SFG vibrational spectroscopy of fluid cell membrane models

Studying the structure of cell membranes and their interaction with other molecules is fundamental for advancing cell biology. Mimetic membrane models such as lipid vesicles, supported lipid bilayers, and Langmuir films are often used for that purpose. Langmuir films are highly versatile and may be studied by various techniques, with Sum-Frequency Generation (SFG) vibrational spectroscopy being powerful.¹ SFG spectroscopy yields the vibrational spectra of lipid monolayers for probing the average conformation of the hydrophobic chains, which is directly related to the degree of molecular packing.¹ For saturated lipids, it has been shown that the amplitude ratio (d⁺/r⁺) of stretch vibrations of CH₂ and CH₃ groups is a quantitative indicator of the average chain conformation.^2,3 Our study extends these previous investigations to lipid monolayers featuring more complex chains, such as branched (DPhPC) and unsaturated lipids (DOPC and POPC). Our findings yield a valuable "calibration curve" for the amplitude ratio (d⁺/r⁺) as a function of monolayer density, for each type of lipid. This study will extend the utility of SFG spectroscopy to investigate more realistic membrane models and their interaction with drugs or other biological compounds.

References

1. Volpati, D.; Aoki, P. H. B.; Alessio, P.; Pavinatto, F. J.; Miranda, P. B.; Constantino, C. J. L.; Oliveira, O. N.. Adv Colloid Interface Sci 2014, 207, 199–215.
2. Guyot-Sionnest, P.; Hunt, H.; Shen, Y. R. Phys Rev Lett 1987, 59.
3. Miranda, P. B.; Pflumio, V.; Saijo, H.; Shen, Y. R. Thin Solid Films 1998, 327–329, 161–165.