Ascorbic acid c6h8o6

Analytical-grade reagents were used to synthesize Cu nanoparticles, ZnO nanotubes, rGO, and their composites. Copper sulfate pentahydrate (CuSO₄·5H₂O) was obtained from Fluka, and cetyl trimethyl ammonium bromide (CTAB) was obtained from Otto Chemicals. Zinc acetate, sulfuric acid, phosphoric acid, potassium permanganate, sodium hydroxide, and ascorbic acid (C₆H₈O₆) were obtained from Sigma-Aldrich. Deionized water was used in the experiments.

A CdCl₂ stock solution (Merck; cat. # 2011; 2.5 mM dissolved in ddH₂O) was used throughout the study and diluted 1:500–1:1000 in serum-free medium. Iron salts and Na⁺-ascorbate stock solutions were freshly prepared for each experiment. Stock solutions were as follows: FeSO₄ (Sigma-Aldrich; cat. # F8048) or FeCl₃ (Sigma-Aldrich; cat. # 157740), 5 mM in ddH₂O or in 500 mM Na⁺-ascorbate, pH 7.4 where ascorbic acid (C₆H₈O₆) (Sigma-Aldrich; cat. # A5960) was dissolved in ddH₂O, pH titrated to 7.4 with 1 M NaOH and final volume adjusted to obtain a 500 mM stock solution. Stock solutions of iron salts and Na⁺-ascorbate were diluted 1:50 or 1:100 in serum-free medium for individual experiments. Stock solutions of 10 mmol/l desferrioxamine mesylate salt (Sigma-Aldrich; cat. # D9533) dissolved in phosphate-buffered saline (PBS) were freshly prepared prior to use.

The 2,2-azinobis-3-ethylbenzothiazoline-6-sulphonic acid (ABTS+) method was based on the method described by Gião et al. (2007) [25 (link)] modified to microplate [26 (link)]. The free radical-scavenging activity of the extracts was determined by this method. ascorbic acid (C₆H₈O₆) (Sigma, Darmstadt, Germany) at different concentrations (50.00–500.00 µM) was used as a standard curve and results were expressed as mg of ascorbic acid equivalents and all the assays were performed in triplicate.

Reactive Blue 4 (RB4), an anthraquinone dye (1-amino-4-[3-(4,6-dichlorotriazin-2-ylamino)-4-sulfophenylamino]anthraquinone-2-sulfonic acid), was obtained from Merck (Darmstadt, Germany). Demineralized water was used to prepare the solutions. Cu(NO₃)₂, KF, KCl, K₂CO₃, Na₂HPO₄, K₃PO₄, Na₂SO₄, KNO₃, NaC₂H₃O₂, KClO₄, K₂C₂O₄ and ascorbic acid (C₆H₈O₆) were purchased from Merck. Stock solution (10^–2 mol/L) of analytes was prepared by direct dissolution of their proper amount in deionized water. All other chemicals were of analytical grade and used as received. The buffer solution was prepared using 4-(2-hydroxyethyl)-1-piperazine ethane sulfonic acid (HEPES).
A Shimadzu 1601 PC UV-Vis double beam spectrometer (Kyoto, Japan) was used to record all UV-Vis spectra in quartz cuvettes 10.0 mm in diameter. A Bruker Vector 22 Fourier transform infrared spectrometer (Billerica, MA, USA) recorded the FTIR spectra using KBr pellet method. A digital Jenway 3510 digital pH meter (London, UK) calibrated with two standard buffer solutions was used to measure various pH values. A Hamilton syringe of 50 µL was used to deliver desired amounts of analyte solution into the cuvette.

The materials employed in this research were of reagent-grade quality and had not undergone any earlier purifying procedures. The chemical substances included SnCl₄·5H₂O (Merck, Darmstadt, Germany), AgNO₃ (Merck, Germany), urea (CH₄N₂O, Merck, Germany), acetic acid (CH₃COOH, Merck, Germany) and NaOH pellets and HCl (Active Fine Chemicals Ltd., Dhaka, Bangladesh). Ascorbic acid (C₆H₈O₆), di-ammonium oxalate monohydrate ((NH₄)₂C₂O₄·H₂O), and 2-propanol ((CH₃)₂CHOH) were also supplied by Merck (Darmstadt, Germany). Metronidazole (C₆H₉N₃O₃) was sourced from Corden Pharma, Italy. Throughout the experiments, a HITECH laboratory water purification system generated deionized water (DI), which was utilized.

All reagents used were of analytical grade and the water used was deionized (Milli-Q Millipore 18.2 MΩ cm⁻¹). Prussian blue or ferric ferrocyanide (PB) was obtained from Gwent Group (Torfaen, United Kingdom). Water-soluble polyvinyl alcohol photopolymer (PVA-AWP) was purchased from Toyo Kogyo Corporation (Chiba, Japan). Monobasic potassium phosphate (KH₂PO₄), dibasic potassium phosphate (K₂HPO₄), potassium chloride (KCl), hypoxanthine (HX), bovine milk xanthine oxidase enzyme (XOD) were all purchased from Sigma Aldrich Corporation (Nasdaq-Sial, Darmstarm, Darmst, Germany). Ascorbic acid (C₆H₈O₆) was purchased from Merck (Seelze, Germany). The 50 mmol·L⁻¹ K-PBS buffer solution (K₂HPO₄ 33.33 mmol·L⁻¹, KH₂PO₄ 16.67 mmol·L⁻¹) containing 10 mmol·L⁻¹ KCl (pH 7.5) was used in the preparation of the enzymatic solutions (stock and work), solutions of the substrate hypoxanthine (HX) 5 mmol·L⁻¹ and as the electrolyte in electrochemical measurements. It was also used as a solvent in tea infusions and dissolution of effervescent vitamins C.