Theoretical study on amphi-ionophorability of peptide nanorings

In order to study amphi-ionophorability in peptide nanorings (PNRs), we calculated the electronic and molecular structures of X/BPNR using a cation of alkaline metal (AM) and alkali earth metal (AEM) atoms or an anion of halogen (HL) atoms as the guest ion X and by changing the number of component amino acid residues (n = 5, 6, 8). Three characteristic clathrate forms, waffle, saturn, and volcano, were found. These forms are well classified in terms of the ratio of the radii of the guest ion X and the host nPNR. We further study the first-optical excitonic state having a spin singlet or triplet multiplicity by UHF and CIS approaches. Photoexcitation tends to expand the pore size of PNR, but the electron correlation weakens the corresponding deformation. Consequently, the optimized forms of the photoexcited X/6PNR clathrate compounds resemble those obtained in the ground state