Study On The Factors Of The Effect On Liposomes Stability Done By Metal Cations

Phospholipids construct the biological membrane and provide the most suitablecondition for the membrane protein functioning. Those phospholipid molecules formingmembrane can assemble themselves in certain circumstances. And the micro-mechanisminterpreting it is fundamental for us to understand the common features of this materialforming life. With the liposome as a micro cell, the properties of these molecules can beworked out. Moreover, the atomic force microscope (AFM) which can picture and analyze thesystem in a tender way has been used on the reverse-phase evaporation lipid vesicles (REV)made of phosphatidylcholine (PC) and cholesterol (Chol) with different molar ratios. And byreferencing many previous research on this field and basic mechanism in basicthermodynamics, results got by the AFM was discussed in a more theoretical way.The effect on the lipid membrane caused by metal cations should not be neglected. Witha not such appropriate range in concentration, cations usually make the lipid membraneunstable, and then the defects take place, which would also lead the liposome to fusion,diffusion, and rupture. Different types of metal cations have different affinities with the polargroup of phospholipids, thus the proper range of their concentrations for keeping liposomesstable turns out to be various. The interaction between cations and membrane molecules alsohas influences on two controversial side. One is to change the zeta potential of lipidmembrane and liposomes and in this case, a certain range of concentrations can be helpful toboom up the stability, otherwise it has an effect of impairing. The other side is the electrostaticscreening phenomenon make the Van der Waals’ force of attracting overwhelm the otherrepulsive forces between molecules, and make the membrane more stable.Metal cations can also make lipid membranes distributing on water phase have atendency to compose big vesicles automatically. Both thermodynamics benefit and strongelectrostatic repulsion between positively charged net on the surface of membranes resultedby the binding of cations make this process happen.This thesis specially concentrate on the performances of the PC-Chol liposomes underthe calcium cations environment and depict the mechanism mentioned former with this instance.It also compare the features of the liposomes constructed by lipids extracted frommitochondria in swine heart muscle and cholesterol (mole ratio≈1:1)with those made of purePC and cholesterol in mole ratio=1:1, and discuss on the results.The morphology images can be deducted into the micro mechanism of the interactionbetween molecules involved. The constituents, or to say the recipes of REV decide theirproperties directly and indirectly through these mechanisms.