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

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.