ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The anisotropic rotational motion of the backbone and the side chains of poly(L-glutamic acid) in the α-helical structure was investigated using the 13C-T1 and T2 relaxation times of all carbon atoms with directly attached protons, obtained at a 13C-Larmor frequency of 67.89 MHz. The evaluation of the nmr data was carried out according to the previously derived anisotropic diffusion model, in which the macromolecule is considered a rigid rod. The rotation of the backbone is characterized by two diffusion constants, D1 and D3, describing the rotation perpendicular to and around the symmetry axis. The additional internal motion of the Cβ-methylene group is described as a jump process with a jump rate, k1, between two allowed rotametric states. Steric considerations indicate that the occupation of the third rotameric position is forbidden. The rotation of the Cγ-methylene group is decribed as a one-dimensional diffusion process around the Cβ-Cγ bond. Investigation of the temperature dependence of the relaxation parameters led to the temperature dependence of the dynamic parameters. Activation energies were determined from these data. The dynamic parameters obtained for poly(L-glutamic acid) at 291 K are compared with the corresponding results of a previous study of poly(L-lysine).The development of an anisotropic diffusion model for the motions of the rod-shaped poly(L-lysine) α-helix and its application to the interpretation of the 13C-relaxation data of this molecule have already been published previously. In this model, both the overall molecular tumbling and the various internal motions have been characterized by diffusion constants or jump rates typical for each process. These dynamic parameters can be calculated from the spin-lattice relaxation times, the spin-spin relaxation times and the NOE factors of the Cα, Cβ, and Cγ nuclei of the polypetide.In the present paper, we describe the application of the above-mentioned dynamic model to the interpretation of 13C-relaxation studies of a further homopolypeptide, poly(L-glutamic acid), in the α-helical structure. Furthermore, we studied the temperature dependence of the relaxation times of this polymer and determined the anisotropic diffusion parameters at each temperature. From their temperature dependence and from comparison of our present results with the data of our previous study of poly(L-lysine), we were able to derive new insights into the intramolecular diffusion processes and the excitation of various motions.
Additional Material:
4 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.360240704
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