title: Solvent- and phase-controlled photochirogenesis. Enantiodifferentiating photoisomerization of (Z)-cyclooctene sensitized by cyclic nigerosylnigerose-based nanosponges crosslinked by pyromellitate.
abstract: Cyclic nigerosylnigerose (CNN), a saucer-shaped cyclic tetrasaccharide with a shallow concave surface, was reacted with pyromellitic dianhydride in 1:2 and 1:4 ratios to give two CNN-based polymers of different degrees of crosslinking, both of which swelled upon soaking in water, acting as a ‘nanosponge’ (NS). These NSs evolved several phases from isotropic solution to flowing and rigid gels via suspension by gradually increasing the concentration in water. The CNN-NSs thus prepared effectively mediated the enantiodifferentiating photoisomerization of (Z)-cyclooctene (1Z) to chiral (E)-isomer (1E). The enantiomeric excess (ee) of 1E obtained was a critical function of the solvent composition and the phase evolved at different CNN-NS concentrations in water. In isotropic solution, the enantioselectivity was generally low (−4% to +6% ee) but the chiral sense of 1E was inverted by increasing the methanol content. Interestingly, the product's ee was controlled more dramatically by the phase evolved, as was the case with the cyclodextrin-based nanosponge (CD-NS) reported previously. Thus, the ee of 1E was low in solution and suspension, but suddenly leaped at the phase border of flowing gel and rigid gel to give the highest ee of 22–24%, which are much higher than those obtained with CD-NSs (6–12% ee), revealing the positive roles of the chiral void space formed upon gelation of the crosslinked saccharide polymer.
authors.affiliation: College of Chemistry, State Key Laboratory of Biotherapy, West China Medical School and State Key Laboratory of Polymer Materials Engineering, Sichuan University, 29 Wangjiang Road, Chengdu 610064, China. yangchengyc@scu.edu.cn.
authors.forename: Xueqin
authors.initials: X
authors.lastname: Wei
authors.forename: Wenting
authors.initials: W
authors.lastname: Liang
authors.forename: Wanhua
authors.initials: W
authors.lastname: Wu
authors.forename: Cheng
authors.initials: C
authors.lastname: Yang
authors.forename: Francesco
authors.initials: F
authors.lastname: Trotta
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Caldera
authors.forename: Andrea
authors.initials: A
authors.lastname: Mele
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Nishimoto
authors.forename: Yoshihisa
authors.initials: Y
authors.lastname: Inoue
mesh_terms: D001565:Benzoates / Q000737:chemistry*; D002942:Circular Dichroism; D003432:Cross-Linking Reagents / Q000737:chemistry; D003505:Cyclodextrins / Q000737:chemistry*; D005782:Gels; D005936:Glucans / Q000737:chemistry*; D000432:Methanol / Q000737:chemistry; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry*; D036103:Nanotechnology / Q000379:methods; D010777:Photochemistry / Q000379:methods*; D017319:Photosensitizing Agents / Q000737:chemistry; D011108:Polymers / Q000737:chemistry; D011134:Polysaccharides / Q000737:chemistry; D012997:Solvents / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D014867:Water / Q000737:chemistry
chemical_list: D001565:Benzoates; D003432:Cross-Linking Reagents; D003505:Cyclodextrins; D005782:Gels; D005936:Glucans; D017319:Photosensitizing Agents; D011108:Polymers; D011134:Polysaccharides; D012997:Solvents; C516208:cyclic nigerosylnigerose; D014867:Water; C012018:pyromellitic acid; D000432:Methanol