otential evaluation. Materials and Methods Materials Egg phosphatidylcholine Nilotinib bcr-Abl inhibitor and daunorubicin were from Sigma and used as received. All other chemicals were from Merck. Solutions were prepared with HEPES buffer. The ionic strength was adjusted with NaCl. Vesicle Preparation Liposomes were prepared by the thin film hydration method. In this method, a solution of lipid in chloroform was evaporated to dryness with a stream of nitrogen. The lipid film, in an amount that would provide a final lipid concentration of around 2 mM, was then left under vacuum overnight to remove all traces of the organic solvent. The resultant dried lipid film was dispersed using HEPES buffer and the mixture vortexed to yield multilamellar vesicles.
Lipid suspensions were equilibrated at 25 C for 30 min and further extruded SGX-523 1022150-57-7 10 times through polycarbonate filters with a diameter pore of 100 nm, to form large unilamellar vesicles. The EPC concentration in all vesicle suspensions was determined by phosphate analysis using the Fiske and Subbarow phosphomolybdate method. Henderson Hasselbalch equation, gives a 94% positive ionization at the working pH value. Amphiphilic drugs that carry a positive charge can interact electrostatically with the negatively charged phosphate of the headgroup region of the bilayer, while the nonpolar portion inserts into the hydrophobic core. The overall result is an interfacial partitioning of the drug. The daunorubicin partition in the membrane reflects the different types of interaction that an amphiphilic molecule can perform with a lipidic membrane, as a result of the structured bidimensional membrane, that holds a polarized superficial layer and a nonpolar inner core.
This structure Diosmetin allows amphiphilic molecules to penetrate and orientate their polar part to the surface and nonpolar part to an inner position. Such an inner interaction can lead to a spectral modification as electronic distribution in the drug molecule is perturbed by the nonpolar environment, which can in extent lead to bathochromic effects, visible in the derivative spectra here presented. On the other hand, a drug bearing a charged group can establish electrostatically driven interactions with positive or negative groups of the membrane, such as the negative phosphate or the positive amine groups. Such interactions appear, in the case of anthracyclines, to play a very important role in cardiotoxic effects.
Daunorubicin presents a spectral variation when it interacts with the membrane, which is an indication that the molecule establishes an inner partition. Nevertheless, an electrostatic interaction is also likely to occur, especially for lower drug concentrations, before membrane charging begins to cause electrostatic repulsion. Figure 4 shows that the results obtained by zeta potential are higher than the results fromderivative spectrophotometry for lower drug concentrations, possibly because of a superficial electrostatic attraction of the positive drug by the negative liposome. As drug concentration increases, this effect diminishes due to neutralization and then inversion of the liposome charge. When corrected for electrostatic effects, both techniques yield similar results. It appears that for lower drug concentrations, electrostatic interaction plays an important