Diporphyrin tweezer for multichannel spectroscopic analysis of enantiomeric excess

Payne, Daniel T.; Chahal, Mandeep K.; Březina, Václav; Webre, Whitney A.; Ariga, Katsuhiko; D’Souza, Francis; Labuta, Jan and Hill, Jonathan P. (2020). Diporphyrin tweezer for multichannel spectroscopic analysis of enantiomeric excess. Frontiers of Chemical Science and Engineering, 14(1) pp. 28–40.

DOI: https://doi.org/10.1007/s11705-019-1869-1

Abstract

Chiral 1,1’-binaphthyl-linked diporphyrin ‘tweezers’ (R)-1/(S)-1 and the corresponding zinc(II) complexes (R)-2(S)-2 were prepared as chiral host molecules, and their utility for chiral analyses (especially enantiomeric excess (ee) determinations) were evaluated. Tris(1-n-dodecyl)porphyrins were used for the first time as the interacting units. Host capabilities of the diporphyrin tweezers were investigated by titrations with (R,R)- and (S,S)-cyclohexane-1,2-diamine (CHDA). The host molecules could be used as multichannel probes of ee by using UV-vis, circular dichroism (CD), fluorescence emission and 1H nuclear magnetic resonance (1H-NMR) methods. Chiral configurations could also be differentiated using CD or 1H-NMR spectroscopy. All three optical techniques give good resolution of ee with reasonable sensitivity considering the low concentrations used (ca. 10−6 mol·L−1). The ee determination of CHDA enantiomers using NMR spectroscopy is also possible because of the reasonably well separated resonances in the case of (R,R)- and (S,S)-CHDA. Non-metallated (R)-1/(S)-1 hosts could not be used to detect chiral information in a strongly acidic chiral guest. This work demonstrates the utility of 1,1’-binapthyl-linked chiral hosts for chiral analysis of ditopically interacting enantiomers.

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