Curcumin‐derived Transients: A Pulsed Laser and Pulse Radiolysis Study

Abstract

In this paper we report a time-resolved investigation of transients derived from curcumin, which may be intimately involved in the processes leading to its biological activity. Fluorescence and triplet quantum yields are respectively 0.06 and 0.11. The high percentage of internal conversion is proposed to proceed via H-transfer within the thermodynamically favored enol structure of what is formally a 1,3-diketone. The triplet energy (191 +/- 2 kJ mol-1), natural lifetime (1.5 microseconds) and self-quenching rate constant (5.0 x 10(8) L mol-1 s-1) have been determined. Oxygen quenching of the triplet leads to the production of singlet oxygen with unit efficiency. Curcumin quenches the latter species very inefficiently (2.5 x 10(5) L mol-1 s-1). The curcumin radical has been produced via three mechanistically distinct methods. This species is unreactive toward oxygen but is repaired by vitamins C and E and anthralin.

The Molecular Basis for the Pharmacokinetics and Pharmacodynamics of Curcumin and Its Metabolites in Relation to Cancer

“…1B). The tendency of the keto↔enol equilibrium to shift toward the enol tautomer in these solvent systems has been confirmed experimentally by Fourier transform infrared spectroscopy (FT-IR) (Kolev et al, 2005), nuclear magnetic resonance spectroscopy (NMR) (Roughley and Whiting, 1973;Unterhalt, 1980;Gorman et al, 1994;Khopde et al, 2000), fluorescence spectroscopy (Khopde et al, 2000;Nardo et al, 2008), and absorption spectroscopy (Khopde et al, 2000;Nardo et al, 2008) as well as computationally (Kolev et al, 2005;Balasubramanian, 2006;Payton et al, 2007;Galano et al, 2009). In nonpolar solvents, the steadystate absorption spectra of curcumin in cyclohexane (Nardo et al, 2008), toluene , benzene (Khopde et al, 2000), and others (Tønnesen et al, 1995) exhibit a concrete red band or shoulder, which has been ascribed to the diketo tautomer (Khopde et al, 2000;Nardo et al, 2008Nardo et al, , 2009.…”

“…The 1 O 2 yields after irradiation of curcumin with resonant visible light are strongly solvent dependent , which indicates that the energy transfer from triplet state curcumin to O 2 proceeds from the b-dicarbonyl moiety. In nonpolar (toluene and benzene) and polar aprotic (acetonitrile) solvents, the quantum yield of 1 O 2 formation is 0.11-0.12 Gorman et al, 1994), whereas in polar protic solvents such as ethanol and iso-propanol as well as in surfactant micelles (sodium dodecyl sulfate and Triton X-100) the quantum yields are approximately 10-fold lower 240 (Wagner, 1976), and curcumin partially adopts a diketo conformation in aprotic solvents (Fig. 1B).…”

“…Curcumin also reacts with physiologically produced nitrogen-centered radicals (nitric oxide, •NO, and nitrogen dioxide radicals) (Unnikrishnan and Rao, 1995;Sreejayan and Rao, 1997;Onoda and Inano, 2000), sulfur-centered radicals (oxidized glutathione) (Khopde et al, 1999), and oxidants such as hydrogen peroxide (H 2 O 2 ) (Tønnesen and Greenhill, 1992;Iwunze, 2004;Ak and Gulcin, 2008;Griesser et al, 2011) as well as singlet oxygen ( 1 O 2 ) (Tønnesen et al, 1986;Chignell et al, 1994;Subramanian et al, 1994;Das and Das, 2002). Curcumin is further capable of reacting with nonphysiological radicals such as azide radicals (Gorman et al, 1994;Priyadarsini, 1997;Khopde et al, 1999;Priyadarsini et al, 2003), 2,2-diphenyl-1-picrylhydrazyl (DPPH, a stable nitrogen-centered radical) (Venkatesan and Rao, 2000;Priyadarsini et al, 2003;Fujisawa et al, 2004;Ak and Gulcin, 2008;Feng and Liu, 2009), 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) radical cations (ABTS •+ ) (Venkatesan and Rao, 2000;Ak and Gulcin, 2008;Feng and Liu, 2009), dimethyl-4-phenylenediamine dihydrochloride radical cations (Ak and Gulcin, 2008), halocarbonperoxyl radicals (Priyadarsini, 1997; Khopde et al, 1999), dibromine radical anions (Khopde et al, 1999), galvinoxyl radicals (Feng and Liu, 2009), and Triton-X 100 radicals (Priyadarsini, 1997). Lastly, it has been shown to interact with nonphysiological peroxides such as tert-butyl hydroperoxide (Sugiyama et al, 1996).…”

Excited-State Intramolecular Hydrogen Atom Transfer and Solvation Dynamics of the Medicinal Pigment Curcumin

“…12,[31][32][33][34] In all cases, these studies focused on excited-state intramolecular hydrogen atom transfer (ESIHT) of curcumin because this phenomenon has been associated with the medicinal properties of other pigment molecules, including hypericin and hypocrellin. [35][36][37][38][39] Two of these studies agree that the fluorescence lifetime of curcumin in methanol has a dominant component with a time constant of roughly 130 ps.…”

Pro- and antioxidant activity of curcuminoids with lecithin in sunflower oil

“…Commercial preparations of curcuminoids usually contain approximately 77%, 17% and 3% of curcumin, demethoxycurcumin and bisdemethoxycurcumin respectively. Several studies in recent years have shown that curcumin has antioxidant, anti-inflammatory, antimicrobial, anti-bacterial, anti-parasitic, anti-mutagen and anticancer properties [5,6]. It is believed that curcumin is a potent agent against many diseases such as anorexia, coughs, diabetes, hepatic disorders, rheumatism and Alzheimer disease [7][8][9].…”