EXTERNAL INFRARED REFLECTION-ABSORPTION SPECTROMETRY MONOLAYER FILMS AT THE AIR-WATER-INTERFACE

The theory and practice of external infrared reflection absorption spe ctrometry (IRRAS) as applied to monomolecular films at the air-water i nterface are reviewed. The observed IR frequencies for films of amphip hilic species provide information about the conformational states of t he hydrocarbon chains and the hydrogen bonding and ionization states o f the polar head groups, under conditions of controlled surface pressu re. Determination of molecular orientation is also feasible and requir es detailed consideration of the reflection-absorption properties of t he three-phase (air-monolayer-water) system. Current theoretical appro aches are described. Applications of IRRAS to the study of single- and double-chain amphiphiles and proteins are reviewed, and initial excur sions into biochemistry (interfacial enzyme catalysis) and physiology (pulmonary surfactant function) are reported.