Spectral and Photochemical Properties of Curcumin

Abstract

Curcumin, bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione, is a natural yellow-orange dye derived from the rhizome of Curcuma longa, an East Indian plant. In order to understand the photobiology of curcumin better we have studied the spectral and photochemical properties of both curcumin and 4-(4-hydroxy-3-methoxy-phenyl)-3-buten-2-one (hC, half curcumin) in different solvents. In toluene, the absorption spectrum of curcumin contains some structure, which disappears in more polar solvents, e.g. ethanol, acetonitrile. Curcumin fluorescence is a broad band in acetonitrile (lambda max = 524 nm), ethanol (lambda max = 549 nm) or micellar solution (lambda max = 557 nm) but has some structure in toluene (lambda max = 460, 488 nm). The fluorescence quantum yield of curcumin is low in sodium dodecyl sulfate (SDS) solution (phi = 0.011) but higher in acetonitrile (phi = 0.104). Curcumin produced singlet oxygen upon irradiation (lambda > 400 nm) in toluene or acetonitrile (phi = 0.11 for 50 microM curcumin); in acetonitrile curcumin also quenched 1O2 (kq = 7 x 10(6) M-1 s-1). Singlet oxygen production was about 10 times lower in alcohols and was hardly detectable when curcumin was solubilized in a D2O micellar solution of Triton X-100. In SDS micelles containing curcumin no singlet oxygen phosphorescence could be observed. Curcumin photogenerates superoxide in toluene and ethanol, which was detected using the electron paramagnetic resonance/spin-trapping technique with 5,5-dimethyl-pyrroline-N-oxide as a trapping agent. Unidentified carbon-centered radicals were also detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Excited-State Intramolecular Hydrogen Atom Transfer of Curcumin in Surfactant Micelles

“…37,38 A comparison between the UV-vis absorption and emission spectra of curcumin in micelles with those in a number of organic solvents and water provides valuable insights. The UV-vis absorption spectra of curcumin in the TX-100 and DTAB micelles resemble those of curcumin in aprotic solvents, including chloroform and toluene, 23,39 suggesting similarities between the environments. However, the emission spectra of curcumin in these micelles are red-shifted compared to those in the aprotic solvents, potentially due to interactions with water molecules at the interface and within the micelle, [40][41][42][43][44] as will be discussed further in a later section.…”

Susceptibility of clinical isolates of Candida to photodynamic effects of curcumin

“…The use of fluences higher than 18 J/cm 2 did not improve the effectiveness of PDT for inactivating the Candida species. This could be as a result of the CUR photobleaching which leads to photodegradation of the PS solution and decreases in reactive oxygen species production [23,25].…”

“…An increasing number of investigations have suggested that CUR exhibits potential therapeutic applications that may be enhanced by combination with light, as it displays a high light absorption in the visible spectral region, around 400-500 nm [23][24][25][26]. Recently, this natural compound has been shown to possess phototoxic potential against yeast cells [23].…”

Validation of Photodynamic Action via Photobleaching of a New Curcumin-Based Composite with Enhanced Water Solubility

“…By changing the properties of the solvent, such as polarity, the spectroscopic properties may vary dramatically [22,23]. In addition, curcumin can be synthetized with metallic ions in its structure, also changing its spectroscopic properties [24].…”