Abstract: Nuclear magnetic resonance provides several unique means of investigating the interactions between different inorganic ions and various macromolecules. (23)Na is a quadrupolar nucleus, meaning that relaxation analysis of the various coherences allows the measurement of its binding to biological macromolecules. In this study, we analyzed the quadrupolar relaxation of (23)Na(+) longitudinal magnetization and single- and triple-quantum coherences in aqueous systems containing RNA, bovine serum albumin and sodium dodecyl sulfate micelles. The effectiveness of the James-Noggle method for determining binding constants was evaluated in these systems, and also the applicability of various (23)Na coherences in providing information on the extent and affinity of binding to the three different classes of biomolecules.
Abstract: Experimentsthat selectively excite I = 32 nuclei exhibiting residual quadrupolar splittings are used to acquire 23Na NMR spectra from a range of biologically relevant samples containing sodium in ordered environments. Three complementary approaches to the analysis of such spectra are described: (i) measurement of relaxation rates, (ii) extraction of homogeneous linewidths from two-dimensional Jeener-Broekaert spectra, and (iii) simultaneous fitting of detailed theoretical functions to a series of one-dimensional Jeener-Broekaert spectra. Analysis of relaxation rates provides evidence for compartmentation in bovine nasal cartilage. Each approach is used to demonstrate the presence of anisotropy in transverse relaxation in porcine tendon. For certain samples containing collagen, a good theoretical fit to the spectra was obtained using a model that allows for anisotropic relaxation by including the effects of slow lateral and radial diffusion.
