Physics > Chemical Physics
[Submitted on 20 Apr 2015 (v1), last revised 18 Jul 2015 (this version, v2)]
Title:Isotopic fractionation in proteins as a measure of hydrogen bond length
View PDFAbstract:If a deuterated molecule containing strong intramolecular hydrogen bonds is placed in a hydrogenated solvent it may preferentially exchange deuterium for hydrogen. This preference is due to the difference between the vibrational zero-point energy for hydrogen and deuterium. It is found that the associated fractionation factor $\Phi$ is correlated with the strength of the intramolecular hydrogen bonds. This correlation has been used to determine the length of the H-bonds (donor-acceptor separation) in a diverse range of enzymes and has been argued to support the existence of short low-barrier H-bonds. Starting with a potential energy surface based on a simple diabatic state model for H-bonds we calculate $\Phi$ as a function of the proton donor-acceptor distance $R$. For numerical results, we use a parameterization of the model for symmetric O-H.... O bonds. We consider the relative contributions of the O-H stretch vibration, O-H bend vibrations (both in plane and out of plane), tunnelling splitting effects at finite temperature, and the secondary geometric isotope effect. We compare our total $\Phi$ as a function of $R$ with NMR experimental results for enzymes, and in particular with an empirical parametrisation $\Phi(R)$, used previously to determine bond lengths.
Submission history
From: Ross McKenzie [view email][v1] Mon, 20 Apr 2015 05:24:17 UTC (33 KB)
[v2] Sat, 18 Jul 2015 02:39:35 UTC (23 KB)
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