Host-guest interaction of hemicucurbiturils with phenazine hydrochloride salt

The host-guest interactions between phenazine hydrochloride salt (PheH(+)) and hemicucurbit[n]uril (n=6 or 12) (HemiQ[6 or 12]) have been studied by H-1 NMR, UV-vis, IR, mass spectrometry (MS) and quantum chemistry. In H-1 NMR spectra, the broadening of proton resonances of the hosts suggests the interactions of PheH(+) with HemiQs. The quantitative stabilities of the host-guest systems have been obtained by UV-vis titration experiments, that is, the stoichiometric interactions of PheH(+) with HemiQ[6] have been observed with an association constant of K-a=(2.5 +/- 1.2)x10(6)Lmol(-1), while the 2:1 ratio complexes of PheH(+) with HemiQ[12] are formed with stepwise association constants of K-1=(9.2 +/- 2.8)x10(4)Lmol(-1) and K-2=(6.4 +/- 0.9)x10(5)Lmol(-1), respectively, which induce a total association constant of K-a=5.9x10(10)L(2)mol(-2). Both the 1:1 and 2:1 complexes have been detected by MS. Quantum chemistry calculations have been used to understand the static structures and thermodynamic stabilities of the supramolecular assemblies.