Octacalcium phosphate (OCP) has received considerable attention in the field of ceramic biomaterials as an advanced functional material. It exhibits a layered structure composed of apatitic and hydrated layers and can incorporate various dicarboxylate ions into the hydrated layer. Saturated dicarboxylic acids (HOOC(CH₂)_nCOOH) with an odd number of methylene groups (–CH₂–) exhibit lower incorporation fractions than those with an even number of methylene groups, possibly owing to a compositional dependence on the synthetic method. In this study, calcium carbonate, phosphoric acid, and various amounts of glutaric acid were used to produce glutarate-ion-incorporated OCP by a wet chemical method, which is different from the conventional synthetic strategy. While utilising 1–20 mmol of glutaric acid during synthesis did not produce the desired product, using 25 mmol of glutaric acid resulted in the formation of single-phase glutarate-ion-incorporated OCP with a Ca/P molar ratio of 1.57 and a 90% incorporation fraction of glutarate ions. This glutarate-ion-incorporation fraction is significantly higher than that reported in the previous studies (35%). Thus, the synthetic procedure proposed herein was able to produce single-phase OCP containing glutarate ions with a high incorporation fraction. Our findings can contribute to development of novel functional ceramic biomaterials in the future.

We successfully synthesised octacalcium phosphate with terephthalate ion derivatives and demonstrated that these materials exhibited unique fluorescence.

We successfully synthesised octacalcium phosphate with incorporated 3,3′-dithiodipropionate ions.

Octacalcium phosphate (OCP) is a calcium phosphate compound with a layered structure in which apatite layers, which have a structure similar to hydroxyapatite, and hydrated layers are stacked alternately. OCP can incorporate various carboxylate ions into its interlayers. OCPs with incorporated carboxylate ions, also known as OCP carboxylates (OCPCs), are organically modified at the molecular level. OCPCs are an attractive research target in a wide range of fields, from basic inorganic chemistry to applied materials chemistry. Therefore, it is expected that a comprehensive overview of recent research on OCPCs will be useful in progressing this field. This review focuses on recent advances in OCPCs, namely their synthesis, the identification of new types of carboxylate ions that can be incorporated into OCP interlayers, the steric structure estimation of the interlayer carboxylate ions, and applications of OCPCs as functional materials. OCPC-based functional materials include fluorescent materials, artificial bones, and adsorbents. Furthermore, based on existing studies, challenges in OCPC research and future research directions are described.