The chemical diversity of antioxidants makes it difficult to separate and quantify antioxidants from the vegetable matrix. Therefore, it is desirable to establish a method that can measure the total ...antioxidant activity level directly from vegetable extracts. The current literature clearly states that there is no “total antioxidant” as a nutritional index available for food labeling because of the lack of standard quantitation methods. Thus, this work reports the development of a simple, widely applicable antioxidant capacity index for dietary polyphenols and vitamins C and E, utilizing the copper(II)−neocuproine Cu(II)-Nc reagent as the chromogenic oxidizing agent. Because the copper(II) (or cupric) ion reducing ability of polyphenols is measured, the method is named by our research group “cupric reducing antioxidant capacity” abbreviated as the CUPRAC method. This method should be advantageous over the ferric reducing antioxidant power (FRAP) method because the redox chemistry of copper(II)as opposed to that of ferric ioninvolves faster kinetics. The method comprises mixing of the antioxidant solution (directly or after acid hydrolysis) with a copper(II) chloride solution, a neocuproine alcoholic solution, and an ammonium acetate aqueous buffer at pH 7 and subsequent measurement of the developed absorbance at 450 nm after 30 min. Because the color development is fast for compounds such as ascorbic acid, gallic acid, and quercetin but slow for naringin and naringenin, the latter compounds were assayed after incubation at 50 °C on a water bath for 20 min after Cu(II)-Nc reagent addition so as to force the oxidation reaction to reach completion. The flavonoid glycosides were hydrolyzed to their corresponding aglycons by refluxing in 1.2 M HCl-containing 50% MeOH so as to exert maximal reducing power toward Cu(II)-Nc. Certain compounds also needed incubation after acid hydrolysis to fully exhibit their reducing capability. The CUPRAC antioxidant capacities of synthetic mixtures of antioxidants were experimentally measured as Trolox equivalents and compared to those theoretically found by making use of the principle of additivity of absorbances assuming no chemical interaction between the mixture constituents. Because ascorbic acid is not resistant to elevated temperature incubation, it should be assayed initially by measuring the absorbance (at 450 nm) difference of original and ascorbate oxidase-added mixture solutions at the end of 1 min of Cu(II)-Nc reagent addition. Thus, the total CUPRAC antioxidant capacity of a mixture containing various antioxidants should be that finally measured after a suitable combination of hydrolysis and incubation procedures, added to the initially measured capacity due to ascorbate. The antioxidant polyphenolic compounds tested demonstrate that the highest capacities in the CUPRAC method were observed for epicatechin gallate, epigallocatechin gallate, quercetin, fisetin, epigallocatechin, catechin, and caffeic acid in this order, in accordance with theoretical expectations, because the number and position of the hydroxyl groups as well as the degree of conjugation of the whole molecule are important. The antioxidant potency of flavonoids is nearly proportional to the total number of −OH groups and is positively affected by the presence of an o-dihydroxy moiety in the B-ring. β-Carotene, which did not react with the CUPRAC reagent in alcoholic aqueous medium, could be assayed in dichloromethane solvent. Linear calibration curves for ascorbic acid and flavonoids were redrawn in synthetic solutions containing a mixture of antioxidants, and also in real matrices such as grape and orange juices, green tea, and blackberry tea, showing an initial nonzero absorbance with the CUPRAC reagent. The parallellism of the linear calibration curves of pure compounds in a given complex matrix effectively demonstrated that there were no interferent chemical interactions among the solution constituents and that the antioxidant capacities of the tested antioxidants were additive. The CUPRAC reagent is reasonably selective, stable, easily accessible, and sensitive toward thiol-type oxidants, unlike the FRAP method. The reaction is carried out at nearly physiological pH as opposed to the unrealistic acidic pH of FRAP. Keywords: Antioxidant activity; cupric reducing antioxidant capacity (CUPRAC); dietary antioxidants; polyphenols; flavonoids; copper(II)−neocuproine reagent
•Crystal structure of the Ni(neoc)2(NO3)+ with three different anions including TCNQ.•New Ni(II) complex with two NO3− groups coordinated in two different ways.•Influence of NO3− group on the crystal ...structure of M(neoc)(NO3)2(H2O).•Application of several crystallization methods.•Detailed structural analysis with emphasis on inter/intramolecular interactions.
The cationic complex Ni(neoc)2(NO3)+ with NO3− (1), TCNQ− (3), or (TCNQ-TCNQ)2− (4) as counterions, and the neutral complex Ni(neoc)(NO3−-κ1O)(NO3−-κ2O,O´)(H2O) (2) can be obtained from different reactions involving Ni(II), neoc, NO3− and TCNQ. The molecular and extended crystal structure of compound 2, which displays two different coordination modes for NO3−, are compared to those of the analogous Mn, Fe and Co compounds, revealing a correlation between the coordination geometry of the nominally monodentate nitrato ligand and the covalent radius of the central metal atom. Despite the differences in molecular geometry, the extended structures of the Ni (2) and Mn compounds are similar to each other but different from those of the Fe and Co complexes, which are similar to each other. Complex 1 was further used in the preparation of a new heterospin compound Ni(neoc)2(NO3)(TCNQ) (3), having an ionic structure with the same complex cation present in 1, accompanied by centrosymmetric anion-radicals (ARs) TCNQ•−. Through a different preparation process, complex 4, with the formula Ni(neoc)2(NO3)2(TCNQ-TCNQ), containing the same complex cation as in complexes 1 and 3, but now with the centrosymmetric σ-dimerized dianion (TCNQ-TCNQ)2− has been obtained. The influence of NO3−, TCNQ•− and TCNQ-TCNQ2− anions on the crystal structure of the cation Ni(neoc)2(NO3)+ in the compounds has been studied. All of the complexes reported here have supramolecular structures governed by hydrogen bonding systems, adding to their stability.
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Synthesis of three new europium(III) complexes with 1,3-bis(4-methoxyphenyl)propane-1,3-dionato (HBMPD) ligand and ancillary ligands such as 2,2′-biquinoline (biq) or neocuproine (neo) has been ...reported in this report. The synthesized complexes were characterized by IR (infrared), 1H and 13C NMR (nuclear magnetic resonance) spectroscopy, CHN (carbon, hydrogen and nitrogen) elemental analysis, XRD (X-ray diffraction), TGA (thermogravimetric analysis) and photoluminescence (PL) spectroscopy. The emission spectra of europium(III) complexes displayed both the low intensity 5D1–3→7F0–3 transitions in 410–560nm blue-green region and high intensity characteristic 5D0→7F0–3 transitions in 575–640nm orange-red region correspond to the emission of ancillary ligands and europium ion respectively, which can lead to white luminescence due to integration of blue, green and red color emissions. The photoluminescence investigations indicate that the absorbed energy of the HBMPD ligand transferred to the central europium(III) ion in an efficient manner, which clearly explained by antenna effect. The excellent results of thermal behavior and photophysical properties like luminescence spectra, CIE (Commission Internationale Eclairage) chromaticity coordinates, luminescence decay curves and high quantum efficiency of the complexes make them a promising component of the white light-emitting diodes in display devices.
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•A new HBMPD ligand has been synthesized by an ecofriendly microwave irradiation.•Three new Eu(III) complexes have been prepared from HBMPD and ancillary ligands.•IR, NMR, CHN, XRD, TGA, UV–visible, PL techniques for the complexes•These complexes can be used as luminescent material in display devices.
•Copper(II) complexes with non-steroidal anti–inflammatory drugs were characterized.•One structure was characterized by single-crystal X-ray crystallography.•The complexes show noteworthy antioxidant ...activity.•The complexes may bind reversibly to bovine serum albumin.•Intercalation is the interaction mode of complexes with calf-thymus DNA.
Four novel copper(II) complexes with the non-steroidal anti-inflammatory drugs tolfenamic acid (Htolf), mefenamic acid (Hmef), naproxen (Hnap) and sodium diclofenac (Na dicl) were prepared in the presence of the N,N’–donor neocuproine (neoc) as co–ligand and were characterized by physicochemical and spectroscopic techniques. The complexes bear the formulas: Cu(tolf)2(neoc) (complex 1), Cu(mef)2(neoc) (complex 2), Cu(nap)2(neoc) (complex 3) and Cu(dicl)2(neoc) (complex 4), respectively. Single-crystal X-ray crystallography was employed to determine the crystal structure of complex Cu(tolf)2(neoc). The in vitro scavenging activity of the complexes against 1,1–diphenyl–picrylhydrazyl and 2,2′–azinobis(3–ethylbenzothiazoline–6–sulfonic acid) free radicals and the ability to reduce H2O2 were studied in the context of the antioxidant activity studies. The compounds interact with calf-thymus DNA via intercalation, as indicated by UV–vis spectroscopy and DNA–viscosity titration studies, and competitive studies with ethidium bromide. Additionally, the complexes were checked for their binding affinity to bovine serum albumin by fluorescence emission spectroscopy, and demonstrated significant and reversible binding to the albumin.
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Four copper(II) complexes with non-steroidal anti-inflammatory drugs as ligands and neocuproine as co-ligand were prepared and characterized. The compounds present significant antioxidant activity, interact with calf-thymus DNA via intercalation and can bind tightly and reversibly to bovine serum albumin.
•The Cu (Neocup)(Triazine)H2O(NO3)2 complex has been synthesized.•The complex intercalates into the base pair of DNA.•The antimicrobial activities of bacteria and fungi are observed for the ...complex.•The complex has excellent anticancer activity against HepG2.
In this paper, a new copper (II) complex with neocuproine and triazine has been synthesized and characterised. In the complex Cu (Neocup)(Triazine)H2O(NO3)2 (where neocup=2,9-dimethyl-1;10-phenanthroline,Triazine=3-(2-pyridyl)5,6-diphenyl-1.2,4-triazine) is characterized by using UV Spectra, FT-IR, EPR, and thermal analyses. UV spectra, fluorescence spectra, and cyclic voltammetry techniques were used to determine the binding mechanism of the Cu (II) complex with calf thymus DNA (CT-DNA). The stability of the prepared Cu (II) complex has been evaluated through the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy gab. In addition, the molecular docking studies were indicating the Cu (II) complex into the base pairs of CT-DNA. Furthermore, the Cu (II) complex was exposed to human liver cancer cell in vitro cytotoxicity assays, using the MTT assay, one can assess cellular metabolic activity as a sign of cell viability, proliferation, and cytotoxicity. The resultant complex shows potent cytotoxic behaviour against human cell lines (HepG2). The IC50 and R2 values of an optimized complex of Cu (II) complexes are noted as 60.81 µg/ml, 19.19 µg/ml and 0.991%, 0.789% respectively. The results revealed that copper complex Cu(Neocup)(Triazine) H2O(NO3)2 showed high potent cytotoxicity effects against human cell line (HepG2) than Cu(phen)(tryp)I. The complex has been implied for antibacterial properties against the staphylococcusaureus (Gram-negative (+Ve)) and the klebsiella pneumonia, Escherichia coli (Gram-negative (-Ve)) bacterial strains and the antifungal activity against C.albicanspecies, respectively. The optimized results revealed that the Cu (II) complex exhibits excellent antibacterial and antifungal activity.
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•CUPRAC reagent was modified onto GPE surface via electrostatic interaction.•Proposed electrode was used for FI amperometric determination of N2H4.•Low-cost and fast electrochemical method was ...fabricated for N2H4 determination.
Hydrazine (N2H4) is a hazardous chemical widely used as rocket propellant and industrial intermediate, therefore its sensitive and accurate analysis in environmental samples is very important. In this study, a new approach for flow injection amperometric detection of N2H4 is proposed based on its electrocatalytic oxidation at a bis(neocuproine)copper (II) chelate complex/sodium dodecyl sulfate-modified graphite pencil electrode (Cu(II)-Ncp/SDS/GPE). The proposed electrode was prepared by consecutive adsorption of anionic surfactant (SDS) and Cu(II)-Ncp onto pencil leads and the surface morphologies of electrodes prepared were elucidated by recording of their SEM images. Cyclic voltammograms (CVs) showed that Cu(II)-Ncp exhibited an excellent redox mediator property for the electrocatalytic oxidation of N2H4, because oxidation potential of N2H4 at bare GPE shifted to more negative direction with the use of Cu(II)-Ncp/SDS/GPE. Then, flow injection (FI) electroanalysis of N2H4 was performed by utilizing the electrocatalytic oxidation of N2H4 at Cu(II)-Ncp/SDS/GPE. A wide linear range (0.25–250 µM) with a limit of detection (LOD) of 0.07 μM and a sensitivity of 262 μAmM−1cm−2 were obtained for the FI amperometric detection of N2H4. Satisfactory recoveries were obtained for N2H4 detection in water samples, showing that this method can be accurately applied to real water samples.
A simple and rapid method for simultaneous separation and preconcentration of ultra-trace amounts of nitrate and nitrite using in-syringe liquid microextraction is developed. The extraction procedure ...is based on the selective ion-pairing complex formation of nitrate and nitrite with Cu(I)-neocuproine in 100 μL of 1-butyl-3-methylimidazolium hexafluorophosphate as an extracting phase within a syringe. The atomic-absorption signal of copper in the ionic liquid layer is proportional to the nitrate and nitrite concentrations. When barbituric acid is used, nitrite is converted into violuric acid and thus it is removed from the environment. In this case, the selectivity of the modified-ligand is limited to nitrate. Under optimum experimental conditions, the calibration graph was in the range from 0.1 to 25 μg L−1 for nitrate and 0.05 to 10 μg L−1 for nitrite, respectively. The detection limits for these two anions were around 0.013 μg L−1. The resultant repeatability expressed as relative standard deviations (RSDs, n = 6) was <5.1%. The accuracy of the proposed method was confirmed using addition/recovery test and analyzing with the reference method. At two different addition levels for each analyte, recoveries were determined to be within the range from 94.2 to 103.3% for nitrate and 93.4 to 98.2% for nitrite, respectively. There was also no significant difference between the results when t-test is used with 95% confidence (n = 6). The applicability of the method was extended to the extraction and preconcentration of nitrate and nitrite from tuna fish, tomato paste and infant food sample.
The graphical abstract representation of in-syringe liquid microextraction procedure for ultra-trace determination of nitrate and nitrite. Display omitted
•A method for ultra-trace determination of nitrate and nitrite in food samples is developed.•In-syringe liquid microextraction is combined with ET AAS.•The method is based on selective ion-pairing complex formation of nitrate and nitrite.•This method has no need to centrifugation, thermal dispersion and organic solvents.
•An HPLC method with post-column detection in the visible region was proposed.•Post-column reagent for reducing sugars was alkaline Cu(II)−neocuproine solution.•Post-column reaction gave a single ...product of Cu(I)-Nc perfectly obeying Beer's law.•The reducing sugars of commercial food products were successfully specified.•After hydrolysis process, the amount of sucrose could be determined.
A novel liquid chromatographic analysis method with post-column detection for sugars was developed to improve existing methods in regard to operation time, selectivity, and sensitivity. This method involves separation of reducing sugars on HPLC column at 30 °C and 0.8 mL min−1 flow rate, post−column reaction of sugars with Cu(II)-neocuproine (Nc) reagent at 80 °C and 0.3 mL min−1 flow rate, and measurement of Cu(I)-Nc product at 450 nm. The proposed assay was applied to glucose, fructose, maltose, and lactose as reducing sugars. Non-reducing sucrose was determined indirectly, after conversion to its constitutive monomers glucose and fructose by hydrolysis, and analysis with a relative error from -2.41 to 2.09%. Honey, apple juice, and milk samples were evaluated as commercial products. The results obtained with the proposed assay compared to those of the alkaline Cu(II)−Nc reference method were found close to each other, and compatible with the label values of commercial products. The accuracy of the developed method was performed by spiking glucose to honey and lactose to milk samples using two different concentrations. The obtained recoveries with respect to the post-column HPLC method were between 97 and 105% for honey and 96–107% for milk. The method gave linear responses against sugar concentration with correlation coefficients greater than 0.996 for the four analytes (glucose, fructose, maltose and lactose) in a range of 9.0 - 342.3 mg L−1 with LOD values ≤ 7.4 mg L−1. With the developed method, it was possible to sensitively determine reducing sugars in various food samples at a lower temperature of post-column reaction (compared to literature values) with easy application of low cost reagents requiring minimal preliminary operation.
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A set complexes were synthesized and characterized with the formula Cu(N^N)(PMePh2)2ClO4 (4 and 6) or Cu(N^N)(dppe)ClO4 (5 and 7){N^N = 2,2′-biquinoline, neocuproine}. Crystal ...structures of the neocuproine-containing complexes (5 and 7) were obtained and described. The methyldiphenylphosphine-containing complexes are stable in solutions (compared to PPh3) due to: (1) slightly better σ-donation compared to PPh3 and (2) smaller Tolman cone angle of ∼136° (compared to ∼145° in PPh3). In the other hand, Cu(N^N)(dppe)ClO4 complexes were demonstrating evidence of Cu(N^N)2+, highlighting the importance of the P-Cu-P angle. The angle P-Cu-P is around 123° in 5 compared to ∼92° in 7. Absorption spectra of 4 and 5 exhibit low intensity broad shoulder in the visible light domain assigned as MLCT. Complexes 4 and 5 were examined in Castro-Stephens coupling reaction and found to be active, achieving complete conversion of the starting materials in contrast to the unstable Cu(2,2′-biquinoline)(PPh3)2+ cation.
Four complexes were synthesized and characterized with the formula Cu(N^N)(PMePh2)2ClO4 (4 and 6) or Cu(N^N)(dppe)ClO4 (5) and 7){N^N = 2,2′-biquinoline, neocuproine}. Crystal structures of the neocuproine-containing complexes (5 and 7) were obtained and described. The methyldiphenylphosphine-containing complexes are stable in solutions (compared to PPh3) due to: (1) slightly better σ-donation compared to PPh3 and (2) smaller Tolman cone angle of ∼136° (compared to ∼145° in PPh3). In the other hand, Cu(N^N)(dppe)ClO4 complexes were demonstrating evidence of forming Cu(N^N)2+ in solutions, highlighting the importance of the P-Cu-P angle. The angle P-Cu-P is around 123° in stable complex 5 compared to ∼92° in 7. Absorption spectra of 4 and 5 exhibit low intensity broad shoulder in the visible light domain assigned as MLLCT by computational studies. While Cu(2,2′-biquinoline)(PPh3)2+ cation was losing catalytic activity in Castero-Stephens cross-coupling over time as indicated by the low conversion rate, complexes 4 and 5 found to be active and achieved complete conversion of the starting materials.
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We report on the application of a simple and versatile antioxidant capacity assay for dietary polyphenols, vitamin C and vitamin E utilizing the copper(II)-neocuproine (Cu(II)-Nc) reagent as the ...chromogenic oxidant, which we term the CUPRAC (cupric reducing antioxidant capacity) method. It involves mixing the antioxidant solution (directly or after acid hydrolysis) with solutions of CuCl
2
, neocuproine, and ammonium acetate at pH 7, and measuring the absorbance at 450 nm after 30 min. Slowly reacting antioxidants required an incubation at 50 °C for 20 min for color development. The flavonoid glycosides were hydrolyzed to their corresponding aglycones by refluxing in 1.2 M HCl-containing 50% MeOH for fully exhibiting their antioxidant potencies. Certain compounds also needed incubation after acid hydrolysis for color development. The CUPRAC absorbances of mixture constituents were additive, indicating lack of chemical deviations from Beer’s law. The CUPRAC antioxidant capacities of a wide range of polyphenolics are reported in this work and compared to those found by ABTS/persulfate and Folin assays. The trolox-equivalent capacities of the antioxidants were linearly correlated (
r
= 0.8) to those found by ABTS but not to those of Folin. The highest antioxidant capacities in the CUPRAC method were observed for epicatechin gallate, epigallocatechin gallate, quercetin, fisetin, epigallocatechin, catechin, caffeic acid, epicatechin, gallic acid, rutin, and chlorogenic acid in this order, in accordance with theoretical expectations. The experiences of other CUPRAC users also are summarized.
