ORGANIZATION OF A GLOBULAR PROTEIN FILM ON SOLID-SURFACES - AN X-RAY PHOTOELECTRON-SPECTROSCOPY STUDY

The organization of legumin films deposited on different solid substra tes using the Langmuir-Blodgett technique has been studied by X-ray ph otoelectron spectroscopy (XPS). The XPS data provide information on th e identity of the chemical elements present as well as on chemical bon ding. From the decomposed XPS C 1s spectra, the different types of car bon (peptidic, aliphatic etc.) have been identified. The variation in atomic ratios as a function of the take-off angle shows a structural o rientation of the protein films in which the hydrophobic aliphatic ami no acids are at the external surface whereas the hydrophilic amino aci ds are oriented towards the solid substrate. Moreover, the attenuation in the S 2p signal intensity with decreasing take-off angle due to th e protein layer suggests that the adsorbed protein forms a continuous overlayer on a glass substrate whereas the weak dependence of the F 1s signal intensity with the take-off angle suggests an incomplete cover age of the polytetrafluoroethylene substrate.