title: Regulation of saccharide binding with basic poly(ethynylpyridine)s by H+-induced helix formation.
abstract: A basic host polymer exhibiting pH-regulatable saccharide recognition has been investigated. Poly(m-ethynylpyridine) bearing dialkylamino groups forms helical complexes with saccharides to show induced circular dichroism (ICD). When trifluoroacetic acid was titrated on these complexes, the ICD was gradually enhanced until the amount of the acid reached ca. 0.5 molar equivalence versus the pyridine rings in the polymer, and further addition of the acid suppressed the ICD. The proper addition of the acid also increased the binding constants between the polymer and saccharides. These findings would be due to stabilization of the helical structure consisting of cisoid conformations for each of the adjacent pyridine pairs, which were caused by half-protonation of the pyridine rings. Computational analyses indicated that the pyridinium-pyridine dimeric structure prefers its cisoid conformation to its transoid one.
authors.affiliation: Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama 930-0194, Japan. abeh@ms.toyama-mpu.ac.jp
authors.forename: Hajime
authors.initials: H
authors.lastname: Abe
authors.forename: Nozomi
authors.initials: N
authors.lastname: Masuda
authors.forename: Minoru
authors.initials: M
authors.lastname: Waki
authors.forename: Masahiko
authors.initials: M
authors.lastname: Inouye
mesh_terms: D006601:Hexoses / Q000737:chemistry*; D015394:Molecular Structure; D008970:Molecular Weight; D011108:Polymers / Q000737:chemistry*; D011522:Protons; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry*; D013057:Spectrum Analysis; D017186:Titrimetry; D014269:Trifluoroacetic Acid / Q000737:chemistry
chemical_list: D006601:Hexoses; D011108:Polymers; D011522:Protons; D011725:Pyridines; C507758:ethynylpyridine; D014269:Trifluoroacetic Acid