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

Abstract

The self-assembled supramolecular host [Ga(4)L(6)](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 (1)H 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 (1)H 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.

Can a Single Molecule of Water be Completely Isolated Within the Subnano‐Space Inside the Fullerene C60Cage? A Quantum Chemical Prospective

“…[77] Chemical shifts: The magnetic shielding tensors were calculated by using the widely-used GIAO method, which has been demonstrated to provide accurate values for analogous systems. [78] The absolute values of the isotropic chemical shielding (s) computed for the gas-phase equilibrium geometry of H 2 O and in a simulated tetrahydrofuran (THF) medium are approximately 31.6 and 31.0 ppm for 1 H, and approximately 326.3 and 332.4 ppm for 16 O, respectively. Previously reported values of s H and s O are approximately 30.9 and 337.9 ppm with CCSD(T) [79] and, approximately 30.9 and 336.9 ppm with CCSD, [80] respectively, whereas a value of 30.0 ppm has been proposed for the absolute hydrogen chemical shielding in gaseous water.…”

“…Chemical shifts : The magnetic shielding tensors were calculated by using the widely‐used GIAO method, which has been demonstrated to provide accurate values for analogous systems 78. The absolute values of the isotropic chemical shielding ( σ ) computed for the gas‐phase equilibrium geometry of H 2 O and in a simulated tetrahydrofuran (THF) medium are approximately 31.6 and 31.0 ppm for 1 H, and approximately 326.3 and 332.4 ppm for 16 O, respectively.…”

Inner and Outer Beauty

“…Right: Energy profile of this distortion the interior of the cluster is strongly de-shielding, while the spaces close to the walls and apertures instead shield guests. The result is that encapsulated species have diagnostic shifts, which provide information about the guest orientation within the cavity of the M 4 L 6 assembly [23] (Fig. 14).…”

Aromatic character of Oh‐C24N24. A cavernous nitride fullerene bearing N4‐macrocycle motifs

“…In last years, the aromatic, nonaromatic, and antiaromatic properties of planar N 4 ‐macrocycles have been well discussed by Fliegl and Sundholm, among other authors, highlighting the capabilities of sustaining extended ring currents under an applied magnetic field. These are informative in the formation of host‐guest structures standing in the characterization and quantitative analysis provided by regular NMR experiments . The O h ‐C 24 N 24 cavernous cage appears as the next step, allowing to evaluate the magnetic response properties of N 4 ‐macrocycles in a confined spherical structure.…”