title: Double-threaded dimer and supramolecular oligomer formed by stilbene modified cyclodextrin: effect of acyl migration and photostimuli.
abstract: We observed changing supramolecular structures of stilbene-α-cyclodextrin (StiO-α-CD) by photoirradiation and migration. Stilbene derivatives show photoinduced isomerization under irradiation with λ = 340 nm to give 2-cis-StiO-α-CD and with λ = 254 nm to give 2-trans-StiO-α-CD. Photoisomerization of StiO-α-CD shows the photostationary state during 30 min. 2D NMR and diffusion coefficient studies revealed that 2-trans-StiO-α-CD forms a double-threaded dimer but 2-cis-StiO-α-CD changes to a supramolecular oligomer by photoirradiation. We found that the mutual migration of a stilbene group (StiO) on α-CD occurs under neutral conditions. The StiO group of α-CD (StiO-α-CD) moves between the C2 and C3 positions on the secondary hydroxyl group of StiO-α-CD (the wider rim of α-CD) to give 3-trans-StiO-α-CD. 3-trans-StiO-α-CD forms a supramolecular oligomer, whereas 3-cis-StiO-α-CD changes to a double-threaded dimer, indicating that 3-StiO-α-CDs gives the opposite results in the supramolecular structures of 2-StiO-α-CDs. The thermal isomerization (migration) is very slow. It takes about 300 h to reach the equilibrium state. Moreover, the migration rate constant (k(trans3→2)) of the trans-StiO group from the C3 position to the C2 position of α-CD is faster than k(trans2→3) from the C2 position to the C3 position of α-CD. On the other hand, k(cis2→3) of the cis-StiO group from the C2 position to the C3 position of α-CD is faster than k(cis3→2) from the C3 position to the C2 position, meaning k(cis2→3) > k(cis3→2), which is the opposite result for k(trans3→2) > k(trans2→3). The formation of a stable double-threaded dimer would suppress the migration of the StiO group of StiO-α-CDs in aqueous solutions.
authors.affiliation: Department of Macromolecular Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Kanaya
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Takashima
authors.forename: Akira
authors.initials: A
authors.lastname: Harada
mesh_terms: D000577:Amides / Q000737:chemistry*; D003505:Cyclodextrins / Q000737:chemistry*; D019281:Dimerization; D007536:Isomerism; D046911:Macromolecular Substances / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D010777:Photochemistry; D013267:Stilbenes / Q000737:chemistry*; D047391:alpha-Cyclodextrins / Q000737:chemistry*
chemical_list: D000577:Amides; D003505:Cyclodextrins; D046911:Macromolecular Substances; D013267:Stilbenes; D047391:alpha-Cyclodextrins