| Abstract
| - We have studied surface and spectroscopic properties ofPhotosystem II core complex (PS II CC) for thefirst time in monolayers at the nitrogen/water interface. A newinstrument was thus specially built toperform absorption and fluorescence spectroscopic measurements directlyat the nitrogen/water interface.The effect of initial surface density, incubation time, andcompression speed have been studied. WhenPS II CC was spread at an initial surface pressure of 5.7 mN/m andimmediately compressed at a speedof 40 nm2/molecule·min, it retained its nativespectroscopic characteristics. Even though a slowerspeedof compression (10 nm2/molecule·min) produced morehomogeneous films, the absorption maxima suffereda blue shift, indicating denaturation of PS II CC. Compression ata speed of 80 nm2/molecule·min producedaggregates of intact PS II CC as indicated byΔV−A isotherms, absorption spectra, andfluorescencemicrographs. We also conclude that spreading of PS II CC at aninitial surface pressure of 0.6 mN/mfollowed by a 30 min incubation time is inadequate to maintain PS II CCsurface and spectral properties.Indeed, π−A and ΔV−Aisotherms measured in that condition showed transitions which suggestedthatPS II CC underwent physical changes during compression. Moreover,absorption and fluorescence maximawere blue shifted, indicating that PS II CC is denatured under thatcondition.
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