Abstract
Hydroxyapatite, Ca10 (PO4) 6 (OH) 2 (HAp) is a main constituent of teeth and bones, and one of “Lattice Ion Ion-exchangers”, discovered by T. Suzuki. Two structure modified HAp were successfully synthesized and they have been found to have better ion-exchange characteristics for Zn2+and Cd2+ions than those of normal HAp. The one included CO32-ions (CAp) and the other included SiO44-ions (SiAp) in HAp structure. The reason why the ion-exchange characteristics were improved, was considered to be due to the loosened crystal structure by the substitution of CO32-and SiO44-ions for PO43-ions of HAp and thus activated Ca2+ions in HAp.
The SiAp was found to be chaneged gradually to HAp in water and many OH-ions were released as shown in the following reaction.
3Ca10 (PO4) 4 (SiO4) 2+18H2O 2Ca10 (PO4) 6 (OH) 2+10Ca2++6H3SiO4-+140H-
Since Escherichia coli (E. coli) is known to be disinfected in high pH environment, the SiAp was investigated as a disinfectant. The SiAp exhibited a rapid and effective bactericidal activity in water. Generally, HAp has high affinity to bacteria such asE.coli, so it can't be thought that HAp shows some bactericidal activity. Thus, this bactericidal activity was considered to be caused by a synergistic effect of both the OH-ons in water diffused from the surface of the SiAp and the direct contact ofE.colicells with concentrated OH-layers formed on the surface of suspended SiAp particles.
