Mulder Alart, Juković Amela, van Leeuwen Fijs W B, Kooijman Huub, Spek Anthony L, Huskens Jurriaan, Reinhoudt David N
Laboratory of Supramolecular Chemistry and Technology, MESA+ Research Institute, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands.
Chemistry. 2004 Mar 5;10(5):1114-23. doi: 10.1002/chem.200305567.
Two photoswitchable dithienylethene-tethered beta-cyclodextrin dimers were synthesized to function as host molecules with an externally controllable binding affinity. The cyclodextrin cavities of these dimers are linked through their secondary sides by a photochromic dithienylethene unit that is connected to the secondary rim either directly (4) or through propyl spacers (9). Irradiation with light switches these dimers between a relatively flexible (open) and a rigid (closed) form. The binding properties of the dimers depend on the configuration of the dithienylethene spacer, as is shown by microcalorimetry performed with tetrakis-sulfonatophenyl porphyrin (TSPP) as a guest molecule. The differences in binding properties are most pronounced for the more rigid dimer 4, which binds TSPP 35 times more strongly in the open form (4 a) than in the closed form (4 b). The values found for the enthalpy of binding (deltaH degrees ) indicate that this difference in binding is due to the loss of cooperativity between the two beta-cyclodextrin cavities in the closed form. Molecular modeling shows that 4 b is not able to bind TSPP effectively in both cyclodextrin cavities. The open and closed forms of the more flexible dimer 9 show no substantial difference in their binding of TSPP. Thermodynamic values indicative of strong binding of TSPP by two beta-cyclodextrin cavities were measured for both forms of the dimer, and molecular modeling confirms that both are flexible enough to tightly bind TSPP. The binding differences between the forms of dimer 4 allow the photocontrolled release and uptake of TSPP, which renders control of the ratio of complexed to free TSPP in solution possible.
合成了两种可光开关的二噻吩乙烯连接的β-环糊精二聚体，用作具有外部可控结合亲和力的主体分子。这些二聚体的环糊精空腔通过其二级侧由光致变色二噻吩乙烯单元连接，该单元直接（4）或通过丙基间隔基（9）连接到二级边缘。用光照射可使这些二聚体在相对灵活的（开放）形式和刚性的（封闭）形式之间切换。二聚体的结合特性取决于二噻吩乙烯间隔基的构型，这通过以四磺酸苯基卟啉（TSPP）作为客体分子进行的微量热法得以证明。对于更刚性的二聚体4，结合特性的差异最为明显，其在开放形式（4 a）中结合TSPP的强度比在封闭形式（4 b）中高35倍。结合焓（ΔH°）的值表明，这种结合差异是由于封闭形式下两个β-环糊精空腔之间协同性的丧失。分子建模表明，4 b无法在两个环糊精空腔中有效地结合TSPP。较灵活的二聚体9的开放和封闭形式在其对TSPP的结合上没有实质性差异。对二聚体的两种形式都测量了表明TSPP被两个β-环糊精空腔强烈结合的热力学值，分子建模证实两者都足够灵活以紧密结合TSPP。二聚体4不同形式之间的结合差异使得TSPP的光控释放和摄取成为可能，这使得控制溶液中络合的TSPP与游离的TSPP的比例成为可能。
