Laser trapping-induced assembling and crystallization of cyclodextrins and their application to chiral photochemistry
|關鍵字:||雷射補陷;環糊精;結晶化;掌性光化學;Laser trapping;cyclodextrin;crystallization;chiral photochemistry|
We succeeded in demonstrating laser trapping-induced assembling and crystallization of beta- or gamma-cyclodextrin (β- or γ-CD), 2-anthracenecarboxylate (2-AC), and their inclusion complexes in H2O and D2O, and performed its chiral photodimerization reaction. When an intense continuous-wave near-infrared laser beam was focused at an air/solution interface of each sample solution, their assembling or crystallization was always induced even in unsaturated solution. For β- or γ-CD in H2O and D2O solutions, laser trapping provided either plate-like or prism-like crystal at the focus, depending on laser power and initial solution concentration. Considering their morphology, crystallization and dissolution behaviors of each polymorph, a novel crystal form of CDs is considered to be realized by laser trapping. For 2-AC in base aqueous solution, needle-like crystal was always induced by laser trapping at the focus. Thus, we succeeded for the first time in demonstrating laser trapping-induced crystallization of organic compounds except amino acids. For mixed solutions of γ-CD and 2-AC, laser irradiation led to assembling and/or crystallization at/around the focus. We performed chiral photodimerization reaction for the resultant assemblies and crystals under halogen lamp illumination. Although further investigation should be necessary, we found that the enantiomeric excess of photoproducts and the ratio of relative orientation of 2-AC inside γ-CD were different from those reported on conventional photodimerization reaction. The dynamics and mechanism of the laser trapping-induced crystallization and the chiral photodimerization reaction are discussed in terms of local concentration increase, dense cluster domain formation, and cluster structure in the dense domain.