PM IRRAS Studies of Organized Molecular Films at a Gold Electrode Surface

Abstract

This feature article illustrates the potential of polarization modulation infrared reflection absorption spectroscopy (PM IRRAS) to provide molecular-level information about the structure, orientation and conformation of constituents of thin films at electrode surfaces. PM IRRAS relies on the surface selection rules stating that the p-polarized IR beam is enhanced, while the s-polarized beam is attenuated at the metal surface. The difference between p- and s-polarized beams eliminates the background of the solvent and provides IR spectra at a single electrode potential. In contrast, two other popular in situ IR spectroscopic techniques, namely, subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) and surface-enhanced infrared absorption spectroscopy (SEIRAS), provide potential difference spectra to remove the signal from the bulk solution. In this feature article, we provide a brief tutorial on how to run the PM IRRAS experiment and describe the methods used for background elimination first. The application of the PM IRRAS in the biomimetic research is then illustrated by three examples: construction of a tethered bilayer, reconstitution of colicin into a phospholipid bilayer and determination of the orientation of nucleolipids in a monolayer assembled at a gold electrode surface. Finally, the structural changes of graphene oxide during its electrochemical reduction are described to highlight the promising application of PM IRRAS in materials science.

Keywords

polarization modulation infrared reflection absorption spectroscopy / biomimetic membranes / graphene oxide reduction

Conflict of interest

The authors declare that they have no conflict of interest.

Acknowledgments

This research was funded by Discovery Grants from the Natural Sciences and Engineering Research Council of Canada (JL: RGPIN-2022-03958; AC: RGPIN-2022-04238). A. Chen acknowledges NSERC and the Canada Foundation for Innovation (CFI) for the Canada Research Chair Award in Electrochemistry and Nanoscience. JL expresses his gratitude to Professor Ian Burgess for discussion of recent developments in SEIRAS.

Data availability:

This review does not involve the use of primary data. All information is based on previously published studies.

Author contribution

Jacek Lipkowski: Conceptualization (Lead), Formal analysis (Lead), Writing - original draft (Lead), Writing - review & editing (Lead); Zhang-Fei Su: Data curation (Equal), Formal analysis (Equal), Writing - original draft (Equal), Writing - review & editing (Equal); Ai-Cheng Chen: Conceptualization (Equal), Supervision (Equal), Writing - review & editing (Equal)

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