Mutual induced-fit controlled signal amplification of hydrogen-bonded capsule formation

Mutual induced-fit is well known process in biological system and playing crucial role in enzymatic catalysis, peptide-bond synthesis, protein synthesis, etc horizontal ellipsis , proceeds by mutual interactions of two or more than two components. However, in an artificial system, to mimic such process is challenging, especially by purely organic components. In this report, we have shown importance of mutual induced-fit in signal amplification of hydrogen-bonded capsule formation. Two different types of highly flexible ligands (one N-bridged and another triazine-bridged) are used. N-bridged tripodal ligand acting as clip over the adduct obtained from triazine-bridged ligand, bringing the resultant adduct in the cone-shape conformation. The resulting cone-shape conformation undergo solvent polarity dependent hydrogen-bonded capsule formation as a sole product. In absence of N-bridged tripodal ligand, only 50% capsule formation is observed through 1H NMR at 100 mM concentration. However, in the presence of N-bridged tripodal ligand, organic components undergo mutual interactions to opt the cone-shape conformation and 100% capsule is formed (independent of concentration). The complete process is characterized by IR-spectra, 1H and 13C NMR spectra, concentration dependent 1H NMR titration spectra, 1H-1H COSY, 1H-1H NOESY, DOSY NMR, high resolution ESI mass spectra, and also by energy-minimized structure. Molecular clipping is required for effective hydrogen-bonded molecular capsular formation through dynamic self-assembly in response to the solvent polarity of the surrounding environment.image