Biomimetic\nImmobilization of Carboxylated Porphyrin\non Apatite

As an innovative concept, we successfully controlled\nthe porphyrin/apatite\ninterfacial formation processes by a bone regeneration process. In\nparticular, the molecular state of anionic porphyrin (α,β,γ,δ-tetrakis(4-carboxyphenyl)porphyrin\n(TCPP)) immobilized on apatites by mimicking the bone mineralization\nmechanism is precisely investigated and controlled for surface design\nin biomedical applications. As a result, TCPP spontaneously became\nincorporated into and immobilized on the apatite surfaces during the\nnucleation stages of calcium-deficient hydroxyapatite (CDHA) and carbonate\nion containing hydroxyapatite (CHA), which showed that the porphyrin\nring plane was vertically and planarly oriented as the molecular states,\nrespectively. During the CDHA nucleation stage, we achieved the much\nhigher percentage (98%) of the vertically molecular-oriented state,\nin which the dominant state is formed by exchanging phosphate ions\nin CDHA with the end group of −COO<sup>–</sup> in TCPP.\nIn contrast, TCPP with the planarly molecular-oriented state on CHA\nimproves the photofunctions such as internal fluorescence quantum\nyield and singlet oxygen generation ability. This knowledge can contribute\nto the immobilization technique of the drug molecules on apatite nanocarriers\nfor photodynamic therapy as well as the elucidation of the interactive\nbehaviors of the −COO<sup>–</sup>–terminatory\norganic ions with apatites in bones.