Synchronous fluorescence spectroscopic study of solvatochromic curcumin dye (original) (raw)
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Journal of Photochemistry and Photobiology B: Biology, 2016
In aqueous solution, curcumin is photodegradable (light sensitive), it is also self-degradable in the dark. In basic medium, the second process is enhanced. The dark process has been studied in water and also in a number of protic and aprotic solvents, and aqueous solutions of ionic liquids, pluronics, reverse micelles and salt. The kinetics of the process followed the first order rate law; a comparative as well as individual assessment of which has been made. The kinetics of curcumin self-degradation has been found to be fairly dependent on salt (NaCl) concentration. Curcumin molecules in solution may remain in the enol or keto-enol form. From the visible spectral analysis, an estimate of the proportions of these forms in aqueous ethanol medium has been made. The temperature effect on the visible and fluorescence spectra of curcumin has been also studied. The steady state fluorescence anisotropy of the photoactive curcumin has been evaluated in different solvent and solution media. The reversibility of the steady state fluorescence anisotropy of curcumin on heating and cooling conditions has been examined. The results herein presented are new and ought to be useful as the study of physicochemistry of curcumin has been gaining importance in the light of its biological importance.
Journal of Solution Chemistry, 2010
Curcumin, a chemical compound present in the well-known Indian spice turmeric, has uses in many different fields ranging from medicinal chemistry to the dye industry. Its poor water solubility, though, makes Curcumin difficult to handle, making it less appealing for potential uses. The principal aim of this work is to perform a computational study of the structural and electronic properties of Curcumin {IUPAC name: 1,7-bis(4hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione} in several solvents, and a comparison with experimental data. Rotameric equilibria, vibrational and thermochemical analysis, and electronic absorption spectra (with ab initio and semi-empirical methodologies) have been studied, both in vacuum and in three selected solvents. Different computational techniques have been applied and the results compared. Combined approaches resulted in very satisfactory results. Interesting results have emerged, which suggest subsequent investigations about the nature of the excited states and potential derivatives of Curcumin that possibly have non-linear optical applications, as a π-core for innovative materials in laser engineering and photonics. a 1 eV = 1.602176487(40) ×10 −19 J
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.
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.
Fluorescence Quenching Studies of Curcumin by Hydrogen Peroxide in Acetonitrile Solution
Monatshefte f�r Chemie / Chemical Monthly, 2004
Steady state quenching studies of curcumin, 1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6heptadiene-3,5-dione, fluorescence by hydrogen peroxide were conducted in acetonitrile solution. A quenching rate constant, k q , of 1.05 Â 10 10 M À1 Á s À1 was obtained with a short fluorescence lifetime of 347 ps. The reaction rate constant, which is within the diffusion-limited regime, is activation-controlled. The rate constant of deactivation of the thermally excited curcumin was 1.2 orders of magnitude more nonradiative (2.67 Â 10 9 s À1) than radiative (2.16 Â 10 8 s À1). The reaction was exothermic with a DG of À1.97 eV and solvent reorganization energy of 1.37 eV. These values indicate that the electron transfer reaction is solvent-mediated with electron transfer rate constant, k ET , of 2.16 Â 10 10 s À1 .
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.
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.
Quantum-Mechanical Characterization and Spectral Study of Curcumin
2017
Curcumin is a natural substance with anti-inflammatory, antioxidant, antiviral, anti-cancer and cholesterol reduction effects. A quantum-mechanical characterization for Curcumin tautomers was performed by using Density Function Theory (DFT) method from Spartan’14 program. The contribution of different types of interactions to spectral shifts in solutions of the studied molecule was established by solvatochromic study. The excited state dipole moments of the curcumin tautomers are estimated.
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.