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Nitroorganics present a general concern for a safe environment due to their health hazards. However, some nitroorganics such as metronidazole (Mtz) and chloramphenicol (CAM) also possess medicinal value. Mtz and CAM can undergo reductive bioactivation presumably via their nitroso derivatives. We show, using UV-vis spectroscopy, that sperm whale myoglobin (swMb) and its distal pocket mutants retaining H-bonding capacity react with Mtz in the presence of dithionite to generate products with spectra suggestive of the Fe-bound nitroso (Fe–RNO; ${\lambda }_{max}$$\sim$420 nm) forms. We have crystallized and solved the X-ray crystal structure of an H64Q swMb-acetamide compound to 1.76 Å resolution; the formation of this compound results from the serendipitous crystallographic trapping, by the heme center, of acetamide from the reductive decomposition of Mtz. Only one of the swMb proteins, namely H64Q swMb with a relatively flexible Gln64 residue, reacted with CAM presumably due to the bulky nature of CAM that generally may restrict its access to the heme site.

Recently, it has been reported that α-tricalcium phosphate (α-TCP) dental cements containing antibiotics can make good results when used over carious dentine. However, the release behavior of antibiotics and Ca from the cement is not clarified. Therefore, the aim of this study is to examine the in vitro release profile of the antibiotic-containing α-TCP cements. Three kinds of antibiotics (Metronidazole, Cefaclor and Ciprofloxacin) were added to two commercially available α-TCP cements. The set cements were immersed in water at 37°C and the released antibiotics and Ca were determined at regular intervals until three months. The release profile of the antibiotic-containing α-TCP cements was depended on the antibiotics added. The release rate of Ciprofloxacin was not so high in the early stage but it tended to elute continuously for three months, though the release of Metronidazole and Cefaclor reached plateaus within one month. The release rates of Ca from the antibiotic-containing α-TCP cements were higher than that from the control. The amounts of Ca released from Type II were higher than that from Type I. These differences in the release profile between Type I and II cements seemed to reflect the setting reaction of these cements.