Combining time-resolved fluorescence with synchronous fluorescence spectroscopy to study bovine serum albumin-curcumin complex during unfolding and refolding processes.

We investigated the complex interaction between bovine serum albumin (BSA) and curcumin by combining time-resolved fluorescence and synchronous fluorescence spectroscopy. The interaction was significant and sensitive to fluorescence lifetime and synchronous fluorescence characteristics. Binding of curcumin significantly shortened the fluorescence lifetime of BSA with a bi-molecular quenching rate constant of k(q) = 3.17 × 10(12) M(-1) s(-1). Denaturation by urea unfolded the protein molecule by quenching the fluorescence lifetime of BSA. The tyrosine synchronous fluorescence spectra were blue shifted whereas the position of tryptophan synchronous fluorescence spectra was red shifted during the unfolding process. However, denaturation of urea had little effect on the synchronous fluorescence peak of tyrosine in curcumin-BSA complex except in the low concentration range; however, it shifted the peak to the red, indicating that curcumin shifted tryptophan moiety to a more polar environment in the unfolded state. Decreases in the time-resolved fluorescence lifetime and curcumin-BSA complex during unfolding were recovered during refolding of BSA by a dilution process, suggesting partial reversibility of the unfolding process for both BSA and curcumin-BSA complex.

Study on effect of lipophilic curcumin on sub-domain IIA site of human serum albumin during unfolded and refolded states: a synchronous fluorescence spectroscopic study.

Curcumin having pharmaceutical application as anti-oxidant, anti-inflammatory and anti-carcinogenic drug necessitates studying interaction of this molecule with native, unfolded and refolded state of human serum albumin (HSA), carrier protein in the blood. We proposed a simultaneous static and dynamic fluorescence quenching mechanism operating in the complex formation between HSA and curcumin. Location of curcumin in the close proximity of tryptophan with respect to tyrosine was further evident from the observation of two fold increase in rate of depletion of SFS intensity for tryptophan with respect to tyrosine in HSA in SFS spectrum. Alteration of SFS spectral peak position, electronic absorbance, fluorescence intensity and lifetime suggested chemical denaturation by urea expectedly unfold the protein molecule in the absence and presence of curcumin. Denatured HSA had similar fluorescence peak position and lifetime to that of L-tryptophan in the polar environment. During unfolding of HSA the spectral change of tyrosine and tryptophan was resolved through synchronous fluorescence spectra at two different Δλ in absence and presence of curcumin. It is found that curcumin remained bound to unfolded state of HSA and facilitated the process by pushing tryptophan moiety to more polar environment in the unfolded state. Dilution of the denatured protein by phosphate buffer reversibly refolded the sub-domain IIA, by also recovering fluorescence lifetime loss, but it was slow in the presence of curcumin. k(q) values indicate that curcumin-HSA complex is formed in the unfolded and refolded states as observed for native state.

Time-resolved fluorescence study during denaturation and renaturation of curcumin-myoglobin complex.

Curcumin influences the transition point, the concentration of denaturant required to effect 50% of the total change, of myoglobin denaturation. Curcumin enhances absorbance of myoglobin at 280 nm with a binding constant K=3.0×10(4) M(-1) whereas fluorescence of curcumin is quenched by myoglobin with a Stern-Volmer association constant of 2.5×10(5) M(-1). Unfolding process of myoglobin-curcumin induces a recovery in fluorescence lifetime loss. The gain in time-resolved fluorescence lifetime during unfolding has been again lost during refolding of curcumin-myoglobin complex by dilution process suggesting partial reversibility of unfolding process for both myoglobin and curcumin-myoglobin complex.

Unique role of ionic liquid [bmin][BF4] during curcumin-surfactant association and micellization of cationic, anionic and non-ionic surfactant solutions.

Hydrophilic ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroburate, modified the properties of aqueous surfactant solutions associated with curcumin. Because of potential pharmaceutical applications as an antioxidant, anti-inflammatory and anti-carcinogenic agent, curcumin has received ample attention as potential drug. The interaction of curcumin with various charged aqueous surfactant solutions showed it exists in deprotonated enol form in surfactant solutions. The nitro and hydroxyl groups of o-nitrophenol interact with the carbonyl and hydroxyl groups of the enol form of curcumin by forming ground state complex through hydrogen bonds and offered interesting information about the nature of the interactions between the aqueous surfactant solutions and curcumin depending on charge of head group of the surfactant. IL[bmin][BF4] encouraged early formation of micelle in case of cationic and anionic aqueous surfactant solutions, but slightly prolonged micelle formation in the case of neutral aqueous surfactant solution. However, for curcumin IL [bmin][BF4] favored strong association (7-fold increase) with neutral surfactant solution, marginally supported association with anionic surfactant solution and discouraged (∼2-fold decrease) association with cationic surfactant solution.

Synchronous fluorescence spectroscopic study of solvatochromic curcumin dye.

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 Δλ=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 ET30. When Stokes's shift in wavenumber scale was replaced by synchronous fluorescence maximum in nanometer scale, the solvent polarity dependency measured by λSFSmax vs. Lippert-Mataga plot or ET30 values offered similar trends as measured via Stokes' shift for protic and aprotic solvents for curcumin. Better linear correlation of λSFSmax vs. π* scale of solvent polarity was found compared to λabsmax or λemmax 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.