Caffeine, theophylline, theobromine, paraxanthine, glucose, sucrose, formic acid and acetonitrile were purchased from Sigma-Aldrich with analytical grade purity. Double distilled water with resistivity above 18 MΩ cm was employed in all experiments. Sulfuric acid (ACS reagent, 95.0–98.0%), nitric acid (ACS reagent, ≥69%), perchloric acid (ACS reagent, 70%) were tested as supporting electrolytes for CAF sensing. CAF containing beverages were purchased from the local store. Coffee samples were prepared by using medium roasting degree coffee (100% Coffea arabica L. blend) Iperespresso capsule (illycaffè S.p.A., Trieste, Italy). Iperespresso coffee machine (mod. X2, illycaffè S.p.A., Italy) and tap water (total hardness 18–20°f) were used to prepare three different types of espresso beverages according to the typical Italian cup volume known as ristretto, regular or lungo [45 ].
Paraxanthine
Manufactured by Merck Group
Sourced in United States, Belgium
Paraxanthine is a chemical compound used in various laboratory applications. It is a methylxanthine derivative with a structural similarity to caffeine. Paraxanthine is primarily utilized as a research tool and standard in analytical chemistry, pharmaceutical development, and biochemical studies.
Automatically generated - may contain errors
Lab products found in correlation
Caffeine, by Merck Group (19 mentions)
Theobromine, by Merck Group (17 mentions)
Theophylline, by Merck Group (17 mentions)
Formic acid, by Merck Group (6 mentions)
Acetonitrile, by Avantor (6 mentions)
Formic acid, by Avantor (4 mentions)
Methanol, by Avantor (4 mentions)
Caffeine 13c3, by Merck Group (4 mentions)
Xanthine, by Merck Group (3 mentions)
1 methyluric acid, by Merck Group (3 mentions)
1 methylxanthine, by Merck Group (3 mentions)
7 methylxanthine, by Merck Group (3 mentions)
Acetonitrile, by Merck Group (2 mentions)
Theobromine d6, by Merck Group (2 mentions)
8 hydroxyefavirenz, by LGC (2 mentions)
8 14 dihydroxyefavirenz, by LGC (2 mentions)
β glucuronidase, by Merck Group (2 mentions)
Resorufin, by Merck Group (2 mentions)
Methoxyresorufin, by Merck Group (2 mentions)
Ethoxyresorufin, by Merck Group (2 mentions)
25 protocols using paraxanthine
1
Electrochemical Determination of Caffeine
2
Quantification of Methylxanthines and Metabolites
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Caffeine (1 mg/mL), theobromine (0.1 mg/mL), theophylline (1 mg/mL), paraxanthine (1 mg/mL), 13C3-Caffeine (1 mg/mL) stock solutions and theobromine-d6 (98% purity) were purchased from Sigma. Acetonitrile, methanol, and water were LC-MS grade and were from VWR. Formic acid was LC-MS grade and purchased from Amresco.
3
Analytical Determination of Caffeine and Metabolites
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Caffeine (CAF, ≥99%), paraxanthine (PX, ≥98%), theophylline (TP, ≥99%), theobromine (TB, ≥98%) and boric acid (≥95%), purchased from Sigma-Aldrich Chemie GmbH (Steinheim, Germany), were used as received. Sulphuric acid (H2SO4, 95–98%), phosphoric acid (H3PO4, ≥85%), nitric acid (HNO3, ≥65%), acetic acid (≥99%), formic acid (≥95%), sodium hydroxide (NaOH, ≥99%), ethanol, acetonitrile and ethyl acetate were obtained from Sigma-Aldrich with analytical grade purity. Potassium chloride (KCl, ≥3 M) solution for Ag/AgCl reference electrodes was purchased from Sigma-Aldrich. PROPLUS tablets, with a declared amount of 50 mg CAF per tablet, were obtained from a local pharmacy in London, UK. Ultra-pure deionised water (resistivity not lower than 18 MΩ cm at 25 °C) obtained from a Milli-Q unit (Millipore) was used to prepare all the solutions.
4
Quantitative Analysis of Caffeine and Quercetin
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Quercetin capsules (GNC Quercetin 500, 500 mg capsules) were purchased from General Nutrition Centers, Inc., SC, USA. Caffeine, paraxanthine, and acetaminophen (the internal standard) were obtained from Sigma Chemical Co. (St. Louis, MO, USA). Caffeine capsules (100 mg capsules) were purchased from Xinhua Pharmaceutical Company Limited, Shandong, China. HPLC-grade chloroform, isopropanol, formic acid, acetonitrile, and methanol were purchased from Chemical Reagent Factory of Hunan (Changsha, Hunan, China). Ultrapure water was produced by water purification system (Aquapro. CO., LTD, Shanghai, China).
5
Quantifying Metabolic Biomarkers in Biological Samples
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Caffeine (1,3,7 TMX), 1‐methylxanthine (1 MX), 1‐methyluric acid (1 MU), 1,7‐dimethyluric acid (1,7 DMU), 5‐acetylamino‐6‐formylamino‐3‐methyluracil (AFMU), and 1,7‐dimethylxanthine (1,7 DMX) or paraxanthine and theobromine and theophylline were purchased from Sigma–Aldrich (St. Louis, MO). Efavirenz, 8‐hydroxyEfavirenz, 8,14‐dihydroxyEfavirenz, 7‐hydroxyEfavirenz, and β‐glucuronidase were purchased from Toronto Research Chemicals (North York, Ontario, Canada). All other chemicals and solvents were high‐performance liquid chromatography (HPLC) grade or the highest quality commercially available.
6
Quantifying Purine Metabolism Compounds
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Caffeine (58–08–2), Theobromine (83–67–0), Theophylline (58–55–9), Paraxanthine (611–59–6) and Metyrapone (54–36–4) were purchased from Sigma-Aldrich (St. Louis, MO, USA), and 1, 3, 7 trimethyluric acid (5415–44–1) from ChemCruz (Santa Cruz, CA, USA).
7
Caffeine and Apoptosis Study
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Caffeine, paraxanthine, theobromine, rapamycin, isopropyl‐b‐d ‐thiogalactopyranoside (IPTG), dimethyl sulfoxide (DMSO), and theophylline were purchased from Sigma. DMSO stock solution was made refresh prior to use. Annexin V (Pacific Blue conjugate) was purchased from Fisher Scientific. Caffeinated beverages, including Coca Cola, Starbucks coffee, and Red Bull, were purchased from a local grocery store.
8
Silver Nanoparticle Synthesis and Characterization
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The reagents used in this investigation were silver nitrate (>99 %), trisodium citrate, potassium nitrate, sodium borohydride (NaBH4) (98 + %), caffeine (≥99 %), theobromine (∼98 %) and paraxanthine (∼98 %), all of which were purchased from Sigma-Aldrich (Dorset, UK) and supplied as racemates. Acetic acid (analytical reagent grade) was purchased from Fisher Scientific Company (Loughborough, UK), and sodium hydroxide standard solution (0.1 mol/L) was obtained from Riedel de-Haen Company (Seelze, Germany).
9
Quantitative Bioanalysis of Pharmaceutical Compounds
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Caffeine-d9, ciprofloxacin, efavirenz-d4, 8-hydroxyefavirenz, 8,14-dihydroxyefavirenz, fluconazole, losartan, losartan carboxylic acid (E3174), losartan-d4, α-hydroxyMetoprolol, Metoprolol-d7, omeprazole, 5-hydroxyomeprazole, omeprazole-d3, paroxetine, and rifampicin were purchased from Toronto Research Chemicals (Toronto, Canada). 1’-HydroxyMidazolam and Midazolam-d6 were purchased from Lipomed (Lipomed AG, Arlesheim, Switzerland). Metoprolol, paraxanthine, and β-glucuronidase were obtained from Sigma-Aldrich (Sigma-Aldrich Chemie GmbH, Buchs, Switzerland). Midazolam (Hoffmann-La Roche, Basel, Switzerland) and efavirenz (Merck, NJ, USA) were kindly provided by the producers.
Formic acid, high-performance liquid chromatography (HPLC)-grade methanol, and water were purchased from Merck (Merck, Darmstadt, Germany). Stock solutions, calibration spiking solutions, and quality controls were prepared in dimethyl sulfoxide. Calibration standards were prepared by enriching caffeine-free blank human serum using the corresponding spiking solutions. Internal standard solutions containing the deuterated compounds were prepared in methanol.
Formic acid, high-performance liquid chromatography (HPLC)-grade methanol, and water were purchased from Merck (Merck, Darmstadt, Germany). Stock solutions, calibration spiking solutions, and quality controls were prepared in dimethyl sulfoxide. Calibration standards were prepared by enriching caffeine-free blank human serum using the corresponding spiking solutions. Internal standard solutions containing the deuterated compounds were prepared in methanol.
10
Synthetic Urine Preparation and Analysis
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Uric acid, theobromine, theophylline, caffeine and paraxanthine were purchased from Sigma-Aldrich (St. Louis, MO, USA). Synthetic urine components were obtained from Panreac (Montcada i Reixac, Barcelona, Spain). Chemicals of analytical reagent-grade purity were dissolved in ultra-pure deionized water from a Milli-Q system and filtered through 0.45 µm pore filters before use. Uric acid stock solution was prepared daily by dissolving 1 g Uric acid in 0.5 L of water with 1 M NaOH addition. Synthetic urine was prepared by mixing equal volumes of A and B solutions (Table 1 ), neither of which contained calcium or oxalate, thus preventing the crystallization of calcium oxalate. The pH of both solutions was adjusted depending on the experiment.
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