Proton transfer in H5O2+ and H3O2? with an external restraining force

Abstract

mA comparative study between proton transfer in H,OZ and H,O; has been carried out using the 6-31 + G** basis set at the MP level. An external harmonic force is imposed between the two terminal hydrogens (one on either end of the complex) to restrain the H bond lengths to a range where two minima exist in the potential energy surface, while providing the OH, and OH-groups appropriate flexibility to approach one another during the course of transfer. The H bond length in the anion is found to be longer and more linear than that in the cation. Geometries and orientations of the subunits play an important role in determining the H bond length and the nonlinearity of the bond. Similar trends are noted for both the ions as the spring stiffens: The barrier reaches its asymptotic maximum for intermolecular force constants larger than about 7 mdyn/& as do the equilibrium and transition-state values of R(O0). The energy barrier for the anion is higher than that of the cation. For both systems, the intrinsic reaction coordinate divides the transfer process into two consecutive steps: The approach of the two 0 atoms is followed by the actual motion of the proton. In fact, the hydrogen-bonded hydrogen moves upward, perpendicular to the line joining the 0 atoms, during the first step. The first steps account for about 30% of the energy required for proton transfer in the cation, whereas for the anion it is about 45%. 0

Intramolecular Proton Transfer in Mono- and Dihydrated Tautomers of Guanine: An ab Initio Post Hartree−Fock Study

“…As mentioned earlier 24a,b this kind of change is common for biological molecules and is associated with the possibility of a decrease in the value of the proton transfer barrier. Such a conclusion also has been confirmed by recent studies. 24d,e …”

“…An analysis of the structural parameters in hydrogen bonded systems A−H···B (where A and B are heavy atoms which are involved in hydrogen bonding) is crucial for an understanding of the reasons for the lowering of the proton-transfer barrier …”

Rearrangements and tunneling splittings of protonated water dimer

“…Some effort was made in the latter study to interpret the results in terms of tunneling splittings, but the analysis was severely hampered because the tunneling paths could only be guessed at. There have been a number of previous theoretical studies of this system, [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31]63 and Valeev and Schaefer have recently characterized the two lowest-lying stationary points using coupled cluster methods based upon a Bruekner reference determinant. 32 Their results serve as a useful benchmark for the present calculations.…”

Electronic structure calculations of small molecule adsorbates on (110) and (100) TiO2

“…25 His work at the SCF and second order perturbation theory levels would indicate that the barrier height would increase with heavy atom internuclear distance. 26 The barrier to proton transfer for H 2 O 5 ϩ was 7.3…”