1H NMR Chemical Shift Calculations as a Probe of Supramolecular Host–Guest Geometry

• Published in: Journal of the American Chemical Society 2011-07, Vol.133 (29), p.11205-11212
• Main Authors: Mugridge, Jeffrey S, Bergman, Robert G, Raymond, Kenneth N
• Format: Article
• Language: English
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja202254x

The self-assembled supramolecular host [Ga4L6]12- (1; L = 1,5-bis[2,3-dihydroxybenzamido]naphthalene) can encapsulate cationic guest molecules within its hydrophobic cavity and catalyze the chemical transformations of bound guests. The cavity of host 1 is lined with aromatic naphthalene groups, which create a magnetically shielded interior environment, resulting in upfield shifted (1–3 ppm) NMR resonances for encapsulated guest molecules. Using gauge independent atomic orbital (GIAO) DFT computations, we show that 1H NMR chemical shifts for guests encapsulated in 1 can be efficiently and accurately calculated and that valuable structural information is obtained by comparing calculated and experimental chemical shifts. The 1H NMR chemical shift calculations are used to map the magnetic environment of the interior of 1, discriminate between different host–guest geometries, and explain the unexpected downfield chemical shift observed for a particular guest molecule interacting with host 1.