Characterization of structure and 1H NMR of methyl viologen encapsulated noria and substituted noria hosts from density functional theory

Abstract

Density functional theory has been employed to characterize electronic structure, molecular electrostatic potential and 1H NMR of waterwheel-like macrocyclic host noria and its methyl derivative. Molecular electrostatic potential topography analyses reveal that substitution of methyl groups at reactive hydroxyls of noria engender deeper minima near the portal and inside the cavity of host. The complexes between noria or Me-noria hosts and methyl viologen (MV2+) exhibit distinct binding patterns. The structure of MV2+@noria shows penetration of MV2+ inside the central hole of the host whereas Me-noria complex possesses one of the aromatic rings of MV2+ resides near the host portal. Calculated interaction energy for complexation of Me-noria turns out to be 239kJmol−1, which is ∼20 times larger than that for noria host. Calculated 1H NMR chemical shifts predict deshielding of guest protons encapsulated within the cavity of host in the MV2+@noria complex compared to the isolated guest. The protons near the host portal led to up-field signals in the spectra of MV2+@Me-noria. Host-guest binding pattern and 1H NMR for complexation of noria and its methyl derivative are compared with those observed in well-known macrocycles such as β-cyclodextrin, cucurbit[8]uril, calix[5]arene and pillar[5]arene hosts.