Imaging phospholipid conformational disorder and packing in giant multilamellar liposome by confocal Raman microspectroscopy

- Conformational disorder has been imaged for the first time in a multilamellar vesicle by Raman microspectroscopy.
- Structural variations, the intra- and inter chain interactions, helped to identify phase and packing efficiencies.
- Non-uniform molecular interactions observed in multilamellar vesicles.
- Gel phase rich domains and heterogeneous lateral packing within a giant liposome has been imaged.
- Our method can help to understand structural deformations induced by external factors such as pH, temperature etc.

Liposomes are closed phospholipid bilayer systems that have profound applications in fundamental cell biology, pharmaceutics and medicine. Depending on the composition (pure or mixture of phospholipids, presence of cholesterol) and preparation protocol, intra- and inter-chain molecular interactions vary leading to changes in the quality (order and packing) of liposomes. So far it is not possible to image conformational disorders and packing densities within a liposome in a straightforward manner. In this study, we utilized confocal Raman microspectroscopy to visualize structural disorders and packing efficiency within a giant multilamellar liposome model by focusing mainly on three regions in the vibrational spectrum (CC stretching, CH deformation and CH stretching). We estimated properties such as trans/gauche isomers and lateral packing probability. Interestingly, our Raman imaging studies revealed gel phase rich domains and heterogeneous lateral packing within the giant multilamellar liposome.

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