Phospholipids isotropic chemical shift

Finally, structural investigations of a human calcitonin-derived carrier peptide in a membrane enviromnent by solid-state NMR have been reported. The typical axially symmetric powder patterns of NMR spectra were used to confirm the presence of lamellar bilayers in the samples studied. The chemical shift anisotropy of the NMR spectra was monitored in order to reveal weak interaction of the peptide with the lipid headgroups. In addition, paramagnetic enhancement of relaxation rates and NMR order parameters of the phospholipid fatty acid chains in the absence and presence of the carrier peptide were measured. All peptide signals were resolved and fully assigned in 2D proton-driven spin diffusion experiments. The isotropic chemical shifts of CO, C and provided information about the secondary structure of the carrier peptide. In addition, dipolar eoupling measurements indicated rather high amplitudes of motion of the peptide. 

Figure 5 P-NMR spectra of phospholipids with different modes of molecular motion, a rigid limit b fast axial rotation about X-axis averages Y- and Z-components of the chemical shift tensor. In the spectrum one can observe two principal values of = 112(ayy + azz) and ct =oxx c a typical case of fluid membrane. Along with fast X-axial rotation molecular motion also partially averages ct and ctj. In the spectrum one observes effective values a n < CT I and a < CT. d Isotropic case (high resolution NMR) a/5o = 1/3(axx + cryy-Pazz)-...

Figure U-6 NMR-spectra for macroscopic polymorphic phases of phospholipids in bilayers, hexagonal Hn and isotropic phases (small vesicles, micelles, inverted micelles and cubic phases). Similar spectra are recorded for any one phase regardless of which phospholipid type forms the phase because the chemical shift differences for different phospholipids is smaller (2-4 ppm) than the anisotropy of chemical shift ( 30-50 ppm) (reproduced from [63] with permission from Elsevier Science, Amsterdam, The Netherlands).

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