Surface pressure induced structural effects in photosynthetic reaction center Langmuir-Blodgett films

The structural modifications of photosynthetic reaction centers from Rhodobacter sphaeroides arranged in Langmuir films and after deposition onto solid substrate have been investigated as well as the variations in protein orientation as a function of surface pressure. While at low surface pressure (15-25 mN/m) protein integrity appears to be affected by the action of the surface tension, as results from the film behavior at the air-water interface and from optical spectroscopy data. When the surface pressure (30-45 mN/m) is increased, protein structure is much better preserved. Moreover, at those deposition pressures, the film is characterized not only by a higher surface density but also by an increased anisotropy, as revealed by polarized absorption spectroscopy and confirmed by optical ellipsometry. Measurements of water content desorption in deposited films by means of a gravimetric transducer have consistently confirmed the preservation of protein structure at higher surface pressures.