Structurally characterized zinc complexes of flavonoids chrysin and quercetin with antioxidant potential

Taxifolin as a Metallo-β-Lactamase Inhibitor in Combination with Augmentin against Verona Imipenemase 2 Expressing Pseudomonas aeruginosa

Among the various mechanisms that bacteria use to develop antibiotic resistance, the multiple expression of β-lactamases is particularly problematic, threatening public health and increasing patient mortality rates. Even if a combination therapy-in which a β-lactamase inhibitor is administered together with a β-lactam antibiotic-has proven effective against serine-β-lactamases, there are no currently approved metallo-β-lactamase inhibitors. Herein, we demonstrate that quercetin and its analogs are promising starting points for the further development of safe and effective metallo-β-lactamase inhibitors. Through a combined computational and in vitro approach, taxifolin was found to inhibit VIM-2 expressing P. aeruginosa cell proliferation at <4 μg/mL as part of a triple combination with amoxicillin and clavulanate. Furthermore, we tested this combination in mice with abrasive skin infections. Together, these results demonstrate that flavonol compounds, such as taxifolin, may be developed into effective metallo-β-lactamase inhibitors.

CuII Pyrazolyl-Benzimidazole Dinuclear Complexes with Remarkable Antioxidant Activity

Three dinuclear coordination complexes generated from 1-n-butyl-2-((5-methyl-1H-pyrazole-3-yl)methyl)-1H-benzimidazole (L), have been synthesized and characterized spectroscopically and structurally by single crystal X-ray diffraction analysis. Reaction with iron(II) chloride and then copper(II) nitrate led to a co-crystal containing 78 % of [Cu(NO3 )(μ-Cl)(L')]2 (C1 ) and 22 % of [Cu(NO3 )(μ-NO3 )(L')]2 (C2 ), where L was oxidized to a new ligand L' . A mechanism is provided. Reaction with copper chloride led to the dinuclear complex [Cu(Cl)(μ-Cl)(L)]2 (C3 ). The presence of N-H⋅⋅⋅O and C-H⋅⋅⋅O intermolecular interactions in the crystal structure of C1 and C2 , and C-H⋅⋅⋅N and C-H⋅⋅⋅Cl hydrogen bonding in the crystal structure of C3 led to supramolecular structures that were confirmed by Hirshfeld surface analysis. The ligands and their complexes were tested for free radical scavenging activity and ferric reducing antioxidant power. The complex C1 /C2 shows remarkable antioxidant activities as compared to the ligand L and reference compounds.

Cytotoxicity and Antibacterial Potentials of Mixed Ligand Cu(II) and Zn(II) Complexes: A Combined Experimental and Computational Study

[Cu(C₁₅H₉O₄)(C₁₂H₈N₂)O₂C₂H₃]·3H₂O (1) and [Zn(C₁₅H₉O₄)(C₁₂H₈N₂)]O₂C₂H₃ (2) have been synthesized and characterized by ultraviolet-visible (UV-vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, mass spectrometry, thermogravimetric analysis/differential thermal analysis (TGA/DTA), X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), and molar conductance, and supported by density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations. Square pyramidal and tetrahedral geometries are proposed for Cu(II) and Zn(II) complexes, respectively, and the XRD patterns showed the polycrystalline nature of the complexes. Furthermore, in vitro cytotoxic activity of the complexes was evaluated against the human breast cancer cell line (MCF-7). A Cu(II) centered complex with an IC₅₀ value of 4.09 μM was more effective than the Zn(II) centered complex and positive control, cisplatin, which displayed IC₅₀ values of 75.78 and 18.62 μM, respectively. In addition, the newly synthesized complexes experienced the innate antioxidant nature of the metal centers for scavenging the DPPH free radical (up to 81% at 400 ppm). The biological significance of the metal complexes was inferred from the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy band gap, which was found to be 2.784 and 3.333 eV, respectively for 1 and 2, compared to the ligands, 1,10-phenathroline (4.755 eV) and chrysin (4.403 eV). Moreover, the molecular docking simulations against estrogen receptor alpha (ERα; PDB: 5GS4) were strongly associated with the in vitro biological activity results (E _B and K _i are -8.35 kcal/mol and 0.76 μM for 1, -7.52 kcal/mol and 3.07 μM for 2, and -6.32 kcal/mol and 23.42 μM for cisplatin). However, more research on in vivo cytotoxicity is suggested to confirm the promising cytotoxicity results.

Organic-inorganic hybrid salt and mixed ligand Cr(III) complexes containing the natural flavonoid chrysin: Synthesis, characterization, computational, and biological studies

Organic-inorganic hybrid salt and mixed ligand Cr(III) complexes (Cr1 and Cr2) containing the natural flavonoid chrysin were synthesized. The metal complexes were characterized using UV-Vis, Fourier-transform infrared, MS, SEM-EDX, XRD, and molar conductance measurements. Based on experimental and DFT/TD-DFT calculations, octahedral geometries for the synthesized complexes were suggested. The powder XRD analysis confirms that the synthesized complexes were polycrystalline, with orthorhombic and monoclinic crystal systems having average crystallite sizes of 21.453 and 19.600 nm, percent crystallinities of 51% and 31.37%, and dislocation densities of 2.324 × 10^-3 and 2.603 × 10^-3 nm^-2 for Cr1 and Cr2, respectively. The complexes were subjected to cytotoxicity, antibacterial, and antioxidant studies. The in vitro biological studies were supported with quantum chemical and molecular docking computational studies. Cr1 showed significant cytotoxicity to the MCF-7 cell line, with an IC₅₀ value of 8.08 μM compared to 30.85 μM for Cr2 and 18.62 μM for cisplatin. Cr2 showed better antibacterial activity than Cr1. The higher E _HOMO (-5.959 eV) and dipole moment (10.838 Debye) values of Cr2 obtained from the quantum chemical calculations support the observed in vitro antibacterial activities. The overall results indicated that Cr1 is a promising cytotoxic drug candidate.

Synthesis, structural characterization and study of antioxidant and anti-PrPSc properties of flavonoids and their rhenium(I)-tricarbonyl complexes

This study aims at the synthesis and initial biological evaluation of novel rhenium-tricarbonyl complexes of 3,3',4',5,7-pentahydroxyflavone (quercetin), 3,7,4΄-trihydroxyflavone (resokaempferol), 5,7-dihydroxyflavone (chrysin) and 4΄,5,7-trihydroxyflavonone (naringenin) as neuroprotective and anti-PrP agents. Resokaempferol was synthesized from 2,2΄,4-trihydroxychalcone by H₂O₂/NaOH. The rhenium-tricarbonyl complexes of the type fac-[Re(CO)₃(Fl)(sol)] were synthesized by reacting the precursor fac-[Re(CO)₃(sol)₃]⁺ with an equimolar amount of the flavonoids (Fl) quercetin, resokaempferol, chrysin and naringenin and the solvent (sol) was methanol or water. The respective Re-flavonoid complexes were purified by semi-preparative HPLC and characterized by spectroscopic methods. Furthermore, the structure of Re-chrysin was elucidated by X-ray crystallography. Initial screening of the neuroprotective properties of these compounds included the in vitro assessment of the antioxidant properties by the DPPH assay as well as the anti-lipid peroxidation of linoleic acid in the presence of AAPH and their ability to inhibit soybean lipoxygenase. From the above studies, it was concluded that the complexes' properties are mainly correlated with the structural characteristics and the presence of the flavonoids. The flavonoids and their respective Re-complexes were also tested in vitro for their ability to inhibit the formation and aggregation of the amyloid-like abnormal prion protein, PrP^Sc, by employing the real-time quaking-induced conversion assay with recombinant PrP seeded with cerebrospinal fluid from patients with Creutzfeldt-Jakob disease. All the compounds blocked de novo abnormal PrP formation and aggregation.

Chrysin Induces Apoptosis via the MAPK Pathway and Regulates ERK/mTOR-Mediated Autophagy in MC-3 Cells

Chrysin is a flavonoid found abundantly in substances, such as honey and phytochemicals, and is known to exhibit anticancer effects against various cancer cells. Nevertheless, the anticancer effect of chrysin against oral cancer has not yet been verified. Furthermore, the mechanism underlying autophagy is yet to be clearly elucidated. Thus, this study investigated chrysin-mediated apoptosis and autophagy in human mucoepidermoid carcinoma (MC-3) cells. The change in MC-3 cell viability was examined using a 3-(4,5-dimethylthiazolyl-2)-2, 5-diphenyltetrazolium bromide cell viability assay, as well as 40,6-diamidino-2-phenylindole, annexin V, and propidium iodide staining. Western blotting was used to analyze the proteins related to apoptosis and the mitogen-activated protein kinase (MAPK) pathway. In addition, the presence or absence of autophagy and changes in the expression of related proteins were investigated using acridine orange staining and Western blot. The results suggested that chrysin induced apoptosis and autophagy in MC-3 oral cancer cells via the MAPK/extracellular signal-regulated kinase pathway. Moreover, the induced autophagy exerted a cytoprotective effect against apoptosis. Thus, the further reduced cell viability due to autophagy as well as apoptosis induction highlight therapeutic potential of chrysin for oral cancer.

Heteroligand α-Diimine-Zn(II) Complexes with O,N,O'- and O,N,S-Donor Redox-Active Schiff Bases: Synthesis, Structure and Electrochemical Properties

A number of novel heteroligand Zn(II) complexes (1-8) of the general type (Lⁿ)Zn(NN) containing O,N,O'-, O,N,S-donor redox-active Schiff bases and neutral N,N'-chelating ligands (NN) were synthesized. The target Schiff bases LⁿH₂ were obtained as a result of the condensation of 3,5-di-tert-butyl-2-hydroxybenzaldehyde with substituted o-aminophenols or o-aminothiophenol. These ligands with combination with 2,2'-bipyridine, 1,10-phenanthroline, and neocuproine are able to form stable complexes upon coordination with zinc(II) ion. The molecular structures of complexes 4∙H₂O, 6, and 8 in crystal state were determined by means of single-crystal X-ray analysis. In the prepared complexes, the redox-active Schiff bases are in the form of doubly deprotonated dianions and act as chelating tridentate ligands. Complexes 6 and 8 possess a strongly distorted pentacoordinate geometry while 4∙H₂O is hexacoordinate and contains water molecule coordinated to the central zinc atom. The electrochemical properties of zinc(II) complexes were studied by the cyclic voltammetry. For the studied complexes, O,N,O'- or O,N,S-donor Schiff base ligands are predominantly involved in electrochemical transformations in the anodic region, while the N,N'-coordinated neutral nitrogen donor ligands demonstrate the electrochemical activity in the cathode potential range. A feature of complexes 5 and 8 with sterically hindered tert-butyl groups is the possibility of the formation of relatively stable monocation and monoanion forms under electrochemical conditions. The values of the energy gap between the boundary redox orbitals were determined by electrochemical and spectral methods. The parameters obtained in the first case vary from 1.97 to 2.42 eV, while the optical bang gap reaches 2.87 eV.

Synthesis, characterization, and biological activities of zinc(II), copper(II) and nickel(II) complexes of an aminoquinoline derivative

Interest is increasingly focused on the use of transition metal complexes as biochemical, medical, analytical, pharmaceutical, agronomic, anticancer, and antibacterial agents. In this study, three complexes of [Zn(H2L)Cl] (1), [Cu(H2L)(H2O)(NO3)] (2) and [Ni(H2L)(NO3)].2H2O (3) were synthesized from a 2-chloroquinoline-3-carbaldehyde derived ligand [H3L = ((E)-2-(((2-((2-hydroxyethyl)amino)quinolin-3-yl)methylene)amino)ethanol. The compounds were characterized using physicochemical and spectroscopic methods. The results demonstrate that the free ligand behaves as a tridentate ligand with one oxygen and two nitrogen (ONN) donor atoms in 1:1 metal:ligand ratio. The formation constants of the complexes were found to be (KZn(II) = 2.3 × 106, KCu(II) = 2.9 × 106, and KNi(II) = 3.8 × 105). The thermodynamic parameters indicated that the reactions were spontaneous with exothermic nature of metal-ligand interaction energies. Based on the analyses of the experimental (EDX, FTIR, PXRD, MS and TGA) and DFT results, a distorted tetrahedral, a distorted square pyramidal and square planar geometry for Zn(II), Cu(II) and Ni(II) complexes, respectively, were proposed. The B3LYP calculated IR frequencies and TD-B3LYP calculated absorption spectra were found to be in good agreement with the corresponding experimental results. The powder XRD data confirmed that the Zn(II), Cu(II) and Ni(II) complexes have polycrystalline nature with average crystallite sizes of 27.86, 33.54, 37.40 Å, respectively. In vitro antibacterial activity analyses of the complexes were studied with disk diffusion method, in which the complexes showed better activity than the precursor ligand. Particularly the Cu(II) complex showed higher percent activity index (62, 90%), than both Zn(II) (54, 82%) and Ni(II) (41, 68%) complexes against both E. coli and P. aeruginosa, respectively. Using the DPPH assay, the complexes were further assessed for their antioxidant capacities. All metal complexes showed improved antioxidant activity than the free ligand. Zn(II) and Cu(II) complexes, which had IC50 values of 10.46 and 8.62 μg/ml, respectively, showed the best antioxidant activity. The calculated results of Lipinski’s rule of five also showed that the target complexes have drug-like molecular nature and similarly, the results of binding mode of action of these compounds against E. coli DNA gyrase B and P. aeruginosa LasR.DNA were found to be in good agreement with the in vitro biological activities.

Novel Zinc(II) and Copper(II) Complexes of 2-((2-Hydroxyethyl)amino)quinoline-3-carbaldehyde for Antibacterial and Antioxidant Activities: A Combined Experimental, DFT, and Docking Studies

In the present work, two novel complexes of zinc(II) and copper(II) were synthesized from the ligand 2-((2-hydroxyethyl)amino)quinoline-3-carbaldehyde (H ₂ L) in a 1:2 metal-to-ligand ratio in methanol. The complexes were characterized by UV-visible spectroscopy, fluorescence spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDX), mass spectrometry (MS), nuclear magnetic resonance (NMR) spectroscopy, and thermogravimetric analysis (TGA) experimental techniques and density functional theory (DFT) calculations. The spectral data revealed that the mono-deprotonated (HL) ligand acted as a bidentate ligand, which bound to both Zn(II) and Cu(II) ions via the nitrogen atom of the amine (N-H) and the hydroxyl (O-H) groups through the deprotonated oxygen atom. Formation constants and thermal analysis indicated that both metal complexes are stable up to 100 °C with thermodynamically favored chemical reactions. The Cu(II) complex showed antibacterial activities with the zones of inhibition of 20.90 ± 2.00 mm against Pseudomonas aeruginosa, 19.69 ± 0.71 mm against Staphylococcus aureus, and 18.58 ± 1.04 mm against Streptococcus pyogenes. These results are relatively higher compared with the Zn(II) complex at the same concentration. The minimum inhibitory concentration (MIC) results for the complexes also showed similar trends against the three bacteria. On the other hand, radical scavenging activities of both Cu(II) and Zn(II) complexes showed half-maximal inhibitory concentrations (IC₅₀) of 4.72 and 8.2 μg/mL, respectively, while ascorbic acid (a positive control) has a value of 4.28 μg/mL. The Cu(II) complex exhibited better communication with the positive control, indicating its potential use for biological activities. The calculated and in silico molecular docking results also strongly support the experimental results.

Chromium Flavonoid Complexation in an Antioxidant Capacity Role

The plethora of flavonoid antioxidants in plant organisms, widespread in nature, and the appropriate metal ions known for their influence on biological processes constitute the crux of investigations toward the development of preventive metallodrugs and therapeutics in several human pathophysiologies. To that end, driven by the need to enhance the structural and (bio)chemical attributes of the flavonoid chrysin, as a metal ion complexation agent, thereby rendering it bioavailable toward oxidative stress, synthetic efforts in our lab targeted ternary Cr(III)-chrysin species in the presence of auxiliary aromatic N,N′-chelators. The crystalline metal-organic Cr(III)-chrysin-L (L = bipyridine (1) and phenanthroline (2)) compounds that arose were physicochemically characterized by elemental analysis, FT-IR, UV-Visible, ESI-MS, luminescence, and X-ray crystallography. The properties of these compounds in a solid state and in solution formulate a well-defined profile for the two species, thereby justifying their further use in biological experiments, intimately related to cellular processes on oxidative stress. Experiments in C2C12 myoblasts at the cellular level (a) focus on the antioxidant capacity of the Cr(III)-complexed flavonoids, emphasizing their distinct antiradical activity under oxidative stress conditions, and (b) exemplify the importance of structural speciation in Cr(III)-flavonoid interactions, thereby formulating correlations with the antioxidant activity of a bioavailable flavonoid toward cellular pathophysiologies, collectively supporting flavonoid introduction in new metallo-therapeutics.

Neuroprotective Potential of Tamarillo (Cyphomandra betacea) Epicarp Extracts Obtained by Sustainable Extraction Process

Tamarillo (Cyphomandra betacea (Cav.) Sendt.), or tree tomato, is a tropical fruit from the Andean region of South America; it is highly rich in vitamins, minerals, and polyphenolic compounds. In this study, extracts from tamarillo epicarp (TE) were obtained by pressurized liquid extraction (PLE), and their in-vitro neuroprotective potential was assessed. A central composite design with response surface methodology was performed to optimize PLE as a function of solvent composition and temperature. Selected response variables were extraction yield, total phenolic content (TPC), total flavonoid content (TFC), total carotenoid content (TCC), antioxidant (ABTS), and anti-inflammatory (LOX) activities, and anti-acetylcholinesterase (AChE) inhibitory capacity. According to the desirability function, the optimal conditions were 100% ethanol and 180°C with a 0.87 desirability value. Next, the anti-butyrylcholinesterase enzyme (BChE), reactive oxygen species (ROS), and reactive nitrogen species (RNS) inhibition as well as cytotoxicity in HK-2, THP-1 monocytes, and SH-5YSY neuroblastoma cell lines were studied for the TE extract obtained under optimized conditions. The optimum TE extract provided the following results: extraction yield (36.25%), TPC (92.09 mg GAE/g extract), TFC (4.4 mg QE/g extract), TCC (107.15 mg CE/g extract), antioxidant capacity (ABTS, IC₅₀ = 6.33 mg/ml extract), LOX (IC₅₀ = 48.3 mg/ml extract), and AChE (IC₅₀ = 97.46 mg/ml extract), and showed no toxicity at concentration up to 120 μg/ml extract for all the tested cell lines. Finally, chemical characterization by liquid chromatography-tandem mass spectrometry (UHPLC-q-TOF-MS/MS) of the optimum TE extract exhibited an important presence of hydroxycinnamic acid derivatives and other phenolic acids as well as quercetin hexoside and rutin, as main metabolites responsible for the observed biological properties. All these results suggested that TE, which represents between 8 and 15% of the total fruit, could become a promising natural by-product with a potential "multitarget" activity against Alzheimer's disease.

HPLC Characterization of Phytochemicals and Antioxidant Potential of Alnus nitida (Spach) Endl

Antioxidants isolated from plants have attracted the interest of clinicians and common people to be used for systemic uses rather than synthetic antioxidants because of their active role in maintaining human health with minimal side effects. Alnus nitida (Spach) Endl. is an important medicinal plant native to western Himalaya and is widely distributed throughout Pakistan. The present study evaluates the phytochemical composition of this plant using HPLC along with the total content of phenolics and flavonoids. The antioxidant activities were determined following the Brand William assay. The methanolic extract (Met. Ext) of leaves, stem bark, seeds, and roots of A. nitida were used to scavenge synthetic free radicals such as DPPH and ABTS. From HPLC fingerprinting of the A. nitida selected portion, six possible phytochemicals were confirmed. Among the identified phytochemicals, there are six compounds (malic acid, chlorogenic acid, epigallocatechin gallate, quercetin, ellagic acid and pyrogallol) in the leaves of A. nitida, three (epigallocatechin gallate, ellagic acid, and pyrogallol) in the stem bark, six in the seeds (malic acid, vitamin C, epigallocatechin gallate, quercetin, ellagic acid, and pyrogallol), and five (malic acid, epigallocatechin gallate, quercetin, and ellagic acid) in root. Comparatively, the highest antioxidant potentials were recorded for the leaves extract (IC50 of 340 and 645 µg/mL against DPPH and ABTS, respectively). The percentages of inhibition were compared with the positive control ascorbic acid, which produced an IC50 value of 60 μg/mL each against the free radicals DPPH and ABTS. The highest phenolics (43.81 mg GAE/g sample) were found in the roots, while the highest flavonoid contents (53.25 mg QE/g sample) were in the leaves. It was assumed that observed antioxidant potentials of the tested plant might be due to their phytochemicals confirmed through HPLC, and thus, this plant may be a valuable candidate in treating oxidative stress and related disorders. However, further investigations are needed to isolate responsible components in pure from. Furthermore, toxicological effects in in vivo animal models are also needed to confirm the results observed in this study.

Chrysin: Perspectives on Contemporary Status and Future Possibilities as Pro-Health Agent

Chrysin belongs to the group of natural polyphenols. It can be found, among others, in honey, propolis and fruits and has a wide range of biological activities, including the prevention of oxidative stress, inflammation, neurodegeneration and carcinogenesis. Being a part of the human diet, chrysin is considered to be a promising compound to be used in the prevention of many diseases, including cancers, diabetes and neurodegenerative diseases such as Alzheimer's or Parkinson's. Nevertheless, due to the low solubility of chrysin in water and under physiological conditions, its bioavailability is low. For this reason, attempts at its functionalization have been undertaken, aiming to increase its absorption and thus augment its in vivo therapeutic efficacy. The aim of this review is to summarize the most recent research on chrysin, including its sources, metabolism, pro-health effects and the effects of its functionalization on biological activity and pharmacological efficacy, evaluated both in vitro and in vivo.