Abstract

An FT-IR spectrophotometer has been interfaced to a miniaturized surface film apparatus for external reflection studies of insoluble monolayers <i>in situ</i> at the air/water interface. Signal-to-noise ratios of 200:1 were routinely achieved for the CH₂ stretching vibrations of phospholipids. We have monitored, using the acyl chain symmetric CH₂ stretching frequency near 2850 cm⁻¹ as a structural probe, lipid conformational order changes that occur during the surface pressure-induced two-dimensional phase transition in monolayers of 1,2-dipalmitoylphosphatidylserine. In addition, the small volume of the miniaturized film apparatus (30 mL) permitted replacement of H₂O with D₂O in the subphase. This capability, in turn, permits the acquisition of spectral data in the amide I region of proteins. We report the first external reflection FT-IR spectrum of an insoluble protein monolayer. The protein studied is pulmonary surfactant SP-C.

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