Spectroscopic studies on gallic acid and its azo derivatives and their iron(III) complexes

Monitoring deprotonation of gallic acid by Raman spectroscopy

“…This value is in excellent agreement with the reference value of 8.71 . However, it is different from the one measure by ultraviolet–visible spectroscopy by Masoud et al . This is probably due to oxidation phenomenon because the usual optical spectroscopic measurements were not carried out under nitrogen atmosphere as we did in this study.…”

“…This value is in excellent agreement with the reference value of 8.71. [20] However, it is different from the one measure by ultraviolet-visible spectroscopy by Masoud et al [18] This is probably due to oxidation phenomenon because the usual optical spectroscopic measurements were not carried out under nitrogen atmosphere as we did in this study. For instance, Powell et al [19] measured pK2, using ultraviolet-visible spectroscopy in nitrogencontrolled atmosphere as we did, and found 8.55 ± 0.01 that is close to the reference value and to our measured value (Table S2).…”

“…These reported results suggested a probable misinterpretation between oxidation and pK2. Taking into account this explanation, we can consider that all reported pK2 values agree with prediction, except the value reported by Masoud et al . Masoud et al .…”

“…This value is in agreement with both the reference values and the experimental pKa values. [18][19][20][21][22]…”

“…For instance, GA has antioxidant and pro-oxidant properties, anti-cancer effect, antiviral, antibacterial, and allelopatic effects. [4][5][6][7][8][9][10][11][12][13][14][15] The pH highly impacts GA properties, as usually demonstrated through the formation of complexes [16][17][18][19] . It is therefore important to measure precisely the protonation of GA through the determination of the acid dissociation constants pKa, for GA concentration monitoring in environment where pH naturally varies.…”