It is very intriguing to study the mechanisms of reactions in biological systems as compared to similar reactions in gas phase, solution or solid state environment. Proteins feature a hierarchy of structural elements which is reflected in a hierarchy of intrinsic dynamics. Thus the combination of molecular physical and biochemical processes - on time scales from femtoseconds to seconds - becomes most complex and allows the adaptation to a wide field of biological functions at different external conditions. A crucial role for the course and outcome of a specific reaction is played by the static and dynamic cofactor-protein interaction.
Our contribution to this field concentrates on the study of light induced processes in a number of biologically relevant systems. Triggering the process by very short (fs-ps) laser pulses allows to study the ultrafast chemical and physical processes that determine the fate of the reaction on much longer, "biologically significant" time scales. We employ pump/probe femtosecond time resolved absorption experiments in a wide spectral range, i.e. in the UV/VIS regime addressing the dynamics of chromophore electronic states and in the mid-IR regime addressing the ultrafast dynamics of vibrational states of the chromophore and of its ligands resp. its protein environment. The ultrafast IR-method is of high potential. It yields additional information that cannot be obtained easily by transient absorption spectroscopy of electronic states. Most important in this respect is information on reaction induced structural dynamics via changes in the transient vibrational spectra as well as changes of the vibrational transition dipole vector utilizing polarized light. Further important processes resp. parameters include energy redistribution and vibrational relaxation as well as hydrogen bonding and protonation state.