Inverse Temperature Dependence of Nuclear Quantum Effects in DNA Base Pairs

Despite the inherently quantum mechanical nature of hydrogen bonding,
it is unclear how nuclear quantum effects (NQEs) alter the strengths
of hydrogen bonds. With this in mind, we use ab initio path integral
molecular dynamics to determine the absolute contribution of NQEs
to the binding in DNA base pair complexes, arguably the most important
hydrogen-bonded systems of all. We find that depending on the temperature,
NQEs can either strengthen or weaken the binding within the hydrogen-bonded
complexes. As a somewhat counterintuitive consequence, NQEs can have
a smaller impact on hydrogen bond strengths at cryogenic temperatures
than at room temperature. We rationalize this in terms of a competition
of NQEs between low-frequency and high-frequency vibrational modes.
Extending this idea, we also propose a simple model to predict the
temperature dependence of NQEs on hydrogen bond strengths in general.