X-ray Photoelectron Spectroscopy Study of Mg Adsorption on Nanocrystalline Hydroxyapatite
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y Photoelectron Spectroscopy Study of Mg Adsorption on Nanocrystalline Hydroxyapatite Yu. A. Teterina, b, *, V. N. Rudina, A. V. Severina, M. E. Paul’a, K. I. Maslakova, A. Yu. Teterinb, and S. V. Dvoryaka aMoscow
b
State University, Moscow, 119991 Russia Kurchatov Institute National Research Centre, Moscow, 123182 Russia *e-mail: [email protected] Received March 29, 2019; revised May 11, 2020; accepted May 27, 2020
Abstract—We have studied Mg2+ adsorption on hydroxyapatite (HAp) nanocrystals and constructed its isotherm at equilibrium cation concentrations in the range 0–0.35 mol/L. For a number of samples, corresponding to characteristic points in the adsorption isotherm, the composition and the oxidation state of the elements present on the surface of the sorbent have been determined by X-ray photoelectron spectroscopy (XPS). The surface magnesium concentration determined by XPS, which detects only ions in a surface layer a few nanometers in thickness, has been found to be considerably lower than the total amount of cations in the solid phase, evaluated from the experimentally determined adsorption isotherm. We assume that, during the sorption process, some of the magnesium ions substitute for calcium ions in the bulk of the HAp and some adsorb in the form of MgCl2. The results obtained in this study constitute a fundamental basis for practical solutions in designing integrated medications based on HAp with magnesium. Keywords: X-ray photoelectron spectroscopy, adsorption, hydroxyapatite DOI: 10.1134/S0020168520100155
INTRODUCTION Biological hydroxyapatite (HAp) is a major mineral component of human and animal bone tissue, present in the form of nanocrystals bound to collagen [1]. In connection with this, assessing characteristics of HAp nanocrystals and the state of biologically active molecules and ions adsorbed on their surface remains a topical issue. A living organism produces biological HAp to be used as a structural component of bone. Synthetic HAp has the same chemical composition as biological HAp (Ca10(PO4)6(OH)2) and replicates many properties of natural bone tissue [2, 3]. Besides, bone contains other ions as well, for example, Na+, Mg2+, K+, and Cl–. A special role is played by magnesium ions. The ability to monitor and maintain magnesium homeostasis is important for bone tissue to remain intact. Normally, the structure of bone is constantly remodeled via coordination of interactions between osteoclasts and osteoblasts. Disbalance of their functioning leads to prevalence of bone resorption (disintegration) processes, degradation of the bone structure, decrease in the density of the bone, and, as a consequence, osteoporosis development. Synthetic nanocrystalline HAp per se is successfully used to treat various bone fractures [4]. At the same time, the use of
HAp doped with Mg2+ ions [2, 3, 5] helps increase the activity of osteoblasts under the effect of the enzyme system of the body, augmenting its reparative capabilities. However, if magnesium is added via cocrystallization [2], its accessibi
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