Ahmed Legrouri

Ion exchange of different phosphate ions into the zinc-aluminium-chloride layered double hydroxide

A well-crystallised [Zn–Al–Cl] layered double hydroxide was prepared by coprecipitation at constant pH. The chloride ion of this solid was then exchanged in solution with a series of phosphate ions having different sizes and charges; namely, PO3−, H2PO4−, HPO42−, PO43−, P2O74− and P3O105−. Powder X-ray diffraction and Fourier transform infrared spectroscopy have allowed a correlation to be made of the structural features of the precursor and the exchanged materials.

Adsorption of bovine serum albumin on poorly crystalline apatite: influence of maturation

The surface reactivity of synthetic poorly crystalline apatites, similar to bone mineral, is reported in this study. Considerable changes of crystallinity and chemical composition of the solids occurred with time. The maturation process was expressed as a gradual evolution of the initial precipitate toward a highly crystalline apatitic phase, a relocation of nonapatitic phosphate groups accompanied by an increase of apatitic phosphate and the incorporation of hydroxyl ions in the lattice. The adsorption isotherms obtained for the samples investigated in KCl solutions are Langmuirian. The interaction of bovine serum albumin molecules with the solid was related to the structure, the short-range order, and the composition of the crystals. The evolution of the adsorption parameters with the content of labile phosphate groups indicates that these surface species play a leading role in the adsorption process and could consequently affect their biological functions.

Infrared, Raman and NMR investigations of risedronate adsorption on nanocrystalline apatites

The aim of the current work was to study the physico-chemical interactions of a bisphosphonate molecule, risedronate, with a well-characterised synthetic nanocrystalline apatite (NCA) as a model bone mineral. We adopted a global approach, using complementary physico-chemical techniques such as FTIR, RAMAN and NMR spectroscopies in order to learn more about the interaction process of risedronate with the apatitic surface. The results obtained suggest that risedronate adsorption corresponds to an ion substitution reaction with phosphate ions occurring at the crystal surface. This mechanism explains the greater amount adsorbed (N) for NCA, compared to well crystallised stoichiometric hydroxyapatite, attributable to the well-developed hydrated layer at the surface of the nanocrystals. However, most calcium ions remain attached to the solid phase and the formation of insoluble risedronate calcium salts must also be considered as a competitive reaction to the adsorption. Thus a calcium risedronate salt was synthesised and fully characterised for comparison to the solids after adsorption. Following spectroscopic results, it can be concluded that a strong interaction was established between risedronate ions and calcium ions at the apatitic surface. However, under these experimental conditions there is no nucleation of a distinct calcium risedronate salt and the apatite crystals retain their integrity.

Chloride-hydrogenophosphate ion exchange into the zinc–aluminium–chloride layered double hydroxide

The ion exchange of chloride by hydrogenophosphate in the [Zn–Al–Cl] layered double hydroxide was investigated by using X-ray diffraction and infrared spectroscopy. The effects of [Zn2+/[AI3+] ratio in [Zn–Al–Cl], anion concentration in the solution, aging time and temperature of the solution on the ion exchange were studied. The best sample in terms of crystallinity and extent of ion exchange was obtained by carrying out the exchange reaction at 25°C in a 0.01 M HPO42− solution at pH 8 with at least 5 h of aging time. A sample prepared under these conditions was further characterized by X-ray microanalysis.

Adsorption on apatitic calcium phosphates for drug delivery: interaction with bisphosphonate molecules

Bisphosphonates (BPs) are well established as an important class of drugs for the treatment and prevention of several bone disorders including osteoporosis. This work investigated the interaction of two bisphosphonates, risedronate and tiludronate, with several apatitic supports, a well-crystallised hydroxyapatite (HA) and nanocrystalline apatites with varying maturation times, chemical composition and surface characteristics. The purpose was to fully understand the adsorption mechanism and desorption process, by the evaluation of the effect of several physicochemical parameters (temperature, pH and concentration of calcium and phosphate ions). Whatever the nature of the BP and the structure and composition of the apatite, the adsorption of such anti-resorptive agents can be well described as an ion exchange-reaction between phosphates species on the apatitic surface and BP molecules in solution. However, the parameters of adsorption can vary depending on the physicochemical conditions of the adsorption reaction. In addition, the structure and composition of the apatitic surface also influence the adsorption properties. Finally, BPs molecules are slowly released from apatitic supports, because most of the adsorbed molecules are irreversibly bound and not spontaneously released by dilution or simple washing. Moreover, similar to their adsorption, the release of bisphosphonates is strongly affected not only by the chemical properties of the molecule, but also by the chemical and structural characteristics of the apatitic substrates. The understanding of the adsorption and release processes provides fundamental tools for the development of drug delivery systems using apatite materials.

Preparation of a well-ordered layered nanocomposite from zinc–aluminum–chloride layered double hydroxide and hydrogenophosphate by ion exchange

The ion exchange of hydrogenophosphate ion in Zn–Al–chloride layered double hydroxides was investigated. The chloride precursors prepared by coprecipitation at pH 10 preserved their lamellar structure following ion exchange. It was found that the aging time is important in controlling the crystallization of the phosphate-exchanged compounds; long aging times of more than 8 h lead to poorly crystallized phases. The grafting of the anion onto hydroxylated sheets by moderate thermal treatment was confirmed by a combination of several techniques, including powder X-ray diffraction (XRD), infrared (IR) spectroscopy, and thermal analyses.

Exchange Reactions at Calcium Phosphates Surface and Applications to Biomaterials

The interaction of calcium phosphates with biological molecules under controlled conditions permits the formulation of meaningful conclusions concerning the driving forces. The uptake and release at the material-solution interface is the result of the various interactions between and within the system components which include the solid surface, the adsorbate, the solvent and other solutes present. The understanding of adsorption and desorption mechanisms with respect to active molecules can be exploited for the development of drug delivery applications.

Obstacles facing the diffusion of drip irrigation technology in the Middle Atlas region of Morocco

Research was conducted by the author and an inter-disciplinary team at Al Akhawayn University, Morocco, under a Canadian (IDRC) grant between 2009 and 2011. Using various methodologies, including survey research, the team found several significant obstacles facing the diffusion of drip irrigation technology in the Middle Atlas region of Morocco. These obstacles include lack of access to capital, land titles that cannot be mortgaged, and a weak presence of the relevant bureaucracies at the farm level. The implications of these obstacles in terms of responding to climate change and aquifer depletion are addressed as part of the paper.

A new nanostructured material based on fluorophosphate incorporated into a zinc–aluminium layered double hydroxide by ion exchange

Layered double hydroxides (LDHs), also called anionic clays, consist of cationic brucite-like layers and exchangeable interlayer anions. These hydrotalcite-like compounds, with Zn and Al in the layers and chloride in the interlayer space, were prepared following the coprecipitation method at constant pH. The effect of pH, aging time and anion concentration on the intercalation of fluorophosphate