Time-Resolved Measurements of Biological Processes

The detailed knowledge of the different steps of biological processes on a molecular level is one of the ambitious goals of molecular biology. The importance of this field was underlined by the award of the Nobel Prize in chemistry in 1988 to J. Deisenhofer, R. Huber, and H. Michel for the elucidation of the primary steps in photosynthesis and the visual process 

Excitation with polarized light creates a partial orientation of selectively excited molecules. The relaxation rate of these excited molecules and its dependence on the degree of orientation can be studied either by the time-resolved absorption of polarized light by the excited molecules, or by measuring the polarization of the fluorescence and its time dependence [15.130]. 

Probably the most important biochemical process on earth is the photosynthesis within the chlorophyl cells in green plants. Recently, it was discovered 

These examples reveal that these extremely fast biochemical processes could not have been studied without time-resolved laser spectroscopy. It not only provides the necessary spectral resolution but also the sensitivity essential for those investigations. More examples and details on the spectroscopy of ultrafast biological processes can be found in [15.134-15.138]. 

Hemoglobine (Hb) is a protein which is used in the body of mammals for the transportation of O2 and CO2 through the blood circulation. Al- 

Probably the most important biochemical process on earth is the photosynthesis within the chlorophyl cells in green plants. Recently it was discovered that the primary processes within the reaction center of chlorophyl proceeds on a time scale of 30 to 100 fs. The excitation energy is used for a proton transfer which finally delivers the energy for the photosynthetic reaction [15.104]. 

Hemoglobin (Hb) is a protein that is used in the body of mammals for the transportation of O2 and CO2 through blood circulation. Although its structure has been uncovered by X-ray diffraction, not much is known about the structural change of Hb when it absorbs O2 and becomes oxyhemoglobin Hb02, or when it releases O2 

Another example is the femtosecond-transient absorption and fluorescence after two-photon excitation of carotenoids. The excited /3-carotene decays with a time constant of 9 0.2 ps. The energy transfer process from the excited Si state in light-harvesting proteins can be monitored by the observed chlorophyl fluorescence [1537]. 

---