Interaction of curcumin with phosphatidylcholine: A spectrofluorometric study

Curcumin [1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione], the main constituent of the rhizomes of the plant Curcume longa L. (turmeric), is a powerful antioxidant in both enzymatic and nonenzymatic systems. The interactions of curcumin with egg and soy phosphatidylcholine were followed by fluorescence spectroscopy. Curcumin had very weak fluorescence in aqueo us system, which was enhanced in apolar environments. Curcumin emitted at 4 90 nm after being excited at 451 nm in phosphatidylcholine micelles. The eq uilibrium constants for the interaction of curcumin with egg and soy phosph atidylcholine were (3.26 +/- 0.2) x 10(5) and (2.64 +/- 0.2) x 10(5) M-1, r espectively. From the Scatchard plot of the fluorometric data, it was infer red that one molecule of curcumin could bind six molecules of phosphatidylc holine. The equilibrium constant for the phosphatidylcholine-curcumin inter action decreased with temperature, indicating the amphiphilc nature of curc umin. The Delta G, Delta H, and Delta S values obtained for the interaction of egg phosphatidylcholine-curcumin were -7.8 +/- 0.3 kcal/mol, -9.6 +/- 0 .4 kcal/mol, and -6.8 +/- 0.2 cal/mol/K, respectively. The fluorescence ani sotropy measurements of curcumin with phosphatidylcholine suggested that th e anisotropy of the curcumin molecule did not change in phosphatidylcholine . The interaction of divalent metal ions with phosphatidylcholine - curcumi n in comparison with phosphatidylcholine 1-anilino-8-naphathalenesulfonic a cid complex suggested the strong binding of curcumin to metal ions.