Cyclophanes circular dichroism

As usual in stereochemical research, four main approaches have been applied to the problem of assigning chiralities to optically active cyclophanes. They are listed in order of their reliabilities i) anomalous X-ray diffraction (Bijvoet method), ii) chemical correlations with compounds of known chiralities (preferably established by the Bijvoet method), iii) kinetic resolutions and/or asymmetric syntheses, iv) interpretation of chiroptical properties (mainly circular dichroism) on the basis of (sector) rules including theoretical methods. 

Unique inclusion behavior in reflection of the induced-fit binding mechanism is observed when an organic stock solution of octopus cyclophane 3 is injected into an aqueous medium containing ANS for the host-guest complexation study [17], A circular dichroism (CD) spectrum does not undergo any change for 3 upon complexation with ANS, indicating that the conformation around l-... 

Forman, J. E., Barrans, R. E., Dougherty, D. A., Circular-dichroism studies of molecular recognition with cyclophane hosts in aqueous-media. J. Am. Chem. Soc. 1995, 117, 9213-9228. 

Recent Theoretical and Experimental Advances in the Electronic Circular Dichroisms of Planar Chiral Cyclophanes... 

Keywords Chiroptical properties, Electronic circular dichroisms, Planar chirality, Quantum chemical calculations, Cyclophane... 

Grimme S, Bahlmann A (2004) Electronic circular dichroism of cyclophanes. In Gleiter R, Hopf H (eds) Modem cyclophane chemistry. Wiley-VCH, Weinheim, pp 311-336... 

Mori T, Inoue Y, Grimme S (2007) Quantum chemical study on the circular dichroism spectra and specific rotation of donor-acceptor cyclophanes. J Phys Chem A 111 7995-8006... 

Fig. 16A-D. Mechanical switching in rotaxanes. A Rotaxanes may exist in isomeric states by the movement of the ring component between dissymmetric sites on the string component. B A redox- or pH-switchable [2]rotaxane. While the cyclophane complexes the native benzidine site (spectrum, curve a), the reduced or protonated benzidine repels the cyclophane, causing it to move to the dioxybiphenylene site (spectrum, curve b). C An azobenzene-based switchable [2]rotaxane. The cyclodextrin ring complexes the azobenzene site in the trans-state, but it is repelled from the ds-azobenzene. The state of the system is measurable by circular dichroism (plot). D A pH-switchable rotaxane. When the amine on the string component is protonated, it complexes the crown ether ring by hydrogen-bonding interactions (40a). When the amine is deprotonated, however, the ring component moves to the bipyridinium unit, where it is complexed by n donor-acceptor interactions (40b). The plots in B and C are adapted from [67] and [69], respectively, with permission...

Griinine, S. and Bahlmann, A., Electronic circular dichroism of cyclophene, in Modem Cyclophane Chemistry, Gleiter, R. and Hopf, H., Eds., Wiley-VCH Verlag GmbH, Weinheim, 2004, pp. 311. 

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