Chirality recognition in concerted proton transfer process for prismatic water clusters

Abstract

Proton transfer and chiral conversion via hydrogen bonds (HBs) are important processes in applications such as chiral recognition, enzymatic catalysis, and drug preparation. Herein, we investigate the chiral conversion and interlayer recognition, via concerted intralayer proton transfer (CIPT) processes, of small prismatic water clusters, in the form of bilayer n−membered water rings (BnWRs, n = 4, 5, 6). Density functional theory (DFT) calculations show that despite the small energy variations between the initial and final states of the clusters of less than 0.3 kcal·mol−1, the vibrational circular dichroism (VCD) spectrum provides clear chiral recognition peaks in the range of 3,000 to 3,500 cm−1. The vibrational modes in this region correspond to stretching of intralayer HBs, which produces strong signals in the infrared (IR) and Raman spectra. The electronic circular dichroism (ECD) spectrum also reveals obvious chiroptical characteristics. The molecular orbitals involved in the interlayer interaction are dominated by O 2p atomic orbitals; the energy of these orbitals increased by up to 0.1 eV as a result of the CIPT processes, indicating corresponding recognition between monolayer water clusters. In addition, isotopic substitution by deuterium in the BnWRs results in characteristic peaks in the VCD spectra that can be used as fingerprints in the identification of the chiral structures. Our findings provide new insights into the mechanism of chiral recognition in small prismatic water clusters at the atomic level as well as incentives for future experimental studies.