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2D 1H-13C HMBC

In homonuclear correlati S. Balayssac, S. Trefi, V. Gilard, M. Malet-Martino, R. Martino and M. A. Delsuc, J. Pharm. Biomed. Anal., 2009, 50, 602 CrossRef CAS PubMed . Due to the limited scope of this review, not every technique can be discussed, but detailed information about the application of other methods for supramolecular structures can be found elsewhere. This applies for dynamic light scattering (DLS), 9 X-ray powder diffraction, 10,11 scanning tunnelling microscopy (STM), 12 magnetic measurements 13 and circular dichroism spectroscopy (CD). 14 2 Nuclear magnetic resonance spectroscopy Technique NMR spectroscopy is amongst the most popular structural characterisation methods in synthetic chemistry research. It combines easy sample preparation and wide applicability to a range of molecules with rich structural detail, in particular regarding through-bond and through-space interactions. Consequently, NMR spectroscopy is also commonly used to characterise supramolecular compounds, e.g. host–guest complexes. 15–17 S. J. Duncan, R. Lewis, M. A. Bernstein and P. Sandor, Magn. Reson. Chem., 2007, 45, 283 CrossRef CAS PubMed . M. Sawada, Y. Takai, T. Kaneda, R. Arakawa, M. Okamoto, H. Doe, T. Matsuo, K. Naemura, K. Hirose and Y. Tobe, Chem. Commun., 1996, 1735–1736 RSC.

C. D. Putnam, M. Hammel, G. L. Hura and J. A. Tainer, Q. Rev. Biophys., 2007, 40, 191–285 Search PubMed. Additional proof came from ion mobility mass spectrometry, which showed smaller CCS values for the species [ 17 2 − H] − and [ 17 2 + S − H] − compared to [ 17 2 + PF 6] − and [ 17 2 + PF 6 + S] − (with S = acetone, ΔCCS = 8 Å, Fig. 12A on the left side). This again underlines the exo complexation of PF 6 −, since the biggest change in CCS values should be caused by the species that is attached to the cavity rather than encapsulated in its interior. Moreover, the authors assumed a spherical shape for the molecules and calculated their diameter based on CCS values. For the dimeric species in general, the comparison of those values (between 2.2 and 2.3 nm) with the hydrodynamic radius obtained from DOSY NMR (2.0 nm) and with the X-ray crystal structure (1.9 nm) proved similar structures of the host–guest complex in solution, gas phase and in the solid state.

2D NOESY

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