NMR study of synthetic lecithin bilayers in the vicinity of the gel-liquid--crystal transition

Abstract

1H, 2H, and 31P NMR methods have been employed in the study of dimyristoyl lecithin bilayers hydrated with D2O in the gel (L beta'), intermediate (P beta') and liquid-crystalline (L alpha) phases. For D2O/lipid molar ratios, n, in the range 7 less than or equal to n less than or equal to 11 discontinuities are observed in the deuterium NMR splittings at both main and pretransitions. A partial phase diagram based on NMR and differential scanning calorimetry data is presented. 1H NMR dipolar splittings are observed for macroscopically oriented samples in all three phases. Changes in the 1H splittings are correlated with 2H and 31P data and interpreted to show that the chain tilt in the gel phase undergoes a discontinuous change on transition to the intermediate phase, which brings the chain axes closer to the bilayer normal. An estimate of chain tilt in the gel phase is made on the basis of NMR data and found to be approximately 23 degrees for a sample with n = 11 at 18 degrees C.

Motional narrowing of the 2H NMR spectra near the chain melting transition of phospholipid/D2O mixtures

“…The transition onset and peak temperatures, as determined using DSC, are shown for comparison (from Bryant et al 1992). Figure 2a shows data for POPC-they are qualitatively similar to those previously obtained for other PCs (Pope et al 1981;Strenk et al 1985;Hawton and Doane 1987), with the splitting approximately the same magnitude in both the gel and fluid lamellar phases, and zero splitting near the phase transition.…”

“…This additional motional narrowing of the spectra near the chain melting phase transition of phospholipids was first reported by Salsbury et al (1972), and has since been studied by several authors (Ulmius et al 1977;Pope et al 1981;Strenk et al 1985;Hawton and Doane 1987). Similar effects have been seen in the gel-fluid phase transition of bilayer forming soaps (Abdolall et al 1977(Abdolall et al , 1978.…”

“…In addition, Hawton and Doane (1987) have shown that the spectra for PC do not have a nonzero asymmetry parameter. Pope et al (1981) explained the effect by suggesting that the water molecules undergo rapid exchange between two environments with order parameters of equal magnitude and opposite sign. This explanation poses the question: why should such a special pair of environments appear over tens of degrees about the transition?…”

Millimeter Wave Radiations Affect Membrane Hydration in Phosphatidylcholine Vesicles

“…Since the heavy water quadrupole splitting, ∆ν q , can be related to changes in the bilayer structures [15,19,20], it is a useful probe of membrane surface geometry and membrane hydration. For a powder sample of multilamellar vesicles (MLVs), ∆ν q is the distance (Hz) between the highest peaks of the powder spectrum (see Figure 1A) and is given by the sum of the contribution of water bound to different sites along the phosphocholine headgroup of the membrane [15,19,20]: $∆{\nu }_q=\frac{3}{4}{\nu }_q\sum p_{b,i}{S}_{b,i}$ where, ν q = 220 KHz is the water quadrupole coupling constant; p b,i and S b,i are, respectively, the fraction and the molecular order parameter of bound water at the i th binding site. The last parameter takes the fast anisotropic molecular reorientations of water molecules at the membrane interface into account.…”

Determination of DMPC hydration in the Lαand Lβ′phases by2H solid state NMR of D2O

“…In rare cases where a quantitative study is possible, as by DSC, one is restricted to the state close to a main phase transition. When attempting to quantify hydration as a function of temperature or phase nature, the most suitable technique appears to be deuterium NMR of D 2 O [10–16]. To our knowledge the number of water molecules bound per DMPC in both gel and fluid phases is still unknown; hence we have determined this using NMR and DSC techniques.…”