title: Strong binding affinity of a zinc-porphyrin-based receptor for halides through the cooperative effects of quadruple C-H hydrogen bonds and axial ligation.
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 C-H···X hydrogen bond interactions resulted in the strong binding affinity of 1 to halides.
authors: Department of Chemistry, College of Science, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 120-749, Korea.
authors: Chi-Hwa
authors: CH
authors: Lee
authors: Sangeun
authors: S
authors: Lee
authors: Hongsik
authors: H
authors: Yoon
authors: Woo-Dong
authors: WD
authors: Jang
mesh_terms: D006219:Halogens / Q000737:chemistry*; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D008665:Metalloporphyrins / Q000737:chemistry*; D015394:Molecular Structure; D013056:Spectrophotometry, Ultraviolet; D015032:Zinc / Q000737:chemistry*
chemical_list: D006219:Halogens; D008665:Metalloporphyrins; C017802:zinc hematoporphyrin; D015032:Zinc