Physikalische und chemische Strukturänderungen in Purpurmembranvarianten

In this work, a process of self-organization of PM during drying to films was observed. It has been found that from a periodicity of about 59 Å a stable lamellar structure with perpendicular to the film surface oriented PM occurs, corresponding to four layers of water molecules between the membranes. In addition, a scattering isotropy occurs during rotation of the sample in the experiment SAXS about an axis perpendicular to the film surface. In can be suggested that PM in the film have a short-range and no long-range order. It can be assumed that these four water layers are 2+2 layers, the first and the second hydration shell of PM. The presented in situ experiments show a weak interaction of PM with the second hydration shell. This can be observed in the drying and freeze-drying experiments. It has been shown that in an aqueous suspension PM outside the immediate water-air interface have chaotic distributions. Inside the interface, the membranes are oriented perpendicular to the water surface because of its hydrophilic and hydrophobic properties. The PM is oriented perpendicular to the air-water interface with their hydrophobic edges. Upon drying the suspension concentrates, the top layer approaches the lower layers and induces the orientation of the next layer. Sedimentation and substrates have no effects on the orientation of the PM during formation of the film from aqueous suspensions, and PM in the films are oriented perpendicular to the film surface in all PM films prepared here. The regular distribution of PM in PM-glycerol films may be the result of a mutual repulsion of the negatively charged membranes. Thus, two effects can be observed: The formation of the preferred orientation of the membranes with respect to the film surface as well as the formation of a stable lamellar structure, which is the regular distribution of PM in films with glycerol. The stability of the lamellar structure with a periodicity of up to about 200 nm is probably due to the high viscosity of glycerol and therefore the lower mobility of PM in the film. According to the current knowledge, it is astonishing that PM spread in films with glycerol not only to almost single-mode periodicity, but also show a preferred orientation. Similar to the case of pure PM-films, a substrate or sedimentation have no effect on the selfassembly of PM in films with glycerol. It was shown that drying of aqueous suspensions of PM in the presence of gelatine at a temperature of the starting suspension of 35°C and at a ratio PM to gelatine of 1/1, the membranes in the dried film form a periodic, lamellar structure and have a preferred orientation. An increase in temperature of the starting suspension result in films without a periodic, lamellar structure, but the PM in these films has a preferred orientation in one spatial direction. In the presence of PVA, the periodicity of the PM of a lamellar structure amounts 47 Å, this is as large as in a film of pure PM, that is, PVA is located outside the PM stacks in the film, while the membranes show a preferred orientation in the film. In this work, the different distributions of PM in films with direct contact between the membranes (PM-PVA films) or without contact (PM and PM-glycerol-gelatin films) were shown. This is important for the further understanding of the properties of PM-films. PM formed various lamellar structures during drying with glycerol, gelatin, or PVA, but all films show the same preferred orientation of PM. The self-assembly of PM upon drying was observed in the presence of these substances, without examining the interaction between PM and these substances, which are often used as matrices for PM-films for various applications. The interaction of PM with a water surface and the interaction between the PM are resulting in the orientation of PM during the drying process, leading to self-assembly of PM. This in turn results in a number of film variants to a monomodal periodicity of PM. These interactions leading to self-assembly are so strong, that they are not affected by the presence of different matrices such as glycerol, gelatin, or PVA in the suspension. In this work, it was demonstrated how a single-point mutation in the core of BR results in PMs undergoing structural changes from a non crystalline state to a 2D-crystalline state, depending on the physicochemical conditions. In BR variant D85T, the primary proton acceptor aspartic acid 85 is replaced by threonine, the equivalent residue in halorhodopsin, which converts BR into a chloride pump. By means of small-angle X-ray scattering (SAXS), it was demonstrated that PM-D85T, non crystalline under most conditions, is converted to a highly ordered hexagonal 2-D crystalline state as soon as the physicochemical conditions favor chloride binding of BR-D85T, i.e., pH values below pH 6 and high salinity. A model is presented which explains the crystallization tendency of PM-D85T in terms of conformational changes on the level of single BR-D85T molecules. Upon two-photon absorption of BR photoproducts outside the classical photocycle occur, changes in the hexagonal lattice of PM take place, but the PM as a whole is preserved. So these photophysical and photochemical induced changes can be used, e.g., for data storage. The present work is not only of theoretical, but also of practical importance. The studies presented here allow the evaluation of the orientation of PM in films and the control of the crystal structure of the membranes at various stages of film production.