Abdallah Aissa

Sorption of tartrate ions to lanthanum (III)-modified calcium fluor- and hydroxyapatite

The present article details the formation of lanthanum-modified apatites and the binding process of tartrate ions with these obtained apatites. Chemical analyses, FT-IR and (31)P NMR spectroscopies, XRD powder, TGA, and TEM analyses were employed for studying the reaction between Ca(10)(PO(4))(6)(OH)(2) (HAp) or Ca(10)(PO(4))(6)(F)(2) (FAp) and LaCl(3). The reaction was found to take place mainly through partial dissolution of the apatite followed by precipitation of a new phase containing lanthanum phosphate. When La(3+) was introduced in the presence of L(+)-tartaric acid (TAH(2)), no fundamental changes were observed in the HAp or FAp structures. However, there did occur a formation of a new phase of Ca or/and La tartrate salt.

Surface modification of calcium-nickel hydroxyapatite by grafting organic moieties

Investigated compounds represent a novel group of αsubstituted-β-aminophosphonic acids which show similarity to phosphorus herbicides commonly used in agriculture. On the contrary to α-aminophosphonic acids, structural information on their β-analogs is limited to eight compounds only [1]. An X-ray analysis based on a low temperature data accompanied by the ab initio MP2 and B3LYP [2] calculations revealed that strong electron density delocalizations exist in all structures. In particular, the phosphorus – oxygen double bond has a strongly pronounced dipolar character. This situation prompts electron density back-donation from the oxygen lone-pairs towards the phosphorus atom bearing the large positive charge. Investigated compounds adopt anti conformation with the central P-C-C-N torsion angles close to 180°. This arrangement prompts mutual σ(C-N)-σ*(C-P) interactions. All oxygen and nitrogen atoms are involved in hydrogen bonding. In particular, the strongest symmetrical hydrogen bonds link oxygen atoms of the neighbouring phosphoryl groups. Additionally, several intraand intermolecular interactions exist in the crystals. All those interactions are analysed using the Natural Bond Orbital [3] and Atoms in Molecules [4] approach at the ab initio level of theory. Wavefunctions are calculated either for the isolated molecules or within the periodic boundary conditions framework.

Surface modification of hydroxyapatite by grafting alkyl phosphonic dichloride

The inorganic-organic hybrids have interesting applications resulting from the combination of some characteristic properties of the inorganic substrate (mechanical and chemical properties, exchange capacity, bioreactivity, optical properties...) with those of the organic grafting (polymerizability, superficial tension...). Such modified materials are used in catalysis, chromatography, biomedical domain... A suspension of calcium hydroxyapatite Ca10(PO4)(OH)2 was treated by the different alkylphosphonates (R-POCl2, R= methyl or octyl) in organic solvent using a molar ratio x=2 or 4, x=n(organic)/ n(apatite). The surface of the modified CaHAp was characterized using X-ray diffraction, IR and 31P MAS-NMR spectroscopies, chemical analysis and Atomic Force Microscopy (AFM). No remarkable change in XRD patterns was observed after grafting. FTIR results indicated that new vibration modes related to phosphonate groups appear essentially at 2930, 1315, 945, 764 and 514 cm-1. The 31P MAS-NMR spectra of treated hydroxyatite show new signals due to the formation of organic –inorganic bonds in the surface between the superficial hydroxyl groups of the apatite (≡CaOH and ≡POH) and alkyl phosphonic dichloride. AFM proved that the texture surface was changed and roughness decreased. The number of phosphonate groups grafted, in the modified materials, was calculated from chemical analysis results.