Raman spectroscopic study of polycrystalline mono- and polyunsaturated 1-eicosanoyl-d39-2-eicosenoyl-sn-glycero-3-phosphocholines: Bilayer lipid clustering and acyl chain order and disorder characteristics

Abstract

Polycrystalline lipid samples of a series of mono- and polyunsaturated, double bond positional isomers of 1-eicosanoyl-d(39)-2-eicosenoyl-sn-glycero-3-phosphocholines [C(20-d(39)):C(20:1 Delta(j))PC, with j = 5, 8, 11, or 13; C(20-d(39)):C(20:2 Delta(11,14))PC; and C(20-d(39)):C(20:3 Delta(11, 14,17))PC] were investigated using vibrational Raman spectroscopy to assess the acyl chain packing order-disorder characteristics and putative bilayer cluster formation of the isotopically differentiated acyl chains. Perdeuteration of specifically the saturated sn-1 acyl chains for these bilayer systems enables each chain's intra- and intermolecular conformational and organizational properties to be evaluated separately. Various saturated chain methylene CD(2) and carbon-carbon (C&bond;C) stretching mode peak height intensity ratios and line width parameters for the polycrystalline samples demonstrate a high degree of sn-1 chain order that is unaffected by either the double bond placement or number of unsaturated bonds within the sn-2 chain. In contrast, the unsaturated sn-2 chain spectral signatures reflect increasing acyl chain conformational disorder as either the cis double bond is generally repositioned toward the chain terminus or the number of double bonds increases from one to three. The lipid bilayer chain packing differences observed between the sn-1 and sn-2 chains of this series of monounsaturated and polyunsaturated 20 carbon chain lipids suggest the existence of laterally distributed microdomains predicated on the formation of highly ordered, saturated sn-1 chain clusters.

Direct Observation of Domains in Model Stratum Corneum Lipid Mixtures by Raman Microspectroscopy

“…For both ceramides and cholesterol, the bands around 2845 and 2880 cm Ϫ1 are associated with the symmetric and antisymmetric CH 2 vibration stretching modes ( s CH 2 and a CH 2 ) (Bulkin and Krishnan, 1971;Faiman, 1977;Williams et al, 1992;McCarthy et al, 2000). The bands at 2895 and 2930 cm Ϫ1 of the ceramides spectra have been associated with a broad contribution due to Fermi resonance involving the chain terminal CH 3 symmetric stretching (v s CH 3 ) mode and binary combinations or overtones of the CH 2 deformations modes (Williams et al, 1992;McCarthy et al, 2000). The band at 2865 cm Ϫ1 in the cholesterol spectrum has been associated to the s CH 3 mode whereas the band at 2902 cm Ϫ1 was assigned to methyl on the steroid rings or ternary C-H (Bulkin and Krishnan, 1971).…”

“…The spectra obtained for the dry and the hydrated samples are very similar, the main difference being the appearance of the O-D stretching band associated with D 2 O at around 2500 cm Ϫ1 . As the methylene and methyl stretching regions are sensitive to chain order (Mantsch and McElhaney, 1991;Wegener et al, 1997;Lawson et al, 1998;McCarthy et al, 2000), the similarity of the band profiles in the C-H and C-D stretching regions indicates that the hydration does not lead to considerable changes of acyl chain order. This result is in agreement with previous results obtained by IR (Moore et al, 1997;Lafleur, 1998) and 2 H NMR (Abraham and Downing, 1991;Fenske et al, 1994) spectroscopy, indicating highly ordered acyl chains in the hydrated samples.…”

“…The mixture spectra can actually be simulated by a linear combination of the individual spectra in the appropriate proportions. The additive property of the spectra implies that, in these solid mixtures, there is no significant changes in the spectra that would be associated with intermolecular interactions because the C-H (as well as the C-D) stretching modes are sensitive to the acyl chain conformational order (Mantsch and McElhaney, 1991;Wegener et al, 1997;Lawson et al, 1998;McCarthy et al, 2000). Because of the spectral additivity, the proportion of cholesterol in a sample can be estimated from the subtraction of the cholesterol spectrum from the spectrum of the mixture to obtain a spectrum similar to that of pure ceramides, once the spectral intensities have been normalized.…”

“…This mixture has revealed a rich polymorphism that shows similar features as those displayed by the intact SC (Kitson et al, 1994;Bouwstra et al, 1996). Raman spectroscopy is a precious tool to analyze lipid structure and organization (Wegener et al, 1996(Wegener et al, , 1997Lawson et al, 1998;McCarthy et al, 2000) as the sampling requires no or little modification of the sample. The micro-Raman mapping allows the acquisition of chemical and morphological information over an area of the sample with a spatial resolution of the order of 1 m. Using a visible laser light with an ordinary optical light microscope and a motorized X-Y stage, Raman spectra can be collected from small volume elements of a region of a sample and maps can be generated by analyzing characteristic bands.…”

Effects of permeation enhancers on flufenamic acid delivery in Ex vivo human skin by confocal Raman microscopy

“…Further analysis of the CH stretching region, to shed light on excipient-induced perturbation, is complicated by the presence of the isolated CH stretch band arising from incomplete deuteration of the solvents. This and the intricacy of the contour which reflects the degree of lipid acyl chain packing and conformational order (Gaber and Peticolas, 1976;McCarthy et al, 1999;Yellin and Levin, 1977), prevents further comment until additional control experiments are conducted. Regardless, the highest concentrations of FluA appear to penetrate through the SC via the network of Oct-d inclusions which are not observed in the viable epidermis.…”