Raman structural characterization of clear human lens lipid membranes

Raman spectroscopy was used for the first time to characterize the structure of lipid membranes prepared from the nuclear and cortical regions of 48 and 69 year old clear human lenses. The interface region carbonyl band appears as a doublet at 1742 and 1728 cm-1. The lower frequency band is characteristic of a hydrogen bonded carbonyl group, perhaps to bilayer water. From the intensity of the curve fit bands, we calculate that 43% of the carbonyl groups are hydrogen bonded. Our data show that the hydrocarbon chains of the nuclear lipids are 1.4 times more saturated than those of the cortical lipids. The molar ratio of phospholipid CH2/= C-H groups was calculated to be 13 and 18 for cortical and nuclear lipids, respectively. Hydrocarbon chain disorder was estimated to be 72 and 58% (+/- 8% disorder) for the cortical and the nuclear lipids, respectively. Raman spectroscopy is sensitive to structural differences in various regions of the lipid bilayer and could be an effective tool to explore lipid and protein interactions in terms of lens region, age and opacity.