Abstract
Zeta potential of liposomes is often measured in studies of their properties and/or applications. However, there are not many papers published in which zeta potential was determined during enzymatic reaction of a lipid. Therefore in this paper size, polydispersity index, and zeta potentials of 1,2-dipalmitoylsn-glycero-3-phosphatidylcholine (DPPC) and 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) liposomes were investigated in 1 mM NaCl (pH 6.2) and phosphate buffer (pH 8.1) during 60 min of phospholipase C action at 20 and 37 °C. The hydrocarbon chains saturation differ these two phospholipids what appears in some differences in the zeta potential changes during the hydrolysis reaction run. The polydispersity index of the liposomes indicates that they are relatively stable and monodisperse, except for DPPC in phosphate buffer where up to 30 % of the initial amount forms larger size moieties, possibly aggregates of the liposomes, enzyme and the hydrolysis products. However, in this buffer zeta potential of the liposomes practically does not change during PLC action. Also the changes of zeta potential of DOPC liposomes are minor, although their negative values are much smaller than those of DPPC at both temperatures. These small changes of the potential may be due to compression of the diffuse double layer by present phosphate buffer. However, distinct changes of the zeta potentials in the presence of PLC take place in NaCl solution. The observed changes can be explained by reorientation of the phospholipid polar heads and their different density on DPPC and DOPC surface of the liposomes. Although it appeared that the zeta potential is not a very sensitive parameter for tracking the hydrolysis reaction in phosphate buffer, generally zeta potential enables the characterization of such reactions through determination of electrokinetic properties of liposomes as well as the polydispersity and size distribution of the liposomes do.
Highlights
Liposomes are often used in studies of model biological membranes, phase transition and spacing, targeted drug delivery to specific areas of a human body, etc
These results show that except for two systems, polydispersity of the rest liposomes lies in the range of 0.15–0.20 at both temperatures and do not change much during 60 min of their contact with the phospholipases C (PLC) enzyme
Very similar size DPPC and DOPC liposomes were obtained by Maharani et al (2012) who used the same method of their preparation
Summary
Liposomes are often used in studies of model biological membranes, phase transition and spacing, targeted drug delivery to specific areas of a human body, etc. Cholesterol molecules happens to be incorporated into the phospholipid’s bilayer causing increase separation between the choline head groups, reduces the hydrogen bonding strengths and electrostatic interaction. This makes the membrane more stable and lowers its permeability to water and other molecules In the studies of liposomes often their zeta potential is determined in various aspects, like stability of novel liposomes, encapsulation of drugs, decoration of the surface with a polymer, adsorption of ions, various pharmaceutical applications, etc. It seemed us interesting investigation of the zeta potential changes accompanying the hydrolysis of DPPC and DOPC liposomes caused by PLC enzyme and calculation of their surface charge
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