Elementary reactions in biology studied with

Elementary reactions in biology, like the transport of protons and electrons, the breaking or formation of a hydrogen bond or the rearrangement of some molecular groups, occur on an ultrashort timescale: 10-14-10-8 s. To study such processes in real time photoactive biomolecules in which the process can be initiated with an ultrashort laserpulse are required. Examples of biological events that are studied in the LCVU include energy and electron transfer in photosynthesis,
isomerization of p-coumaric acid in the Photoactive Yellow Protein, early events in light-driven signal transduction, etc. In a typical experiment, the system is excited with a short laser pulse, the ‘pump’, while the response of the system is monitored by a ‘probe’ pulse that arrives at the same spot of the sample after a well-defined delay. Often the ‘probe’ is a spectrally broad ‘white’ pulse, which
after passage through the sample is dispersed by a spectrograph and imaged on a diode array. By repeating the experiment for different delays of the probe, the spectral evolution of the system under study is obtained. A schematic view of the pump-probe experiment is shown below.

The Biophysics group has recently extended the spectral detection window to the mid-IR (1000-2000 cm-1), which allows us to measure transient absorption changes due to structural changes in chromophores, the response of cofactors and amino acids to electron and proton transfers, etc.

Contact: Rienk van Grondelle, e-mail: R.van.Grondelle@few.vu.nl
Biophysics

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Schematic view of a pump-probe experiment.