The chemical reaction of progesterone with superoxide anion O 2 .− in 0.1 mol/L NaHCO 3 medium is studied by polarography. Differing from the indirect inhibition of O 2 .− generation by synthesized glucocorticoids in mechanism, the function that progesterone scavenges O 2 .− is ascribed to that O 2 .− directly oxidizes the C = C double bond conjugated with the carbonyl moiety of progesterone molecule to a free radical, and then is reduced to H 2 O 2 . The result obtained in this work gives new evidence for biomedical research. The equation of rate constant of the oxidization reaction is deduced, and the apparent rate constant obtained is 308 L · mol −1 · s −1 .

In a 0.125 mol/L phosphate (pH 6.6)/2.5 × 10-4 mol/L 2-iodoacetamide solution, lomefloxacin yields a response of a polarographic catalytic current. The second-order derivative peak current of the catalytic wave of lomefloxacin is proportional to its concentration in the range of 1.0 × 10-8 - 1.0 × 10-6 mol/L (r = 0.998). The sensitivity of the catalytic wave is 25-times higher than that of the corresponding reduction wave for 5.0 × 10-7 mol/L lomefloxacin. The proposed method was applied to the determination of lomefloxacin in pharmaceutical preparations. The polarographic reduction wave is ascribed to a one-electron reduction of the C=C bond of lomefloxacin zwitterion accompanied by an acid-base equilibrium. The catalytic wave should be caused by regeneration of the lomefloxacin molecule at electrode surface due to the one-electron reduction product being further oxidized by electroreductive intermediate products of 2-iodoacetamide.

In 0.1 mol·L-1 NaHCO3 medium, the chemical reaction of hydrocortisone with superoxide anion O2 .- is studied by voltammetry. Experimental results prove that hydrocortisone, as a scavenger of O2 .-, can catalyze the dismutation reaction of O2 .-. The apparent reaction progression of the catalytic dismutation is zero for O2 .-, but two for hydrocortisone. The equation of rate constant for the catalytic dismutation reaction is deduced, and the apparent rate constant obtained is 8.76 × 105 L·mol-1·s-1. The result obtained gives new evidence for biomedical research. Besides the indirect inhibition of O2 .- generation by such synthesized glucocorticoids as hydrocortisone suppressing the activity of phospholipase A2, chemically hydrocortisone can also directly scavenge O2 .- produced. Therefore, the activity of hydrocortisone as an anti-inflammatory drug is ascribed to the combination of its biologic effectiveness and chemical scavenging for O2 .-.

Polarographic responses of the dissolved oxygen in phosphate (pH 7.4)-anion surfactant sodium dodecyl sulfate (SDS) medium were investigated by cyclic voltammetry and normal pulse voltammetry. The obtained results indicate that when the SDS concentration is up to 1.0×10−4 mol/l there are three reduction waves corresponding to the following electrode processes of oxygen species: O2+e→O2.−, O2.−+2HA+e→H2O2+2A− and H2O2+2HA+2e→2H2O+2A− (where HA presents proton donor), which is different from that in aqueous solution containing such surfactants as triphenylphosphine oxide or quinoline. This new medium system is available for studying the chemical reaction and kinetics of scavenging O2.− by low molecular weight organic compounds and drugs, and was used to investigate the dismutation of O2− catalyzed by tyrosine. The reaction rate constant of O2− with tyrosine determined, 2.69×104l/mol/s, is in agreement with that obtained by quenching chemiluminescence. The model of electric field concerned with the anion surfactant on electrode surface was proposed. It is suggested that there is, for SDS, an additional contribution to the inhibition of O2− diffusion from the electrode towards bulk solution by the electric field in ion exchange layer formed by ionogenic groups of the adsorbed surfactant molecule, besides the anhydrous environment of electrode surface caused by adsorption of the anion surfactant.