Effects of Curcumin Concentration and Temperature on the Spectroscopic Properties of Liposomal Curcumin

Abstract

The spectroscopic properties of liposomal curcumin in pH 7.0 sodium phosphate buffer were studied at various curcumin concentrations and temperatures. At 25 °C, liposomal curcumin exhibited much higher values than free curcumin in absorption maximum, fluorescence maximum, and fluorescence anisotropy. When curcumin concentration was increased from 2 to 20 μM, the values of fluorescence anisotropy of liposomal curcumin decreased gradually, consistent with the reduction of phase transition temperature of liposome. This observation revealed that liposomal curcumin can disrupt the packing of phospholipid bilayer and give a loose and disordered structure. On the other hand, as the temperature was increased from 25 to 80 °C, the relative intensity of maximum absorption of liposomal curcumin showed a more pronounced decrease above the phase transition temperature than lower temperatures, suggesting a weaker curcumin protection from the liquid crystalline phase of phospholipid bilayer than the rigid gel phase. However, it was observed that the fluorescence anisotropy of liposomal curcumin had higher values as the temperature increased. This phenomenon was explained as the result of location change of curcumin toward the core of phospholipid bilayer, although the structure of the phospholipid bilayer tended to be looser at higher temperatures.

Influence of Lipid Composition, pH, and Temperature on Physicochemical Properties of Liposomes with Curcumin as Model Drug

“…6. Increase in the r value of curcumin, when incorporated into the liposome, occurred because of restricted motion, confirming its entrapment 15,60 .…”

“…Incorporation of curcumin into liposomes caused fluorescence enhancement with a significant blue shift in λ em values, indicating its transfer to the less polar region of the liposome 15,24,57,58 . These results suggest that curcumin resides in the palisade layer of liposomes because of its amphiphilic nature.…”

“…Curcuminloaded liposomes were centrifuged at 14,500 g for 1 h in an Eppendorf TM tube to sediment the drug-entrapped liposomes 15 . The sediment was analyzed colorimetrically by dissolving it in an appropriate volume of methanol to quan-tify the encapsulated curcumin.…”

“…The sediment was analyzed colorimetrically by dissolving it in an appropriate volume of methanol to quan-tify the encapsulated curcumin. This procedure was used because methanol completely destroys the vesicles, leaving free curcumin 15 . EE for curcumin was calculated as 38 :…”

“…With increasing temperature, hydrocarbon chain packing of the bilayer becomes randomized, thereby reducing membrane rigidity because of pore like defect and bilayer disc formation. This ultimately reduces the stability of a molecular probe or a drug incorporated in the liposome 15 .…”