摘要
用修饰的α-,β-,γ-环糊精(CDs)的包结增感作用研究(Z)-环辛烯(1Z)向手性(E)-异构体(1E)的超分子对映差向光异构反应。建立定量圆二色(CD)和差圆二色(DCD)公式,研究修饰α-,β-,γ-环糊精衍生物与1Z包结反应的构象、化学量和稳定常数。实验发现结合诱导的CD光谱变化是温度和修饰环糊精浓度的临界函数。同时发现光稳态E/Z随照射时间增长而增加最后达到光稳定状态,但明显依赖于增感剂结构和溶液中甲醇含量,它与环糊精手性空腔被客体1Z占有率有直接关系。考查含o-,m-,p-羧酸甲酯基团的苯甲酸β-环糊精酯衍生物的光增感和对映差向能力,更好地认识到在CDs空腔内的有效光能转换是怎样发生的。用邻苯二甲酸β-环糊精酯的对映体过剩(ee)从2.9%增加到24%。有趣的是产物的ee值与取代基常数(Hammett,σ)间没有明显的关系,却与某些苯甲酸-βCD酯的主体占有率有直接关系,即是通过分析在不同甲醇含量的水溶液中被一些-βCD衍生物增感的对映差向光异构反应中的ee,得出被底物1Z占有主体空腔的百分率。
Supramolecular enantiodifferentiating photoisomerization of （ Z ）-cyclooctene （ 1 Z） to chiral （ E ）-isomer （1E） has been studied via inclusion and sensitization by modified α-,β,γ-cyclodextrins（CDs）. Quantitative circular dichroism（CD） and differential circular dichroism （DCD） formula are established for studing the conformation, stoiehiometry and stability constant of the eomplexation of 1Z with the modified α-,β, and γ-eyelodextrin derivatives. We found experimentally that the CD spectral change induced upon complexation is a critical function of temperature and concentration of modified β-eyclodextrin. In addition, it is found that the photostationary-state E/Z increases with increasing irradiation time to reach a photostationary state, but significantly depends on the sensitizer structure and the methanol content in solution, which is directly related to the occupancy of the CD＇s ehiral cavity by vip I Z. Photosensitizing and enantiodifferentiating abilities of the β-CD-benzoate derivatives, possessing α-,β,γ- methoxyearbonyl group, are examined to better understand how the effective photoenergy transfer occurs inside the CDs cavity, and the enantiomeric excess （ ee ） is enhanced from 29 % to 24% by using the β-CD-phthalate. Interestingly, the product＇ s ee obtained did not show a clear relationship with the substituent＇ s constant （ Hammett＇ s a ）, it is found to be directly related to the host occupancy for some β-CD-benzoate, i.e. the percentage of host cavity occupied by the substrate l Z through the analyses of the ee obtained upon the enantiodifferentiating photoisomerization sensitized by several β-CD derivatives in aqueous solutions of varying methanol contents.
出处
《化学进展》
SCIE
CAS
CSCD
北大核心
2006年第5期533-541,共9页
Progress in Chemistry
基金
国家自然科学基金项目资助(No.852982
8900872
9873062)
关键词
修饰环糊精
超分子光化学
不对称合成
对映差向光异构反应
光增感作用
modified cyclodextrins
supramolecular photochemistry
asymmetric synthesis
enantiodifferentiating photoisomerization
photosensitization
