Interaction between cucurbit[8]uril and HCl salts of 3,4,7,8-tetramethyl-1,10-phenanthroline

To explain 1 H NMR results where two different inclusion orientation isomer complexes of cucurbit[ 8] urils ( Q[ 8], host) and protonated 3,4,7,8-tetramethyl-1,10-phenanthroline ( guest) were observed. The STO-3G and B3LYP/3-21G* calculations were performed on the inclusion complexes of cucurbit[ 8] urils ( Q[ 8], host) and protonated or free 3,4,7,8-tetramethyl-1,10-phenanthroline (guests). The results of ab initio and DFT energy calculations reveal that the "anti-" orientation was a preponderant alternative structure in 1: 2 complexes of Q[ 8] and the guest, and the inclusion complexes were stabilized by protonation of the guest. The pH influence was investigated which further con. rmed these calculation results by electronic absorption spectroscopy.