Lorentzian line reorientation

The NMR provided invaluable information on the structures of a variety of assemblies of 6-quartets. In the presence of Na and K. an octameric structure of 5 -CMP is formed in water.The analysis of the non-Lorentzian line shapes of the Na-NMR signals afforded a measurement of the correlation time of the reorienting, rigid, supramolecular entity, confirming the size of the aggregate, in complement to the H- and - P-NMR structural data. ... 

The shapes of both /w and 7hv lines are assumed to be represented by simple Lorentzians. For a totally symmetric vibration with a low polarization ratio as in the present case, the vibrational and reorientational relaxation times Tv and can be determined from the half-widths of the isotropic and anisotropic spectra. Since the value of /hv is much smaller than that of /w for the 1050 cm" line, the contribution of /gv to the isotropic intensity can be neglected ... 

The figure shows that the Lorentzian fits represent the spectra very well at all temperatures, thus justifying the assumption that the rotation about a single axis basically shapes the spectral line. This justifies also the assumption that the motion is essentially a diffusive reorientation of this axis. Under these conditions we can calculate the reorientation time from the linewidth T0 by means of the equation ... 

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