jp510522z_si_001.pdf (1.73 MB)
Effect of H2 Binding on the Nonadiabatic Transition Probability between Singlet and Triplet States of the [NiFe]-Hydrogenase Active Site
journal contribution
posted on 2015-02-12, 00:00 authored by Danil
S. Kaliakin, Ryan R. Zaari, Sergey A. VarganovWe investigate the effect of H2 binding on the spin-forbidden
nonadiabatic transition probability between the lowest energy singlet
and triplet electronic states of [NiFe]-hydrogenase active site model,
using a velocity averaged Landau–Zener theory. Density functional
and multireference perturbation theories were used to provide parameters
for the Landau–Zener calculations. It was found that variation
of the torsion angle between the terminal thiolate ligands around
the Ni center induces an intersystem crossing between the lowest energy
singlet and triplet electronic states in the bare active site and
in the active site with bound H2. Potential energy curves
between the singlet and triplet minima along the torsion angle and
H2 binding energies to the two spin states were calculated.
Upon H2 binding to the active site, there is a decrease
in the torsion angle at the minimum energy crossing point between
the singlet and triplet states. The probability of nonadiabatic transitions
at temperatures between 270 and 370 K ranges from 35% to 32% for the
active site with bound H2 and from 42% to 38% for the bare
active site, thus indicating the importance of spin-forbidden nonadiabatic
pathways for H2 binding on the [NiFe]-hydrogenase active
site.