Kyung Ok Kwon

Effects of lysozyme and bovine serum albumin on membrane characteristics of dipalmitoylphosphatidylglycerol liposomes

The effects of adsorption of two kinds of proteins on the membrane characteristics of liposomes were examined at pH 7.4 in terms of adsorption amounts of proteins on liposomes, penetrations of proteins into liposomal bilayer membranes, phase transition temperature, microviscosity and permeability of liposomal bilayer membranes, using positively charged lysozyme (LSZ) and negatively charged bovine serum albumin (BSA) as proteins and negatively charged L-alpha-dipalmitoylphosphatidylglycerol (DPPG) liposomes. The saturated adsorption amount of LSZ was 720 g per mol of liposomal DPPG, while that of BSA was 44 g per mol of liposomal DPPG. The penetration of LSZ into DPPG lipid membranes was greater than that of BSA. The microviscosity in the hydrophobic region of liposomal bilayer membranes increased due to adsorption (penetration) of LSZ or BSA, while the permeability of liposomal bilayer membranes increased. The gel-liquid crystalline phase transition temperature of liposomal bilayer membranes was not affected by adsorption of LSZ or BSA, while the DSC peak area (heat of phase transition) decreased with increasing adsorption amount of LSZ or BSA. It is suggested that boundary DPPG makes no contribution to the phase transition and that boundary DPPG and bulk DPPG are in the phase-separated state, thereby increasing the permeability of liposomal bilayer membranes through adsorption of LSZ or BSA. A possible schematic model for the adsorption of LSZ or BSA on DPPG liposomes was proposed.

Effects of fluoroalkyl chain length and added moles of oxyethylene on aggregate formation of branched-tail fluorinated anionic surfactants

Abstract The effects of fluorocarbon chain length and oxyethylene chain length were examined on the aggregate formation of newly synthesized double chain-type fluorinated anionic surfactants. The solution properties of double chain-type fluorinated anionic surfactants with two moles of added oxyethylene ( n FS(EO) 2 ) were found to depend on the fluorocarbon chain length. Thus, the Krafft temperature rose abruptly as the length of fluorocarbon chain increased, while the concentration at which the lowest surface tension is attained or aggregates are formed lowered with increasing chain length. In contrast, for double chain-type fluorinated anionic surfactants with two more moles of added oxyethylene ( n FS(EO) 4 ), their solution properties were almost inaffected by fluorocarbon chain length. That is, almost no change was seen in the concentration that indicates the lowest surface tension or aggregate formation when the chain length was altered, whereas the Krafft temperature was below 0°C for all members, providing them with a high solubility in water. In addition, spontaneous vesicle formation was observed in solution of n FS(EO) 4 and the size distribution of the vesicles thus formed had plural peaks (discrete size distribution).

Effects of calcium ions on phospholipid aggregates at subzero temperatures

Abstract The thermodynamic behavior of phospholipid aggregates in the presence of calcium ions has been investigated by differential scanning calorimetry (DSC) with special emphasis on the change in the subzero region. The phospholipids used were dipalmitoylphosphatidylcholine (DPPC), dipalmitoylphosphatidylethanolamine (DPPE) and dipalmitoylphosphatidylglycerol (DPPG). The thermograms at subzero temperatures for phospholipids—calcium ion—buffer solution systems showed a characteristic behavior with increasing calcium ion concentration. Applying thermodynamic theory to the data obtained from the DSC measurements, the interaction between the phospholipid aggregates and the calcium ions was discussed. It was found that the effects of the calcium ions on the phospholipid aggregates follow the order DPPG ⪢ DPPC ⪢ DPPE.