Reaction-induced infrared difference spectroscopy

As outlined in the introduction, the goal of reaction-induced infrared -difference spectroscopy is to determine (1) the contribution of single amino acid residues to the mechanism of enzymatic reactions, (2) the interaction of substrates and cofactors with the protein, (3) intermediate states of substrates and cofactors, and (4) structural changes of the protein caused by the interaction. Because only a small part of the total system... 

Zscherp, C. and Barth, A. (2001). Reaction-induced infrared difference spectroscopy for the study of protein reaction mechanisms. Biochemistry 40 1875—1883. 

It is this aspect that makes the combination of infrared (IR) spectroscopy with electrochemical reactions so attractive. The infrared spectrum in the wavelength range from 4 to 20 pm reflects the structural properties of a polypeptide molecule, both for backbone and the side chain conformations. However, the potential of IR spectroscopy is better exploited with reaction-induced IR difference spectroscopy. 

Nabedryk, E., Light-induced Fourier transform infrared difference spectroscopy of the primary electron donor in photosynthetic reaction centers, in Infrared Spectroscopy of Biomolecules, Mantsch, H.H. and Chapman, D., Eds., Wiley, New York, 1996, chap. 3. 

Polarisation modulation infrared rejiection-absorption spectroscopy (PM-IRRAS or JRRAS). Potential modulation IR studies rely on switching the potential at a reflective electrode between rest and active states, generating difference spectra. However, the EMIRS technique has several drawbacks the relatively fast potential modulation requires that only fast and reversible electrochemical process are investigated the absorption due to irreversibly chemisorbed species would be gradually eliminated by the rapid perturbation. Secondly, there is some concern that rapid modulation between two potentials may, to some extent, in itself induce reactions to occur. 

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