Abstract
The interaction of metal ion with sericin was investigated by ultramicro-electrophoresis, X-ray diffraction, IR-spectra, DTA and pH titration.
The following results were obtained:
1) In the pH region lower than isoelectric point, both sericin bind with Sn2+ and Th4+ but not with Cd2+ and Al3+. Similar tendency was found with sericins prepared under the different condition. The binding amount of metal ion to sericin was less than that in alkaline region.
2) From the results of pH titration of metal salts and of electrophoresis of metal ion-negative AgI sol (pI 4), it is concluded that SnCl2 is hydrolyzed in the pH region lower than the isoelectric point of sericin and Al(NO3)3 is hydrolyzed in the higher pH region. It was found that free energies of binding to AgI sol for Sn2+ and Al3+ are as large as that of Th4+. These results are in good agreement with those in electro-phoresis for sericin bound with metal ions.
3) In sericin cocoon layers treated with Al(NO3)3 or Th(NO3)4 at pH 6.0, two endothermic peaks were observed at about 233°C and 270°C (dec. temp.), while that treated with Th (NO3)4 at pH 2.5 had a single endothermic peak and the decomposition temperature was lowered to 253°C.
4) The strong scattering was observed about the center (d>12.5A) in X-ray diffraction pattern of sericin cocoon layer treated with Th (NO3)4 at pH 2.5.
5) At both pH 2.5 and pH 6.0, poly-L-glutamic acid bound easily with Th4+, while poly-L-lysine almost did not bind with Th4+ at pH 2.5.
