Abstract
We report on the design and synthesis of a new type of 4-aminoquinoline-based molecular tweezer 1 which forms a stable host-guest complex with protoporphyrin IX (PPIX) via multiple interactions in a DMSO and HEPES buffer (pH 7.4) mixed solvent system. The binding constant for the 1 : 1 complex (K 11) between 1 and PPIX is determined to be 4 × 106 M-1. Furthermore, 1 also forms a more stable complex with iron(iii) protoporphyrin IX (Fe(iii)PPIX), the K 11 value for which is one order of magnitude greater than that for PPIX, indicating that 1 could be used as a recognition unit of a synthetic heme sensor. On the other hand, the formation of the stable PPIX·1 complex (supramolecular photosensitizer) prompted us to apply it to photodynamic therapy (PDT). Cell staining experiments using the supramolecular photosensitizer and evaluations of its photocytotoxicity indicate that the PDT activity of PPIX is improved as the result of the formation of a complex with 1.
Highlights
Supramolecular chemistry and host–guest chemistry have primarily drawn their inspirations from molecular interactions of biomolecules such as proteins, DNA, RNA, lipids, and related molecules.[1,2] Over the past three decades, a variety of synthetic host–guest systems have been developed
We report on the design and synthesis of a new type of 4-aminoquinoline-based molecular tweezer 1 which forms a stable host–guest complex with protoporphyrin IX (PPIX) via multiple interactions in a DMSO and HEPES buffer mixed solvent system
Ca. 50% cell death was induced by PPIX alone when the photoirradiation time was extended to 4 min (Fig. 10 and S33 in the Electronic supplementary information (ESI)†), the lowered photodynamic therapy (PDT) activity of PPIX could be attributed to the weak interactions between the anionic PPIX and negatively charged cell surface rather than the aggregation of PPIX on the cell membrane. These results demonstrate that the PDT activity of PPIX is improved by formation of the complex with 1, indicating the usefulness of such supramolecular approaches based on non-covalent interactions for PDT.[96,97,106]
Summary
Supramolecular chemistry and host–guest chemistry have primarily drawn their inspirations from molecular interactions of biomolecules such as proteins, DNA, RNA, lipids, and related molecules.[1,2] Over the past three decades, a variety of synthetic host–guest systems have been developed. Cell staining experiments using the supramolecular photosensitizer and evaluations of its photocytotoxicity indicate that the PDT activity of PPIX is improved as the result of the formation of a complex with 1.
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