Protonation State and Proton Conductivity Mechanism in Supramolecular Three-Armed Histamine-Based Derivative Self-Assembly

N,N ',N ''-Tris(2-(1H-imidazole-5-yl)ethyl)benzene-1,3,5-tricarboxamide (A3), a histamine-based derivative with three imidazole units with a distinctive hydrogen-bond packing structure, can stimulate proton conductivity. Here, we performed molecular dynamics simulations to clarify the molecular responses to the possibility of proton transfer of A3 in various stimuli. A P-form model represents the protonation-state of the molecule. The molecular motions and conformational changes of the P-form model after increasing temperatures indicated that the tau(1) torsion angle of the imidazole ring shifted to a lower angle relating to the changes in N(Im)-NH(Im) pair interacting sites. In the methanol-assisted system (M-form), the anchoring imidazole unit at the tau(1) torsion angle was significantly altered with an increase in the torsion angle distribution. The intermolecular hydrogen bond interaction between A3 molecule and proton transporter solvents was analyzed. Mean squared displacements by the Einstein relation of water and methanol in the M-form increased when the system was heated up to 70 degrees C. More settled methanol surrounding A3 in the M-form according to the hydrogen bond formation implies that the supramolecular organized structure in the M-form remarkably supported the proton transfer possibility.