Abstract
Host-guest complexation of cucurbit[8]uril (Q[8]) with two enantiomers, D-3-(2-naphthyl)-alanine (D-NA) and L-3-(2-naphthyl)-alanine (L-NA), has been fully investigated. Experimental data indicate that double guests reside within the cavity of Q[8] in both aqueous solution and solid state, generating highly stable homoternary complexes D-NA2@Q[8] and L-NA2@Q[8].
Highlights
The recognition and sensing of amino acids, peptides and proteins in aqueous solution by artificial receptors has attracted much interest in supramolecular host-guest chemistry and pharmaceutical science in the recent past1–5
Given that the changes induced by Q[8] host in the 1H NMR spectra of guests D-NA (Fig. 2) and L-NA (Figure S2) are similar, guest D-NA is taken as a representative to depict their binding interactions
The proton H1 and one of the CH2 protons of D-NA move downfield slightly, which indicates that they are located outside the cavity
Summary
The recognition and sensing of amino acids, peptides and proteins in aqueous solution by artificial receptors has attracted much interest in supramolecular host-guest chemistry and pharmaceutical science in the recent past. Urbach and co-workers studied the combining power of Q[7] to a number of amino acids, peptides and proteins, and found that the Q[7] prefer to bind guests containing an N-teminal aromatic residue. Previous investigation revealed that the host Q[8] is large enough to accommodate two phenyl, naphthyl or other aromatic groups simultaneously through host-stabilized charge-transfer interactions. Previous investigation revealed that the host Q[8] is large enough to accommodate two phenyl, naphthyl or other aromatic groups simultaneously through host-stabilized charge-transfer interactions14,36–38 This observation prompted us to explore the possibility of the formation of homoternary complexes between Q[8] and enantiomeric amino acid containing naphthyl residue, D-3-(2-naphthyl)-alanine and L-3-(2-naphthyl)-alanine (abbreviated as D-NA and L-NA, respectively, Fig. 1b). We studied the host-guest complexation of Q[8] with D-NA and L-NA in aqueous solution by NMR, UV and fluorescence spectroscopy, MS and isothermal titration calorimetry (ITC), and in the solid state by X-ray crystallography
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