Effect of pH and temperature on conformational equilibria and aggregation behaviour of curcumin in aqueous binary mixtures of ethanol

Bhatia, Nidhi Kaur; Kishor, Shyam; Katyal, Nidhi; Gogoi, P. K.; Narang, Payal; Deep, Shashank

doi:10.1039/c6ra24256a

Cited by 78 publications

(88 citation statements)

References 39 publications

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“…The absorption spectral features of the peptide–curcumin complex indicate the presence of a monoanionic enol form of curcumin. 47 This observation and the presence of a positively charged peptide support the role of electrostatic interaction between the peptide and curcumin along with hydrogen bonding. The role of enolization of curcumin and electrostatic interactions with different systems has been highlighted by Gupta et al, 48 and Banerjee and Chakravarty show that monoanionic curcumin retains its therapeutic potential even in its bound state.…”

Section: Resultsmentioning

confidence: 79%

Enhancing Aqueous Solubility and Antibacterial Activity of Curcumin by Complexing with Cell-Penetrating Octaarginine

2020

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Bacterial resistance to antimicrobial drugs is one of the biggest threats to human health and novel drugs, and strategies are needed to obviate this resistance crisis. An innovative strategy for designing novel antimicrobial drugs is based on the hybridization of an antimicrobial agent with a second functional entity. Here, we use a cell-penetrating peptide–octaarginine (R8) as the second functional entity and develop a complex or hybrid of R8 and curcumin that possibly targets the bacterial cell membrane. Minimum inhibitory concentration assays show that the antibacterial activity of the complex is enhanced in a synergistic manner and rapid killing kinetics are obtained, emphasizing a bactericidal mode of action. In addition, electron microscopy images reveal bacterial membrane disruption by the complex. The R8–curcumin complex also displays activity against HeLa cells.

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Section: Resultsmentioning

confidence: 79%

Enhancing Aqueous Solubility and Antibacterial Activity of Curcumin by Complexing with Cell-Penetrating Octaarginine

2020

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“…Structurally, it contains three main functional groups: Two aromatic ring systems containing o-methoxy phenolic groups, and one alpha beta-unsaturated beta-diketone moiety. In aqueous solutions, curcumin undergoes keto-enol tautomerism with its structure depending on pH: The keto form dominates under acidic and/or neutral conditions, while the enolate form dominates under alkaline conditions ( Figure 2 ) [ 19 , 20 , 21 ]. The enol form is more chemically labile than the keto form, accounting for the poor chemical stability of curcumin in basic solutions [ 21 ].…”

Section: Chemistry Of Curcuminmentioning

confidence: 99%

Formulation of More Efficacious Curcumin Delivery Systems Using Colloid Science: Enhanced Solubility, Stability, and Bioavailability

2020

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Curcumin is a bioactive constituent isolated from turmeric that has historically been used as a seasoning, pigment, and herbal medicine in food. Recently, it has become one of the most commonly studied nutraceuticals in the pharmaceutical, supplement, and food areas because of its myriad of potential health benefits. For instance, it is claimed to exhibit antioxidant, anti-inflammatory, antimicrobial, antiparasite, and anticancer activities when ingested as a drug, supplement, or food. Toxicity studies suggest that it is safe to consume, even at relatively high levels. Its broad-spectrum biological activities and low toxicity have meant that it has been widely explored as a nutraceutical ingredient for application in functional foods. However, there are several hurdles that formulators must overcome when incorporating curcumin into commercial products, such as its low water solubility (especially under acidic and neutral conditions), chemical instability (especially under neutral and alkaline conditions), rapid metabolism by enzymes in the human body, and limited bioavailability. As a result, only a small fraction of ingested curcumin is actually absorbed into the bloodstream. These hurdles can be at least partially overcome by using encapsulation technologies, which involve trapping the curcumin within small particles. Some of the most commonly used edible microparticles or nanoparticles utilized for this purpose are micelles, liposomes, emulsions, solid lipid particles, and biopolymer particles. Each of these encapsulation technologies has its own benefits and limitations for particular product applications and it is important to select the most appropriate one.

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“…In order to further confirm the shift of the tautomeric equilibrium of curcumin, steady‐state fluorescence measurements were performed. The fluorescence properties of curcumin were first measured in water (Figure SI3), which is known to decrease the energy gap between enol and keto, most notably through strong intramolecular C=O⋅⋅⋅H−O‐H⋅⋅⋅O=C interactions stabilizing the keto form . Fluorescence spectra were measured at two different excitation wavelengths, 338 and 418 nm, corresponding to the maximum absorption wavelengths of the keto and enol forms in water, respectively.…”

Section: Resultsmentioning

confidence: 99%

“…This property has been used and largely exploited in the past, in particular showing how modification of the solvent polarity, of the pH, and of the temperature has a strong influence on the diketo‐enol ratio.…”

Section: Introductionmentioning

confidence: 99%

Triggering Tautomerization of Curcumin by Confinement into Liposomes

et al. 2019

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Although solvent polarity, pH and temperature have been reported to affect the keto-enol equilibrium of curcumin, the synergistic effect of concentration and confinement is demonstrated for the first time herein. To this end, curcumin was encapsulated into vesicles of soy lecithin of about 100 nm in diameter. The keto form is favoured in the dilute regime (up to 2 μM). Above this concentration, tautomerization is shifted towards the enol form, as shown by fluorescence and compression isotherm studies. Moreover, molecular modeling and free-energy profiles, together with simulation of the optical properties of the curcumin isomers, allowed us to dissect the interaction of the keto and enol forms with a model membrane and confirm the concentration-triggered tautomerization of curcumin under confinement.

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Effect of pH and temperature on conformational equilibria and aggregation behaviour of curcumin in aqueous binary mixtures of ethanol

Abstract: Conformational equilibria of curcumin, a potential therapeutic agent, can be modulated by changing pH, temperature and solvent composition.

Cited by 78 publications

References 39 publications

Enhancing Aqueous Solubility and Antibacterial Activity of Curcumin by Complexing with Cell-Penetrating Octaarginine

Enhancing Aqueous Solubility and Antibacterial Activity of Curcumin by Complexing with Cell-Penetrating Octaarginine

Formulation of More Efficacious Curcumin Delivery Systems Using Colloid Science: Enhanced Solubility, Stability, and Bioavailability

Triggering Tautomerization of Curcumin by Confinement into Liposomes

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