The coefficients of intracrystalline self-diffusion of t h e n-alkanes from propane to n-hexane adsorbed in zeolite ZSM-5 are studied by means of the pulsed field gradient (PFG) NMR method with field gradient amplitudes up to 25 T m-' over a temperature range from -20 to +380"C. The diffusivities are found to decrease monotonically with increasing chain lengths. They are in satisfactory agreement with the results of quasielastic neutron scattering and MD simulations as well as with non-equilibrium measurements by the frequency response and single-step adsorption technique. However, in comparison with zero-length-column (ZLC) desorption and permeation studies, these data, though exhibiting the same trends of chain length dependence, are ca. two orders of magnitude larger. A s expected, the diffusivities are intermediate between those for zeolite NaX and NaCaA, exhibiting, however, the smallest activation energies. This indicates that t h e differences in the potential energies of t h e adsorbate molecules on their intracrystalline trajectories are in general smaller than in zeolites NaCaA and NaX.

Solid gramicidin A and S and their interaction with DPPC bilayers were examined by 2H NMR as well as 31P NMR and differential scanning calorimetry (DSC). The deuterium spectra arose from deuterons associated with the peptide through chemical exchange in 2H2O. The spectra from both peptides were characterized by a quadrupolar splitting parameter, omega Q/2 pi approximately 150 kHz, and an asymmetry parameter, eta approximately 0.17. An additional 33 kHz, eta = 0 component arising from deuterons on mobile ornithine side chains was present in gramicidin S. In the gel phase of dipalmitoylphosphatidylcholine liposomes the gramicidins gave spectra that had components identical with those obtained from the solids. In the liquid-crystalline phase gramicidin A containing samples gave multicomponent spectra with a maximum quadrupolar splitting value of 133 kHz, eta = 0. A minimum in the T2e was observed, coinciding with the onset of the broadened phase transition measured by DSC and 31P NMR, due to the onset of axial rotation of the peptide in the bilayer. The different powder patterns in the liquid-crystalline spectra from gramicidin A probably arise from different amide sites along the transmembrane channel. The broad component of the 2H NMR spectra from gramicidin S in liposome preparations was not affected by the lipid-phase transition. The T2e was also constant over this temperature range. The results are consistent with a location of gramicidin S at the membrane surface.

The major coat protein of bacteriophage M13 was incorporated in mixed dimyristoylphosphatidylcholine/dimyristoylphosphatidylglycerol (80/20 w/w) vesicles probed with different spin-labeled phospholipids, labeled on the C-14 atom of the sn-2 chain. The specificity for a series of phospholipids was determined from a motionally restricted component seen in the electron spin resonance (ESR) spectra of vesicles with the coat protein incorporated. At 30 degrees C and pH 8, the fraction of motionally restricted phosphatidic acid spin-label is 0.36, 0.52, and 0.72 for lipid/protein ratios of 18, 14, and 9 mol/mol, respectively. The ESR spectra, analyzed by digital subtraction, resulted in a phospholipid preference following the pattern cardiolipin = phosphatidic acid greater than stearic acid = phosphatidylserine = phosphatidylglycerol greater than phosphatidylcholine = phosphatidylethanolamine. The specificities found are related to the composition of the target Escherichia coli cytoplasmic membrane.

Coat protein of bacteriophage M13 is examined in micelles and vesicles by time-resolved tryptophan fluorescence and anisotropy decay measurements and circular dichroism experiments. Circular dichroism indicates that the coat protein has alpha-helix (60%) and beta-structure (28%) in 700 mM sodium dodecyl sulfate micelles and predominantly beta-structure (94%) in mixed dimyristoylphosphatidylcholine/dimyristoylphosphatidic acid (80/20 w/w) small unilamellar vesicles. The fluorescence decay at 344 nm of the single tryptophan in the coat protein after excitation at 295 or 300 nm is a triple exponential. In the micelles the anisotropy decay is a double exponential. A short, temperature-independent correlation time of 0.5 +/- 0.2 ns reflects a rapid depolarization process within the coat protein. The overall rotation of the coat protein-detergent complex is observed in the decay as a longer correlation time of 9.8 +/- 0.5 ns (at 20 degrees C) and has a temperature dependence that satisfies the Stokes-Einstein relation. In vesicles at all lipid to protein molar ratios in the range from 20 to 410, the calculated order parameter is constant with a value of 0.7 +/- 0.1 from 10 to 40 degrees C, although the lipids undergo the gel to liquid-crystalline phase transition. The longer correlation time decreases gradually on increasing temperature. This effect probably arises from an increasing segmental mobility within the coat protein. The results are consistent with a model in which the coat protein has a beta-structure and the tryptophan indole rings do not experience the motion of the lipids in the bilayer because of protein-protein aggregation.

Fourier-transform pulsed-field-gradient NMR m e a s u r e m e n t s h a v e been used to analyse the diffusion of some n-alkanes (methane, n-butane and n-pentane) in zeolite ZSM-5. The intention of t h e NMR study was to compare results obtained by molecular dynamics calculations and by uptake measurements, using t h e same systems. Methane clearly exhibits a bi-exponential spin-echo attenuation. This indicates two types of diffusion : intracrystalline diffusion and long-range diffusion, which is a combination of intera n d intra-crystalline diffusion. In t h e case of small crystals the diffusion of methane into t h e macropores between t h e crystals dominates t h e decay. However, a s expected, for larger crystals, t h e contribution of intracrystalline (or micropore) diffusion increases significantly. From t h e curves, t h e coefficient of intracrystalline diffusion of methane in ZSM-5 has been determined (3.8 x lo-' m2 s-' at 25°C). The NMR methane diffusion data are in good agreement with values obtained by molecular dynamics calculations. Subsequent NMR measurements of n-butane and npentane diffusion in ZSM-5 indicate that t h e diffusion decreases sharply with increasing chain length of t h e hydrocarbons (11 x lo-'' a n d 4.4 x lo-'' m2 s-', respectively, at 25°C and 20 kPa loading). To allow for a comparison with t h e diffusivities obtained independently by other techniques, t h e concentration dependence of t h e NMR self-diffusion coefficient of n-pentane in ZSM-5 was determined and was found to decrease with increasing sorbate concentration. In addition, from t h e temperature dependence of the diffusion rates the activation energies for t h e n-butane and n-pentane diffusion in ZSM-5 have been determined (8.4 and 12.6 kJ mol-' at 20 kPa, respectively). The PFG NMR and M D results for the diffusion of light n-alkanes in ZSM-5 have also been compared with relevant diffusion data from t h e literature (obtained using other techniques, i.e. uptake methods, ZLC, MT). The microscopic self-diffusivity (from PFG N M R and MD) differs systematically by ca. two orders of magnitude from t h e much slower, macroscopic diffusion observed by uptake, ZLC and MT methods. On t h e other hand, t h e r e is satisfactory agreement between t h e self-diffusivity of n-butane obtained with PFG NMR and t h e transport diffusivity of t h e same system measured using t h e frequency response method.