From helix to macrocycle: anion-driven conformation control of π-conjugated acyclic oligopyrroles.
Anion-responsive pyrrole-based linear receptor oligomers were newly synthesized and their anion-driven dynamic conformation changes were investigated. Phenylene-bridged dimers and a tetramer of dipyrrolyldiketone boron complexes as π-conjugated acyclic anion receptors formed anion-driven helical structures in the solid and solution states. In fact, single-crystal X-ray analyses of the receptor-anion complexes exhibited various helical structures, such as [1+1]- and [1+2]-type single helices and a [2+2]-type double helix according to the lengths of oligomers and the existence of terminal aryl substituents. Anion-binding modes and behaviors of the oligomers in solution state were also examined by (1)H NMR and UV/Vis spectra along with ESI-TOF MS. Differences in the binding modes were observed in the solid and solution states. The oligomers showed augmented anion-binding constants and anion-tunable electronic and optical properties in comparison with the monomer receptor. A negative cooperative effect in the tetramer was observed in the second anion binding of the [1+2]-type single helix due to electrostatic repulsion between two anions captured in the helix. Further, an anion-template coupling reaction from the linear dimer provided a receptor macrocycle, which was obtained as a Cl(-) complex with distinct electronic and optical properties. The macrocycle exhibited extremely high anion-binding constants (>10(10) m(-1) in CH(2)Cl(2)) through multiple hydrogen bonding.
College of Pharmaceutical Sciences, Institute of Science and Engineering, Ritsumeikan University, Kusatsu 525-8577, Japan.
Yohei
Y
Haketa
Hiromitsu
H
Maeda
D000838:Anions / Q000737:chemistry*; D001665:Binding Sites; D018360:Crystallography, X-Ray; D006571:Heterocyclic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D006860:Hydrogen Bonding; D046911:Macromolecular Substances / Q000138:chemical synthesis / Q000737:chemistry*; D008968:Molecular Conformation; D015394:Molecular Structure; D011485:Protein Binding; D011758:Pyrroles / Q000737:chemistry*
D000838:Anions; D006571:Heterocyclic Compounds; D046911:Macromolecular Substances; D011758:Pyrroles