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A method to determine the relative antioxidant capacity of radical scavengers based on the inhibition of the oscillations of the BriggsÀRauscher (BR) oscillating reaction was previously reported. A semiquantitative mechanistic interpretation of the inhibitory effects required two steps to obtain simulated inhibition times in very good agreement with the experimental ones. The first step is inhibitory, involving H-atom transfer from antioxidant to the HOO . radical; the second step is a first-order degradation of the antioxidant to unspecified products. Since the degradation may be due to oxidation and/or iodination of the antioxidant, we studied the kinetics of the subsystems IO À 3 (H ) antioxidant and I 2 (H ) antioxidant. We used 2,5-and 2,6-dihydroxybenzoic acids, caffeic acid ( 3-(3,4-dihydroxyphenyl)prop-2-enoic acid), ferulic acid ( 3-(4-hydroxy-3-methoxyphenyl)prop-2-enoic acid), pyrocatechol ( benzene-1,2-diol), and hydroquinone ( benzene-1,4-diol) as antioxidants. Spectra in the wavelength range 500 ± 250 nm were repeated at given time intervals to follow the peaks of the iodine and oxidation products, which were mainly quinones. For the iodination of the above diphenols ( benzenediol derivatives) the substitution and/or addition reactions with I 2 or HOI were found to be relatively slow compared to oxidation by IO À 3 . Approximate rate constants for oxidation were obtained on the basis of a reasonable kinetic model by using a suitable numerical integration program. Although these complexities can arise also in the completely inhibited BR oscillator, we believe that the inhibitory effects are due to the HOO . scavenging action by diphenols or by quinones since HOO . radicals are also potential reducing agents. We propose two steps that could maintain a small reservoir of diphenol, while both quinone and diphenol deplete HOO . radicals. In short, the complexities do not affect the method for monitoring the relative activity of antioxidants based on the BR oscillating reaction. The effects of temperature on the inverse of the oscillatory time in the BR-uninhibited system, on the inverse of inhibition times, and on the time length of the resumed oscillations for four antioxidants were also investigated. Apparent average activation energies were obtained.

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Developing scientific reasoning (SR) is a central goal of science-teacher education worldwide. On a fine-grained level, SR competency can be subdivided into at least six skills: formulating research questions, generating hypotheses, planning experiments, observing and measuring, preparing data for analysis, and drawing conclusions. In a study focusing on preservice chemistry teachers, an organic chemistry lab course was redesigned using problem-solving experiments and SR video lessons to foster SR skills. To evaluate the intervention, a self-assessment questionnaire was developed, and a performance-based instrument involving an experimental problem-solving task was adapted to the target group of undergraduates. The treatment was evaluated in a pre-post design with control group (cook-book experiments, no SR video lessons) and alternative treatment group (problem-solving experiments, unrelated video lessons). Interrater reliability was excellent (ρ from 0.915 to 1.000; ICC (A1)). Data analysis shows that the adapted instrument is suitable for university students. First insights from the pilot study indicate that the cook-book lab (control group) only fosters students’ skill in observing and measuring, while both treatment groups show an increase in generating hypotheses and planning experiments. No pretest-posttest differences were found in self-assessed SR skills in the treatment groups. Instruments and data are presented and discussed.

The antioxidant capacity of aqueous extracts of 20 vegetables and 16 fruits have been determined using the Briggs-Rauscher (BR) reaction method. Like other methods, the BR reaction method is also based on the generation of free radicals in the reaction mixture. Antioxidant scavengers of free radicals added to an active oscillatory BR regime cause an immediate cessation of the oscillatory regime, an inhibition time that linearly depends on the amount of the antioxidant added, and subsequent regeneration of oscillations. The BR reaction method works at pH≈2, which is similar to that of the fluids in the human stomach. It is known that a vegetarian diet can reduce the risk of stomach cancer and it is therefore interesting to determine the activity of antioxidants at low pH values.Different plants were tested with the BR reaction method, recording potentiometrically the inhibition times produced by their extracts on an active BR mixture. The results concerning the order of the antioxidant activity of the examined plants are illustrated and discussed.A comparison with the ranking order obtained with other methods is also given.