilamel-lar bilayers composed of mixtures of 1,2-di-0-hexadecylrac-glycero-3-phosphocholine (DHPC) with 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) and of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) with 1,2-di-0-hexadecyl-sn-glycero-3-phosphoethanolamine (DHPE). This study extends previous investigations of the mixing properties of ester-linked and ether-linked phospholipids (Kim et al, 1987;Laggner et al, 1987;Lohner et al, 1987;Devlin and Levin, 1989;Hing et al, 1991;Hing and Shipley, 1995).…”

“…With the current study all possible two-component mixtures of DPPC, DHPC, DPPE, and DHPE have been investigated (Kim et al, 1987;Laggner et al, 1987;Lohner et al, 1987;Devlin and Levin, 1989;Hing et al, 1991;Hing and Shipley, 1995). The observation that can be drawn from these studies is that the miscibility properties of the phospholipid mixtures are determined by the nature of the phospholipid headgroups and are independent of the character of the hydrocarbon chain linkages, except when DHPC is a component.…”

The interdigitated gel phase in mixtures of cationic and zwitterionic phospholipids

“…Unlike DHPC, the ether lipid DHPE does not interdigitate due to intermolecular hydrogen bonding and reduced headgroup repulsion of the phosphatidylethanolamine (PE) head group [20,48]. In other mixtures, such as DPPC/DHPC [49][50][51] and DPPC/EDPPC [25], there is little or no phase coexistence except perhaps at the phase transition regions.…”

Quantitative Label-Free Imaging of Lipid Composition and Packing of Individual Cellular Lipid Droplets Using Multiplex CARS Microscopy

“…The most dominant peaks, in this congested and complex spectral region, are those from the acyl-chain methylene symmetric (;À2845 cm À1 ) and asymmetric (;À2880 cm À1 ) stretch vibrations. The ratio I À2880 /I À2845 was shown to provide a measure for acyl-chain order (13) through its sensitivity to the amount of gauche kinks in the acyl chains and concomitant reduction in lateral chain-chain interactions (32). This ratio will be used to quantify the order of lipids (i.e., their fluidity) within LDs, and will be referred to as the parameter CC order .…”