Thermodynamics and Structures of Complexation between Tetrasulfonated 1,5-Dinaphtho-38-crown-10 and Diquaternary Salts in Aqueous Solution

The
readily available recognition motifs with high affinity and
selectivity can undoubtedly expedite the development of host–guest
chemistry from fundamental research to practical application in miscellaneous
fields. In this work, a series of guest-mediated [2]­pseudorotaxanes
are successfully constructed by the incorporation of tetrasulfonated
1,5-dinaphtho-38-crown-10 (14–) with
three kinds of dicationic substrates, i.e., the diquaternary salts
of 4,4′-bipyridine, 1,10-phenanthroline, and 2,7-diazapyrene,
which are comprehensively explored by means of UV/vis, 1H NMR spectra, X-ray crystallography, and microcalorimetric titrations.
Significantly, the interpenetration of 14– with N,N′-dimethyl-2,7-diazapyrenium
salt (DMDAP2+) gives an extraordinarily strong association
constant (Ka) up to 108 M–1 order of magnitude in water. Moreover, the spectroscopic
and crystallographic analyses jointly demonstrate that there is a
competitive binding process in the complexation of 14– with DMDAP2+ and methyl viologen (MV2+), in which DMDAP2+ is internally encapsulated
in the cavity of 14–, whereas MV2+ is externally embedded in the crystallographic lattice to
form the ternary supramolecular assembly of MV2+·DMDAP2+⊂14–. We also envision
that the Ka gradient obtained in our systematic
work illustrates a new and elegant strategy for attaining multicomponent
nanomaterials engineered at a molecualr level.