Theoretical study on physicochemical properties of curcumin.

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Pharmacology

Background:

• Curcumin, a pigment with diverse biological activities, has poorly understood physicochemical properties.
• Existing research on curcumin's properties has led to unresolved questions.

Purpose of the Study:

• To elucidate the fundamental physicochemical properties of curcumin.
• To investigate the predominant form of curcumin in solution.
• To clarify the proton dissociation mechanism of curcumin.

Main Methods:

• Density Functional Theory (DFT) calculations.
• Time-Dependent Density Functional Theory (TD-DFT) calculations.
• Analysis of thermodynamic and spectral parameters.
• Calculation of absorption spectra for curcumin anions.

Main Results:

• Thermodynamic and spectral data confirm curcumin predominantly exists in its enol form in solution.
• Calculated absorption spectra of curcumin anions provide evidence that the lowest pK(a) relates to enolic proton dissociation.
• The findings reconcile existing controversies regarding curcumin's properties.

Conclusions:

• DFT and TD-DFT calculations are valuable tools for understanding curcumin's fundamental properties.
• The enol form is dominant, and its proton dissociation is key to curcumin's radical-scavenging mechanisms.
• This study resolves debates and offers insights into curcumin's pharmacological actions.