Femtosecond transient absorption spectroscopy of copper(ii)–curcumin complexes

Abstract

Ligand-metal interaction between curcumin and Cu(II) in methanol and sodium dodecyl sulfate (SDS) micelles was investigated using fluorescence spectroscopy and transient absorption spectroscopy. The Cu(II) ion exhibits a high efficiency in quenching the fluorescence of curcumin. By quantifying fluorescence quenching as a function of Cu(II) concentration, the complexation constants, K(1) and K(2), for the formation of the 1 : 1 and 1 : 2 Cu(II)-curcumin complexes, [Cu(II)-Cur](+) and [Cu(II)-Cur(2)], have been determined. In methanol, K(1) and K(2) are (1.33 ± 0.47) × 10(8) M(-1) and (6.79 ± 1.77) × 10(5) M(-1), respectively, whereas those in SDS micelles are (9.90 ± 1.68) × 10(5) M(-1) and (1.70 ± 0.48) × 10(6) M(-1), respectively. The transient absorption spectra of curcumin and the Cu(II)-curcumin complexes from 520 nm to 700 nm show a combination of stimulated emission and excited state absorption (ESA). However, the transient absorption signal at 500 nm corresponds to ESA exclusively. For curcumin, the ESA kinetics exhibit two rising components with time constants of 0.9 ps and 8.2 ps in methanol, and 0.5 ps and 2.5 ps in SDS micelles, which are consistent with solvation dynamics of excited state curcumin in these media. In addition, the ESA kinetics show a decay component with a time constant of 125 ps in methanol and 64 ps in SDS micelles, reflecting the excited state intramolecular hydrogen atom transfer of curcumin in these media. The ESA kinetics of the Cu(II)-curcumin complexes exhibit a sharp rise and a fast decay with a time constant of approximately 1 ps in both media due to the strong interaction between Cu(II) and curcumin.

Quantum chemical insights into Alzheimer's disease: Curcumin's chelation with Cu(II), Zn(II), and Pd(II) as a mechanism for its prevention

“…The chelated complexes of these transition metal ions are more stable than curcumin, and thus causing spectroscopic shifts in the UV‐visible and IR bands. Consequently, experimentally observed spectral shifts in the primary absorptions peaks, in the visible region near 433 nm and in the UV region have been attributed to the chelation of metal ions with curcumin . Furthermore, the open‐d‐shell transition metal ions such as Cu(II) and Pd(II) also contain additional weak bands in the 500–650 nm region that are attributable to the d‐d transitions which are conspicuously missing for the uncomplexed curcumin.…”

“…A primary mechanism is their ability to catalyze polymerization of amyloid‐β and promote further misfolding of amyloid‐β into neurotoxic conformations found in brain cell plaques. Curcumin appears to be a promising candidate as a chelating agent in scavenging these neurotoxic transition metal ions through a competitive chelate complexation mechanism . Moreover, curcumin prevents further misfolding of amyloid‐β into neurotoxic conformations that have been isolated in plaques of brain cells .…”

“…Moreover, metal complexes of curcumin, especially those of ruthenium, palladium, copper, zinc and group(13) elements (Al, Ga, In) exhibit anticancer activity, and thus these metal complexes with curcumin appear to be promising candidates for treatment of certain forms of cancer such as lung cancer cells . Consequently, a number of experimental and a few theoretical studies have been devoted to the study of curcumin's chelation complexes with transition metal ions …”

“…A primary experimental evidence for curcumin's scavenging propensity with these transition metal ions is obtained through spectroscopic techniques . Transition metal ions chelate with curcumin through the loss of an enolic proton of curcumin, where chelation takes place.…”

Dichotomous Effect of Caffeine, Curcumin, and Naringenin on Genomic DNA of Normal and Diabetic Subjects

“…This implies the possibility of intercalation among the bases and π - π * interaction between DNA and curcumin [34]. Disappearance of peak on addition of copper to DNA-curcumin complex suggests weaker affinity between oxygen ligand of curcumin and copper ion (soft Lewis acid) [35]. Effect of copper on phytocompounds interaction with DNA is important to know the extent of metal influence on stability.…”