The influence of manganese oxide minerals (cryptomelane, hausmannite, and pyrolusite) on the formation of iron oxides was studied in the FeCl2-NH4OH system at different Mn/Fe molar ratios (0, 0.01, 0.1, and 1.0) and pHs (3.0, 4.0, 5.0, and 6.0) by X-ray powder diffraction, infrared absorption, transmission electron microscopic, and chemical analyses. In the absence of Mn minerals, lepidocrocite (γ-FeOOH) precipitated at pHs 5.0 and 6.0; however, no precipitate formed at lower pHs. All the Mn minerals studied promoted the precipitation of iron oxides and oxyhydroxides. In the presence of Mn oxides, Fe2+ was oxidized to Fe3+, which hydrolyzed and precipitated as noncrystalline and/or different crystalline iron oxides and oxyhydroxides, depending on the nature of the Mn oxides present in the system. Simultaneously, Mn2+ was detected in solution after the reaction by electron spin resonance spectroscopy. The presence of cryptomelane and hausmannite resulted in the formation of åkaganeite (β-FeOOH) and magnetite (Fe3O4), respectively. Thus, the effect of Mn oxides on the formation of Fe oxide minerals in the weathering zone merits attention.

Ischaemia reperfusion injury is a common and important phenomenon that occurs predictably in patients undergoing such procedures as cardiopulmonary bypass, thrombolysis, surgery under tourniquet, organ transplantation or embolectomy. Oxidative stress and the resulting lipid peroxidation play a major role in reperfusion injury. Membrane and cellular dysfunction result and, subsequently, organ injury or failure may ensue. Traditional methods of quantifying ischaemia reperfusion injury, including measurement of malondialdehyde, lack specificity and sensitivity. It was reported in 1990 that isoprostanes, a series of prostaglandin-like compounds, are produced by the free radical-catalyzed peroxidation of arachidonic acid. Measurement of the isoprostane concentration in urine or plasma provides the most reliable, non-invasive method currently available to assess oxidative stress in vivo. Serial measurement of isoprostanes in biological fluids has enhanced our understanding of the mechanisms underlying ischaemia reperfusion injury itself and its role in certain diseases. Furthermore, measurement of the isoprostane concentration provides a means to assess the effects of prophylactic and therapeutic interventions. In the future, the development of rapid, simple assays for isoprostanes offers the potential to assess prognosis during and after ischaemia reperfusion events.