A study of liposome formation using a solution (isoperibol) calorimeter

Area of Science:

• Biophysical Chemistry
• Lipid Bilayer Studies
• Calorimetry

Background:

• Phospholipid vesicles are crucial in biological systems and drug delivery.
• Understanding vesicle formation is key to controlling their properties.
• The influence of solvents like chloroform on lipid behavior requires detailed investigation.

Purpose of the Study:

• To investigate the thermodynamics of phospholipid vesicle formation using solution calorimetry.
• To determine the effect of chloroform on the enthalpy of vesicle formation.
• To elucidate the role of lipid hydrocarbon chains in vesicle formation and hydration.

Main Methods:

• Utilized an isoperibol solution calorimeter for thermodynamic measurements.
• Hydrated phospholipid films above their phase transition temperature with agitation.
• Analyzed the enthalpy changes associated with vesicle formation in the presence and absence of chloroform.

Main Results:

• Chloroform retention significantly altered the apparent enthalpy change of vesicle formation.
• The observed enthalpy changes indicated chloroform's effect on lipid hydration processes.
• Egg phosphatidylcholine vesicle formation was exothermic, while dimyristoylphosphatidylcholine was endothermic.

Conclusions:

• Chloroform's influence on vesicle formation enthalpy is primarily due to alterations in the hydration process.
• Differences in enthalpy between various phospholipids are attributed to hydrocarbon chain interactions during hydration and vesicle formation.
• Calorimetric data provides critical insights into the physical chemistry of phospholipid self-assembly.