Tadayuki Uno

Formation of a surface complex between polymer and surfactant and its effect on the dispersion of solid particles

Formation of an intermolecular complex between a polymer and a surfactant on the surface of a particle, and its effect on the suspension stability are discussed for the systems (1) kaolinite-sodium dodecyl sulfate (SDS)-polyvinylpyrrolidone (PVP), (2) kaolinite-SDS-hydroxypropylcellulose (HPC), (3) hydroxyapatite (HAP)-SDS-PVP, and (4) HAP-SDS-bovine serum albumin (BSA). The complex is formed by electrostatic and hydrophobic interactions, both of which often operate simultaneously. The effect of the surface complex on the suspension is explained in relation to the mean diameter of the secondary particles and the rheological properties of the suspensions. The significance of these studies for physicochemical and biological sciences is briefly discussed.

Cytochrome d axial ligand of the bd-type terminal quinol oxidase from Escherichia coli

Using various spectroscopic techniques, we studied the structure of the dioxygen reduction site of the bd‐type terminal quinol oxidase in the aerobic respiratory chain of Escherichia coli. Resonance Raman and FT‐IR spectroscopies identified the v(Fe2+‐CO) and v(C‐O) stretching frequencies at 471 and 1980.7 cm−1, respectively, at the cytochrome d center of the dithionite‐reduced CO‐bound enzyme. The CO ligation in the cytochrome bd complex is considerably different from those of the heme‐copper terminal oxidases. Anaerobic addition of NO to the air‐oxidized enzyme caused an exchange of cytochrome d‐bound dioxygen with NO leading to an appearance of cytochrome d‐NO EPR signal. But there is no superhyperfine structure originating from the cytochrome d proximal 14N ligand in the central resonance of the NO EPR signal. These results suggest that cytochrome d axial ligand of the cytochrome bd complex is likely a histidine residue in an anomalous condition or other than a histidine residue and, therefore, the molecular structure around the dioxygen‐binding site is different from that of the heme‐copper terminal oxidases.

Formation of Hydroxyapatite in the Presence of Phosphorylated and Sulfated Polymer in an Aqueous Phase

Hydroxyapatite (HAP) is known as the main inorganic component of hard tissues such as bones and teeth. It directly crystallizes and grows in the solution when the degree of supersaturation is low. On the other hand, it is formed via amorphous calcium phosphate (ACP), octacalcium phosphate (OCP), or dicalcium phosphate dihydrate (DCPD) when the degree of supersaturation in the mother solution is high. Formation of hard tissues and crystallization of HAP in the human body are affected physicochemically by many kinds of proteins, especially phosphoproteins. These proteins are called regulator proteins which play an important role in the regulation of mineral deposition and HAP growth on various organic matrices in animal/human body. The function of phosphoproteins, however, has been still complicated. It has been suggested that both matrix-bound and soluble phosphoproteins may serve dual roles; making the initial mineral deposition on the collagen matrix and inhibiting the calcification of soft tissues.

Crystal Growth of Calcium Phosphates in the Presence of Polymeric Inhibitors

Biological hydroxyapatite (HAP, Ca10(PO4)6(OH)2) is the main inorganic component of mammalian hard tissues such as bones and teeth1–5 and synthetic HAP is being developed as a biomedicai material for artificial bones and teeth. HAP is also used in chromotography for separation and purification of biopolymers from their mixture or raw extract by elution with a phosphate buffer. Recently, HAP has been used as an immunoadsorbent.4 Other calcium phosphates are also important in agriculture as fertilizers, in wastewater treatment processes, in chemical industry, and in other various fields.

ADSORPTION OF HYDROXYPROPYLCELLULOSE ON HYDROXYAPATITE VIA FORMATION OF SURFACE COMPLEX WITH SODIUM DODECYLSULFATE

Adsorption of hydroxypropylcellulose (HPC) on hydroxyapatite (HAP) in the presence of sodium dodecylsulfate (SDS) and its effect on stability of the HAP suspension were studied. Although the adsorption amount of HPC was low in the absence of SDS, it increased with the amount of SDS after the formation of the intermolecular complex between them on the surface of HAP. The adsorption of SDS by HAP is due to electrostatic attractive force between dodecylsulfate anion (DS-) and Ca2+ on the surface and due to isomorphous substitution of the sulfate group of DS- for the surface phosphate ion. Formation of the surface complex is by virtue of hydrophobic interaction between hydrophobic groups of DS- thus adsorbed and those of HPC captured from the bulk solution. Adsorption of SDS by HAP was reversible with respect to dilution with its solvent (a NaCl solution). As for HPC, however, the desorption was rather complicated, depending on the dilution procedure whether with water or with an aqueous solution of a given concentration of SDS. This observation suggests that the adsorbed SDS is offering the adsorption sites for HPC on the surface after implantation of the hydrophobic groups on the surface. Mean diameter (d) of the secondary particles of HAP was determined by means of a Coulter counter as a function of concentrations of SDS and HPC. The d-value decreased after attaining a maximum with an HPC concentration when an SDS concentration was kept constant. This result suggests that an SDS-HPC complex plays a role of a dispersing/flocculating agent against the HAP suspension. In fact, the behavior of the complex is quite similar to that of a polyelectrolyte as a dispersing/flocculating agent.