Oriented circular dichroism analysis of chiral surface-anchored metal-organic frameworks grown by liquid-phase epitaxy and upon loading with chiral guest compounds
Weidler, Peter G.
Ulrich, Anne S.
Wöll, Christof H.
KAUST DepartmentAdvanced Membranes and Porous Materials Research Center
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AbstractOriented circular dichroism (OCD) is explored and successfully applied to investigate chiral surface-anchored metal-organic frameworks (SURMOFs) based on camphoric acid (D- and Lcam) with the composition [Cu2(Dcam) 2x(Lcam)2-2x(dabco)]n (dabco=1,4-diazabicyclo- [2.2.2]-octane). The three-dimensional chiral SURMOFs with high-quality orientation were grown on quartz glass plates by using a layer-by-layer liquid-phase epitaxy method. The growth orientation, as determined by X-ray diffraction (XRD), could be switched between the  and  direction by using either OH- or COOH-terminated substrates. These SURMOFs were characterized by using OCD, which confirmed the ratio as well as the orientation of the enantiomeric linker molecules. Theoretical computations demonstrate that the OCD band intensities of the enantiopure [Cu2(Dcam)2(dabco)] n grown in different orientations are a direct result of the anisotropic nature of the chiral SURMOFs. Finally, the enantiopure [Cu 2(Dcam)2(dabco)]n and [Cu2(Lcam) 2(dabco)]n SURMOFs were loaded with the two chiral forms of ethyl lactate [(+)-ethyl-D-lactate and (-)-ethyl-L-lactate)]. An enantioselective enrichment of >60 % was observed by OCD when the chiral host scaffold was loaded from the racemic mixture. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
SponsorsThis work was funded by the Deutsche Forschungsgemeinschaft (DFG) through SPP 1362 and through the Center for Functional Nanostructures (CFN, subproject C3.3). Z.G.G. and Z.W. are grateful for PhD fellowships donated by the China Scholarship Council (CSC). H.G. thanks the Landesstiftung Baden-Wurttemberg GmbH for financial support.
JournalChemistry - A European Journal