On the Azo/Hydrazo Equilibrium in Sudan I Azo Dye Derivatives

Ferreira, Gilson R.; Garcia, Humberto C.; Couri, Mara R.C.; Santos, Hélio F. Dos; Oliveira, Luiz Fernando Cappa de

doi:10.1021/jp310229h

Cited by 46 publications

(32 citation statements)

References 41 publications

(46 reference statements)

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“…The Sudan I molecules may mainly be protonated at multiple position, including the oxygen atom and two azo nitrogen atoms (N1 and N2), because they are the basic sites in the molecule. Furthermore, considering that Sudan I exists as a mixture of tautomers that is referred to as the azo (OH) and the hydrazone (NH) form, see Figure , protonation may occur at different sites for two kinds of Sudan I tautomers resulting in six different possible forms of protonated Sudan I molecule (MH‐1 to MH‐6). To identify the most favorable protonation site, the molecular electrostatic potential map (MEP) of Sudan I in azo and hyrdrazone form, and the proton affinity (PA) were calculated for six possible protonated forms of Sudan I molecule [M+H] + , respectively.…”

Section: Resultsmentioning

confidence: 99%

How Does Azo Bond Cleave in the Gas Phase? Computational and Experimental Study on the Fragmentation Mechanism of Protonated Sudan I

Liang

Wang

et al. 2019

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As a cheap but harmful additive in food industry, 1-phenylazo-2-naphthol (Sudan I) has attracted lots of attentions, which mainly focused on the determinations using the HPLC-ESI-MS/ MS techniques. However, the fragmentation mechanisms are generally scarce. In this paper, the fragmentation pathways of protonated Sudan I in gas-phase were investigated by a combination of electrospray ionization-tandem mass spectrometry and density functional theory (DFT) calculations. Initially, the cleavage of azo bond is triggered by ionizing proton migration from the oxygen atom of O-protonated Sudan I to adjacent N atom through a six-member ring transition state, leading to a single ion-neutral complex (INC-s). Subsequently, the direct decomposition of INC-s gives the naphtol nitrene ion at m/z 156. Meanwhile, INC-s may occur an intermolecular single electron transfer (SET) reaction via the crossing points (INC-mecp), affording the triple ion-neutral complex (INC-t) consisting of naphtol nitrene radical and aniline radical ion. Finally, followed by the decomposition of INC-t, the aniline radical ion at m/z 156 is formed. Further studies on Electrostatic potential map, Natural population analysis (NPA) and frontier molecular orbitals (FMOs) during the proposed mechanism are also found to be in good agreement with experimental observations. Taken together, our results presented here not only provide mechanistic information for better understanding the Sudan I, but also give insights into other related harmful additives in food industry.

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Section: Resultsmentioning

confidence: 99%

How Does Azo Bond Cleave in the Gas Phase? Computational and Experimental Study on the Fragmentation Mechanism of Protonated Sudan I

Liang

Wang

et al. 2019

ChemistrySelect

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“…Recently we have shown [3] by theoretical calculations and by analysis of the existing crystallographic data of structurally similar compounds [4][5][6][7][8] that the structures of the enol and keto tautomers of 4-((2-hydroxynaphthalen-1-yl)diazenyl)-3,5-dinitrobenzoic acid as previously predicted by Adegoke are incorrect. In the same study [3] the tautomerism of 1-((2nitrophenyl)diazenyl)naphthalen-2-ol (1, Scheme 1) was investigated by using DFT calculations and UV-Vis spectroscopy.…”

Section: Introductionmentioning

confidence: 88%

4-Carboxyl-2,6-dinitrophenylazohydroxynaphthalenes tautomerism NMR re-explained and other methods verified

et al. 2017

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In two consecutive studies the tautomerism in 4-((2-hydroxynaphthalen-1-yl)diazenyl)-3,5dinitrobenzoic acid and the structurally similar 1-((2-nitrophenyl)diazenyl)naphthalen-2-ol has been considered from viewpoint of theoretical chemistry, UV-Vis spectroscopy and NMR.Although the theoretical data (at M062X level) show that both compounds exist only as a keto tautomer, the experiment proves existence of the enol form. The difference in the results obtained by UV-Vis spectroscopy and NMR requires a deeper consideration and verification of the NMR approach, which is based on using model compounds to provide the NMR signal pattern of individual tautomers.

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“…S2 and S3 in the ESI). The phase analysis revealed that Sudan I consists of 82% of the polymorph I (Oliveri et al 1989), 8% of the polymorph II (Liu et al 1997), and 10% of the polymorph III (Ferreira et al 2013), whereas 4-methylumbelliferone exists in the anhydrous form (Panini et al 2014). …”

Section: Powder X-ray Diffractionmentioning

confidence: 99%

Improving Fluorometric Determination of Water Content in Aprotic Solvents

et al. 2017

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A fluorometric method allowing quantification of minute amounts of water in highly lipophilic solvents is proposed. This approach takes advantage of resonance energy transfer between 4-methylumbelliferone and Sudan I. The conditions required to observe effective energy transfer have been elucidated. The emission band of the donor molecule (4-methylumbelliferone) depends strongly on the water content-its position is affected by protolytic reactions occurring between the fluorescent dye and water in lipophilic solvent media. In consequence, the extent of overlap between the emission band of the donor and absorption peak of the acceptor scales with the water concentration. The sensitivity of this optical system can be considerably increased by addition of organic bases. The dependence of the emission band of 4-methylumbelliferone/Sudan I system on minute amount of water present in lipophilic solutions opens up possibility of determination of water content in these media at the unique wavelength, in a turn on mode. The presented system was successfully applied to determine water in model commercial oil samples. It was shown that using herein proposed method the increase of water contents in the sample can be observed as increase of the emission intensity, despite the native fluorescence of the vegetable oil samples. For these samples, a good correlation with golden standard Karl Fischer titration was obtained.

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On the Azo/Hydrazo Equilibrium in Sudan I Azo Dye Derivatives

Cited by 46 publications

References 41 publications

How Does Azo Bond Cleave in the Gas Phase? Computational and Experimental Study on the Fragmentation Mechanism of Protonated Sudan I

How Does Azo Bond Cleave in the Gas Phase? Computational and Experimental Study on the Fragmentation Mechanism of Protonated Sudan I

4-Carboxyl-2,6-dinitrophenylazohydroxynaphthalenes tautomerism NMR re-explained and other methods verified

Improving Fluorometric Determination of Water Content in Aprotic Solvents

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