Monitoring Intramolecular Proton Transfer with Two-Dimensional Infrared Spectroscopy: A Computational Prediction

2015-12-16T21:33:41Z (GMT) by Z. L. Terranova S. A. Corcelli
Proton transfer processes are ubiquitous and play a vital role in a broad range of chemical and biochemical phenomena. The ability of two-dimensional infrared (2D IR) spectroscopy with a carbon–deuterium (C–D) reporter to monitor the kinetics of proton transfer in the model compound malonaldehyde was demonstrated computationally. One of the two carbonyl/enol carbon atoms in malonaldehyde was labeled with a C–D bond. The C–D stretch vibrational frequency provides ∼150 cm<sup>–1</sup> of sensitivity to the two tautomers of malonaldehyde. Mixed quantum mechanics/molecular mechanics simulations employing the self-consistent-charge density functional tight binding (SCC-DFTB) method were used to compute 2D IR line shapes for the C–D stretch of labeled malonaldehyde in aqueous solution. The 2D IR spectra reveal cross peaks from the chemical exchange of the proton. The kinetics for the growth of the cross-peaks (and the decay of the diagonal peaks) precisely match the proton transfer rate observed in the SCC-DFTB simulations.