A new, aqueous ¹H NMR shift reagent based on host-guest molecular recognition principles for organic compound structural analysis: Non-covalent π-π and hydrophobic interactions using a supramolecular host, [Cp*Rh(2′-deoxyadenosine)]₃(OTf)₃

We have discovered that the supramolecular host [Cp*Rh(2′-deoxyadenosine)]₃(OTf)₃ (1, Cp* = η⁵-C₅Me₅, OTf = CF₃SO₃^-) has utility as a new, aqueous ¹H NMR shift reagent, via a host-guest molecular recognition process that occurs by non-covalent π-π and hydrophobic interactions, with a wide variety of H₂O-soluble organic substrates. These organic compound guests that we present, to illustrate the utility of host 1 as a novel, aqueous ¹H NMR shift reagent, encompass examples such as aromatic carboxylic acids, phenylacetic acid (G1), 1-naphthoic acid (G2), and 2-naphthoic acid (G3), an aliphatic carboxylic acid, cyclohexylacetic acid (G4), as well as biological compounds, a di- and a tetrapeptide containing terminal L-tryptophan (Trp) or L-phenylalanine (Phe) groups, L-Trp-L-Phe (G5) and L-Trp-L-Met-L-Asp-L-Phe amide (G6) in the pH range 5-10. A discussion of the molecular recognition parameters that effect the ¹H NMR shifts of the organic guests and a comparison with the water-soluble lanthanide shift reagents (LSRs) will be presented to demonstrate the usefulness of this aqueous molecular receptor as an aid for organic compound structural analysis.