Solid-state proton orientation experiments

Solid-state NMR methods allow the investigation of local orientation, dynamics and conformational order of polymer chain segments. Si chemical shifts contain information about molecular moieties and about the conformation of chain segments. The line width of a wideline spectrum characterizes the strength of the dipolar couplings among protons and, therefore, the molecular mobility. H spin diffusion, mediated by the homonuclear dipolar couplings, is a powerful technique to obtain information about the spatial proximity of molecular moieties. These concepts have recently been combined in a two-dimensional Wideline Separation Experiment (WISE-NMR spectroscopy)... 

D NOESY experiments revealed the distances between some relevant protons in the box-like assembly [8]. These studies provide sufficient evidence for the D3-symmetric structure of assemblies (X)3 (DEB)6 (X = 1-7) in solution which is the result of an anti-parallel orientation of the two melamines at each calix[4]arene with respect to each other (Figure 1). This is in particular supported by a very strong NOE connectivity between the NCHa protons of 2 (R = NO2) and one of the ethyl-CH2 groups of DEB, which can only arise from the close proximity of protons which are part of the two different rosettes within the same assembly. The anti-parallel orientation is also observed in the solid state structure (Figure 9). 

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