The potential pitfalls of using 1,1-diphenyl-2-picrylhydrazyl to characterize antioxidants in mixed water solvents.
Approaching living systems, aqueous solutions are appropriate to characterize antioxidants, whereas the frequently used standard 1,1-diphenyl-2-picrylhydrazyl (DPPH) is insoluble in water. Therefore, mixed water-ethanol solvents were investigated using the electron paramagnetic resonance (EPR) spectroscopy. Two forms of DPPH were identified: at higher ethanol ratios a quintet spectrum characteristic of solutions, and at lower ratios, a singlet spectrum typical for solid DPPH, were found. Mixed solvents with 0-50% (v/v) water reproduced the same antioxidant equivalent points well and the reaction rate between DPPH and the antioxidant may increase considerably with increasing water ratios, as demonstrated using vitamin E as an antioxidant. But at still higher water ratios (70-90% (v/v)) the antioxidant activities dropped, since a part of the DPPH in the aggregated form does not react sufficiently with the antioxidants. Characteristics of the most common antioxidants were determined in ethanol or its 50% (v/v) aqueous solution.
Stasko
Andrej
A
Faculty of Chemical and Food Technology, Institute of Physical Chemistry and Chemical Physics, Slovak University of Technology in Bratislava, Radlinského 9, Bratislava, SK-812 37, Slovak Republic. andrej.stasko@stuba.sk
Brezová
Vlasta
V
Biskupic
Stanislav
S
Misík
Vladimír
V
D000975:Antioxidants / Q000737:chemistry*; D001671:Biochemistry / Q000379:methods*; D001713:Biphenyl Compounds / Q000494:pharmacology*; D004578:Electron Spin Resonance Spectroscopy; D000431:Ethanol / Q000737:chemistry; D006834:Hydrazines / Q000494:pharmacology*; D000432:Methanol / Q000737:chemistry; D008956:Models, Chemical; D010100:Oxygen / Q000737:chemistry; D010851:Picrates; D012997:Solvents / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors; D014810:Vitamin E / Q000737:chemistry; D014867:Water / Q000737:chemistry
D000975:Antioxidants; D001713:Biphenyl Compounds; D006834:Hydrazines; D010851:Picrates; D012997:Solvents; D014867:Water; D014810:Vitamin E; D000431:Ethanol; C004931:1,1-diphenyl-2-picrylhydrazyl; D010100:Oxygen; D000432:Methanol