Twist-Turn-Twist Motif Chaperoned Inside Molecular Baskets.

Two molecular baskets , each with three ()glutamic acids at its rim, were found (NMR, ITC) to complex diammonium alkanes (HN(CH)NH, = 710) giving ternary [-⊂] assemblies ( = 1010 M). From the magnetic perturbation of proton nuclei (H NMR, NICS), we deduced that each guest assumed a U shape within the binary complex, [-⊂]. Two ammonium groups were bound in the "anionic nest" at the top of , while the hydrocarbon chain resided in its nonpolar cavity. From detailed ITC analyses, we showed that the binary complex [-⊂] forms first and then another capped [-⊂] to give [-⊂], via interactions of the carboxylates at the rims with ammoniums on the guest. Long-range NOEs revealed that U-shaped and coiled into highly strained twist-turn-twist formations, for the first time observed within an abiotic host while curiously resembling helix-turn-helix motif found in DNA binding proteins.