Fourier transform infrared spectroscopy (FTIR spectroscopy) is a method of molecular spectroscopy which is used for study of vibrational properties of molecules. The absorption of infrared radiation excites vibrational transitions of molecules.
The positions of an infrared absorption bands are determined by the vibrating masses and the type of bond (single, double, triple), as well as by the intra- and intermolecular environment and by coupling with other vibrations.
Infrared spectroscopy provides an opportunity to study vibrations of pigments, quinones and protein matrix of reaction centers of photosynthesis. In particular, light-induced differential FTIR spectroscopy has a very high sensitivity to molecular interactions, allowing to identify changes of individual chemical bonds in the chromophores and the protein subunits of the photosynthetic reaction centers in response to the electron transfer and charge separation.
The figure shows the scheme of measurement of the light-induced differential FTIR spectrum.
Adapted from the Introduction to Fourier Transform Infrared Spectrometry, 2001 Thermo Nicolet corporation.
In photosynthesis, FTIR spectroscopy is widely used for the study of:
- the secondary structure of proteins;
- structure and transformations of active sites of enzymes;
- interactions of the electron transfer cofactors with protein environment in photosynthetic reaction centers;
- molecular mechanism of functioning of photosystem 2 oxygen evolving complex;
- proton transfer coupled to electron transfer;
- properties of metal ligands;
- properties and role of water molecules in the structure of photosynthetic complexes.
During the school it is planned to measure the infrared absorption spectrum of the reaction center (RC) of purple bacterium Rhodobacter (Rb.) sphaeroides R‑26, a light-induced differential FTIR spectrum of formation of charge-separated state P+QA− in Rb. sphaeroides R‑26 RCs and perform an assignment of major IR bands with appropriate molecular groups.
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