NMR diffusion spectroscopy for the characterization of multicomponent hydrogen-bonded assemblies in solution

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Abstract
NMR diffusion measurements on 10 different multicomponent hydrogen-bonded assemblies, viz. the three single rosettes SR1–SR3 (133·2a333, 133·2b33, 133·2c333) the double rosettes DR1–DR5 (3a333·2a666, 3b333·2b666, 3c333·2a666, 3d333·2a666, 3e33·2a666), and DR6 (4a333·16), and the tetrarosette TR (533·2a1212) are described. Some of the above rosettes have been previously identified as well-defined assemblies (viz.SR1, DR1–DR3, and TR) using established characterization techniques ( 1H NMR spectroscopy, X-ray diffraction, and MALDI-TOF MS after Ag+-labeling). The diffusion coefficients of these assemblies were studied and used as a reference for the identification of three new assemblies (DR4–DR6), the characterization of which could not be established unequivocally using other characterization tools. A good correlation was found between the experimental and calculated diffusion coefficients when DR1 was used as a reference. A relatively good correlation was obtained between the effective hydrolytic radii calculated from the diffusion data and those extracted from gas phase-minimized structures with SR1 and DR2 being exceptions. The diffusion measurements show that assembly DR4 is a thermodynamically stable species, while assemblies DR5 and DR6 are less stable and only present to a minor extent.

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