Yoshiaki Tanizawa

Structural change of keratin protein in human hair by permanent waving treatment

Abstract The damage to human hair caused by permanent waving treatment was examined from the viewpoint of structure with several spectroscopic methods, 13C CP/MAS n.m.r., wide angle X-ray diffraction (WAXD), FTi.r. and Raman methods. The partial disruption of α-helical structure constituting the microfibril in hair fibre was revealed by this study, although the incomplete re-oxidation of the disulphide bond has been considered to be the main damage caused by the treatment. Moreover, this disruption was mainly caused in the first reduction process. In particular, 13C CP/MAS n.m.r. gave the quantitative evaluation for change of α-helical content in the microfibril with permanent waving treatment. In addition, FTi.r. and Raman spectra indicated that the α-helix was partially changed to random coil, rather than to β-sheet structure.

Effects of silicate ions on the formation and transformation of calcium phosphates in neutral aqueous solutions

The effects of silicate ions on calcification reactions have been investigated in neutral solutions containing calcium and phosphate ions. The results have shown that the silicate ions enhanced the precipitation of amorphous calcium phosphate (ACP) and dihydrated dicalcium phosphate (DCPD). Transformation of these precursors to hydroxyapatite (HAP), However, was inhibited by silicate ions. X-Ray photoelectron spectroscopy (XPS) results have shown that a type of silicate was formed at the surface of the precursors in the early stage of the calcification process, resulting in inhibition of the transformation. On the contrary, silica, investigated for comparison with silicate ions, was found to provide favourable sites for ACP and DCPD nucleation. Thus, silica played the role merely of substrate for the nucleation, and as a result silica did not inhibit the conversion of the precursors to HAP.

Reaction characteristics of dental and synthetic apatites with Al3+ and La3+ ions in acidic solutions

Previous studies have shown that divalent cations such as Sn2+, Zn2+ and Fe2+ are taken up by dental and synthetic hydroxyapatities by a cation-exchange reaction with molar ratios of Ca2+/Sn2+, Zn2+, Fe2+≈ 1.0. In the present study the reaction characteristics of dental apatite and synthetic hydroxyapatites, the latter being model substances of the dental apatites, have been investigated in detail in trivalent cation solutions. In acidic solutions with pH values below 4.0, Al3+ ions were easily taken up by apatite samples to yield stable amorphous AlPO4·nH2O. In alkaline solutions at pH 11.0, however, the Al(OH)–4 formed in solution had a low reactivity with the hydroxyapatite. La3+ ions reacted with the apatite samples to form stable crystalline LaPO4 in acidic solution. The ionic radii of Ca2+(1.05 A) and La3+(1.22 A) are close enough together that solid solutions could be formed. XPS studies, however, suggested that an ion-exchange reaction forming a solid solution of La-H apatite would be unlikely. Both Al3+ and La3+ ions were taken up into the apatites by an attack reaction of these ions for Ca2+ ions of the apatite samples, assisted by loosening the crystal structures of the apatite samples with H+ ions in solution. These results should provide important physicochemical information for clinical investigations of the roles played by the trivalent cations in inhibiting dental caries and dentine hypersensitivity.

Reaction characteristics of dental and synthetic apatites with Fe2 + and Fe3 + ions

Various effects of Fe2+ and Fe3+ ions on the reaction characteristics of dental and synthetic apatites have been investigated. It has been found that both Fe2+ and Fe3+ ions inhibit crystallization of calcium phosphates during the calcification process, and that the colour of the reaction product turns brown owing to the incorporation of these ions. The dental and the synthetic hydroxyapatites, the latter being a pure model substance of dental apatite, were also coloured when they were treated with Fe2+ solutions. The results show that Ca2+ ions in the apatites are exchanged for Fe2+ ions in solution and the ion-exchanged Fe2+ ions are partially oxidized to Fe3+ ions by dissolved oxygen in solution. Furthermore, the dissolution rate of the dental apatite treated with Fe2+ is inhibited in organic acid solution. For the reaction of the dental and the synthetic hydroxyapatites with Fe3+ ions, both the reaction rate and the removal of Fe3+ are far larger than those of Fe2+ and the product is a stable amorphous solid even in acidic solution of pH 3.0–5.0. These interesting phenomena are explained in terms of formation of an amorphous ferric phosphate hydrate by an attack reaction of Fe3+ ions in solution for Ca2+ ions of the apatite, assisted by the loosening effect of H+ ions on the skeletal structure of the apatite.

X-ray photoelectron spectroscopy study on chemical states of fluoride in bovine dentine treated with NaF

The reaction of bovine dentine as carbonate–hydroxyapatite (CHAP) with NaF has been investigated. XPS studies have shown that the dentine behaved similarly to the non-carbonated HAP as far as formation of fluoridated hydroxyapatite (FHAP) was concerned. However, CaF2 was also formed even in neutral conditions in contrast to the case of stoichiometric hydroxyapatite, and CaF2 was subsequently transformed partially into FHAP in phosphate buffer solution.

Reaction characteristics of hydroxyapatite with F– and PO3F2– ions. Chemical states of fluorine in hydroxyapatite

The reactions of F– and PO3F2– ions with hydroxyapatite (HAP) are of interest owing to their dental application. The mechanism of the anti-caries effect of the fluorides, however, is still not clearly understood. In the present study the reaction characteristics of HAP with sodium fluoride (NaF) and sodium monofluorophosphate (Na2PO3F) in aqueous solutions have been investigated using various techniques. F– ions were more easily taken up by HAP than were PO3F2– ions, but no significant change in the X-ray diffraction pattern was observed, though CaF2 was formed only in acidic solutions. X-Ray photoelectron spectroscopy studies have shown that F– ions were ion-exchanged for structural OH– ions of HAP to produce fluorapatite in neutral solution at an F– concentration of 1000–10000 ppm, and that PO3F2– ions were chemisorbed onto the HAP surface or ion-exchanged for HPO2–4 ions. The PO3F2– ions were then partially hydrolysed to free F– and orthophosphate ions, and this was followed by incorporation of F– into HAP. Na+ ions were not incorporated into HAP in contrast to the divalent cations such as Sn2+ and Zn2+ ions reported previously.

Carbon-13 n.m.r. studies of keratin intermediate filament of human hair

Abstract 13C n.m.r. spectra of low sulfur fraction in S-(carboxymethyl) keratine, (SCMKA), which corresponds to the hard keratin intermediate filament (KIF) in human hair were observed in aqueous solution. The spectra were compared with those of SCMKA in 8 M urea and high sulfur fraction in S-(carboxymetyl) keratine, (SCMKB), in aqueous solution. The circular dichroism spectrum of SCMKA indicated 40% α-helix in the aqueous solution, and changed to that of random coil in 8 M urea. The SCMKB in aqueous solution also took random coil. The observed peaks in the 13C n.m.r. spectra of SCMKA in aqueous solution come mainly from the amino acid residues such as Thr, Ser, Pro and Gly in the N- and C-terminal domains with random coil structure. Thus it is suggested that these domains had high mobility. However, the amino acid residues, Leu, Ile, Glu, Arg and Lys, in the rod domain give essentially no peaks because of very restricted motion of the chain with coiled-coil structure.