NMR relaxation processes of 31P in macromolecules

✍ Scribed by Heisaburo Shindo

• Publisher: Wiley (John Wiley & Sons)
• Year: 1980
• Tongue: English
• Weight: 735 KB
• Volume: 19
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.1980.360190306

✦ Synopsis

Abstract

^31^P‐Nmr relaxation parameters (spin‐lattice relaxation time, linewidth, and nuclear Overhauser effect) were obtained at three different frequencies for poly(U) and a well‐defined (145 ± 3 base‐pair) fragment of DNA in solution. Data sets for the two samples were analyzed by theories which included relaxation by the mechanisms of ^31^P chemical shift anisotropy as well as by ^1^H‐^31^P dipole–dipole interaction. Neither data set could be satisfactorily described by a single correlation time. A model of a rigid rotor most nearly fits the data for the DNA molecule. Parameters obtained from the least‐square fit indicate (1) that the DNA undergoes anisotropic reorientation with a correlation time τ~0~ = 6.5 × 10^−7^ sec for the end‐to‐end motion, (2) the ratio of diffusion constants D~∥~/D~⊥~ is 91, and (3) that the linewidth is due to chemical shift dispersion to the extent of 0.5 ppm. Some deviations of the calculated from the observed values suggested that significant torsional and bending motions may also take place for this DNA. Another model which contains isotropic motion but with a broad distribution of correlation times was required to fit the data for poly(U). A log − χ^2^ distribution function of correlation times [Scheafer, J. (1973) Macromolecules 6, 881–888] described well the motion of poly(U) with the average correlation time τ = 3.3 × 10^−9^ sec and a distribution parameter p = 14.