Wet or dry mechanochemical synthesis of calcium phosphates? Influence of the water content on DCPD-CaO reaction kinetics.

Mechanosynthesis of calcium phosphates can be performed under wet or dry conditions. In most papers and patents, grinding under wet conditions was selected. So far, only a few papers were devoted to dry mechanosynthesis of calcium phosphates. To understand why wet mechanosynthesis was preferred, the influence of water addition on the kinetics of the mechanochemical reaction of dicalcium phosphate dihydrate with calcium oxide was investigated. The DCPD disappearance rate constant k and the final reaction time t(f) were determined in each case and correlated with the water content present in the slurry. Results showed that the addition water (i) slowed down the reaction rate and (ii) increased the powder contamination by mill material (hard porcelain) due to ball and vial erosion; and that (iii) wet milling did not generate the expected products, in contrast to dry grinding, because porcelain induced hydroxyapatite decomposition with the formation of beta-tricalcium phosphate and silicon-stabilized tricalcium phosphate. Consequently, dry mechanosynthesis appears preferable to wet milling in the preparation of calcium phosphates of biological interest.

Effect on composition of dry mechanical grinding of calcium phosphate mixtures.

For diverse reasons, calcium phosphates used to prepare hydraulic calcium phosphate cements can be ground mixed. The grinding with a rotating micromill of monocalcium phosphate monohydrate or anhydrous, dicalcium phosphate dihydrate or anhydrous with calcium oxide, calcium hydroxide, calcium carbonate, tetracalcium phosphate, or alpha- or beta-tricalcium phosphate was studied for different calcium to phosphate (Ca/P) ratios, rotating rates, masses of balls, and environmental conditions. During dry grinding by ball milling, anhydrous or hydrated acid calcium phosphates can mechanochemically react with anhydrous or hydrated basic calcium salts to form dicalcium phosphate dihydrate or anhydrous, noncrystalline calcium phosphate, and/or calcium deficient or stoichiometric hydroxyapatite, depending on the Ca/P ratio in the mixture and the time of grinding. The reaction rate is a function of the rotation rate and the mass of the balls. Water is not necessary to initiate the reaction but facilitates it because hydrated salts react faster than the corresponding anhydrous salts. Neither carbon dioxide nor carbonate ions seem to have any influence on the transformation kinetics. The transformations that occur during grinding influence the final mechanical properties of hydraulic calcium phosphate cements prepared from these materials. Thus, if a grinding step of the starting materials is planed, the grinding conditions will have to be particularly well defined to obtain reproducible results.

Effect of mechanical grinding of MCPM and CaO mixtures on their composition and on the mechanical properties of the resulting self-setting hydraulic calcium phosphate cements.

Calcium bis-dihydrogenophosphate monohydrate (or monocalcium phosphate monohydrate, MCPM) is often used as the acid calcium phosphate in hydraulic calcium phosphate cement formulations. But commercial MCPM is not pure; it contains a small amount of orthophosphoric acid and moisture. Consequently, MCPM is difficult to mill and the powder is sticky and presents aggregates. Because granularity influences the mechanical properties of the hardened cements, a possible way to get around this difficulty that has been proposed is to premix it with other materials before grinding. We therefore ground commercial MCPM with CaO. A rapid decrease in the amount of MCPM was observed during mechanical grinding by a solid-solid reaction with calcium oxide. The final products were anhydrous or dihydrate dicalcium phosphate and/or hydroxyapatite or calcium-deficient hydroxyapatite depending on the initial calcium-to-phosphate (Ca/P) ratio. The mechanical properties (compressive strength and setting time) of cements made from MCPM and CaO were affected whatever the Ca/P ratio as a consequence of the change in composition of the starting materials. Storage at different temperatures of MCPM and CaO mixtures manually ground in a mortar for only 2 min and without mechanical grinding did not affect their composition, but a decrease was observed in the compressive strength of cements made from these mixtures.

Physical properties and self-setting mechanism of calcium phosphate cements from calcium bis-dihydrogenophosphate monohydrate and calcium oxide.

An apatitic calcium phosphate cement was developed from calcium bis-dihydro-genophosphate monohydrate (or monocalcium phosphate monohydrate, MCPM) and calcium oxide (CaO). The powder had a Ca/P molar ratio of 1.67, and the liquid was either pure water or 0.25 M-1 M sodium phosphate buffer, pH 7.4. The influence of the powder-to-liquid (P/L) ratio on the setting time and the mechanical strength were studied. The best results were obtained for the 1 M phosphate buffer with a P/L ratio of 1.53; the setting time was 7 min and the compressive strength was 25 MPa after 24 h and 33 MPa after 11 d. The mechanism and kinetics of the setting reaction were investigated by X-ray diffraction, differential scanning calorimetry, 31P magic angle spinning-nuclear magnetic resonance and infrared spectrometry. The setting reaction was found to be biphasic: in the first step, during the mixing time, MCPM reacted with CaO immediately to give calcium hydrogenophosphate dihydrate (or dicalcium phosphate dihydrate, DCPD) which, in the second step, reacted more slowly with the remaining CaO to give hydroxyapatite. The conversion of the starting materials to hydroxyapatite was complete within 24 h when the liquid was water, but was slower and incomplete with the phosphate buffers. Of the starting materials, 30% remained after 3 d.

Correlations between n-octanol/water partition coefficients and RP-HPLC capacity factors of 1,2-dithiole-3-thiones and 1,2-dithiol-3-ones.

From the experimental n-octanol/water partition coefficients (log Poct) of 33 1,2-dithiole-3-thiones and 18 1,2-dithiol-3-ones and their respective log k, Collander-type relationships were established at various volume fractions of methanol in the mobile phase and on an ODS 2 stationary phase. Collander-type relationships were also established between log Poct and log K0 (capacity factor extrapolated to 0% of organic modifier). The correlations are good, and their parameters depend on the volume fraction of organic modifier, as expected. These relationships were used to evaluate the log Poct of seven very lipophilic dithiolethiones (3.7 < log P < 7.2). Extrapolated values were compared with calculated values from fragmental constants determined in a previous work and with those given by Rekker.

Ionization constants of ginkgolide B in aqueous solution.

The thermodynamic ionization constants (pK(a)(1), pK(a)(2), and pK(a)(3)) of ginkgolide B (9H-1,7a-(epoxymethano)-1H,6aH-cyclopenta[c]furo[2,3-b]furo-[3',2':3,4]cyclopenta[1,2-d]furan-5,9,12-(4H)-trione, 3-tert-butylhexahydro-4,7b,11-trihydroxy-8-methyl-) in aqueous solution have been settled by pH-metric and NMR studies. The three macroscopic pK(a) values as well as the water solubility and the water/n-octanol partition coefficient have been extracted from pH-metric data by means of a nonlinear regression methodology. NMR spectroscopy provided confirmation of the values of the macroscopic constants, information about the effective ionization pathways, and an estimation of the proportions of the various forms under physiologically relevant conditions.

A new pH-metric methodology for the determination of thermodynamic inclusion constants of guest/cyclodextrin complexes.

A new methodology of pH-metric data treatment was developed to extract the stoichiometry and the thermodynamic association constants of guest-cyclodextrin inclusion complexes in dilute aqueous solution when the guest is a participant in an acid-base equilibrium. pH-metric titration curves in the presence of cyclodextrin (CD) were treated by a curve-fitting technique according to a nonlinear least-squares regression. Equations corresponding to the different kinds of acid-base pairs (AH/A-, BH+/B) and stoichiometries (1:1 and 1:2) were established. The methodology was validated by studying the 5-phenylbarbituric acid complexation with beta-CD and the 4-cyanobenzoic acid complexation with alpha-CD. Then it was applied to chlorpromazine. Both the acid form (constant K1 = 3260) and the base form (constant G1 = 13,100) gave complexes with beta-CD according to 1:1 stoichiometry.

Water/n-octanol partition coefficients of 1,2-dithiole-3-thiones.

Water/n-octanol partition coefficients (log P) for 33 1,2-dithiole-3-thiones and for 18 1,2-dithiol-3-ones were determined by RP-HPLC measurement of the concentration of the solute in aqueous solution after equilibrium. Depending on the nature of the substituents (alkyl or aryl) and their position(s) (4,5, or both) on the dithiole nucleus, some peculiar behaviors were revealed. Therefore, different fragmental constants containing the 1,2-dithiole-3-thione nucleus were inferred in order to calculate in a complementary work, a priori, the log P values of new dithiolethiones and dithiolones.

[Techniques for evaluating the level of pollution in operating rooms due to gaseous or volatile anesthetics]. / Techniques d'évaluation du taux de pollution des salles d'opération par les anesthésiques gazeux ou volatils.

To evaluate the air pollution in operating rooms when anesthesia is carried out with an open-circuit anesthesia delivery system, two analyzers were tested both in the laboratory and in an operating room. The TIF 5500, a laptop instrument, allows the detection of gas with low ionisation potential such as chloro-fluorocarbons (lower detection threshold: 3 ppm). The Bruel & Kjaer 1302 allows the simultaneous determination of the concentrations of the different inhalation anesthetics in the room by photoacoustic spectrometry. For this type of study, the latter proved an excellent instrument.