Studies of interfacial organizations and interactions of multi-component phospholipid membranes
by Zhining Wang
xix, 222 p. : ill. ; 30 cm
This thesis is mainly concerned with the effects of monoglycerides (MG), fullerene and endohedral metallofullerenes (EMFs) on the phospholipid membranes at the liquid/solid and gas/liquid interfaces by using dissipative quartz crystal microbalance (QCM) and Langmuir monolayer techniques. 2...[ Read more ]
This thesis is mainly concerned with the effects of monoglycerides (MG), fullerene and endohedral metallofullerenes (EMFs) on the phospholipid membranes at the liquid/solid and gas/liquid interfaces by using dissipative quartz crystal microbalance (QCM) and Langmuir monolayer techniques.
Firstly, the effects of the unsaturation degree and length of the MG’s chain on the adsorption behaviors of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC)/MG vesicles at Tris buffer/SiO2 interface have been studied using dissipative QCM. The results were thoroughly analyzed from the molecular geometry viewpoint, namely the unsaturation degree and length of the hydrocarbon chain. Furthermore, DPPC/MG Langmuir monolayers were analyzed to understand the mechanical properties of the mixed monolayers and the interaction between the binary components. It was revealed that both the unsaturated and short chain MG interfere the close packing of the DPPC molecules in the monolayer and bilayer, resulting in a decrease of the phase transition temperature and the elasticity of the DPPC membrane. Consequently, the MG molar fraction in the binary system for vesicles rupture and SLBs formation increases in a consequence of XMO (XMO = 0.3) < XML (XML = 0.6) < XMM (XMM = 0.8) < XMS (intact vesicle adsorption). This study provided a fundamental linkage between the mechanical properties of the monolayers and bilayer vesicles. Both the mixed bilayers and monolayers could be used as model systems to understand the effect of MG with different chain structures on the phospholipid biomembranes.
Secondly, with the combined Langmuir monolayer study and AFM imaging of the C60, Dy@C82, and Sc3N@C80 (Ih) embedded DPPC or 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) monolayers, a systematic analysis of the effects of empty fullerene and EMFs on the phospholipid membranes have been carried out. As C60 possesses a high symmetrical spherical structure, it is found that the C60 towers in phospholipid monolayer keep their structures and size under compression till they are extruded from the DPPC monolayer at very high surface pressure (≥ 60 mN/m). The presence of C60 was negligible influence on the isotherms and mechanical properties of the DPPC/C60 monolayers even at a molar ratio as high as XC60=0.3. However, the embedment of Dy@C82 is found to bring the most prominent effect on the properties of the DPPC monolayer. Insertion of Dy@C82 dramatically decreases the elasticity of the film and makes the mixed film more compressible, because of the peculiar characteristics of Dy@C82 such as an ellipsoidal structure and a large dipole moment. Under compression, Dy@C82 molecules in tower shape aggregates have a tendency to reorient themselves from random alignments at the interface to a relatively ordered perpendicular array, accompanied with the attenuation of the tower height and some fallen Dy@C82. Interestingly, Sc3N@C80, owning a spherical structure but which has lower symmetry than C60 does because of the existence of the planar Sc3N cluster in the carbon cage, only affects the DPPC monolayer to a small extent. Incorporation of Sc3N@Dy@C80 only lowers the elasticity of the mixed film in a surface pressure range of 13-25 mN/m, which might be induced by the adjustment of the inclination angel of the Sc3N@C80 molecules. At higher surface pressures, the DPPC/Sc3N@C80 films behave similar to the DPPC/C60 films. We therefore conclude that the structures of fullerene and EMFs play an important role in determining the mechanical properties of the mixed Langmuir films. The higher symmetry the fullerene and EMFs molecules have, the less mechanical impact they have on the Langmuir films. These results are relevant to the understanding of the effects of fullerene, EMFs, and other carbon nanomaterials on biomembranes and also provide useful information for facilitating biological and medical applications, such as the new EMFs magnetic resonance imaging contrast agent.