Protonation of azobenzene derivatives. I. Methyl orange and ortho-methyl orange

Bolton, P. D.; Ellis, James E.; Fleming, K. A.; Lantzke, IR

doi:10.1071/ch9731005

Cited by 9 publications

(4 citation statements)

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“…Methyl orange sodium 4-{[4-(dimethylamino)phenyl]diazenyl}benzene-1-sulfonate is a well-known acid–base indicator that changes colour from red to yellow-orange between 3.1 and 4.4 pH value [15]. In an acidic environment, a strong absorption band in the UV–Vis spectrum with a maximum at 508 nm is observed.…”

Section: Resultsmentioning

confidence: 99%

Polypyrrole–Methyl Orange Raman pH Sensor

et al. 2019

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An easy-to-prepare pH sensor based on electrochemically obtained polypyrrole doped with methyl orange ions is described. It enables the determination of a pH value in the 3–13 range for volumes below 1 µL. In a wide pH range, resonance and pre-resonance methyl orange Raman spectra, excited with the 514.5 nm line of an Ar+ laser, changed noticeably in function of H+ concentration. Two types of measurements were performed. In the first case, Raman spectra of the analyzed solutions were collected for samples placed on the sensor surface using a confocal microscope equipped with a 10x objective. Next, measurements were conducted for the same samples without the sensor. On the basis of these spectra, partial least-squares models were elaborated and validated. Relative standard errors of prediction for calibration, validation, and test samples were found to be in the 3.7%–3.9% range. An analogous model build using spectra registered without the sensor was characterized by slightly worse parameters.

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Section: Resultsmentioning

confidence: 99%

Polypyrrole–Methyl Orange Raman pH Sensor

et al. 2019

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“…Methyl orange (Sodium 4-{[4-(dimethylamino)phenyl]diazinyl}benzene-1-sulfonate) which is used as pH indicator, was prepared by dissolving 40 mg of it in 40 mL of water. Due to its pH transition rate (turns to red at pH < 3.0 and yellow at pH > 4.0), it is suitable for the expected pH value of wines and tartaric acid solutions (at or lower than pH 3.7) [48]. Commercial white wine was purchased for validation of the sensor performance.…”

Section: Reagentsmentioning

confidence: 99%

Porous Cellulose Substrate Study to Improve the Performance of Diffusion-Based Ionic Strength Sensors

et al. 2022

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Microfluidic paper-based analytical devices (µPADs) are leading the field of low-cost, quantitative in-situ assays. However, understanding the flow behavior in cellulose-based membranes to achieve an accurate and rapid response has remained a challenge. Previous studies focused on commercial filter papers, and one of their problems was the time required to perform the test. This work studies the effect of different cellulose substrates on diffusion-based sensor performance. A diffusion-based sensor was laser cut on different cellulose fibers (Whatman and lab-made Sisal papers) with different structure characteristics, such as basis weight, density, pore size, fiber diameter, and length. Better sensitivity and faster response are found in papers with bigger pore sizes and lower basis weights. The designed sensor has been successfully used to quantify the ionic concentration of commercial wines with a 13.6 mM limit of detection in 30 s. The developed µPAD can be used in quantitative assays for agri-food applications without the need for any external equipment or trained personnel.

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“…Such azobenzenes are well known as visual acid–base indicators, and the molecular structures exist as a neutral form in a basic solution or as a protonated form in an acidic solution (Scheme ). − Furthermore, there are two major tautomers for the protonated form: (i) ammonium tautomer or (ii) azonium tautomer, − and the spectral properties of the azonium tautomer suggest that its quinoid resonance contributor is dominant.…”

Section: Introductionmentioning

confidence: 99%

Supramolecular Complexation of Azobenzene Dyes by Cucurbit[7]uril

Kommidi

Smith

2023

J. Org. Chem.

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This report describes cucurbit [7]uril (CB7) complexation of azobenzene dyes that have a 4-(N,N′-dimethylamino) or 4-amino substituent. Absorption and NMR data show that CB7 encapsulates the protonated form of the azobenzene and that the complexed dye exists as its azonium tautomer with a trans azo conformation and substantial quinoid resonance character. Because CB7 complexation stabilizes the dye conjugate acid, there is an upward shift in its pK a , and in one specific case, the pK a of the protonated azobenzene is increased from 3.09 to 4.47. Molecular modeling indicates that the CB7/azobenzene complex is stabilized by three major noncovalent factors: (i) ion-dipole interactions between the partially cationic 4-(N,N′-dimethylamino) or 4-amino group on the encapsulated protonated azobenzene and the electronegative carbonyl oxygens on CB7, (ii) inclusion of the upper aryl ring of the azobenzene within the hydrophobic CB7 cavity, and (iii) a hydrogen bond between the proton on the azo nitrogen and CB7 carbonyls. CB7 complexation enhances azobenzene stability and increases azobenzene hydrophilicity; thus, it is a promising way to improve azobenzene performance as a pigment or prodrug. In addition, the striking yellow/pink color change that accompanies CB7 complexation can be exploited to create azobenzene dye displacement assays with naked eye detection.

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Protonation of azobenzene derivatives. I. Methyl orange and ortho-methyl orange

Cited by 9 publications

References 0 publications

Polypyrrole–Methyl Orange Raman pH Sensor

Polypyrrole–Methyl Orange Raman pH Sensor

Porous Cellulose Substrate Study to Improve the Performance of Diffusion-Based Ionic Strength Sensors

Supramolecular Complexation of Azobenzene Dyes by Cucurbit[7]uril

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