Chiral Discrimination of Diamines by a Binaphthalene-Bridged Porphyrin Dimer

Abstract

A pair of 1,1'-binaphthalene-bridged bisporphyrins, (R)- and (S)-H1, were designed to examine their chiral discrimination abilities toward a range of model diamines by using UV-vis absorption, CD, and H NMR spectroscopy with the assistance of DFT molecular modeling. The spectroscopic titrations revealed that (R)-/(S)-H1 could encapsulate (R)-/(S)-DACH and (R)-/(S)-PPDA in the chiral bisporphyrin cavities, leading to the selective formation of sandwich-type 1:1 complexes via dual Zn-N coordination interactions. In particular, the chiral recognition energy (ΔΔG°) toward (R)-/(S)-DACH was evaluated to be -4.02 kJ mol. The binding processes afforded sensitive CD spectral changes in response to the stereostructure of chiral diamines. Remarkable enantiodiscrimination effects were also detected in the NMR titrations of (R)-/(S)-H1, in which the nonequivalent chemical shift (ΔΔδ) can reach up to 0.57 ppm for (R)-/(S)-DACH. However, due to the large steric effect, another chiral diamine ((R)-/(S)-DPEA) could not be sandwiched in the chiral bisporphyrin cavity; therefore, (R)-/(S)-DPEA could hardly be discriminated by (R)-/(S)-H1. The present results demonstrate a chiral bisporphyrin host with integrated CD and NMR chiral sensing functions and also highlight the binding-mode-dependent character of its enantiodiscrimination performance for different chiral guests.

Estimation of Enantiomeric Excess Based on Rapid Host–Guest Exchange

“…Porphyrin dimers are well established as probes for chiral analyses. Therefore, in this case, we had the additional benefit of a comparison of our new results with a very similar and recently reported meso-tetraphenylporphyrin (TPP) analogue of our system [88], which was also used for chiral analysis. Lu et al [88] observed easy discrimination of the enantiomers of cyclohexane-1,2-diamine (CHDA), using their porphyrin-substituted 1,1 -binaphthyl dimer host, and was mirrored in our report using NMR spectroscopy and other methods.…”

“…Therefore, in this case, we had the additional benefit of a comparison of our new results with a very similar and recently reported meso-tetraphenylporphyrin (TPP) analogue of our system [88], which was also used for chiral analysis. Lu et al [88] observed easy discrimination of the enantiomers of cyclohexane-1,2-diamine (CHDA), using their porphyrin-substituted 1,1 -binaphthyl dimer host, and was mirrored in our report using NMR spectroscopy and other methods. Our report includes additional analytical possibilities for ee determination by using electronic spectrophotometry including UV-vis, CD and fluorescence emission methods.…”

Recognition and Sensing of Chiral Organic Molecules by Chiral Porphyrinoids: A Review

“…Lu et al, reported in 2017 a chiral binaphthalene-bridged bisporphyrin with C2 symmetry (Figure 17a, XX) able to recognize chiral diamines in chloroform [80]. The CD spectra of the two enantiomer pairs point out a mirror image with a bisignate couplet in the porphyrin Soret region (Figure 17b).…”

Benchmarking computational methods and influence of guest conformation on chirogenesis in zinc porphyrin complexes

“…[12][13][14][15][16][17][18][19][20][21][22][23][24][25] Initially, mono-porphyrins were used as chiral sensors, further bis-and tris-porphyrins as well as corresponding supramolecular assemblies were also applied for this purpose. [26][27][28][29][30][31][32][33] Generally, the chirality of the system is probed by circular dichroism (CD) spectroscopy. 12,[20][21][22][23] Recently, a combination of experimental and computational studies on the complexation of a chiral zinc(II) porphyrin tweezer with achiral aliphatic diamines highlighted a critical role played by the diamine guest in modulating the relative orientation of the two porphyrin rings and hence in coupling the electronic transition moments.…”