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

摘要

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- = BPh_4～ -, ClO_4～ -, and Cl～-), in acetonitrile (AN) solution, and DMANH～+Br - in water by observing the 15N spin-lattice relaxation caused by the ～(15)N-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～+BPh_4 - > DMANH～ +ClO_4～ - > DMANH～+Br -/H_2O > 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 counterion; (2) the PT time is probably ～10～(-12) s, which confirms the above assumption used for the NMR relaxation data analyses; and (3) fluctuation of the interactions with the solvent or counterion has a significant role in PT. Quantum nuclear effects on the hydrogen bond were also examined.