Relevance of protein thin films prepared for attenuated total reflection Fourier transform infrared spectroscopy: Significance of the pH

Amide hydrogen-deuterium exchange rates were recorded on thin lysozyme films by attenuated total reflection Fourier transform infrared spectroscopy as a function of the pH of the solution from which the films were prepared. We describe the appropriate spectral corrections for atmospheric water absorption and for Lateral side-chain contribution in the amide I/amide II region required to correctly evaluate the exchange rate from the amide II integrated intensity decrease. We show that the pH dependence of the exchange rate in our experimental conditions (0.4 g water/g protein) parallels the solution behavior. This observation confirms that the technique can be used to monitor pH-sensitive effects and allows exchange curves to be made which include most of the protein amide protons.