Spectral absorption of curcuminoids solubilized in butanol. A) Spectral scan of 6 uM curcuminoids in water-saturated 1-butanol (white area) between wavelength 370 and 460 nm with increments of 1 nm. The gray area delineates the background absorption of water-saturated butanol. B) Dose curve of curcuminoids (1–80 μM) solubilized in water-saturated butanol. Data are presented as absorption (OD) as a function of curcuminoid concentration (μM) at a wavelength of 427 nm. C) Elution profile after reversed phase chromatography of 50 μM curcuminoids dissolved in 27.5% acetonitrile solution (see Methods). The vertical bar represents 20 milliabsorption units (mAU). Elution peaks of curcuminoids at indicated retention times (rt) designate bisdemethoxycurcumin (B), demethoxycurcumin (D), and curcumin (C).