Biomedical subjects

S Shimabayashi

Publications and source records attributed to S Shimabayashi.

12 recordsLinked to original sources

PubMed1992

[Effects of temperature and pH on hydrolysis of monoacetoacetin in an aqueous phase].

The kinetics of hydrolysis of monoacetoacetin (MAA; 1,2-dihydroxy-3-acetoacetyloxypropane) in 300 mM phosphate buffer was studied by means of high performance liquid chromatography. MAA was hydrolyzed to glycerin (Glyc) and acetoacetate (AA), the latter of which furthermore decomposed to acetone (Acet) and CO2 at high temperature. The rate constant, k1, for the reaction of MAA-->AA+Glyc increased with increases in temperature and pH. On the other hand, another one, k2, for the reaction of AA-->Acet+CO2 increased with an increase in temperature but showed a minimum around pH 7.5 when pH was changed at a given temperature. The activation energy for k1 was almost constant in the range of studied pHs (5-8) but the pre-exponential factor, k1,0, increased with an increase in pH. It was concluded that the decomposition reaction of MAA is consecutive in a sequence of MAA-->AA-->Acet. Calculated concentrations of MAA, AA, and Acet through the obtained k1 and k2 together with a given initial concentration of MAA (= 40 mM) were compared with those experimentally observed on the time course of the hydrolysis. They were in good agreement with each other.

Acetoacetates↗

PubMed1991

Effect of phosphorylated organic compound on the adsorption of bovine serum albumin by hydroxyapatite.

The amount of adsorption of bovine serum albumin (BSA) by hydroxyapatite (HAP) increased with a concentration of CaCl2 due to the bridging effect of Ca2+ between adsorbate BSA and adsorbent HAP. On the other hand, it decreased remarkably with a concentration of K2HPO4. This was explained in terms of the effects of ionic strength and competitive adsorption between inorganic phosphate anion (Pi) and BSA, because BSA is in negatively charged over the examined pHs. A similar effect was observed in the presence of phosphorylated compounds such as phosphoserine, phytate, and phosphorylated polyvinylalcohol. The inhibiting effect of these compounds was stronger than that of their mother compounds (serine, inositol, and polyvinylalcohol). This result shows that phosphate groups bound to the mother compounds interfere with the adsorption of BSA by HAP in the same manner that Pi does. Although the adsorption of BSA was almost irreversible with respect to dilution with water, desorption was performed when these organic phosphorylated compounds were added after the accomplishment of the adsorption of BSA. However, the effective concentration of the phosphorylated compounds for the desorption of BSA was fairly higher than that for the competitive inhibition against the BSA adsorption.

Absorption↗

PubMed1989

Interaction of hydroxyapatite with sodium chondroitin sulfate and calcium chondroitin sulfate in an aqueous phase.

The suspension pH at a given concentration of hydroxyapatite (HAP) decreased with the concentration of calcium chondroitin-6-sulfate (CaChs), whereas it increased with the concentration of sodium chondroitin-6-sulfate (Na2Chs). The former effect is due to the increase in the concentration of H+ by ion exchange between H+ on the surface of HAP and Ca2+ of CaChs, and the latter is due to the protonation of phosphate ion (Pi) released from the surface of HAP. The absorbed amount of chondroitin-6-sulfate anion (Chs) by HAP was higher with CaChs than with Na2Chs over the concentration range examined. The equilibrium concentration of Pi decreased with increasing concentration of added CaChs because the concentration of free Ca2+, which dissociates from CaChs, regulates the free concentration of Pi through the restriction of the solubility product of HAP (Ksp). In contrast, that in the presence of Na2Chs increased with increasing concentration of added Na2Chs owing to the anion exchange between Chs and Pi of the HAP surface. The total concentration of Ca2+, which was released from HAP into the solution phase, increased after passing through a minimum with increasing concentration of added Na2Chs. That is, the concentration of Ca2+ free from Chs decreased with an increase in the concentration of released Pi owing to the restriction of the solubility product, whereas that of Ca2+ bound by Chs increased with increasing concentration of added Na2Chs through the ion exchange of Na+ with Ca2+. It was confirmed by the dialysis method that the value of Ksp was almost constant around 10, although HAP dissolves incongruently in the presence of Na2Chs.

Chemical Phenomena↗

PubMed1989

Decrease in the solubility product of hydroxyapatite by the adsorption of surface-active ion.

The solubility product (Ksp) of hydroxyapatite (HAP) in ionic surfactant solutions decreased with an increase in the adsorbed amount of the surface-active ions (dodecylammonium and dodecyl sulfate ions). In the presence of nonionic surfactant (polyoxyethylene(10) octylphenyl ether), Ksp was almost constant within the limit of experimental error. It was concluded that the decrease in Ksp is due to the decrease in the chemical potential of HAP through the adsorption of the surface-active ion on HAP, and due to the spontaneous change in the constituent ions of the HAP surface (i.e., surface complex formation) by ion-exchange with the surface-active ion.

Adsorption↗

PubMed1987