Supramolecular self-assemblies of beta-cyclodextrins with aromatic tethers: factors governing the helical columnar versus linear channel superstructures.
A series of 6-O-(p-substituted phenyl)-modified beta-cyclodextrin derivatives, i.e., 6-O-(4-bromophenyl)-beta-CD (1), 6-O-(4-nitrophenyl)-beta-CD (2), 6-O-(4-formylphenyl)-beta-CD (3), 6-phenylselenyl-6-deoxy-beta-CD (4), and 6-O-(4-hydroxybenzoyl)-beta-CD (5), were synthesized, and their inclusion complexation behavior in aqueous solution and self-assembling behavior in the solid state were comparatively studied by NMR spectroscopy, microcalorimetry, crystallography, and scanning tunneling microscopy. Interestingly, (seleno)ethers 1-4 and ester 5 displayed distinctly different self-assembling behavior in the solid state, affording a successively threading head-to-tail polymeric helical structure for the (seleno)ethers or a mutually penetrating tail-to-tail dimeric columnar channel structure for the ester. Combining the present and previous structures reported for the relevant beta-CD derivatives, we further deduce that the pivot heteroatom, through which the aromatic substituent is tethered to beta-CD, plays a critical role in determining the helix structure, endowing the 2-fold and 4-fold axes to the N/O- and S/Se-pivoted beta-CD aggregates, respectively. This means that one can control the self-assembling orientation, alignment, and helicity in the solid state by finely tuning the pivot atom and the tether length. Further NMR and calorimetric studies on the self-assembling behavior in aqueous solution revealed that the dimerization step is the key to the formation of linear polymeric supramolecular architecture, which is driven by favorable entropic contributions.
Department of Chemistry, State Key Laboratory of Elemento-Organtic Chemistry, Nankai University, Tianjin 300071, PR China. yuliu@public.tpt.tj.cn
Yu
Y
Liu
Zhi
Z
Fan
Heng-Yi
HY
Zhang
Ying-Wei
YW
Yang
Fei
F
Ding
Shuang-Xi
SX
Liu
Xue
X
Wu
Takehiko
T
Wada
Yoshihisa
Y
Inoue
D001555:Benzene Derivatives / Q000138:chemical synthesis*; D003460:Crystallization; D018360:Crystallography, X-Ray; D003505:Cyclodextrins / Q000138:chemical synthesis*; D019281:Dimerization; D006860:Hydrogen Bonding; D009682:Magnetic Resonance Spectroscopy; D016252:Microscopy, Scanning Tunneling / Q000379:methods; D008958:Models, Molecular; D012996:Solutions / Q000737:chemistry; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D047392:beta-Cyclodextrins
D001555:Benzene Derivatives; D003505:Cyclodextrins; D012996:Solutions; D047392:beta-Cyclodextrins; D014867:Water; C031215:betadex