High-pressure infrared spectroscopy of ether- and ester-linked phosphatidylcholine aqueous dispersions

Abstract

Infrared spectra of aqueous dispersions of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and its ether-linked analogue, 1,2-dihexadecyl-sn-glycero-3-phosphocholine (DHPC), were measured in a diamond anvil cell at 28 degrees C as a function of pressure up to 20 kbar. Although these two lipids differ only in the linkages to the saturated hydrocarbon chains, significant differences were observed in their barotropic behavior. Most notable were the magnitudes of the pressure-induced correlation field splittings of the methylene scissoring and rocking modes, and the relative intensities of the corresponding component bands. In the case of the scissoring mode, not only can the correlation field component band be resolved at a lower pressure in DHPC (1.2 kbar, as compared with 2.2 kbar in DPPC), but the initial magnitude of the correlation field splitting in DHPC, particularly less than 9 kbar, is significantly greater than that observed in DPPC. These differences are attributed to the presence of an interdigitated lamellar gel phase in DHPC. At all pressures where the correlation field component band delta'CH2 can be resolved, the relative peak height/intensity ratio R = I delta'/I delta is greater in DPPC than in DHPC, suggesting that this parameter may be useful as a test of interdigitation.

The interfacial structure of phospholipid bilayers: differential scanning calorimetry and Fourier transform infrared spectroscopic studies of 1,2-dipalmitoyl-sn-glycero-3-phosphorylcholine and its dialkyl and acyl-alkyl analogs

“…2) and has been observed by us (this work) and by others (see Kim et al, 1987a,b;Lohner et al, 1987). With DPPC bilayers, correlation field splitting of the CH2 scissoring bands has previously been observed in low-temperature and in high-pressure studies of the gel state (Cameron and Mantsch, 1982;Wong and Mantsch, 1985;Siminovitch et al, 1987a;McElhaney, 1990, 1992b). In high-pressure FTIR spectroscopic studies of DHPC, the observed correlation field splitting was very strong (Siminovitch et al, 1987a), and it has been suggested that this may actually be a signature of chain-interdigitated lipid bilayers (Siminovitch et al, 1987b).…”

Effects of the local anesthetic tetracaine on the structural and dynamic properties of lipids in model membranes: a high-pressure Fourier transform infrared study

“…The anesthetic was incorporated in either its charged form at pH 5.5 or its uncharged form at pH 9.5. For pure DMPC bilayers, the pressure dependence of the methylene scissoring mode band is very similar to that observed for l,2-dipalmitoyl-iM-glycero-3-phosphocholine (DPPC) in multilamellar aqueous dispersions (Wong & Mantsch, 1985a;Siminovitch et al, 1987a). As the pressure is increased, one observes a pressure-induced correlation field splitting of the <5CH2 mode, which at low pressure gives rise to only one band at «=1470 cm"1.…”

“…Effects of Tetracaine on DHPC Bilayers. Recent studies using differential scanning calorimetry (DSC), X-ray diffraction, 14N, 31P, and 2H NMR, and high-pressure FT-IR spectroscopy (Ruocco et al, 1985a,b;Siminovitch et al, 1983Siminovitch et al, , 1987a have shown that the replacement of the fatty acyl chains with the corresponding alkyl chains has a significant effect on the structure and dynamics of lipids in the low-temperature gel phase. As mentioned previously, it has been demonstrated that l,2-di-0-hexadecyl-i«-glycero-3-phosphocholine (DHPC) forms an interdigitated lamellar gel phase at temperatures below the pretransition at 35 °C, whereas DPPC does not.…”

“…From the pressure dependence of the carbonyl stretching band of tetracaine incorporated in DHPC multilamellar dispersions at pH 9.5, it has been shown that the uncharged anesthetic intercalates deeply into DHPC bilayers in the gel state (Auger et al, 1987). In order to see the effects of the incorporation of uncharged tetracaine on the alkyl chain packing of DHPC in the gel phase, we have monitored the pressure dependence of the methylene scissoring and rocking figure 4: Pressure dependence of the frequencies of the 5CH2 mode for (X) DHPC and ( ) DHPC + TTC, pH 9.5. mode bands for DHPC in the presence of uncharged tetracaine and compared the results with those obtained by Siminovitch et al (1987a) for pure aqueous DHPC multilamellar dispersions. The results are presented in Figure 3.…”

Pressure-induced correlation field splitting of vibrational modes: structural and dynamic properties in lipid bilayers and biomembranes

“…This spectral parameter has been used widely to monitor various structural and dynamic properties of a wide range of aqueous lipid bilayers and biomembranes. These structural and dynamic properties are: (i) large angle reorientational fluctuations (Auger, 1988;Tupper, 1992;; (ii) interchain packing (Siminovitch, 1987a;Wong, , 1984aWong, , 1989a; (iii) interchain and intrachain configuration distortion (Wong, 1985a); (iv) mechanism for the formation of the lamellar subgel phase (Wong, 1986); (v) interdigitation (Auger, 1988;Siminovitch, 1987bSiminovitch, , 1987cWong 1989b); (vi) interchain interactions (Hubner, 1990; Siminovitch, 1987b;Tupper, 1992); (vii) unsaturation induced changes in molecular configurations in lipid bilayers (Siminovitch, 1987a(Siminovitch, , 1987d; (viii) the effects of anesthetics (Auger, 1988(Auger, , 1990), toxins (Ahmed, 1992;, drugs (Popovic, 1992;Taylor, 1992), alkanes ), cholesterol (Wong, 1989a(Wong, , 1989c, polypeptides (Carrier, 1990), proteins (Gicquaud, 1992;Philp, 1990), fluorescent probes (Chong, 1989(Chong, , 1992, and other exogenous molecules (unpublished work from this laboratory) on the structural and dynamic properties in the bilayer interior of various lipids, and vice versa; (ix) the location and binding sites of these exogenous molecules in lipid bilayers (Ahmed, 1992;Auger, 1988Auger, , 1990Carrier, 1990;Chong, 1989Chong, , 1992; Gicquaud, 1992;Philp, 1990;…”