A solid-state NMR study of selenium substitution into nanocrystalline hydroxyapatite.

Marcin Sobczak,Ewa Oledzka,Marzena Kuras,Joanna Kolmas

doi:10.3390/ijms160511452

Marcin Sobczak, Ewa Oledzka + Show 2 more

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https://doi.org/10.3390/ijms160511452

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Abstract

The substitution of selenium oxyanions in the hydroxyapatite structure was examined using multinuclear solid-state resonance spectroscopy (ssNMR). The study was supported by powder X-ray diffractometry (PXRD) and wavelength dispersion X-ray fluorescence (WD-XRF). Samples of pure hydroxyapatite (HA300) and selenate (HA300-1.2SeO4) or selenite (HA300-1.2SeO3) substituted hydroxyapatites were synthesized using the standard wet method and heated at 300 °C to remove loosely bonded water. PXRD data showed that all samples are single-phase, nanocrystalline hydroxyapatite. The incorporation of selenite and selenate ions affected the lattice constants. In selenium-containing samples the concentration of Se was very similar and amounted to 9.55% and 9.64%, for HA300-1.2SeO4 and HA300-1.2SeO3, respectively. PXRD and ssNMR data showed that the selenite doping significantly decreases the crystallite size and crystallinity degree. 31P and 1H NMR experiments demonstrated the developed surface hydrated layer in all samples, especially in HA300-1.2SeO3. 1H NMR studies showed the dehydroxylation of HA during the selenium oxyanions substitution and the existence of hydrogen bonding in structural hydroxyl group channels. 1H→77Se cross polarization NMR experiments indicated that selenites and selenates are located in the crystal lattice and on the crystal surface.

Highlights

IntroductionThe hydroxyapatite crystal structure can host a variety of ionic substituents whose presence may affect biological and physicochemical properties [6,7,8]
Since synthetic biomaterials can overcome several problems in bone grafts, intensive efforts have for decades been devoted to developing and improving materials such as bioceramics, polymers, metallic materials and bioglasses [1,2,3].Calcium phosphate bioceramics, especially hydroxyapatite (HA), due to its high biocompatibility, osteoconductivity and similar composition to the inorganic fraction of mineralized tissues, play a crucial role in bone reconstructive surgery [4,5].The hydroxyapatite crystal structure can host a variety of ionic substituents whose presence may affect biological and physicochemical properties [6,7,8]
Data showed that the selenite doping significantly decreases the crystallite size and crystallinity degree. 31P and 1H NMR experiments demonstrated the developed surface hydrated layer in all samples, especially in HA300-1.2SeO3. 1H NMR studies showed the dehydroxylation of HA during the selenium oxyanions substitution and the existence of hydrogen bonding in structural hydroxyl group channels. 1H→77Se cross polarization NMR

Summary

Introduction

The hydroxyapatite crystal structure can host a variety of ionic substituents whose presence may affect biological and physicochemical properties [6,7,8]. Such modified compounds have recently attracted much attention. The OH groups in columns are frequently replaced by various monovalent and bivalent anions: Cl−, F− and CO32−, O2−, S2−, respectively [12,13]. It is important to note that all substitutions may be the source of lattice distortion, vacancies, crystal defects or hydrogen bonds in OH groups’s columns, which in turn play a significant role in HA crystal size and morphology [6,8]

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