Direct electrochemistry of horseradish peroxidase based on hierarchical porous calcium phosphate microspheres

Biomorphic calcium phosphate (CaP) microspheres with hierarchical porous structure were synthesized using natural cole pollen grains as templates and were further employed for the immobilization of horseradish peroxidase (HRP). Scanning electron microscopy and Fourier transform infrared spectroscopy revealed (a) the porous structure of the CaP microspheres, (b) the effective immobilization, and (c) the retention of the conformation of HRP on CaP. The immobilized HRP was placed on a glassy carbon electrode where it underwent a direct, fully reversible, and surface-controlled redox reaction with an electron transfer rate constant of 1.96 s^?1. It also exhibits high sensitivity to the reduction of H₂O_2. The response to H₂O₂ is linear in the 5.00 nM to 1.27 μM concentration range, and the sensitivity is 30357 μA?mM^?1?cm^?2. The detection limit (at an SNR of 3) is as low as 1.30 nM. The apparent Michaelis–Menten constant (K _M ^app ) of the immobilized enzyme is 0.92 μM. This new CaP with hierarchical porous structure therefore represents a material that can significantly promote the direct electron transfer between HRP and an electrode, and is quite attractive with respect to the construction of biosensors.

Sol-gel synthesis of a ceramic based on calcium phosphate

Possibility of synthesizing a number of tricalcium phosphate samples by the sol-gel method was analyzed. The effect of the dispersity of tricalcium phosphate on the physicomechanical characteristics of a ceramic sintered from this material.     

Study of controlled tetracycline release from porous calcium phosphate/polyhydroxybutyrate composites

Porous calcium phosphate ceramics were prepared by sintering of mixtures of nanocrystalline apatitic calcium phosphate and fibrous natural cotton cellulose after pressing at temperatures of 1150 °C and 1250 °C. Micro-and macropores were present in microstructures of ceramic samples. The microstructures of porous ceramics were similar to those observed in bone tissues and fiber-like randomly oriented texture was observed in ceramics. Polyhydroxybutyrate (PHB) biopolymer layers are distributed homogeneously in the samples after evaporation of the diluent (chloroform) from the PHB vacuum impregnated porous samples. The tetracycline (TTC) release rate decreases with the content of polyhydroxybutyrate in the ceramic samples, which corresponds to the rise in amount of biopolymer displaced in the pores of ceramics. The concentration of TTC in the phosphate buffer saline solution varies almost linearly with time after the first seven hours from the start of the release of the calcium phosphate ceramic samples with 2.4 mass % of polyhydroxybutyrate. The initial burst effect was significantly depressed by the preparation method used.     

Formation of composite scaffolds based on chitosan and calcium phosphate

Composite materials based on chitosan and calcium phosphates with the structure and properties close to those of natural human tissues were developed. The possibility of formation of biological apatite, i.e., octacalcium phosphate, was demonstrated. The increase in the strength characteristics was caused by crystallization of the octacalcium phosphate phase on the surface of the material pore space. The materials resemble the extracellular matrix of the body in their structure and composition and can find wide use in the regenerative medicine as a scaffold for osteogenic factors.     

Immobilisation of actinides in phosphate matrices

In the field of the immobilisation of high-activity-level and long-life radwaste (HAVL) for a deep underground repository, several phosphate matrices were already proposed as good candidates to delay the release of actinides in the near-field of such disposal. Among them, thorium phosphate–diphosphate (TPD), monazites/brabantites, britholites, and TPD/monazite composites were extensively studied. The synthesis of samples doped with actinides (Th, U...) through wet and dry chemistry methods then their complete characterisation are reported. Their chemical durability is also examined. These materials appear as promising matrices to immobilise tetravalent and/or trivalent actinides. To cite this article: N. Dacheux et al., C. R. Chimie 7 (2004).

Résumé

Immobilisation des actinides dans des matrices phosphatées. Dans l'optique d'un stockage de déchets radioactifs de haute activité et de vie longue en site géologique profond, plusieurs matrices phosphatées de type céramique ont été proposées afin de retarder le relâchement des actinides dans le champ proche d'un tel stockage. Parmi celles-ci, le phosphate-diphosphate de thorium (PDT), les monazites, les brabantites et les britholites présentent plusieurs des propriétés recherchées pour assurer la rétention de ces éléments sur le long terme. La préparation d'échantillons dopés avec des actinides par voie sèche et/ou humide, leur caractérisation à l'état pulvérulent ou fritté et leur durabilité chimique lors de tests de lixiviation sont examinées ici. Sur la base des propriétés physico-chimiques de ces matrices, des matériaux composites à base de PDT et de monazite ont été préparés puis caractérisés. Tous ces matériaux apparaissent comme des candidats prometteurs pour l'immobilisation des actinides tri- et tétravalents. Pour citer cet article : N. Dacheux et al., C. R. Chimie 7 (2004).     

Nanocomposites based on opal matrices and silica sols doped with rare earth compounds

Ordered 3D composites based on opal matrices and silica sols doped with rare earth elements have been prepared using colloidal chemistry methods. A uniform distribution of rare earth elements (which is important for avoiding luminescence concentration quenching) was achieved by means of repeated filling of the opal matrix interstitial space with silica sols doped with salts or oxides of rare earth elements. Trace amounts (10–30 ppm) of europium in a composite were shown to strongly affect optical properties of the material.     

Radiotracer studies on calcium ion-selective electrode membranes based on poly(vinyl chloride) matrices

Radiotracer studies with ⁴⁵Ca and ³⁶Cl demonstrate that PVC matrix membranes containing Orion 92-20-02 liquid calcium ion-exchanger are permselective to counter-cations. Diffusion coefficients are quoted for the migration of ⁴⁵Ca between pairs of calcium solutions and are discussed in terms of solution concentration, membrane thickness and concentration level of sensor in the membrane. Migration of calcium ions from calcium chloride solution to a Group (II) metal chloride solution through a PVC membrane containing calcium liquid ion-exchanger is discussed in terms of solvent extraction and electrode selectivity coefficient parameters. Thus, magnesium, strontium and barium ions appear to inhibit migration through the membrane by their low affinity for the membrane liquid ion-exchanger sites, while the inhibition by beryllium ions is attributed to site blockage by the strong affinity of dialkylphosphate sites for beryllium.     

Automated sample preparation-fractionation for the measurement of dioxins and related compounds in biological matrices: a review

This article reviews some of the recent developments in the extraction and clean-up areas of biological samples dedicated to dioxin and related compound analysis. A brief introduction on the major dioxin contamination events, which have occurred in the food chain, is given to illustrate the need of fast high throughput methods in case of crises. The emphasis of this paper is the method development based upon reliable instrumental extraction techniques for rapid sample processing and automation such as; supercritical fluid extraction (SFE), microwave-assisted extraction (MAE), pressurized liquid extraction (PLE) and, solid-phase extraction (SPE). The PLE and SPE are also discussed in conjunction with the use of a multi-column automated clean-up system that can accommodate up to 5 g of extracted lipids. The fractionation in sub-groups of analytes during the clean-up process allows the isolation of various types of toxicants from a single sample and illustrates the versatility of the system. An integrated extraction and clean-up instrument is finally presented in terms of feasibility and attainable sample turnover for the parallel processing of liquid and solid biological samples.     

Precipitation of calcium phosphate and calcium carbonate induced over chitosan membranes: a quick method to evaluate the influence of polymeric matrices in heterogeneous calcification

Precipitation of calcium compounds (phosphate and carbonate) was performed on chitosan porous and dense membranes. In order to observe the influence of acetyl groups on the nature of formed precipitates, some chitosan membranes were acetylated in methanol solution before undergoing calcification. Calcification experiments were performed more quickly than using SBF. In this method, a faster precipitation is induced by soaking the membranes in calcium chloride solutions and, in sequence, immersing the same membranes into sodium phosphate or carbonate solutions. This procedure induced the formation of calcium compound precipitates on membrane surfaces, which were analysed through optical microscopy, X-ray diffraction (XRD), Fourier-transformed infrared spectroscopy with attenuated total reflection apparatus (FTIR-ATR) and small angle X-ray scattering (SAXS). The results indicated the biomimetic influence of the organic matrix on morphology, organization and composition of precipitates. The acetyl group induced the formation of organized calcium carbonate better than phosphate, which may correlate with the fact that these two compounds are commonly found together in nature in structures like shells and nacre.     

Microdetermination of calcium in organic compounds

A sensitive method for microdetermination of calcium in organic compounds is described. The combustion in an oxygen stream or oxygen flask with electrical ignition of the sample in porcelain crucible was found advisable. Carbon dioxide has to be expelled and the erroneous effect of phosphate eliminated by adsorption on an anion exchanger prior to the spectrophotometric determination of calcium with glyoxal bis (2-hydroxyanil).     

Interference studies on a PVC-matrix membrane calcium ion-selective electrode based on calcium bis-di[4-(1,1,3,3-tetramethylbutyl)phenyl] phosphate as sensor and tri-n-pentyl phosphate as solvent mediator

Interference potentials, E(M), defined as the difference between the observed potential and the potential calculated assuming that there is no interference, have been determined, and their fit to the equation E(M) = -(RT/F) 1n [1 + K(M)a(B)/(a(Ca))1 2 (z(B)) discussed for a PVC-matrix membrane calcium ion-selective electrode based on calcium bis-di[4-(1,1,3,3-tetramethylbutyl)phenyl]phosphate as sensor with tri-n-pentyl phosphate as solvent mediator in mixed solutions of CaCl(2)BCl(x), where B = Li, Na, K, Mg, Zn or Cu, at total ionic strengths of 0.2, 0.4 and 0.6. Generally, K(M) for the alkali metal ions is considerably less for this electrode than for a comparison electrode based on Orion 92-20-02 liquid ion-exchanger in PVC. Occasionally, the data do not fit the equation. Thus, particularly for the bivalent ions, although the plots of exp[-E(M)F/RT] vs. a(B)/(a(Ca))1 2 (z(B)) are usually linear, they frequently do not intercept the ordinate at 1.00 and/or may give negative slopes and hence negative K(M) values.     

Determination of calcium oxide in calcined phosphate ores

It has been shown that an existing procedure to differentiate calcium oxide from the carbonate and silicate of calcium can be used in the presence of the phosphate, fluoride and sulphate of calcium, and of the carbonate and oxide of magnesium. It is based on the reaction in aqueous solution of calcium oxide with sucrose to form calcium saccharate, and subsequent titration with oxalic acid solution. The method has application for a direct chemical determination of calcium oxide in phosphate rock where calcination of accompanying carbonate is necessary in beneficiation processes.     

Adsorption of dissolved organic compounds on porous polymeric materials

The structure and the adsorption characteristics of porous polymeric materials were studied by the methods of X-ray diffraction analysis and adsorption from solutions. The values of the adsorption capacity, the mean pore size, standard decrease in the molar free energy of adsorption, internal diffusion coefficients of nitrobenzene and p-nitroaniline in the primary and secondary porous structures were calculated.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 21, No. 3, pp. 378–381, May–June, 1985.