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Issue 15, 2014
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Acyclic CB[n]-type molecular containers: effect of solubilizing group on their function as solubilizing excipients

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Abstract

We report the synthesis and X-ray crystal structures of three acyclic CB[n]-type molecular containers (2a, 2h, 2f) that differ in the charge on their solubilizing groups (SO3, OH, NH3+). The X-ray crystal structures of compounds 2h and 2f reveal a self-folding of the ArOCH2CH2X wall into the cavity driven by π–π interactions, H-bonds and ion–dipole interactions. The need to reverse this self-folding phenomenon upon guest binding decreases the affinity of 2h and 2f toward cationic guests in water relative to 2a as revealed by direct 1H NMR and UV/Vis titrations as well as UV/Vis competition experiments. We determined the pKa of 6-aminocoumarin 7 (pKa = 3.6) on its own and in the presence anionic, neutral, and cationic hosts (2a: pKa = 4.9; 2h: pKa = 4.1; 2f, pKa = 3.4) which reflect in part the relevance of direct ion–ion interactions between the arms of the host and the guest toward the recognition properties of acyclic CB[n]-type containers. Finally, we showed that the weaker binding affinities measured for neutral and positively charged hosts 2h and 2f compared to anionic 2a results in a decreased ability to act as solubilizing agents for either cationic (tamoxifen), neutral (17α-ethynylestradiol), or anionic (indomethacin) drugs in water. The results establish that acyclic CB[n] compounds that bear anionic solubilizing groups are most suitable for development as general purpose solubilizing excipients for insoluble pharmaceutical agents.

Graphical abstract: Acyclic CB[n]-type molecular containers: effect of solubilizing group on their function as solubilizing excipients

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Publication details

The article was received on 30 Dec 2013, accepted on 21 Feb 2014 and first published on 21 Feb 2014


Article type: Paper
DOI: 10.1039/C3OB42603C
Citation: Org. Biomol. Chem., 2014,12, 2413-2422
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    Acyclic CB[n]-type molecular containers: effect of solubilizing group on their function as solubilizing excipients

    B. Zhang, P. Y. Zavalij and L. Isaacs, Org. Biomol. Chem., 2014, 12, 2413
    DOI: 10.1039/C3OB42603C

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