Structure and stability of vitamin E – lecithin and phytanic acid – lecithin bilayers studied by 13C and 31P nuclear magnetic resonance

1977 ◽  
Vol 55 (2) ◽  
pp. 220-226 ◽  
Author(s):  
Robert J. Cushley ◽  
Bruce J. Forrest
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Vitamin E ◽  
Magnetic Resonance ◽  
Phytanic Acid ◽  
Relative Rate ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Bilayer Structure ◽  
Spin Lattice ◽  
Relaxation Studies

13C spin–lattice relaxation studies on lecithin bilayers indicate a marked destabilization of the bilayer structure by incorporated vitamin E (d,l-α-tocopherol) and phytanic acid, phytanic acid causing the greatest perturbation.Kinetic analysis of paramagnetic praseodymium infusion into the lecithin vesicles containing various phytyl compounds has been performed using 31P nmr. Relative rates of Pr3+ leakage through the mixed lecithin – phytyl compound bilayer compared with pure lecithin (relative rate = 1.00) were: phytol = 7.8, vitamin E = 47.7, and phytanic acid = 2897.

A nuclear magnetic resonance investigation of n -pentane, n -hexane and cyclo pentane

1954 ◽  
Vol 222 (1151) ◽  
pp. 526-541 ◽  
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Molecular Motion ◽  
Relaxation Times ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Kcal Mole ◽  
Second Moment ◽  
Spin Lattice ◽  
Second Moments

The nuclear magnetic resonance spectra and spin-lattice relaxation times have been measured for the protons in n -pentane (C 5 H 12 ), n -hexane (C 6 H 14 ) and cyclo pentane (C 5 H 10 ) all in the solid state. The temperature range covered was from 70° K to the melting-points of 143·4° K for n -pentane, 177·8° K for n -hexane and 179·4° K for cyclo pentane. In the case of n -pentane and n -hexane the second moments of the absorption lines were found to be smaller than the computed rigid lattice values over the. whole temperature range. Possible molecular motions which might cause this reduction are discussed. It is suggested that the most probable type of motion is reorientation of the methyl groups at the ends of each molecule about the adjacent C—C bonds. An analysis of the spin-lattice relaxation times shows that this reorientation process is governed by an activation energy of 2·7 kcal/mole for n -pentane and 2·9 kcal/mole for n -hexane, values which support the mechanism postulated. At the lowest temperature the absorption lines had not reached their full widths, even though the reorientation frequencies at these temperatures were considerably less than the line-widths. The experimental second moment for cyclo pentane below about 120° K indicates that the lattice is effectively rigid in this temperature region. The uncertainties in both the experimental and theoretical second moments do not allow a distinction to be drawn between the plane and puckered molecular models. At the temperature of the first transition (122·4° K) the line-width second moment and relaxation time all show a sudden decrease. The low value of second moment at the higher temperatures indicates that considerable molecular motion is occurring, the molecules rotating with spherical symmetry. The change in crystal structure at the temperature of the second transition (138·1° K) is thought to be a direct result of this spherical symmetry. As the temperature increases, the results indicate that more molecular motion must be occurring, and it is thought that the rotating molecules are diffusing through the lattice.

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