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Multinuclear Solid‐State‐NMR and FT‐IR‐Absorption Investigations on Lipid/Trichogin Bilayers
Author(s) -
Heuber Christiane,
Formaggio Fernando,
Baldini Chiara,
Toniolo Claudio,
Müller Klaus
Publication year - 2007
Publication title -
chemistry and biodiversity
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.427
H-Index - 70
eISSN - 1612-1880
pISSN - 1612-1872
DOI - 10.1002/cbdv.200790105
Subject(s) - chemistry , bilayer , lipid bilayer , phospholipid , crystallography , lipid bilayer phase behavior , membrane , nuclear magnetic resonance spectroscopy , relaxation (psychology) , solid state nuclear magnetic resonance , molecule , absorption (acoustics) , stereochemistry , nuclear magnetic resonance , organic chemistry , psychology , social psychology , biochemistry , physics , acoustics
Solid‐state NMR and FT‐IR absorption spectroscopy are employed to study the molecular properties of 1,2‐dimyristoyl‐ sn ‐glycero‐3‐phosphocholine (DMPC) lipids as a function of trichogin‐OMe content, a membrane‐active analogue of the peptaibol trichogin GA IV. Variable‐temperature NMR studies are performed, comprising 13 C‐, 31 P‐, and 14 N‐NMR line‐shape and relaxation experiments, to provide information about the mobility and ordering of the phospholipid head group and the acyl‐chain region in the absence and presence of trichogin‐OMe. Likewise, variable‐temperature FT‐IR‐absorption studies are performed, and the conformation‐sensitive CH 2 stretching bands are analyzed to examine the conformational state of the acyl chain. At lower trichogin‐OMe concentrations, the peptide exhibits no remarkable influence on the dynamics and ordering features of the phospholipid molecules. It is concluded that, in this case, trichogin‐OMe is embedded in the lipid bilayer, with its helix axis laying parallel to the bilayer plane, the more hydrophobic part pointing towards the inner part of the bilayer (‘carpet‐like’ superstructure). The lipid dynamics are probed by rotating‐frame spin–lattice‐relaxation (T 1ρ ) experiments for the 13 C and 31 P nuclei, which are assumed to be dominated by collective‐order fluctuations. Variation of T 1ρ with sample composition is attributed to changes of the membrane stiffness. For the sample with the highest lipid/peptide (L/P) molar ratio, i.e. , L/P 5 : 1, phase separation as a result of membrane disruption occurs. In this case, a second spectroscopic component can be separated in the 31 P‐NMR spectra. In addition, the (motionally averaged) magnetic interactions are greatly reduced, the actual values differing for both components. The second spectroscopic component refers to membrane components with high trichogin‐OMe concentration and to strong lipid–trichogin‐OMe interactions, as reflected by significant changes of the head‐group orientation (toroidal model). At the same time, DMPC molecules exist with minor lipid–trichogin‐OMe interactions, most probably in smaller liposomes, trichogin‐OMe being embedded in a ‘carpet‐like’ manner. Moreover, lipid ordering is generally reduced for the highly concentrated sample, which may result from fast lateral lipid motion along the curved bilayer surface.