The Homoleptic Curcumin-Copper Single Crystal (ML2): A Long Awaited Breakthrough in the Field of Curcumin Metal Complexes

The first single crystal structure of the homoleptic copper (II) ML2 complex (M=Cu (II), L = curcumin) was obtained and its structure was elucidated by X-ray diffraction showing a square planar geometry, also confirmed by EPR. The supramolecular arrangement is supported by C-H···O interactions and the solvent (MeOH) plays an important role in stabilizing the crystal packing Crystallinity was additionally assessed by XRD patterns. The log P value of the complex (2.3 ± 0.15) was determined showing the improvement in water solubility. The cytotoxic activity of the complex against six cancer cell lines substantially surpasses that of curcumin itself, and it is particularly selective against leukemia (K562) and human glioblastoma (U251) cell lines, with similar antioxidant activity to BHT. This constitutes the first crystal structure of pristine curcumin complexed with a metal ion.

Antioxidant conjugated metal complexes and their medicinal applications

Antioxidants are naturally available and man-made substances have the ability to protect cells from damage due to a number of intracellular redox activities. Moreover, Antioxidants such as α-lipoic acid, curcumin and catechin are good anticancer agents. In recent years, the usage of metal complexes as therapeutic agents is gaining importance due to their useful biological properties. Most of the metal ions act as the essential components in building drug molecules that serve as medicines for cancer and neurodegenerative diseases. In particular, metals like copper, gold, ruthenium, and platinum have adequate anticancer properties at both micro- and nano-levels. Hence, conjugation of antioxidants with metals and metal-based compounds results in hybrid bioactive materials with improved anticancer properties. In this chapter, medicinal applications of antioxidant conjugated metal complexes are reviewed and discussed.

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.

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.

Synthesis, physicochemical characterization and biological properties of two novel Cu(II) complexes based on natural products curcumin and quercetin

Curcumin and quercetin are two of the most prominent natural polyphenols with a diverse spectrum of beneficial properties, including antioxidant, anti-inflammatory, chemopreventive and chemotherapeutic activity. The complexation of these natural products with bioactive transition metal ions can lead to the generation of novel metallodrugs with enhanced biochemical and pharmacological activities. Within this framework, the synthesis and detailed structural and physicochemical characterization of two novel complex assemblies of Cu(II) with curcumin and quercetin and the ancillary aromatic chelator 2,2'-bipyridine is presented. The two complexes represent the only crystallographically characterized structures with Cu(II) as the central metal ion and curcumin or quercetin as the ligands. The new complexes were biologically evaluated in vitro for their antioxidant potential, both exhibiting strong scavenging activity in the 2,2-diphenyl-1-picrylhydrazyl assay, and their plasmid DNA binding/cleavage properties. Both complexes appear to be non-toxic in the eukaryotic experimental model Saccharomyces cerevisiae and merit further investigation of their pharmacological profile.

Zn(ii) and Cu(ii) complexes containing bioactive O,O-chelated ligands: homoleptic and heteroleptic metal-based biomolecules

Zn(ii) or Cu(ii) highly stable complexes with chelated O,O-donor ligands from natural extractions give rise to drug delivery systems, new biologically active complexes and potential diagnostic agents due to their intrinsic spectroscopic properties.

A curcumin-based TPA four-branched copper(II) complex probe for in vivo early tumor detection

A multibranched Cu(II) complex CuL2 curcumin-based was synthesized and characterized by single-crystal X-ray diffraction analysis. The photophysical properties of the complex have been investigated both experimentally and theoretically. The results show that the target complex exhibits higher quantum yield and larger two-photon absorption (TPA) cross-section in the near infrared (NIR) region compared with its free ligand. The cell imaging studies in vitro and in vivo reveal that the complex shows good photostability and excellent tumor targeting capability to tested cancerous cells, which can be potentially used for early tumor detection.