Conventional electron paramagnetic resonance for studying synthetic calcium phosphates with metal impurities (Mn2+, Cu2+, Fe3+)

Abstract

Calcium phosphate (CaP) based materials are widely recognized as the most suitable matrix for bone tissue engineering. The cationic and anionic substitution of CaP structure by the elements and groups of biological importance is the effective way to improve the properties of CaP based substances to achieve the material’s desired parameters. Some aspects of application of the conventional electron paramagnetic resonance (EPR) approaches for characterization of CaP powders and ceramics such as hydroxyapatite (HAp) and tricalcium phosphates (TCP) containing intrinsic impurities or intentional dopants like manganese, copper, iron are demonstrated. It is shown that the radiation induced EPR spectra for the nominally pure HAp and TCP reveal the presence of stable nitrogen containing or hydrogen radicals and depend on the CaP synthesis route. It is found that the experimental values of the hyperfine splitting (A) for the nitrogen containing radicals in TCP differ from those known for HAp. The observed narrowing of the central EPR line and increase of its amplitude with the concentration of Mn2+ in the range from 0.05 up to 5 wt. % could be exploited for the quantitative determination of manganese in CaP. Analysis of the EPR spectra of the iron containing CaP allows to determine the presence of iron in Fe3+ state. The values of the components of g and A for Cu2+ ions in TCP are determined and it is demonstrated that they can be influenced by the presence of the codoped Mn2+. Therefore, conventional EPR can be used to study cation-cation codoping.

Keywords

• hydroxyapatite
• calcium phosphates
• tricalciumphosphate
• ENDOR
• EPR