Molecular recognition of a cyclophane as a receptor towards arginine methyl ester: Theoretical perspectives

In this study we focus on molecular recognition towards arginine methyl ester with a cyclophane as a receptor. This macrocycle consists of two phenylene-O-phenylene units linked by two EDTA chains and carries four pendant carboxylate groups. To understand the interactions of these systems we performed a conformational search and geometry optimizations with the use of the Density Functional Theory (DFT). We decided to focus on two different scenarios. In the first one, the arginine ester and the cyclophane are not charged. In the second one, both species are ionic and the system as a whole is neutral. The computations revealed that they in fact interact favorably, where the most stable configuration is that in which cationic arginine methyl ester is extended above the cycle and interacts with the pendant deprotonated carboxylate groups.