Extraction of Homogeneous23Na NMR Linewidths from Two-Dimensional Jeener–Broekaert Spectra*

Abstract

The Jeener–Broekaert experiment has recently been applied to heterogeneous biological systems for selective observation of spinI= 3/2 nuclei which exhibit residual quadrupolar splittings. This paper describes the use of a two-dimensional version of this experiment to extract the homogeneous linewidths of such nuclei. The powderlike spectra produced by the one-dimensional Jeener–Broekaert experiment have lineshapes which depend on both homogeneous and inhomogeneous quadrupolar broadening. In two-dimensional Jeener–Broekaert spectra, the inhomogeneous broadening appears along the ω1= ω2and ω1= −ω2diagonal axes, with the result that the two broadenings are separated. The homogeneous linewidth can then be extracted by fitting cross sections through analytically generated lineshapes to the experimental spectra. The reliability of this technique is evaluated by computer simulation, and23Na NMR linewidths are measured experimentally in disordered liquid crystalline and heterogeneous biological samples. The possibility of measuring frequency-dependent variations in the homogeneous linewidth is also discussed.