Evaluation of phase transition temperature of liposomes by using tautomerism of benzoylacetoanilide and effects of cholesterol

Abstract

The properties of liposomes are known to be influenced by many factors. Especially, the stability of liposomes is effected by the change of the phase transition temperature (T,) of lipids. In this work, the keto-enol tautomerism of benzoylacetoanilide (BAA) was used to measure the T,. When BAA is added to the liposome suspensions, the ketonic form exists in bulk water and the enolic form in bilayers of the liposomes. Moreover, when the temperature for the system is changed, the change of the ratio of the enolic to ketonic absorances can be expected to show a sharp peak at a temperature corresponding to the T, of lipids. Therefore, the T, value for liposomes can be estimated from the change of the absorbance ratio caused by the change of the temperature for the system. Three kinds of phosphatidylcholines were used as the standard lipids, and these data were used for determination of the T, of hydrogenated egg lecithins.Further, additional effects of cholesterol in liposomes were investigated in the same way. These results indicated that the T, values of hydrogenated egg lecithins decreased linearly with the increase of iodine values, and the T, values for most liposomes dropped suddenly above the concentration of about 15 mol ?6 cholesterol. This suggests that above this concentration cholesterol molecules are incorporated homogeneously into the bilayers and then the T, values decrease due to formation of the mixed layers such as a palisade type between cholesterol and lipid molecules. Consequently, this method for T, determination can be applied even in the diluted aqueous solution with concentration below 0.15% of lipids and is very simple and useful in comparison with common methods.

Synthesis and Vesicle Formation from Hybrid Bolaphile/Amphiphile Ion-Pairs. Evidence of Membrane Property Modulation by Molecular Design

“…The absorbance maxima due to the vesicle-doped enol and keto forms of BAA were indicated at 315 and 250 nm, respectively. The ratio [ A enol / A keto ] was found to increase sharply during the phase transition of the bilayers, and the maximum was seen at T m . Then it decreased as the temperature increased beyond T m .…”

“…Benzoylacetanilide (BAA) is a water soluble molecule that undergoes keto−enol tautomerism. Ueno used this as a probe for the determination of apparent thermal phase transition temperature ( T m ) of various bilayer membranes . To further examine the concentration dependent melting behavior of these ion-paired systems, we used the same probe in our studies.…”

Thermodynamic and Structural Aspects of Internal Wool Lipids

“…In the latter case, the jump of fluidity is produced close to −20 °C, coinciding with the transition phase temperature of pure PC. The properties and characteristics of the phosphatidylcholine and its capacity to form stable liposomes with a transition phase temperature below 0 °C are well-known . The main reason for the higher fluidity in PC-labeled liposomes could be the many unsaturations on the phosphatidylcholine chain, which favor different stereochemical chain dispositions resulting in a less packed lipid structure.…”

Electroactive Deposits of Anthraquinone-Attached Micelle- and Vesicle-Forming Surfactant Assemblies on Glassy Carbon Surfaces

“…Phase Transition Temperatures ( T m ) of Vesicular Dispersions. The thermotropic phase transition temperatures ( T m ), for the transition from the “frozen” gel-like states to the “fluid” liquid crystalline states, were determined by following the changes in the temperature-dependent keto−enol tautomerism of vesicle-doped benzoylacetoanilide (BAA). 18b, To a solution of BAA in EtOH (2 × 10 -3 M, 100 μL), was dissolved amphiphiles 2 or 3 of concentration (5 × 10 -5 M), and the mixed solution was injected into 10 mL of deionized water. The suspended solution was sonicated using an immersion probe sonifier (at 25 W power setting using Heat Systems, Ultrasonic Processor, Model XL-2020) for above ∼60 °C for 3 min.…”