Exploring the World of Curcumin: Photophysics, Photochemistry, and Applications in Nanoscience and Biology

Abstract

Curcumin is a bright yellow naturally occurring polyphenol which is the principal component of turmeric. It is used as herbal supplement, cosmetics ingredient, and food coloring agent. Over the years, the therapeutic properties of the natural product curcumin have gone unexploited but not unnoticed. Curcumin cannot be employed as a drug due to limitations such as low aqueous solubility and limited bioavailability. Many attempts have been made to overcome these limitations by confining the drug in various confined media to enhance its bioavailability. The biomolecule is emissive and undergoes fundamental excited state processes such as solvation dynamics and excited state intramolecular proton transfer (ESIPT). Curcumin based biomaterials and nanomaterials are also a fast advancing field where curcumin is an intrinsic component necessary for formation of these materials and no longer added as an external free drug. In this review, we will summarize the recent research on the photophysical and photochemical properties of curcumin and its excited state dynamics in various bio-mimicking systems. At the same time we wish to also incorporate the various applications of curcumin, especially in biology. Lastly due to the growing importance of materials science, we will briefly discuss some recent advances on curcumin based biomaterials and nanomaterials. We believe such a compilation of recent research surrounding curcumin will provide an overall understanding of its potentialities in different areas.

Figure 1

The structure of tautomeric forms of curcumin and that of natural curcumin analogues demethoxycurcumin, bisdemethoxycurcumin, cyclocurcumin.

Figure 2

(a) Photographic images of curcumin in DMSO at increasing concentration of NaOH (0 to 1.4 mM from left to right) under the ambient light (left) and under UV irradiation (right); reprinted from reference 24 with permission Copyright (2020) Elsevier B. V.; (b) molecular structure of various deprotonated forms of curcumin; (c) absorption, and (d) emission spectra of curcumin and its deprotonated states; (e) Time‐resolved decay decay of curcumin (CurH₃) and completely deprotonated curcumin (Cur^‐3 (λ_em=537 nm for CurH₃ and λ_em=584 nm for Cur⁻³, respectively); reprinted from reference 26 with permission Copyright (2023) John Wiley and Sons.

Figure 3

(a) Absorption and emission spectra of curcumin in micelles of TX‐100, DTAB, and SDS in H₂O and D₂O, (b) isotope effect observed in upconversion decays of curcumin in micelles of TX‐100, DTAB, and SDS collected at 520 nm (λ_ex=407 nm) in pH 7.4 tris buffer, and deuterated micellar environment at pD=7.4, (c) upconversion decay traces of curcumin in micelles of TX‐100, DTAB, and SDS in pH 7.4 tris buffer at three different wavelengths. The decay traces at the red end show a rising component (610 nm for TX‐100 and DTAB, 630 nm for SDS), indicates solvation dynamics; reprinted from reference 35 with permission Copyright (2010) American Chemical Society; (c) plot for determination of partition coefficient, and (d) plot for determination of binding constant for the system comprising of curcumin in ionic liquid micelles in water; reprinted from reference 36 with permission Copyright (2012) American Chemical Society.

Figure 4

(a) Graphical representation of curcumin containing niosomes comprising of nonionic surfactant and cholesterol, (b) curcumin fluorescence excitation spectrum in niosomes, and curcumin emission spectra in niosomes and micelles, (c) Increase in relative quantum yield of curcumin with increasing concentration of surfactant; reprinted from reference 39 with permission Copyright (2013) American Chemical Society; (d) decrease of curcumin steady‐state fluorescence anisotropy (measured at emission maxima) with decrease in the molar ratio of T80: curcumin at 25 °C, (e) variation in the zeta potential for different ratios of T80: curcumin at 25 °C. The zeta potential decreased from 20: 1 to 8: 1 T80: curcumin molar ratios, and increased from the 7: 1 to 1: 1 T80: curcumin molar ratios; reprinted from reference 42 with permission Copyright (2020) Royal Society of Chemistry.

Figure 5

(a) Design strategy for preparation of curcumin‐piperlongumine hybrid molecule, reprinted from reference 62 with permission Copyright (2024) American Chemical Society; (b) Illustration of synthesis of curcumin nanoparticles and their antifungal activity against the fungi Pythium ultimum, reprinted from reference 69 with permission Copyright (2020) John Wiley and Sons.

Figure 6

(a) Schematic representation of curcumin containing solid lipid nanoparticles surface modified with mannose (Man‐CUR SLNs) to target the mannose receptors on surface of lung cancer cells and bacteria infected macrophages; reprinted from reference 77 with permission Copyright (2024) American Chemical Society; (b) Illustration of curcumin encapsulated composite nanodrug Cur@Fe&TA for treatment of irritable bowel disease (IBD); reprinted from reference 78 with permission Copyright (2024)American Chemical Society.