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In this study, in situ surface-enhanced Raman scattering (SERS) spectroelectrochemistry and angle-resolved X-ray photoelectron spectroscopy (AR-XPS) are used to investigate the redox reaction and adsorption behavior of anthraquinone-2-carboxylic acid (AQ-2-COOH) on an Ag electrode at different pH values. The obtained results indicate that AQ-2-COOH is adsorbed tilted on the Ag electrode through O-atom of ring carbonyl in a potential range from −0.3 to −0.5 V vs. SCE, but the orientation turns to more tilted orientation with both O-atom of the ring carbonyl and carboxylate group in positive potential region for pH 6.0 and 7.4. However, at pH 10.0, the orientation adopts tilted conformation constantly on the Ag electrode with both O-atom of the anthraquinone ring and carboxylate group in the potential range from −0.3 to −0.5 V vs. SCE or at positive potentials. Moreover, the adsorption behavior of AQ-2-COOH has been further confirmed by AR-XPS on the Ag surface. Proposed reasons for the observed changes in orientation are presented. [ABSTRACT FROM AUTHOR]

• AQCA/CMK-3 nanohybrid was employed as a new redox nanoprobe for the first time. • Urchin-like Ce-MOFs were used as favorable platform to accelerate electron transfer. • Sandwich-type aptasensor was constructed with excellent sensitivity and specificity. • This approach was utilized to detect MPT64 in human serum with satisfactory results. Rapid and sensitive tuberculosis (TB) diagnoses remain big challenges to current detection tools. In this work, a sensitive electrochemical aptasensor was constructed for the determination of Mycobacterium tuberculosis antigen MPT64 using a new redox nanoprobe. We found that anthraquinone derivative, anthraquinone-2-carboxylic acid (AQCA), a redox mediator, could be confined in ordered mesoporous carbon material of CMK-3. Due to the large loading amount of AQCA, as well as the confined space and electron transfer promotion effect of CMK-3, the obtained AQCA/CMK-3 nanohybrid with mass ratio of 2:1 showed excellent electroactivity and was employed as a new redox nanoprobe for signal amplification for the first time. Additionally, urchin-like Ce-MOFs were used to load a large amount of deposited gold nanocrystals (dep-Au), leading to dense immobilization of capture probe. The proposed electrochemical aptasensor for MPT64 detection showed a good linear relationship in the range from 100 fg/mL to 10 ng/mL with a low detection limit of 67.6 fg/mL. Besides, the aptasensor was utilized to detect MTP64 in human serum samples for TB diagnosis and presented satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract: We developed an efficient method for the generation of hydrogen peroxide by aerobic photooxidation of 2-propanol using anthraquinone-2-carboxylic acid and molecular oxygen in air and visible light from fluorescent lamps. One-pot epoxidation of α,β-unsaturated ketones using the generated hydrogen peroxide is also reported. [Copyright &y& Elsevier]

Abstract: The adsorption state of anthraquinone-2-carboxylic acid (AQ-2-COOH) deposited from acetone solutions (0.01–1.00mg/ml) on native oxide surfaces of Al films was characterized by inelastic electron tunneling spectroscopy, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy. The oxide was prepared on evaporated Al films at room temperature in an oxygen-dc glow discharge. The morphology of the deposited AQ-2-COOH on the oxide surfaces was observed and analyzed by atomic force microscopy. These surface analyses showed that AQ-2-COOH is adsorbed predominantly as a uniform nanometer-scale film of carboxylate anions on the oxide surfaces deposited from solutions with concentrations lower than or equal to 0.02mg/ml. It was found that AQ-2-COOH is adsorbed as both a uniform film of anions and as micron-sized particles of neutral molecules with heights of a few tens of nanometers when AQ-2-COOH is deposited from solutions with concentrations higher than 0.02mg/ml. A comparison of the results obtained by these surface analytical techniques clearly shows the features and advantages of these analytical techniques. [Copyright &y& Elsevier]

Abstract: The growth-inhibiting activity of Tabebuia impetiginosa Martius ex DC dried inner bark-derived constituents against Helicobacter pylori ATCC 43504 was examined using paper disc diffusion and minimum inhibitory concentration (MIC) bioassays. The activity of the isolated compounds was compared to that of the commercially available anti-Helicobacter pylori agents, amoxicillin, metronidazole, and tetracycline. The biologically active components of Tabebuia impetiginosa dried inner bark (taheebo) were characterized by spectroscopic analysis as 2-(hydroxymethyl)anthraquinone, anthraquinone-2-carboxylic acid, and 2-hydroxy-3-(3-methyl-2-butenyl)-1,4-naphthoquinone (lapachol). With the paper disc diffusion assay 2-(hydroxymethyl)anthraquinone exhibited strong activity against Helicobacter pylori ATCC 43504 at 0.01mg/disc. Anthraquinone-2-carboxylic acid, lapachol and metronidazole were less effective, exhibiting moderate anti-Helicobacter pylori activity at 0.1mg/disc. Amoxicillin and tetracycline were the most potent compounds tested, displaying very strong activity at 0.005mg/disc. 2-(Hydroxymethyl)anthraquinone exhibited moderate activity at this dose. Tetracycline still had strong activity at 0.001mg/disc while amoxicillin had little activity at this dose. In the MIC bioassay, 2-(hydroxymethyl)anthraquinone (2μg/mL), anthraquinone-2-carboxylic acid (8μg/mL), and lapachol (4μg/mL) were more active than metronidazole (32μg/mL) but less effective than amoxicillin (0.063μg/mL) and tetracycline (0.5μg/mL). The anti-Helicobacter pylori activity of seven 1,4-naphthoquinone derivatives (structurally related to lapachol), 1,4-naphthoquinone, 5,8-dihydroxy-1,4-naphthoquinone (naphthazarin), 2-methyl-1,4-naphthoquinone (menadione), 2-hydroxy-1,4-naphthoquinone (lawsone), 5-hydroxy-2-methyl-1,4-naphthoquinone (plumbagin), 5-hydroxy-1,4-naphthoquinone (juglone), and 2,3-dichloro-1,4-naphthoquinone (dichlone) was also evaluated using the paper disc assay. Menadione and plumbagin were the most potent compounds tested with the later still exhibiting very strong activity at 0.001mg/disc. Menadione, juglone and tetracycline had strong activity at this low dose while the latter two compounds and amoxicillin had very strong activity at 0.005mg/disc. Lawsone was unusual in that it had very strong activity at 0.1 and 0.05mg/disc but weak activity at doses of 0.01mg/disc and lower. Naphthazalin, lapachol and dichlone had similar activities while metronidazole had the lowest activity of all compounds tested. These results may be an indication of at least one of the pharmacological actions of taheebo. The Tabebuia impetiginosa dried inner bark-derived materials, particularly 2-(hydroxymethyl)anthraquinone, merit further study as potential Helicobacter pylori eradicating agents or lead compounds. [Copyright &y& Elsevier]

We developed the aerobic photooxidative bromination of aromatic compounds using carbon tetrabromide in the presence of anthraquinone-2-carboxylic acid under visible light irradiation. [ABSTRACT FROM AUTHOR]