Determining Ethanol Distribution in Phospholipid Multilayers with MAS−NOESY Spectra

Abstract

The location of an ethanol molecule within a membrane, an issue of considerable controversy, was investigated directly by NMR with two-dimensional NOESY. Lipid and ethanol 1H NMR resonances of multilamellar liposomes were resolved by magic-angle spinning (MAS). We observed strong proton lipid-ethanol crosspeaks in dispersions of saturated dimyristoylphosphatidylcholine and monounsaturated stearoyloleoylphosphatidylcholine and in polyunsaturated stearoyldocosahexaenoylphosphatidylcholine. Crosspeak intensity has been interpreted in terms of an ethanol distribution function over the lipid bilayer. Ethanol resides with the highest probability at the lipid water interface near the lipid glycerol backbone and upper methylene segments of lipid hydrocarbon chains. Chain unsaturation has only a minor influence on the ethanol distribution function. In all cases, the ethanol concentration in the bilayer core is significantly lower. At ambient temperature all lipid-ethanol crosspeaks are positive. Crosspeak intensity decreases with increasing water content and increasing temperature most likely because of shorter correlation times of lipid and ethanol reorientation. This suggests a lifetime for specific lipid-ethanol contacts of about 1 ns. Lipid-ethanol and lipid-lipid crosspeaks reflect the high degree of motional disorder of lipids and incorporated ethanol in membranes and the rather arbitrary nature of the location of the lipid-water interface.

Mechanisms of action of docosahexaenoic acid in the nervous system

“…The experiments also demonstrated that the unexpected long-range contacts are not taking place within one lipid molecule, but rep- resent magnetization transfer to neighboring lipid molecules that surround the emitter (141). Experiments on sn-1 chain perdeuterated 1-stearoyl-2-docosahexaenoyl-sn-glycero-3-phosphocholine (18:0 d35 ,22:6-PC) not only confirmed that polyunsaturated chains in membranes are similarly disordered, but also offered evidence that conformational disorder of the remaining degrees of freedom of a polyunsaturated chain is higher (135,142). Furthermore, the intensity of cross-and diagonal peaks as a function of mixing times allows judgment about motional correlation times in the polyunsaturated membranes on the time scale from pico-to milliseconds (138).…”

“…This became possible after improving the performance of magic angle spinning (MAS) probes in combination with very high magnetic field strength. MAS NMR reduces the linewidth of lipid resonances to ~10 Hz (135). That is equivalent to or better than resolution of resonances for very small unilamellar liposomes that tumble rapidly enough to eliminate anisotropic interactions.…”

Binding of Peptides with Basic and Aromatic Residues to Bilayer Membranes

“…Cafiso and co-workers (38,39) were the first to use NOESY spectra to investigate the structure of lipid membranes. More recently, NOESY has been exploited to establish the location of small hydrophobic molecules (40,41) and peptides (24,25,42) in membrane bilayers based on the observation of peptide-lipid or small molecule-lipid cross-relaxation. The challenge in these studies has been to distinguish direct contacts from those arising from spin diffusion to correlate cross-peak intensity with internuclear distance in a quantitative fashion.…”

Synthesis of p-tert-butylthiacalix[4]arenes functionalized with tris(2-aminoethyl)amine fragments at the lower rim and their interaction with model lipid membranes

“…It is known that small amphiphilic molecules are often located in the headgroup domain of lipid membranes. [35][36][37][38][39] Moreover, amphiphilic calixarenes have been shown to be embedded in lipid membranes. [40][41][42][43] Thus, we can assume that compounds 4 and 5 which have distinct hydrophilic and hydrophobic domains are located close to phospholipid phosphate headgroups with their protonated NH 3 + groups forming ion-pairs with the phosphate headgroups in addition to hydrogen bonding between P=O····H-N groups.…”