The dissolution behaviors of octacalcium phosphate (OCP), β-tricalcium phosphate (β-TCP), and hydroxyapatite (HA) were compared by implanting the materials in rat subcutaneous pouches for 8 weeks using a filter chamber or immersing them in simulated body fluid (SBF) or Tris-HCl buffer for 2 weeks at pH 7.4 and 37(o)C. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and chemical analysis were conducted on these materials. Degree of supersaturation (DS) in the two solutions immersed with each calcium phosphate material was calculated from their chemical compositions. The results showed that OCP partially converted to apatitic crystals, while β-TCP and HA remained unchanged after the implantation. The DS of the SBF solution remained slightly supersaturated with respect to OCP and β-TCP, but slightly undersaturated in the Tris-HCl buffer. These findings suggest that previously reported OCP and β-TCP biodegradation could be induced through cell-mediated osteoclastic resorption rather than a simple dissolution process.
Samarium(i1) di-iodide, which is a strong one-electron transfer reducing agent, is effective for the reductive coupling of E,P-unsaturated esters with carbonyl compounds, whereby substituted y-lactones can easily be prepared in good to excellent yields under very mild conditions. Two mole equiv. of samarium(ii) di-iodide to each mole equiv. of starting substrate always give reasonable yields. The presence of an alcohol is essential in the reaction, complex unidentified products being formed in the absence of an alcohol; t-butyl alcohol gave more satisfactory results than methanol and ethanol. The alcohol acts as a proton donor, the use of MeOD leading to a deuteriated y-lactone. The reaction is applicable t o both aliphatic and aromatic ketones or aldehydes, whereas the electrochemical method is limited to aliphatic substrates. The diastereoselectivity is examined in the reaction of 4-tbutylcyclohexanone with ethyl acrylate; an anti-isomer is produced predominantly (syn:anti = 1 : 9) as the result of selective axial attack. The reaction may proceed b y a radical mechanism, and reaction may not involve a samarium ester homoenolate. The reaction is extended to the intramolecular reaction of an ~, punsaturated keto ester (8-oxonon-2-enoate) leading to the ready synthesis of a bicyclic y-lactone. * cis: trans = ca. 75125. cis: trans = ca. 65: 35.14 cis: trans = ca. 70: 30.14 8 Hex-5-en-2-one (lo), 70 * The carbon bearing one deuterium should, in principle, appear as a triplet, It was not, however, observed since the concentration of the sample is low (5-10%) and the peak may be concealed in the noise.
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