Probing the effect of the solution environment on the vibrational dynamics of an enzyme model system with ultrafast 2D-IR spectroscopy

Ultrafast 2D-IR spectroscopy has been applied to study the structure and vibrational dynamics of (mu-C(CH3)(CH2S)(2)(CH2S(CH2)(2)Ph)Fe-2(CO)(5), an organometallic model of the active site of the FeFe[hydrogenase] enzyme. 2D-IR spectra have been obtained in solvents ranging from non-polar to polar and protic. The influence of the solvent bath on vibrational relaxation, including rapid intramolecular population transfer, has been characterized. In addition, the temporal dependence of the 2D-IR lineshape has been used to extract information relating to hydrogen bond-mediated spectral diffusion via the frequency-frequency correlation function. Comparisons with previous 2D-IR studies of hydrogenase model systems offer insights into the dependence of the rate of population transfer upon vibrational mode separation and solvent environment, with important implications for the composition and reactivity of the active site of the enzyme.