Molecular Tweezer and Clip in Aqueous Solution: Unexpected Self-Assembly, Powerful Host-Guest Complex Formation, Quantum Chemical 1H NMR Shift Calculation.
The newly prepd. water-sol. naphthalene tweezer 2a (shown as I) and anthracene clip 4a (shown as II; both are substituted with Li methanephosphonate groups in the central spacer unit) undergo an unexpected self-assembly in aq. soln. The highly ordered intertwined structures of the self-assembled dimers [2a]2 and [4a]2 were elucidated by quantum chem. 1H NMR shift calcns. 2A and 4a form extremely stable host-guest complexes with N-methylnicotinamide in MeOH and H2O as well. According to the thermodn. parameters detd. by 1H NMR titrn. expts. at various temps. the self-assembly of 2a and 4a and their strong binding to N-methylnicotinamide obsd. in aq. soln. are enthalpy driven (DH .mchlt. 0); the enthalpic driving force is partially compensated by an unfavorable entropy (TDS < 0). Self-assembly and the host-guest binding are therefore beautiful examples of the nonclassical hydrophobic effect.
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