Strong Binding Affinity of a Zinc–Porphyrin-Based Receptor for Halides through the Cooperative Effects of Quadruple CH Hydrogen Bonds and Axial Ligation
✍ Scribed by Chi-Hwa Lee; Sangeun Lee; Hongsik Yoon; Woo-Dong Jang
- Publisher
- John Wiley and Sons
- Year
- 2011
- Tongue
- English
- Weight
- 580 KB
- Volume
- 17
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
A new type of host compound (1), tetraphenyl zinc–porphyrin (ZnTPP) that contains four triazole groups at the ortho‐position of each phenyl group, has been synthesized and characterized by using ^1^H, ^13^C NMR, and MALDI‐TOF‐MS analyses. The host–guest complex formation between 1 and halides was investigated by using ^1^H NMR spectroscopy in [D~6~]DMSO. The triazole, benzyl, and phenylene proton signals were shifted upfield by the addition of halides in the form of tetrabutylammonium salts, which implies that the triazole protons in 1 are allocated very closely to the porphyrin ring and are directed toward the binding pocket over the porphyrin ring during the formation of hydrogen bonds. The UV/Vis absorption spectra showed that both the Soret and Q band absorptions of 1 underwent a strong redshift due to the addition of halides. Compound 1 exhibited surprisingly strong binding affinities for the halides, where the association constants for Cl^−^, Br^−^, and I^−^ binding were estimated to be larger than 10^8^, 1.79×10^7^, and 1.84×10^5^ M^−1^, respectively. The UV/Vis absorption changes and the result of competitive titration using 4‐tert‐butylpyridine indicated that the cooperative effects of axial coordination and CH⋅⋅⋅X hydrogen bond interactions resulted in the strong binding affinity of 1 to halides.