Metal complexes of curcumin and curcumin derivatives for molecular imaging and anticancer therapy

Interaction of gallium, indium, and vanadyl curcumin complexes with hen egg-white lysozyme (HEWL): Mechanistic aspects and evaluation of antiamyloidogenic activity

Many proteins and peptides can aggregate into amyloid fibrils with high-ordered and cross-β rich structure characteristics. Amyloid deposition is a common feature of neurodegenerative diseases called amyloidosis. Various natural polyphenolic compounds such as curcumin exhibited antiamyloidogenic activities, but less researches were focused on the metal complexes of these compounds. In this study, the inhibitory effects of gallium curcumin (Ga(cur)3), indium curcumin (In(cur)3), and vanadyl curcumin (VO(cur)2) on the amyloid fibrillation of hen egg white lysozyme (HEWL) have been investigated. Moreover, the details of binding interactions of these metal complexes with HEWL have been explored. The results of fluorescence quenching analyses revealed that In(cur)3 and VO(cur)2 have much higher binding affinities than Ga(cur)3 toward HEWL. The interactions of these metal complexes were accompanied by partial conformational changes in the tertiary structure of HEWL. The kinetic curves of the fibrillation process demonstrated that In(cur)3 and VO(cur)2 have higher inhibitory effects than Ga(cur)3 on the amyloid fibrillation of HEWL. The strength of binding to HEWL is completely in accordance with inhibitory activities of these metal complexes of curcumin.

Density Functional Theory-Guided Photo-Triggered Anticancer Activity of Curcumin-Based Zinc(II) Complexes

Photodynamic therapy (PDT) has evolved as a new therapeutic modality for cancer treatment with fewer side effects and drug resistance. Curcumin exhibits PDT activity, but its low bioavailability restricts its clinical application. Here, the bioavailability of curcumin was increased by its complex formation with the Zn(II) center. For a structure-activity relationship study, Zn(II)-based complexes (1-3) comprising N^N-based ligands (2,2'-bipyridine in 1 and 2 or 1,10-phenanthroline in 3) and O^O-based ligands (acetylacetone in 1, monoanionic curcumin in 2 and 3) were synthesized and thoroughly characterized. The X-ray structure of the control complex, 1, indicated a square pyramidal shape of the molecules. Photophysical and TD-DFT studies indicated the potential of 2 and 3 as good visible light type-II photosensitizers for PDT. Guided by the TD-DFT studies, the low-energy visible light-triggered singlet oxygen (1O2) generation efficacy of 2 and 3 was explored in solution and in cancer cells. As predicted by the TD-DFT calculations, these complexes produced 1O2 efficiently in the cytosol of MCF-7 cancer cells and ultimately displayed excellent apoptotic anticancer activity in the presence of light. Moreover, the molecular docking investigation showed that complexes 2 and 3 have very good binding affinities with caspase-9 and p-53 proteins and could activate them for cellular apoptosis. Further molecular dynamics simulations confirmed the stability of 3 in the caspase-9 protein binding site.

Interaction of gallium, indium and vanadyl diacetylcurcumin complexes with lysozyme: mechanistic aspects and evaluation of antiamyloidogenic activity

Diacetylcurcumin as a derivative of curcumin is a strong nitric oxide (NO) and O2-.anion scavenger. One strategy to improve stability of curcumin and its derivatives is complexation with metal. In this study, the binding interactions of gallium diacetylcurcumin (Ga(DAC)3), indium diacetylcurcumin (In(DAC)3), and vanadyl diacetylcurcumin (VO(DAC)2) with hen egg white lysozyme (HEWL) have been investigated. The results of fluorescence quenching analyses revealed that In(DAC)3 and VO(DAC)2 have higher binding affinities than Ga(DAC)3 towards HEWL. The interactions of these metal complexes were not accompanied by considerable conformational changes in the tertiary structure of HEWL. Furthermore, the inhibitory effects of these complexes on the amyloid fibrillation of HEWL were confirmed by the thioflavin T fluorescence assays. The kinetic curves of the fibrillation process illustrated that VO(DAC)2 has the highest inhibitory activity and In(DAC)3 has a significant delaying effect on the formation of amyloid fibrils of HEWL.

Cationic N,S-chelate half-sandwich iridium complexes: synthesis, characterization, anticancer and antiplasmodial activity

A series of pyrazole-based ligands and their corresponding cationic N,S-chelate half-sandwich iridium complexes were successfully synthesized. All iridium complexes exhibited good anticancer activity against the MCF-7 and MDA-MB-231 human breast cancer cells. The cytotoxic activity of unsubstituted iridium complex 1 is greater than that of cisplatin against MCF-7 cells. In addition, the cationic half-sandwich iridium complexes are also efficient in antiplasmodial study and complex 1 displayed the best activity as its IC50 was observed to be approximately 0.11 μM against the CQS-NF54 strain. These iridium complexes generally exhibited enhanced activity against the CQS-NF54 strain in comparison with that against the CQR-K1 strain. An "IC50 speed assay" investigation against the CQS-NF54 strain indicated complexes 1-3 to be fast-acting complexes that reach their lowest IC50 values within 16 hours. All complexes were fully characterized by IR spectroscopy, NMR spectroscopy, and elemental analysis, and the structure of the iridium complex was confirmed by single-crystal X-ray diffraction.

Sea urchin-like Bi2S3/curcumin heterojunction rapidly kills bacteria and promotes wound healing under near-infrared light

Bacterial infection is an urgent public health problem. We design a novel photo-responsive hybrid material by growing small molecules of curcumin (Cur) in situ on a sea urchin-like Bi₂S₃ surface by a one-step hydrothermal reaction method, thus forming an organic-inorganic hybrid material with interfacial contact. The Bi₂S₃/Cur hybrid material has good antibacterial effect under 808 nm near-infrared (NIR) light irradiation. The antibacterial mechanism is that the electron redistribution at the interface of Bi₂S₃/Cur excited by 808 nm NIR light will cause a large number of electrons to gather on the side of Bi₂S₃, forming an internal electric field to drive the excited electrons from Bi₂S₃ to Cur, which accelerates the separation of photoexcited electron-hole pairs and enhances the production of reactive oxygen species (ROS). In conclusion, due to these synergistic effects of the photothermal properties of Bi₂S₃, the production of more ROS and the release of small molecules of Cur from traditional Chinese medicine in Bi₂S₃/Cur, the antibacterial efficacy against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) is 99.96% and 99.03%, respectively. In vivo experiments in animals show that Bi₂S₃/Cur can reduce the inflammatory response and promote wound healing. This paper presents a simple, rapid and safe strategy for the treatment of wound infections with near-infrared light.

Design, Synthesis, and Anticancer Studies of a p-Cymene-Ru(II)-Curcumin Organometallic Conjugate Based on a Fluorescent 4-Amino-1,8-naphthalimide Tröger's Base Scaffold

A unique V-shaped "chiral" supramolecular scaffold, N-(4-pyridyl)-4-amino-1,8-naphthalimide Tröger's base (TBNap), was synthesized in good yield from a precursor N-(4-pyridyl)-4-amino-1,8-naphthalimide (Nap). TBNap was characterized using different spectroscopic methods and the molecular structure was elucidated by diffraction analysis. A new p-cymene-Ru(II)-curcumin conjugate (TB-Ru-Cur) was designed by reacting TBNap dipyridyl donor and ruthenium-curcuminato acceptor [RuCur = (p-cymene)Ru-(curcuminato)Cl] in the presence of silver triflate. TB-Ru-Cur was isolated in quantitative yield and characterized using Fourier transform infrared (FT-IR), NMR (¹H, ¹³C, and ¹⁹F), and electrospray ionization mass spectrometry (ESI-MS), and the molecular structure has been predicted using a computational study. Both TBNap and TB-Ru-Cur exhibited intramolecular charge transfer (ICT)-based fluorescence emission. Furthermore, the anticancer properties of TBNap, Ru-Cur, and TB-Ru-Cur were assessed in different cancer cell lines. Gratifyingly, the conjugate TB-Ru-Cur displayed fast-cellular internalization and good cytotoxicity against HeLa, HCT-116, and HepG2 cancer cells and the estimated IC₅₀ value was much lower than that of the precursors (TBNap and Ru-Cur) and the well-known chemotherapeutic drug cisplatin.

Antiproliferative Ruthenium Complexes Containing Curcuminoid Ligands Tested In Vitro on Human Ovarian Tumor Cell Line A2780, towards Their Capability to Modulate the NF-κBTranscription Factor, FGF-2 Growth Factor, and MMP-9 Pathway

So far, the polyphenolic components of turmeric have shown a significant pharmacological preventative activity for a wide spectrum of diseases, including oncological disorders. This type of natural product could be of great interest for the inhibition of cancer cell proliferation, displaying less side effects in comparison to classical chemotherapeutics. The poor bioavailability and quick metabolism of such natural compounds require new investigative methods to improve their stability in the organisms. A synthetic approach to increase the efficiency of curcuminoids is to coordinate them to metals through the beta-dicarbonyl moiety. We report the synthesis and the biological attempts on human ovarian carcinoma A2780 of ruthenium(II) complexes 1–4, containing curcuminoid ligands. The cytotoxicity of complexes 1–4 proves their antiproliferative capability, and a correlation between the IC50 values and NF-κB transcription factor, FGF-2, and MMP-9 levels was figured out through the principal component analysis (PCA).

Casiopeinas of Third Generations: Synthesis, Characterization, Cytotoxic Activity and Structure-Activity Relationships of Mixed Chelate Compounds with Bioactive Secondary Ligands

Casiopeinas are a family of copper(II) coordination compounds that have shown an important antineoplastic effect and low toxicity in normal cells. These compounds induce death cells by apoptosis through a catalytic redox process with endogenous reducing agents. Further studies included a structural variation, improving the activity and selectivity in cancer cells or other targets. In the present work we report the third generation, which contains a bioactive monocharged secondary ligand, as well as the design, synthesis, characterization and antiproliferative activity, of sixteen new copper(II) coordination compounds with curcumin or dimethoxycurcumin as secondary ligands. All compounds were characterized by elemental analysis, FTIR, UV-Vis, magnetic susceptibility, mass spectra with MALDI-flight time, cyclic voltammetry, electron paramagnetic resonance (EPR) spectroscopy and X-ray diffraction. Crystallization of two complexes was achieved in dimethylsulfoxide (DMSO) with polar solvent, and crystal data demonstrated that a square-based or square-base pyramid geometry are possible. A 1:1:1 stoichiometry (diimine: copper: curcuminoid) ratio and the possibility of a nitrate ion as a counterion were supported. ¹H, ¹³C NMR spectra were used for the ligands. A sulforhodamine B assay was used to evaluate the cytotoxicity effect against two human cancer cell lines, SKLU-1 and HeLa. Electronic descriptors and redox potential were obtained by DFT calculations. Structure–activity relationships are strongly determined by the redox potential (E_1/2) of copper(II) and molar volume (V) of the complexes. These compounds can be used as a template to open a wide field of research both experimentally and theoretically.

Complexes of Zn(II) with a mixed tryptanthrin derivative and curcumin chelating ligands as new promising anticancer agents

In this study, two novel curcumin (H-Cur)-tryptanthrin metal compounds-[Zn(TA)Cl₂], i.e., Zn(TA), and [Zn(TA)(Cur)]Cl, i.e., Zn(TAC)-were synthesized and investigated using 5-(bis-pyridin-2-ylmethyl-amino)-pentanoic acid (6,12-dioxo-6,12-dihydro-indolo[2,1-b]quinazolin-8-yl)-amide (TA) and H-Cur as the targeting and high-activity anticancer chemotherapeutic moieties, respectively. They were then compared with the di-(2-picolyl)amine (PA) Zn(II) complex [Zn(PA)Cl₂], i.e., Zn(PA). When compared with Zn(PA) and cisplatin, the IC₅₀ values of Zn(TA) and Zn(TAC) indicated that the compounds had high cytotoxicity against A549/DDP cancer cells, implying that the H-Cur-tryptanthrin Zn(II) compounds have the potential for use as anticancer drugs. We propose the use of synthesized theragnostic H-Cur-tryptanthrin Zn(II) complexes with nuclear-targeting and DNA-damaging capabilities as a simple therapeutic strategy against tumors. The Zn(TA) and Zn(TAC) complexes could be traced via red fluorescence and were found to accumulate in the cell nuclei and induce DNA damage, cell cycle arrest, mitochondrial dysfunction, and cell apoptosis both in vitro and in vivo. In addition, Zn(TAC) exhibited a higher antiproliferative effect on A549/DDP than Zn(TA) and Zn(PA), which was undoubtedly associated with the key roles of the novel tryptanthrin derivative TA and H-Cur in the Zn(TAC) complex.

Entangled ZnO on Ultrathin Hollow Fibers for UV-Aided Pollutant Decomposition

Zinc oxide (ZnO), a widely used ultraviolet (UV) degrading substance, offers high selectivity for wastewater treatment, but the leaching of ZnO into water could cause secondary contamination. Using porous substrates to fix and load ZnO is a promising technical method to improve the water purification efficiency and recycling durability of ZnO. However, limited by the slow kinetics and shielding effects, it is challenging to use traditional techniques to introduce ZnO into the interior of a hollow structure. Here, inspired by an ancient dyeing procedure, we formed a unique single-molecule bio-interfacial entanglement as an absorption layer to capture the catalyst for ZnO electroless deposition (ELD) on the surface of natural ultrathin hollow-structured Kapok fibers. With curcumin serving as a linking bridge, ELD allowed the spontaneous formation of intensive ZnO nanocrystals on both the outer and inner walls. ZnO-kapok as the catalyst for ultraviolet photodecomposition of organic pollutants (methylene blue (MB) and phenol as model pollutants) delivered a decomposition efficiency of 80% and outstanding durability. Further modification of the ZnO-kapok catalyst by doping with reduced graphene oxide (rGO) showed an improvement in photodegradation performance of 90% degradation under 2-h irradiation with 21.85 W/dm² light power. Moreover, to the best of our knowledge, this is the first report featuring ZnO loading on both the outer and inner walls of a fiber-structured hollow kapok material, which provides inspiration for immobilization of metallic oxides on hollow-structured materials for further applications in renewable catalysis, chemical engineering, and energy storage fields.

Influence of pH, β-Cyclodextrin, and Metal Ions on the Solubility and Stability of the Medicinally Competent Isoxazole Derivative of Curcumin: A Photophysical Study

The β-diketo-modified isoxazole derivative of curcumin (IOC) is well renowned for its anticancer, antioxidant, antimalarial, antiproliferative, and many other biological activities. With the aim of obtaining fundamental knowledge on the photophysics of IOC, the present work was directed toward delineating those at different pH environments and studying the degradation profiles of IOC at five different pH values. Because one of the primary drawbacks of curcumin is its rapid degradation at physiological conditions, the studies showed that the problem could be resolved, as the IOC molecule was extremely stable even in a highly alkaline medium. Further, in order to encounter the problems associated with the low solubility of IOC in aqueous media, β-CD (β-cyclodextrin) was used and calculations of the thermodynamic parameters revealed that the process of development of the host-guest inclusion complex was highly spontaneous in nature. The synthesis of the IOC:β-CD inclusion complex has also been accomplished in the solid state, and the solid formed has been characterized using various physicochemical techniques. Finally, while variations in the pH as well as addition of foreign metal ions in +1 and +2 oxidation states showed minimal effect on the photophysics of the IOC:β-CD inclusion complex, antiproliferative studies performed with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assays revealed their nontoxic nature on fibroblast L929 normal cell lines and extremely toxic activity on human lung cancer A549 cell lines.

A review of the berberine natural polysaccharide nanostructures as potential anticancer and antibacterial agents

Despite the promising medicinal properties, berberine (BBR), due to its relatively poor solubility in plasma, low bio-stability and limited bioavailability is not used broadly in clinical stages. Due to these drawbacks, drug delivery systems (DDSs) based on nanoscale natural polysaccharides, are applied to address these concerns. Natural polymers are biodegradable, non-immunogenic, biocompatible, and non-toxic agents that are capable of trapping large amounts of hydrophobic compounds in relatively small volumes. The use of nanoscale natural polysaccharide improves the stability and pharmacokinetics of the small molecules and, consequently, increases the therapeutic effects and reduces the side effects of the small molecules. Therefore, this paper presents an overview of the different methods used for increasing the BBR solubility and bioavailability. Afterwards, the pharmacodynamic and pharmacokinetic of BBR nanostructures were discussed followed by the introduction of natural polysaccharides of plant (cyclodextrines, glucomannan), the shells of crustaceans (chitosan), and the cell wall of brown marine algae (alginate)-based origins used to improve the dissolution rate of poorly soluble BBR and their anticancer and antibacterial properties. Finally, the anticancer and antibacterial mechanisms of free BBR and BBR nanostructures were surveyed. In conclusion, this review may pave the way for providing some useful data in the development of BBR-based platforms for clinical applications.

Latest Innovations and Nanotechnologies with Curcumin as a Nature-Inspired Photosensitizer Applied in the Photodynamic Therapy of Cancer

In the context of the high incidence of cancer worldwide, state-of-the-art photodynamic therapy (PDT) has entered as a usual protocol of attempting to eradicate cancer as a minimally invasive procedure, along with pharmacological resources and radiation therapy. The photosensitizer (PS) excited at certain wavelengths of the applied light source, in the presence of oxygen releases several free radicals and various oxidation products with high cytotoxic potential, which will lead to cell death in irradiated cancerous tissues. Current research focuses on the potential of natural products as a superior generation of photosensitizers, which through the latest nanotechnologies target tumors better, are less toxic to neighboring tissues, but at the same time, have improved light absorption for the more aggressive and widespread forms of cancer. Curcumin incorporated into nanotechnologies has a higher intracellular absorption, a higher targeting rate, increased toxicity to tumor cells, accelerates the activity of caspases and DNA cleavage, decreases the mitochondrial activity of cancer cells, decreases their viability and proliferation, decreases angiogenesis, and finally induces apoptosis. It reduces the size of the primary tumor, reverses multidrug resistance in chemotherapy and decreases resistance to radiation therapy in neoplasms. Current research has shown that the use of PDT and nanoformulations of curcumin has a modulating effect on ROS generation, so light or laser irradiation will lead to excessive ROS growth, while nanocurcumin will reduce the activation of ROS-producing enzymes or will determine the quick removal of ROS, seemingly opposite but synergistic phenomena by inducing neoplasm apoptosis, but at the same time, accelerating the repair of nearby tissue. The latest curcumin nanoformulations have a huge potential to optimize PDT, to overcome major side effects, resistance to chemotherapy, relapses and metastases. All the studies reviewed and presented revealed great potential for the applicability of nanoformulations of curcumin and PDT in cancer therapy.

Co(II) complexes of curcumin and a ferrocene-based curcuminoid: a study on photo-induced antitumor activity

Co(II) complexes having a ferrocene-based curcuminoid (Fc-curH) ligand viz. [Co(L)₂(Fc-cur)]ClO₄ (1, 2), where L is phenanthroline base, namely, 1,10-phenanthroline (phen in 1) and dipyrido[3,2-a:2',3'-c]phenazine (dppz in 2) have been synthesized, characterized and evaluated as photochemotherapeutic agents in vitro. The corresponding Co(II) complexes of the naturally occurring polyphenol curcumin (curH), namely, [Co(L)₂(cur)]ClO₄ (3, 4), where L is phen (in 3) and dppz (in 4) were synthesized and their photo-induced anticancer activities compared with their ferrocene containing counterparts 1 and 2. The Co(II) acetylacetonato complex viz. [Co(phen)₂(acac)]ClO₄ (5) was structurally characterized through X-ray crystallography and used as control for cellular experiments. The Co(II) complexes having ferrocene-based curcuminoid are remarkably stable at physiological condition with higher lipophilicity compared to their curcumin analogues. The complexes display significant binding propensity to calf thymus (ct) DNA and human serum albumin (HSA). The complexes 1-4 display remarkable visible light induced cytotoxicity with the ferrocenyl analogues showing more phototoxic index (PI). The Co(II) curcumin complexes localize in the nucleus and mitochondria of A549 cells. The primary cell death mechanism is believed to be apoptotic in nature induced by light assisted generation of reactive oxygen species (ROS).Graphic abstract.

2,6-bis(E)-4-methylbenzylidine)-cyclohexan-1-one as a Fluorescent-on Sensor for Ultra Selective Detection of Chromium Ion in Aqueous Media

The ligand 2,6-bis(E)-4-methylbenzylidine)-cyclohexan-1-one sensor has been synthesized as a fluorescence-on sensor/probe for the trace level detection of chromium III ion. The synthesized ligand was characterized by FTIR, ¹H-NMR spectroscopy, and fluorimetery. The sensor exhibited an ultra-selective response to chromium among the tested heavy metal ions. Different parameters were optimized like pH, effect of concentration of sensor C, metal ion and contact time. The binding stoichiometry of C:Cr³⁺ was calculated to be 2:1 (Job's plot) with a significantly low detection limit of 2.3 × 10^{- 9} M. Sensor C were practically employed for detection of chromium in spiked water samples.

An insight into the in vivo imaging potential of curcumin analogues as fluorescence probes

Curcumin and its derivatives have good electrical and optical properties due to the highly symmetric structure of delocalized π electrons. Apart from that, curcumin and its derivatives can interact with numerous molecular targets, thereby exerting less side effects on human body. The fluorescence emission wavelength and fluorescence intensity of curcumin can be enhanced by modifying its π-conjugated system and ß-diketone structure. Some curcumin-based fluorescent probes have been utilized to detect soluble/insoluble amyloid-ß protein, intracranial reactive oxygen species, cysteine, cancer cells, etc. Based on the binding characteristics of curcumin-based fluorescent probes with various target molecules, the factors affecting the fluorescence intensity and emission wavelength of the probes are analyzed, in order to obtain a curcumin probe with higher sensitivity and selectivity. Such an approach will be greatly applicable to in vivo fluorescence imaging.

Theoretical study of the impact of metal complexation on the reactivity properties of Curcumin and its diacetylated derivative as antioxidant agents

The chemical behavior of Curcumin and its derivatives as antioxidant and metal chelator has become the subject of intense experimental research. In this work, a theoretical study was conducted with the aim to investigate whether the acetylation of the aromatic group in Curcumin, which makes it more lipophilic, will alter its biological activities. Also, we selected from the literature metal complexes of Curcumin and its diacetylated derivative with Ga(III) and In(III), in order to discriminate the molecular active sites of the investigated molecules in which the oxidative process occurs and to obtain information about their antioxidation mechanisms. The geometrical structures and electronic properties of these compounds have been obtained using the density functional theory (DFT) method, known for its accurate results. As our other objective is to understand the factors driving biological behavior of all the studied compounds as well as the impact of the metal complexation of Curcumin and its diacetylated derivative, we provided here evidences to explain experimental observations from a molecular reactivity perspective.

Photoactive Thin-Film Structures of Curcumin, TiO2 and ZnO

Curcumin is known as a biologically active compound and a possible antimicrobial agent. Here, we combine it with TiO2 and ZnO semiconductors, known for their photocatalytic properties, with an eye towards synergistic photo-harvesting and/or antimicrobial effects. We deposit different nanoscale multi-layer structures of curcumin, TiO2 and ZnO, by combining the solution-based spin-coating (S-C) technique and the gas-phase atomic layer deposition (ALD) and molecular layer deposition (MLD) thin-film techniques. As one of the highlights, we demonstrate for these multi-layer structures a red-shift in the absorbance maximum and an expansion of the absorbance edge as far as the longest visible wavelength region, which activates them for the visible light harvesting. The novel fabrication approaches introduced here should be compatible with, e.g., textile substrates, opening up new horizons for novel applications such as new types of protective masks with thin conformal antimicrobial coatings.

Iron(III) Complex-Functionalized Gold Nanocomposite as a Strategic Tool for Targeted Photochemotherapy in Red Light

Iron(III)-phenolate/carboxylate complexes exhibiting photoredox chemistry and photoactivated reactive oxygen species (ROS) generation at their ligand-to-metal charge-transfer (LMCT) bands have emerged as potential strategic tools for photoactivated chemotherapy. Herein, the synthesis, in-depth characterization, photochemical assays, and remarkable red light-induced photocytotoxicities in adenocarcinomic human immortalized human keratinocytes (HaCaT) and alveolar basal epithelial (A549) cells of iron(III)-phenolate/carboxylate complex of molecular formula, [Fe(L¹)(L²)] (1), where L¹ is bis(3,5 di-tert-butyl-2-hydroxybenzyl)glycine and L² is 5-(1,2-dithiolan-3-yl)-N-(1,10-phenanthroline-5-yl)pentanamide, and the gold nanocomposite functionalized with complex 1 (1-AuNPs) are reported. There was a significant red shift in the UV-visible absorption band on functionalization of complex 1 to the gold nanoparticles (λ_max: 573 nm, 1; λ_max: 660 nm, 1-AuNPs), rendering the nanocomposite an ideal candidate for photochemotherapeutic applications. The notable findings in our present studies are (i) the remarkable cytotoxicity of the nanocomposite (1-AuNPs) to A549 (IC₅₀: 0.006 μM) and HaCaT (IC₅₀: 0.0075 μM) cells in red light (600-720 nm, 30 J/cm²) while almost nontoxic (IC₅₀ > 500 μg/mL, 0.053 μM) in the dark, (ii) the nontoxicity of 1-AuNPs to normal human diploid fibroblasts (WI-38) or human peripheral lung epithelial (HPL1D) cells (IC₅₀ > 500 μg/mL, 0.053 μM) both in the dark and red light signifying the target-specific anticancer activity of the nanocomposite, (iii) localization of 1-AuNPs in mitochondria and partly nucleus, (iv) remarkable red light-induced generation of reactive oxygen species (ROS: ¹O₂, ^•OH) in vitro, (v) disruption of the mitochondrial membrane due to enhanced oxidative stress, and (vi) caspase 3/7-dependent apoptosis. A similar cytotoxic profile of complex 1 was another key finding of our studies. Overall, our current investigations show a new red light-absorbing iron(III)-phenolate/carboxylate complex-functionalized gold nanocomposite (1-AuNPs) as the emerging next-generation iron-based photochemotherapeutic agent for targeted cancer treatment modality.

Ultra-small natural product based coordination polymer nanodots for acute kidney injury relief

Acute kidney injury (AKI) is frequently associated with reactive oxygen species (ROS) and causes high mortality in clinics annually, and nanotechnology-mediated antioxidative therapy is emerging as a novel strategy for AKI treatment. Herein, four kinds of natural antioxidants are able to coordinate with iron (Fe) ions to form ultra-small coordination polymer nanodots (CPNs) with good water dispersibility and strong ROS scavenging ability. In particular, Fe-curcumin CPNs (Fe-Cur CPNs) are applied for cellular ROS scavenging and rhabdomyolysis-induced AKI relief.

Spicy Bitumen: Curcumin Effects on the Rheological and Adhesion Properties of Asphalt

Over the years, the need for the synthesis of biodegradable materials has facilitated the drift of the asphalt industry towards eco-sustainable and cost-effective production of road pavements. The principal additives in the asphalt industry to improve the performance of road pavements and increase its lifespan are majorly rheological modifiers, adhesion promoters and anti-oxidant agents. Rheological modifiers increase physico-chemical properties such as transition temperature of asphalt binder (bitumen), adhesion promoters increase the affinity between binder and stone aggregates while anti-oxidant agents reduce the effects of oxidation caused by exposure to air, water and other natural elements during the production of asphalt pavements. In this study, we tested the effectiveness of a food grade bio-additive on these three aforementioned properties. We also sought to hypothesize the mechanisms by which the additive confers these desired features on bitumen. We present this study to evaluate the effects of turmeric, a food-based additive, on bitumen. The study was conducted through dynamic shear rheology (DSR), atomic force microscopy, scanning electron microscopy (SEM) and boiling test analysis.

Phytochemicals toward Green (Bio)sensing

Because of numerous inherent and unique characteristics of phytochemicals as bioactive compounds derived from plants, they have been widely used as one of the most interesting nature-based compounds in a myriad of fields. Moreover, a wide variety of phytochemicals offer a plethora of fascinating optical and electrochemical features that pave the way toward their development as optical and electrochemical (bio)sensors for clinical/health diagnostics, environmental monitoring, food quality control, and bioimaging. In the current review, we highlight how phytochemicals have been tailored and used for a wide variety of optical and electrochemical (bio)sensing and bioimaging applications, after classifying and introducing them according to their chemical structures. Finally, the current challenges and future directions/perspective on the optical and electrochemical (bio)sensing applications of phytochemicals are discussed with the goal of further expanding their potential applications in (bio)sensing technology. Regarding the advantageous features of phytochemicals as highly promising and potential biomaterials, we envisage that many of the existing chemical-based (bio)sensors will be replaced by phytochemical-based ones in the near future.

Curcumin Doped SiO2/TiO2 Nanocomposites for Enhanced Photocatalytic Reduction of Cr (VI) under Visible Light

In order to further improve the photocatalytic performance of the SiO2/TiO2 composite under visible light irradiation, curcumin-doped SiO2/TiO2 nanocomposites were synthesized via directly incorporating it into the structure of SiO2/TiO2 during the synthesis using an inexpensive and readily available natural pigment (curcumin) as doping agent. The physicochemical properties of SiO2/TiO2 nanocomposites were characterized in detail by X-ray diffraction, transmission electron microscopy, Fourier transform-infrared spectroscopy, N2 adsorption–desorption isotherms, X-ray photoelectron spectroscopy, and UV-vis diffuse reflectance spectroscopy. The results indicate that all SiO2/TiO2 nanocomposites exhibited an anatase phase with a typical mesoporous structure. It was found that the dope of curcumin in the SiO2/TiO2 composite could decrease the crystal size, slightly improve the specific surface areas, significantly enhance the visible light absorption, and effectively narrow the band gap energy from 3.04 to 10(eV). Compared with bare SiO2/TiO2, the curcumin-doped SiO2/TiO2 resulted in enhanced photocatalytic reduction activity for Cr(VI) under visible light irradiation, and the CTS (12) sample with the appropriate content of curcumin of 12 wt % shows the photocatalytic yield reaching 100% within 2.5 hours, which is larger than CT (12) without silica. This could be attributed to the curcumin doping and the synergetic effects of SiO2 and TiO2 in SiO2/TiO2 nanocomposites.

Ni(II) curcumin complexes for cellular imaging and photo-triggered in vitro anticancer activity

Nickel(II) complexes [Ni(cur)(L)₂](OAc) (1-3) where L is N,N-donor heterocyclic bases namely 1,10-phenanthroline (phen in 1), dipyrido[3,2-d:2',3'-f]quinoxaline (dpq in 2), dipyrido[3,2-a:2',3'-c]phenazine (dppz in 3) and Hcur is curcumin were prepared, fully characterized and light-induced in vitro anticancer activity studied. Three nickel(II) complexes containing acetylacetonato (Hacac) ligand, viz.[Ni(acac)(L)₂](OAc) (4-6) where L is phen (in 4), dpq (in 5), dppz (in 6) were prepared and used as controls. Complex 4 was structurally characterized by single crystal X-ray diffraction technique, which revealed an octahedral NiN₄O₂ geometry around the metal centre. Complexes 1-3 showed an intense curcumin-based band at ∼440 nm in DMSO-Tris-HCl buffer (pH = 7.2) (1:4 v/v) which masks the nickel based d-d band. The curcumin comlexes (1-3) were redox inactive at the nickel centre, whereas the acetylacetonato complexes (4-6) displayed an irreversible voltammetric response at ∼1.00 V vs. Ag/AgCl reference electrode in DMF. The complexes bind to calf thymus DNA (ct-DNA) with considerable affinity and interacted with human serum albumin (HSA) with moderate affinity. The Ni(II) curcumin complexes display significant in vitro light-induced cytotoxicity in HeLa (human cervical carcinoma) and A549 (lung cancer cells) involving reactive oxygen species (ROS), with very low dark toxicity. The complexes were found to be much less toxic to immortalized lung epithelial normal cells (HPL1D). Confocal microscopic images using complex 2 and 3 showed that they primarily localize in the cytosol of A549 cells. The mechanism of cell death is mainly apoptosis in nature showing arrest of sub-G1 phase of cell cycle progression in A549 cells under visible light exposure and involves significant loss of mitochondrial membrane potential as observed from JC-1 assay.

Multitargeting Antibacterial Activity of a Synthesized Mn2+ Complex of Curcumin on Gram-Positive and Gram-Negative Bacterial Strains

Curcumin is an important molecule with a plethora of pharmacological activities and therapeutic potentials. Despite its efficacy, it remained a potential drug candidate owing to hydrolytic instability and poor aqueous solubility. To overcome the limitations related to low solubility, low bioavailability, and the fact that curcumin is never present in solution as a "single unit", its complex was prepared with MnII with the idea that binding to a metal ion might help to resolve these issues. The complex was characterized by elemental and spectral analysis. The structure of the complex was determined by density functional theory calculations. The complex was stable at physiological buffer conditions, unlike curcumin. It did not have any detrimental effect on mammalian cells. There was a significant enhancement in the antibacterial activity of the complex compared to curcumin against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. It showed a strong affinity for deoxyribonucleic acid (DNA) evident from a high binding constant value with calf thymus DNA and also from the retarded electrophoretic mobility of bacterial plasmid DNA. The complex showed "superoxide dismutase-like" activity leading to the generation of reactive oxygen species (ROS). The complex caused bacterial membrane perturbation evident from calcein leakage assay, which was further corroborated by scanning and transmission electron microscopic experiments. Overall, the present study shows improved stability and antibacterial potency of a nontoxic complex over curcumin. Its multitargeting mode of action such as ROS-production, effective binding with DNA, and permeabilization of bacterial membrane together allows it to be an effective antibacterial agent that could be taken further for therapeutic use against bacterial infections.

Role of Curcumin and (-)-Epigallocatechin-3-O-Gallate in Bladder Cancer Treatment: A Review

The incidence of bladder cancer (BC) is increasing, and although current therapeutic approaches are effective in many cases, recurrence of BC is common. Therefore, it seems necessary to search not only for novel therapeutic approaches, but also for new therapeutic agents. Natural polyphenols, such as curcumin (CUR) and epigallocatechin gallate (EGCG), possess remarkable antitumor activity. Their biochemical mechanisms of action include regulation of signaling pathways, modeling of proteins involved in apoptosis and cell cycle inhibition, angiogenesis, and the proliferation, migration and adhesion of tumor cells. Both compounds also present antioxidant, anti-inflammatory, antibacterial and antiviral properties. CUR has been considered a promising candidate for the treatment of cystic fibrosis, Alzheimer's disease or malaria, whereas EGCG can play a supportive role in the treatment of obesity, metabolic and neurodegenerative diseases. The review summarizes the latest research on the role of CUR and EGCG in the treatment of BC. In particular, the effects of CUR and EGCG, and their prospects for use in BC therapy, their inhibition of cancer development and their prevention of multidrug resistance, are described. The literature's data indicate the possibility of achieving the effect of synergism of both polyphenols in BC therapy, which has been observed so far in the treatment of ovarian, breast and prostate cancer.

Bifunctional ruthenium(ii) polypyridyl complexes of curcumin as potential anticancer agents

Ru(ii)-polypyridyl complexes have been widely studied and well established for their antitumor properties. Modifications of the coordination environment around the Ru atom through a proper choice of the ligand can lead to different modes of action and result in greatly improved anticancer efficacy. Herein, two Ru(ii)-polypyridyl complexes of curcumin were synthesized and characterized as potential anticancer agents. In vitro tests indicated that complexes 1 and 2 displayed excellent antiproliferative activity against the tested cancer cell lines, especially complex 2, which exhibited superior cytotoxicity compared to curcumin and cisplatin. Further biological evaluations demonstrated that complexes 1 and 2 can cause cell apoptosis via DNA interaction and MEK/ERK signaling pathway, which is the first example of a Ru(ii)-polypyridyl complex inhibiting the MEK/ERK signaling pathway and DNA intercalation. Overall, this work suggests that coordination with bioactive agents may endow Ru(ii)-polypyridyl complexes with improved pharmaceutical properties and synergistic effects for cancer therapy.

Effects of curcumin complexes on MDA‑MB‑231 breast cancer cell proliferation

Curcumin displays anticancer properties; however, some issues with the drug delivery mode limit its therapeutic use. Although reformulation and derivatization of curcumin have improved its bioavailability, curcumin derivatives may not retain the same anticancer properties as the parent compound. The present study investigated the anticancer properties of two curcumin complexes, the iron‑curcumin [Fe(Cur)3] and boron‑curcumin [B(Cur)2] complexes, in the MDA‑MB‑231 breast cancer cell line. The cellular localization of curcumin, B(Cur)2 and Fe(Cur)3 was determined by fluorescence microscopy. Cell proliferation, migration and invasion were also analysed. Furthermore, apoptosis‑associated proteins were detected by using a proteome profiler array, and ion channel gene expression was analysed by reverse transcription‑quantitative PCR. The results demonstrated that the three compounds were localized in the perinuclear and cytoplasmic regions of the cell, and displayed cytotoxicity with IC50 values of 25, 35 and 8 µM for curcumin, B(Cur)2 and Fe(Cur)3, respectively. In addition, the three compounds inhibited cell invasion, whereas only curcumin and B(Cur)2 inhibited cell migration. Furthermore, cell exposure to curcumin resulted in an increase in the relative expression of the two key proapoptotic proteins, cytochrome c and cleaved caspase‑3, as well as the antiapoptotic protein haem oxygenase‑1. In addition, curcumin increased the expression levels of the voltage‑gated potassium channels Kv2.1 and Kv3.2. Similarly, the expression levels of the chloride channel bestrophin‑1 and the calcium channel coding gene calcium voltage‑gated channel auxiliary subunit γ4 were increased following exposure to curcumin. Taken together, these results indicated that Fe(Cur)3 and B(Cur)2 may display similar anticancer properties as curcumin, suggesting that chemical complexation may be considered as a strategy for improving the potency of curcumin in the treatment of breast cancer.

Application of curcumin and its derivatives in tumor multidrug resistance

Malignant tumor endangers seriously the health of all mankind. Multidrug resistance (MDR) is one of the main causes of clinical tumor chemotherapy failure. Curcumin (CUR) has not only antitumor activity but also reversing tumor MDR effect. CUR reverses tumor MDR via regulating related signal pathways or corresponding expressed proteins or gene. When combined with chemotherapeutic agents, CUR can be a chemotherapeutic sensitive agent to enhance chemotherapy efficacy and weaken tumor MDR. On the other hand, to improve the MDR reversal effect of CUR, its derivatives have been extensively studied. Therefore, this article mainly focuses on reviewing the application of CUR and its derivatives in MDR and its mechanism of reversing MDR.

Synthesis, photophysical properties and theoretical studies of new bis-quinolin curcuminoid BF2-complexes and their decomplexed derivatives

This paper presents the synthesis and characterization of two series of new bis-quinolin curcuminoid BF₂-complexes 11 and their respective decomplexed bis-quinolin curcuminoid derivatives 12, in an attempt to understand their optical properties. The synthesized compounds showed interesting fluorescent characteristics in both solution and in solid-state. The characteristic of the electronic transitions involved in these systems were measured via Uv-vis spectroscopy and fluorescence spectroscopy. Results revealed that the absorption and emission bands are dependent of the structure of compounds 11 and 12 but also of the type of substituent, even showing a push-pull behavior in those derivatives substituted with methyl group. These findings were also confirmed through computational calculations at DFT level via simulations of the Uv-vis spectra and determining the topology of the border orbitals responsible for light absorption.

A novel study on curcumin metal complexes: solubility improvement, bioactivity, and trial burn wound treatment in rats

This paper describes a new technique to enhance the solubility of metal curcumin complexes.

Gallium-68 and scandium-44 labelled radiotracers based on curcumin structure linked to bifunctional chelators: Synthesis and characterization of potential PET radiotracers

Curcumin metal complexes showed widespread applications in medicine and can be exploited as a lead structure for developing new tracers for nuclear medicine application. Herein, the synthesis, chemical characterization and radiolabelling with gallium-68 and scandium-44 of two new targeting vectors based on curcumin scaffolds and linked to the chelators 1,4,7-triazacyclononane,1-glutaric acid-4,7-acetic acid (NODAGA) and 1,4-bis(carboxymethyl)-6-[bis(carboxymethyl)]amino-6-methylperhydro-1,4-diazepine (AAZTA) are reported. Synthesis of the precursors could be achieved with a 13% and 11% yield and radiolabelling generally afforded rapid incorporation under mild conditions (>95%). Stability in physiological media (~75% after 2 h in human blood for [⁶⁸Ga]Ga-/[⁴⁴Sc]Sc-AAZTA-PC21 and ~60% for [⁶⁸Ga]Ga-NODAGA-C21, respectively) are generally enhanced if compared to the previously radiolabelled analogues. MSⁿ fragmentation experiments showed high stability of the AAZTA-PC21 structure mainly due to the pyrazole derivatization of the curcumin keto-enol moiety and a more feasible radiolabelling was noticed both with gallium-68 and scandium-44 mainly due to the AAZTA-chelator properties. [⁶⁸Ga]Ga-NODAGA-C21 showed the most favorable lipophilicity value (logD = 1.3). Due to these findings, both compounds appear to be promising candidates for the imaging of colorectal cancer, but further studies such as in vitro uptake and in vivo biodistribution experiments are needed.

Curcumin and Its Derivatives as Potential Therapeutic Agents in Prostate, Colon and Breast Cancers

Cancer is a life-threatening disease and is the second leading cause of death around the world. The increasing threats of drug-resistant cancers indicate that there is an urgent need for the improvement or development of more effective anticancer agents. Curcumin, a phenolic compound originally derived from turmeric plant (Curcuma longa L. (Zingiberaceae family)) widely known as a spice and a coloring agent for food have been reported to possess notable anticancer activity by inhibiting the proliferation and metastasis, and enhancing cell cycle arrest or apoptosis in various cancer cells. In spite of all these benefits, the therapeutic application of curcumin in clinical medicine and its bioavailability are still limited due to its poor absorption and rapid metabolism. Structural modification of curcumin through the synthesis of curcumin-based derivatives is a potential approach to overcome the above limitations. Curcumin derivatives can overcome the disadvantages of curcumin while enhancing the overall efficacy and hindering drug resistance. This article reports a review of published curcumin derivatives and their enhanced anticancer activities.

Visible light-induced cytotoxicity studies on Co(ii) complexes having an anthracene-based curcuminoid ligand

Herein, two ternary cobalt(ii) complexes, namely [Co(9-accm)(phen)₂](OAc) (1) and [Co(9-accm)(dppz)₂](OAc) (2), where 9-accmH is 1,7-(di-9-anthracene-1,6-heptadiene-3,5-dione), phen is 1,10-phenanthroline and dppz is dipyrido[3,2-a:2',3'-c]phenazine, having an anthracene-based curcuminoid and phenanthroline bases were synthesized and fully characterized, and their in vitro photocytotoxicities were studied in cancer cells. To understand the role of the curcuminoid ligand 9-accm in photo-activated cytotoxicity, two control complexes, viz. [Co(dbm)(phen)₂](OAc) (3) and [Co(dbm)(dppz)₂](OAc) (4), where dbmH is 1,3-diphenyl-1,3-propanedione (dibenzoylmethane), were prepared and used for the control experiments. Complex 3 was structurally characterized by X-ray crystallography. The complexes displayed a quasi-reversible Co(i)/Co(ii) redox couple at ∼-1.1 V and an irreversible Co(ii)/Co(iii) couple at ∼1.3 V vs. Ag/AgCl in DMF-0.1 M [Buⁿ₄N](ClO₄). Highly intense 9-accm ligand-centred bands were observed at ∼250-450 nm, which masked the Co(ii)-based weak d-d bands in the DMF-Tris-HCl buffer (1 : 9 v/v). The complexes displayed a significant binding propensity for calf-thymus (ct) DNA with binding constants in the range from (2.42 ± 0.10) × 10⁵ to (3.24 ± 0.13) × 10⁶ M^-1. They also showed a moderate binding affinity for human serum albumin (HSA), displaying K_b values in the order of ∼10⁴-10⁵ M^-1. The complexes 1 and 2 showed prodigious photoenhanced cytotoxicity in human cervical cancer (HeLa) and breast cancer (MCF-7 and MDA-MB-231) cells with low dark toxicity, whereas they were non-toxic to immortalized lung epithelial normal cells (HPL1D). Flow cytometric studies showed a time-dependent uptake of the complexes 1 and 2 in HeLa cells. The complexes generated reactive oxygen species (ROS) upon excitation with low energy visible light, thereby killing the cancer cells. The results from DAPI staining, AO/EB dual staining and Annexin-V-FITC experiments suggested that the complexes induce cell death primarily via an apoptotic mechanism in HeLa cells.

Zn(II) Curcuminate Complexes with 2,2'-bipyridine and Carboxylates

Two novel zinc(II) compounds with curcuminate (abbreviated as cur-), [Zn(CH3COO)(cur)(bpy)](1)·CH3OH·2H2O (bpy = 2,2'-bipyridine) and [Zn(PhCOO)(cur)(bpy)] (2)·CH3OH, have been synthesized and characterized. Their composition has been determined by single-crystal X-ray structure analysis. Complexes 1 and 2 are similar: in both a five-fold coordination environment of zinc(II) consists of a monodentate carboxylate, a chelating bidentate 2,2'-bipyridine, and curcuminate, which is bound via a deprotonated 1,3-dione moiety. In 1, 2,2'-bipyridine nitrogen atoms and curcuminate oxygen atoms form the base of a square pyramid, whereas the acetate oxygen occupies its apex. The O3N2 donor set in 2 defines a polyhedron which more closely resembles a trigonal bipyramid. The packing in the crystal lattices of both compounds is governed by hydrogen-bonds. Complexes 1 and 2 display higher stability than curcumin in buffered media at pH = 7.0, however, the degradation of coordinated cur- is comparable to that of yellow pigment curcumin (curH) when the pH is raised to 7.2. Both complexes 1 and 2 in DMSO exhibit fluorescence with Stokes shifts of 5367 and 4634 cm-1, respectively.

Modulatory effect of curcumin analogs on the activation of metalloproteinases in human periodontal stem cells

Periodontitis progresses due to increased levels of active metalloproteinases (MMPs) and the imbalance between MMPs and their tissue inhibitors (TIMPs). Natural curcumin limits the lytic activity of MMPs but has low cellular uptake. Use of synthetic curcumin analogs could be a means of overcoming this limitation of treatment efficiency. Human periodontal stem cells were isolated from gingival tissue, gingival ligament fibers, periodontal ligament, and alveolar bone. The effect of five synthetic curcumin analogs was compared with that of natural curcumin by assessing cytotoxicity [by 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide (MTT) assay], the cellular uptake (by fluorometry), the proteolytic activities of MMP-2 and -9 (by zymography), and the levels of TIMP-1 (by ELISA). Our results indicated increased cytotoxicity of synthetic curcumins for doses between 100 and 250 μM. At a concentration of 10 μM, cellular uptake of synthetic curcumins varied depending on their chemical structure. The curcumin compounds modulated pro-MMP-2 levels and increased TIMP-1 production. There was no detectable synthesis of pro-MMP-9 and no activation of MMPs 2 and 9. Gingival tissue and gingival ligament fiber stem cells were most responsive to treatment, showing inverse correlations between pro-MMP-2 and TIMP-1 levels. In conclusion, synthetic curcumins influenced the balance between pro-MMP-2 and TIMP-1 in human periodontal stem cells in vitro, and this could open perspectives for their application as adjuvants in periodontal therapy.

Photosensitizers for Photodynamic Therapy

As an emerging clinical modality for cancer treatment, photodynamic therapy (PDT) takes advantage of the cytotoxic activity of reactive oxygen species (ROS) that are generated by light irradiating photosensitizers (PSs) in the presence of oxygen (O₂ ). However, further advancements including tumor selectivity and ROS generation efficiency are still required. Substantial efforts are devoted to design and synthesize smart PSs with optimized properties for achieving a desirable therapeutic efficacy. This review summarizes the recent progress in developing intelligent PSs for efficient PDT, ranging from single molecules to delicate nanomaterials. The strategies to improve ROS generation through optimizing photoinduced electron transfer and energy transfer processes of PSs are highlighted. Moreover, the approaches that combine PDT with other therapeutics (e.g., chemotherapy, photothermal therapy, and radiotherapy) and the targeted delivery in cancer cells or tumor tissue are introduced. The main challenges for the clinical application of PSs are also discussed.

DNA-binding and in vitro cytotoxic activity of platinum(II) complexes of curcumin and caffeine

Three Pt(II) complexes containing the natural ligands curcumin and caffeine, namely [Pt(curc)(PPh₃)₂]Cl (1), [PtCl(curc)(DMSO)] (2) (curc = deprotonated curcumin) and trans-[Pt(caffeine)Cl₂(DMSO)] (3), were synthesized and fully characterized. The data obtained suggest that, for both 1 and 2, the anion of curcumin is coordinated to the platinum ion via the oxygen atoms of the β-diketonate moiety. Spectroscopic features reveal that in 2 and 3, a DMSO molecule is S-bonded to the metal centre. For 3, all data indicate a square-planar geometry formed by a 9-N bonded caffeine, two trans chloride anions and a DMSO. The three complexes undergo changes in solution upon incubation for 24 h; 1 and 2 release curcumin while 3 isomerizes from trans to cis configuration. The DNA-binding and cytotoxic properties of 1-3 were evaluated in vitro. Despite their structural similarity, curcuminate-containing 1 and 2 exhibit distinct DNA interactions. While 1 appears to intercalate between nucleobase pairs, inducing the oxidative degradation of the biomolecule, 2 behaves as a groove binder, by means of electrostatic forces. Caffeine-containing 3 exhibits a behaviour that is comparable to that of 2. Complexes 1 and 2 showed moderate to high cytotoxicity and selectivity against several cancer cell lines, while 3 is inactive. Compounds 1 and 2 can be further activated by visible-light irradiation.

The progresses in curcuminoids-based metal complexes: especially in cancer therapy

Curcuminoids (CURs), a series of derivatives in turmeric (Curcuma longa), are commonly discovered to control the deterioration of cancers. However, the physiochemical properties and the original side effects of many CURs complexes put barriers in their medical applications. To address them, the investigation of metal-based complexes with CURs is in progress. The complexes were summarized according to articles in recent years. The results showed that the complexes improved the physicochemical properties or therapeutic performances compared with pure CURs. Further, it is possible for the novel complexes to be applied in chemical detecting, paramagnetic-luminescent and bio-imaging fields. Therefore, the formation of the metal-based CURs complexes (MBCCs) is beneficial for the development of CURs especially in medical fields.

Biological properties of metal complexes of curcumin

Curcumin, a naturally occurring phenolic compound isolated from Curcuma longa, has different pharmacological effects, including antiinflammatory, antimicrobial, antioxidant, and anticancer properties. However, curcumin has been found to have a limited bioavailability because of its hydrophobic nature, low-intestinal absorption, and rapid metabolism. Therefore, there is a need for enhancing the bioavailability and its solubility in water in order to increase the pharmacological effects of this bioactive compound. One strategy is curcumin complexation with transition metals to circumvent the abovementioned problems. Curcumin can undergo chelation with various metal ions to form metallo-complexes of curcumin, which may show greater effects as compared with curcumin alone. Promising results with metal curcumin complexes have been observed with regard to antioxidant, anticancer, and antimicrobial activity, as well as in treatment of Alzheimer's disease. The present review provides a concise summary of the characterization and biological properties of curcumin-metal complexes. © 2019 BioFactors, 45(3):304-317, 2019.