(R)-3-Hydroxycarboxylic acids, chiral enantiomers of bacterial polyhydroxyalkanoates (PHA), may be valuable synthons for the production of numerous industrial materials such as β-lactams, fungicides, flavors, pheromones and vitamins. In this study, (R)-3-hydroxycarboxylic acid [(R)-3HAs)] synthons were produced by Streptomyces sp. JM3 (JN166713) under batch fermentation. Initial confirmation of PHA production was achieved by matrix assisted laser desorption ionization-time of flight mass spectroscopy and gas chromatography/mass spectroscopy (GC/MS). Subsequently, (R)-3HAs were produced by in vivo depolymerization and the monomers were separated using acid precipitation and anion exchange chromatography. The (R)-3HAs were identified by GC/MS as 3-trimethylsiloxy esters of decanoic, octanoic and butanoic acids. This was further supported by (13)C nuclear magnetic resonance spectrometry. The (R)-3HAs exhibited antimicrobial activity against Escherichia coli O157:H7, Listeria monocytogenes (ATCC 7644) and Salmonella typhimurium (ATCC 14028) with minimum inhibitory concentration ranging from 12.5 to 25 mg ml(-1). However, the minimum bactericidal concentration data suggest that the (R)-3HAs may be bactericidal for E. coli O157:H7 and bacteriostatic for S. typhimurium and L. monocytogenes. Furthermore, the major purified synthon was shown to minimize the invasion of fibroblasts by S. typhimurium (ATCC 14028) [p < 0.05], using the MTT assay [(3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide)].
The chemical and physical characteristics of nanocrystalline hydroxyapatite particles which formed during the subcutaneous implantation of crab shell in Sprague-Dawley rats were studied using selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). The initial SAED characterization evidence indicated the presence of an amorphous calcium phosphate phase. The electron dense nanophase particles which formed in the wound healing zone displayed broad diffuse rings which usually indicate a low crystalline order or amorphous phase. High resolution transmission electron microscopy (HRTEM) revealed that these mineralized regions contained discrete single crystal particles less than 5nm in size. Micrographs taken at successively higher magnifications revealed very small nanoparticles with a hexagonal arrangement of ion channels with characteristic spacing of 0.54nm and 0.23nm. This study revealed that single crystal hydroxyapatite nanoparticles consisting of only a few unit cells formed via a biomineralization directed process.
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