Cholesteryl sulphate and phosphate in the solid state and in aqueous systems

Area of Science:

• Lipid chemistry
• Solid-state chemistry
• Materials science

Background:

• Cholesteryl sodium sulphate (CS) and cholesteryl dihydrogen phosphate (CP) are sulfate and phosphate esters of cholesterol.
• Understanding their solid-state properties and phase behavior is crucial for applications involving lipid self-assembly.

Purpose of the Study:

• To investigate the solid-state phase transitions and thermal properties of cholesteryl sodium sulphate (CS) and cholesteryl dihydrogen phosphate (CP).
• To determine the phase diagram of cholesteryl dihydrogen phosphate (CP) in aqueous systems.
• To characterize the unique gel phase formed by CP and its monofilm behavior.

Main Methods:

• Differential scanning calorimetry (DSC) for thermal analysis.
• X-ray diffraction (XRD) for crystal structure determination (implied).
• Phase diagram determination for CP in water.
• Monolayer studies at different pH levels.

Main Results:

• CS dihydrate undergoes solid-state phase transitions at 65°C and 95°C, melting at 165°C.
• CP exhibits a phase transition at 50°C and melts at 190°C.
• CP forms stable crystalline hydrates and a lamellar gel phase with extensive water layers (up to 1000 Å) in aqueous systems, unlike unstable CS.

Conclusions:

• Cholesteryl sodium sulphate (CS) and cholesteryl dihydrogen phosphate (CP) display different thermal and phase behaviors.
• CP forms a unique, highly ordered lamellar gel phase in water, suggesting potential for advanced material applications.
• Further investigation into the monofilm properties of CS and CP at varying pH is warranted.