Effects of counterion and solvent on proton location and proton transfer dynamics of N-H···N hydrogen bond of monoprotonated 1,8-bis(dimethylamino)naphthalene.

The proton location and proton transfer (PT) dynamics of a hydrogen bond are under the influence of the static and dynamical properties of the solvent and counterions. In the present study, the N–H distances were determined for salts of 1,8-bis(dimethylamino)naphthalene, DMANH+X– (X– = BPh4–, ClO4–, and Cl–), in acetonitrile (AN) solution, and DMANH+Br– in water by observing the 15N spin–lattice relaxation caused by the 15N–1H magnetic dipolar coupling under assumption that the PT time was shorter than the NH reorientation time (∼10–11 s). The obtained N–H distances decreased in the following order: DMANH+BPh4– > DMANH+ClO4– > DMANH+Br–/H2O > DMANH+Cl–, indicating that interactions with the environment affect the PT potentials. To understand the results at the molecular level, Car–Parrinello molecular dynamics simulations were performed for DMANH+, DMANH+ in water, and DMANH+–Cl– ion-pair in AN. The results of simulation suggest that (1) the N–H distance decreases in the presence of a solvent and counteri...