pH-Dependent Molecular Behaviors of a New Potential Color Additive: 4{[6-(1-carboxyethyl)-2-hydroxy -1-naphthyl]diazenyl}-3,5- dinitro Benzoic Acid

Sunday Olakunle Idowu

doi:10.6000/1929-5030.2012.01.02.5

Authors

Sunday Olakunle Idowu University of Ibadan, Ibadan, Oyo State

DOI:

https://doi.org/10.6000/1929-5030.2012.01.02.5

Keywords:

4-carboxyl-2, 6-dinitrophenylazo hydroxynaphthalenes, color additive, non-genotoxic, isosbestic point, rate-pH profile

Abstract

Phenyl azo hydroxynaphthalene (PAHNP) is the pharmacophore in certain color additives (e.g. sunset yellow, FD & C yellow No. 6) approved for use in human foods, drugs and cosmetics. The azo compound, 4{[6-(1-carboxyethyl)-2-hydroxy -1-naphthyl] diazenyl}-3,5-dinitrobenzoic acid (AZ-03) is a new, non-genotoxic, PAHNP analog, in a mono-azo chemical library. Process understanding of pH dependent behaviors of the highly functionalized molecule, is a critical aid to its identification. Absorption spectra of a fixed concentration of AZ-03 [3.30 x 10-5 M] in buffer solutions of varied pH were recorded. Spectra overlay suggested isosbestic point exists around 520 nm. Absorbance measurements of solutions (1.10 x 10-5 M) of pH 7, 10 and 11 were taken at 522, 524, 526 and 528 nm. Relative contribuiton of variables to overall variance was; wavelength (7%, p = 0.16), pH of media (57%, p < 0.0001), interaction between pH and wavelength (7%, p = 0.46, 2-way ANOVA, Bonferroni test). The probability that signal difference across pH was due to chance was 4 times greater at 522 nm (p=0.29) relative to 524 nm (p=0.08, 1-way ANOVA). The orange, unionized specie and violet, ionized specie both exhibited intense absorption, with molar absorptivities of 14,600 (490 nm) and 12,800 (550 nm) [L mol-1 cm-1 ] respectively. AZ-03 was degraded by pseudo first-order kinetics in alkaline medium by specific-base catalysis. It was shown with some statistical rigor that the dye exhibits isosbestic point at 522 nm . Base-catalyzed degradation gave a non-linear and diagnostic rate-pH profile. These findings could aid precise authentication of this potential color additive, and thus facilitate further understanding and studies of its solution chemistry.

Author Biography

Sunday Olakunle Idowu, University of Ibadan, Ibadan, Oyo State

Department of Pharmaceutical Chemistry, Faculty of Pharmacy

References

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