The rise of FTIR spectroscopy in the characterization of asymmetric lipid membranes

• Published in: Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy Molecular and biomolecular spectroscopy, 2024-01, Vol.305, p.123488, Article 123488
• Main Authors: Pašalić, Lea, Maleš, Petra, Čikoš, Ana, Pem, Barbara, Bakarić, Danijela
• Format: Article
• Language: English
• Subjects: 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC); 1,2-dipalmitoyl-sn-glycero-3-phosphoserine (DPPS); 1H NMR and FTIR spectroscopy, differential scanning calorimetry (DSC); Asymmetric large unilamellar liposomes (aLUVs); Molecular dynamics (MD) simulations
• ISSN: 1386-1425
• DOI: 10.1016/j.saa.2023.123488

[Display omitted] •Asymmetric liposomes constituted from DPPC(out)/DPPS(in) lipids were prepared.•1H NMR spectra and DSC curves of successive heating runs confirmed the asymmetry.•The FTIR signatures of carbonyl, methyl and choline groups distinguish (a)symmetry.•MD simulations suggest hydration and lipid ordering differs due to (a)symmetry. In contrast to symmetric unilamellar liposomes (sLUVs) prepared from a mixture of different lipids, asymmetric ones (aLUVs) with different lipid composition in the inner and outer membrane leaflets are more suitable model systems of eukaryotic plasma membranes. However, apart from the challenging preparation of asymmetric liposomes and small amounts of obtained asymmetric unilamellar liposomes (aLUVs), a major drawback is the qualitative characterization of asymmetry, as each of the techniques used so far has certain limitations. In this regard, we prepared aLUVs composed dominantly of DPPC(out)/DPPS(in) lipids and, along with 1H NMR and DSC characterization, we showed for the first time how FTIR spectroscopy can be used in the presence of (a)symmetry between DPPC/DPPS lipid bilayers. Using second derivative FTIR spectra we demonstrated not only that the hydration of lipids glycerol backbone and choline moiety of DPPC differs in s/aLUVs, but in addition that the lateral interactions between hydrocarbon chains during the phase change display different trend in s/aLUVs. Molecular dynamics simulations confirmed different chain ordering and packing between s/a bilayers, with a significant influence of temperature, i.e. membrane phase.