Stability of curcumin in different solvent and solution media: UV–visible and steady-state fluorescence spectral study (original) (raw)
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Journal of Photochemistry and Photobiology C: Photochemistry Reviews, 2009
Curcumin, with its recent success as an anti-tumor agent, has been attracting researchers from wide ranging fields of physics, chemistry, biology and medicine. The chemical structure of curcumin has two omethoxy phenols attached symmetrically through ␣,-unsaturated -diketone linker, which also induces keto-enol tautomerism. Due to this, curcumin exhibits many interesting photophysical and photochemical properties. The absorption maximum of curcumin is ∼408-430 nm in most of the organic solvents, while the emission maximum is very sensitive to the surrounding solvent medium (460-560 nm) and the Stokes' shift varied from 2000 to 6000 cm −1. The fluorescence quantum yield in most of the solvents is low and reduced significantly in presence of water. The fluorescence lifetime is short (<1 ns) and displayed multi-exponential decay profile. The singlet excited states of curcumin decay by non-radiative processes contributed mainly by intra-and intermolecular proton transfer with very low intersystem crossing efficiency. Polarity,-bonding nature, hydrogen bond donating and accepting properties of the solvent influence the excited state photophysics of curcumin in a complex manner. The triplet excited states of curcumin absorb at 720 nm and react with oxygen to produce singlet molecular oxygen. The photodegradation of curcumin produces smaller phenols and the photobiological activity of curcumin is due to the generation of reactive oxygen species. Being lipophilic in nature, the water solubility of curcumin could be enhanced upon the addition of surfactants, polymers, cyclodextrins, lipids and proteins. Changes in the absorption and fluorescence properties of curcumin have been found useful to follow its interaction and site of binding in these systems. Curcumin fluorescence could be employed to follow the unfolding pattern and structural changes in proteins. The intracellular curcumin showed more fluorescence in tumor cells than in normal cells and fluorescence spectroscopy could be used to monitor its preferential localization in the membrane of tumor cells. This review, presents the current status of research on the photophysical, photochemical and photobiological processes of curcumin in homogeneous solutions, bio-mimetics and living cells. Based on these studies, the possibility of developing curcumin, as a bimolecular sensitive fluorescent probe is also discussed.
Studies on Curcumin and Curcuminoids. XXXIX. Photophysical Properties of Bisdemethoxycurcumin
Journal of Fluorescence, 2011
The steady-state absorption and fluorescence, as well as the time-resolved fluorescence properties of bisdemethoxycurcumin dissolved in several solvents differing in polarity and H-bonding capability were measured. The photodegradation quantum yield of the compound in acetonitrile and methanol was determined. The bisdemethoxycurcumin decay mechanisms from the S 1 state were discussed and compared with those of curcumin. The differences in S 1 dynamics observed between bisdemethoxy-curcumin and curcumin could be ascribed to a difference in H-bond acceptor/donor properties of the phenolic OH and a difference in strength of the intramolecular H-bond in the keto-enol moiety within the two molecules.
Synchronous fluorescence spectroscopic study of solvatochromic curcumin dye
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2011
Curcumin, the main yellow bioactive component of turmeric, has recently acquired attention by chemists due its wide range of potential biological applications as an antioxidant, an anti-inflammatory, and an anti-carcinogenic agent. This molecule fluoresces weakly and poorly soluble in water. In this detailed study of curcumin in thirteen different solvents, both the absorption and fluorescence spectra of curcumin was found to be broad, however, a narrower and simple synchronous fluorescence spectrum of curcumin was obtained at = 10-20 nm. Lippert-Mataga plot of curcumin in different solvents illustrated two sets of linearity which is consistent with the plot of Stokes' shift vs. the E T 30. When Stokes's shift in wavenumber scale was replaced by synchronous fluorescence maximum in nanometer scale, the solvent polarity dependency measured by max SFS vs. Lippert-Mataga plot or E T 30 values offered similar trends as measured via Stokes' shift for protic and aprotic solvents for curcumin. Better linear correlation of max SFS vs. * scale of solvent polarity was found compared to max abs or max em or Stokes' shift measurements. In Stokes' shift measurement both absorption/excitation as well as emission (fluorescence) spectra are required to compute the Stokes' shift in wavenumber scale, but measurement could be done in a very fast and simple way by taking a single scan of SFS avoiding calculation and obtain information about polarity of the solvent. Curcumin decay properties in all the solvents could be fitted well to a double-exponential decay function.
A Kinetic Degradation Study of Curcumin in Its Free Form and Loaded in Polymeric Micelles
The AAPS journal, 2016
Curcumin, a phenolic compound, possesses many pharmacological activities and is under clinical evaluation to treat different diseases. However, conflicting data about its stability have been reported. In this study, the kinetic degradation of curcumin from a natural curcuminoid mixture under various conditions (pH, temperature, and dielectric constant of the medium) was investigated. Moreover, the degradation of pure curcumin at some selected conditions was also determined. To fully solubilize curcumin and to prevent precipitation of curcumin that occurs when low concentrations of co-solvent are present, a 50:50 (v/v) aqueous buffer/methanol mixture was used as standard medium to study its degradation kinetics. The results showed that degradation of curcumin both as pure compound and present in the curcuminoid mixture followed first order kinetic reaction. It was further shown that an increasing pH, temperature, and dielectric constant of the medium resulted in an increase in the de...
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2017
Curcumin is a yellow phenolic compound with a wide range of reported biological effects. However, two main obstacles hinder the use of curcumin therapeutically, namely its poor bioavailability and photostability. We have synthesized two curcumin complexes, the first a boron curcumin complex (B-Cur 2) and the second an iron (Fe-Cur 3) complex of curcumin. Both derivatives showed high fluorescence efficiency (quantum yield) and greater photostability in solution. The improved photostability could be attributed to the coordination structures and the removal of β-diketone group from curcumin. The fluorescence and ultra violet/ visible absorption spectra of curcumin, B-Cur 2 and Fe-Cur 3 all have a similar spectral pattern when dissolved in the same organic solvent. However, a shift towards a lower wavelength was observed when moving from polar to non-polar solvents, possibly due to differences in solvent polarity. A plot of Stokes' shift vs the orientation polarity parameter (Δf) or vs the solvent polarity parameter (E T 30) showed an improved correlation between the solvent polarity parameter than with the orientation polarity parameter and indicating that the red shift observed could be due to hydrogen-bonding between the solvent molecules. A similar association was obtained when Stokes' shift was replaced by maximum synchronous fluorescence. Both B-Cur 2 and Fe-Cur 3 had larger quantum yields than curcumin, suggesting they may be good candidates for medical imaging and in vitro studies.
Journal of the Serbian Chemical Society, 2012
Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5--dione) is a natural biologically active substance with antioxidant activity. The ability of curcumin to inhibit free radical reactions can be used in the prevention of diseases such as cancer and coronary heart disease. UV-Vis spectrophotometric and chemiluminescent dynamic methods for determination of the antioxidant activity of curcumin were developed. The spectrophotometric method includes investigation of the interaction between DNA, isolated from HL-60 cells, and curcumin. The decreasing absorption of curcumin in the presence of HL-60 DNA against the blank sample can be a measurement for some complex formation between curcumin and DNA. The chemiluminescent method involves three tests for the detection of luminol-dependent chemiluminescence based on model systems that generate superoxide, hydroxide and hypochlorite radicals. The strongest decay of chemilunimescence was registered at the highest concentration of curcumin (100 µmol L -1 ).
Effect of Solvent on the Excited-state Photophysical Properties of Curcumin¶
Photochemistry and Photobiology, 2007
Photophysical properties of curcumin, 1,7-bis-(4-hydroxy-3-methoxy phenyl)-1,6-heptadiene-2,5-dione, a pigment found in the rhizomes of Curcuma longa (turmeric) have been studied in different kinds of organic solvent and also in Triton X-100 aqueous micellar media using time-resolved fluorescence and transient absorption techniques having pico and nanosecond time resolution, in addition to steady-state absorption and fluorescence spectroscopic techniques. Steady-state absorption and fluorescence characteristics of curcumin have been found to be sensitive to the solvent characteristics. Large change (⌬ ؍ 6.1 Debye) in dipole moments due to photoexcitation to the excited singlet state (S 1) indicates strong intramolecular charge transfer character of the latter. Curcumin is a weakly fluorescent molecule and the fluorescence decay properties in most of the solvents could be fitted well to a double-exponential decay function. The shorter component having lifetime in the range 50-350 ps and percent contribution of amplitude more than 90% in different solvents may be assigned to the enol form, whereas the longer component, having lifetime in the range 500-1180 ps with less than 10% contribution may be assigned to the di-keto form of curcumin. Our nuclear magnetic resonance study in CDCl 3 and dimethyl sulfoxide-D 6 also supports the fact that the enol form is present in the solution by more than about 95% in these solvents. Excited singlet (S 1) and triplet (T 1) absorption spectrum and decay kinetics have been characterized by pico and nanosecond laser flash photolysis. Quantum yield of the triplet is low (T Յ 0.12). Both the fluorescence and triplet quantum yields being low (f ؉ T Ͻ 0.18), the photophysics of curcumin is dominated by the energy relaxation mechanism via the internal conversion process.
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2004
The stability of curcumin (H 3 Cur) in aqueous media is improved when the systems in which it is present are at high pH values (higher than 11.7), fitting a model describable by a pseudo-zero order with a rate constant k for the disappearance of the Cur 3− species of 1.39 (10 −9 ) M min −1 . There were three acidity constants measured for the curcumin as follows: pK A3 = 10.51 ± 0.01 corresponding to the equilibrium HCur 2− = Cur 3− + H + , a pK A2 = 9.88 ± 0.02 corresponding to the equilibrium H 2 Cur − = HCur −2 + H + . These pK A values were attributed to the hydrogen of the phenol part of the curcumin, while the pK A1 = 8.38 ± 0.04 corresponds to the equilibrium H 3 Cur = H 2 Cur − +H + and is attributed the acetylacetone type group. Formation of quinoid structures play an important role in the tautomeric forms of the curcumin in aqueous media, which makes the experimental values differ from the theoretically calculated ones, depending on the conditions adopted in the study.