1 research outputs found
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-bisÂ(dimethylamino)Ânaphthalene,
DMANH<sup>+</sup>X<sup>–</sup> (X<sup>–</sup> = BPh<sub>4</sub><sup>–</sup>, ClO<sub>4</sub><sup>–</sup>, and
Cl<sup>–</sup>), in acetonitrile (AN) solution, and DMANH<sup>+</sup>Br<sup>–</sup> in water by observing the <sup>15</sup>N spin–lattice relaxation caused by the <sup>15</sup>N–<sup>1</sup>H magnetic dipolar coupling under assumption that the PT time
was shorter than the NH reorientation time (∼10<sup>–11</sup> s). The obtained N–H distances decreased in the following
order: DMANH<sup>+</sup>BPh<sub>4</sub><sup>–</sup> > DMANH<sup>+</sup>ClO<sub>4</sub><sup>–</sup> > DMANH<sup>+</sup>Br<sup>–</sup>/H<sub>2</sub>O > DMANH<sup>+</sup>Cl<sup>–</sup>, 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<sup>+</sup>, DMANH<sup>+</sup> in water, and DMANH<sup>+</sup>–Cl<sup>–</sup> 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<sup>–12</sup> 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