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Calcification within breast cancer is a diagnostically significant radiological feature that generally consists of hydroxylapatite. Samples from 30 cases of breast carcinoma with calcification were investigated using optical microscopy, energy-dispersive X-ray analysis, transmission-electron microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, synchrotron radiation X-ray diffraction and X-ray fluorescence. Under optical microscopy, the calcifications were found to consist of either irregular aggregates with widths > 200 μm or spherical aggregates similar to psammoma bodies with an average diameter of 30 μm. Transmission-electron microscopy showed that short columnar or dumbbell-shaped crystals with widths of 10–15 nm and lengths of 20–50 nm were the most common morphology; spherical aggregates (~1 μm in diameter) with amorphous coatings of fibrous nanocrystals were also observed. Results indicated that hydroxylapatite was the dominant mineral phase in the calcifications, and both CO32– and cation substitutions (Na, Mg, Zn, Fe, Sr, Cu and Mn) were present in the hydroxylapatite structure. Fourier-transform infrared spectra show peaks at 872 and 880 cm–1 indicating that CO32– substituted both the OH– (A type) and PO43– (B type) sites of hydroxylapatite, making it an A and B mixed type. The ratio of B- to A-type substitution was estimated in the range of 1.1–18.7 from the ratio of peak intensities (I872/I880), accompanied with CO32– contents from 1.1% to 14.5%. Trace arsenic, detected in situ by synchrotron radiation X-ray fluorescence was found to be distributed uniformly in the calcifications in the form of AsO43– substituting for PO43–. It is therefore proposed that identifying these trace elements in breast cancer calcifications may be promising for future clinical diagnostics.
Manganese (Mn) oxides have been prevalent on Earth since before the Great Oxidation Event and the Mn cycle is one of the most important biogeochemical processes on the Earth's surface. In sunlit natural environments, the photochemistry of Mn oxides has been discovered to enable solar energy harvesting and conversion in both geological and biological systems. One of the most widespread Mn oxides is birnessite, which is a semiconducting layered mineral that actively drives Mn photochemical cycling in Nature. The oxygen-evolving centre in biological photosystem II (PSII) is also a Mn-cluster of Mn4CaO5, which transforms into a birnessite-like structure during the photocatalytic oxygen evolution process. This phenomenon draws the potential parallel of Mn-functioned photoreactions between the organic and inorganic world. The Mn photoredox cycling involves both the photo-oxidation of Mn(II) and the photoreductive dissolution of Mn(IV/III) oxides. In Nature, the occurrence of Mn(IV/III) photoreduction is usually accompanied with the oxidative degradation of natural organics. For Mn(II) oxidation into Mn oxides, mechanisms of biological catalysis mediated by microorganisms (such as Pseudomonas putida and Bacillus species) and abiotic photoreactions by semiconducting minerals or reactive oxygen species have both been proposed. In particular, anaerobic Mn(II) photo-oxidation processes have been demonstrated experimentally, which shed light on Mn oxide emergence before atmospheric oxygenation on Earth. This review provides a comprehensive and up-to-date elaboration of Mn oxide photoredox cycling in Nature, and gives brand-new insight into the photochemical properties of semiconducting Mn oxides widespread on the Earth's surface.
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