DETERMINATION OF THE CORRELATION TIME FOR A SLOWLY REORIENTING SPIN-3/2 NUCLEUS - BINDING OF NA+ WITH THE 5'-GMP SUPRAMOLECULAR ASSEMBLY

The 23Na NMR lineshape for Na+ exchanging between the free state in aqueous solution and the bound state on a slowly reorienting macromolecule is the superposition of two lorentzians, corresponding to a fast relaxation (60% of the total intensity) and a slow relaxation (40% of the total intensity). Separation of these two components is achieved by full deconvolution of the experimental lineshape. An alternate and more easily implemented procedure uses only measurement of the linewidth at one-half and one-eight of the total height. We apply both methods to the determination of the correlation time τc = 4-9 nsec for Na+ bound to the aggregates resulting from self-assembly, in D2O solution, of the 5′-guanosine monophosphate nucleotide (0.1 M), in the presence of K+ ions (0.4-1 M). These correlation times are discussed in terms of the structure of these aggregates, involving plausibly a C2h dimer obtained from the interaction of planar tetramers whose core includes a K+ ion. © 1979.