Influence Du Rapport Atomique Ca/P Initial Sur La Synthèse Sous Atmosphère Humide D’apatite

Abstract

Le comportement sous atmosphère humide des mélanges initiaux de la calcite et du di-ammonium hydrogénophosphate à différents rapport atomique (Ca/P)_initiala été étudié. L’analyse par diffraction des rayons X (DRX) montre que les produits obtenus ont tous une structure apatitique. Il montre la présence à côté de celle de l’apatite, des raies identifiables à la calcite pour des rapports atomiques initiaux supérieurs à 1.50. Par ailleurs, la spectroscopie d’absorption infrarouge (IR) révèle dans les différents cas, la présence autre que les bandes attribuables aux ions PO₄ ^3?dans une apatite, des bandes à 875 cm^?1caractéristique des groupements HPO₄ ^2?dans une apatite déficiente en ion calcium. De même, le traitement thermique à 1000°C des poudres synthétisés a mis en évidence que les apatites formées sont non st?chiométriques. Les analyses chimiques montrent, par ailleurs, que lorsque le rapport atomique Ca/P du mélange initial est inférieur à 1.50, l’apatite formée a un rapport atomique Ca/P égal à 1.58. Par contre, lorsque le rapport Ca/P initial est supérieur à 1.50, le produit formé est biphasique et a un rapport atomique Ca/P de 1.62. Ce rapport est dû essentiellement à la présence d’un excès de CaCO₃dans le mélange initial (DRX, IR).

Mots clés Apatite; atmosphère humide; calcite; hydrothermal; synthèse

Abstract The behavior, in a humid atmosphere, of the initial mixtures of calcite and diammonium hydrogenophosphate at different atomic ratio (Ca/P) was studied. The X-ray diffraction (XRD) analysis shows that all the products obtained have apatite structure. For initial atomic ratios greater than 1.50, the XRD analysis shows the presence of reflections different from those of apatite, which may be attributed to calcite. Analysis by infrared (IR) absorption spectroscopy allows to distinguish between the two cases: in addition to the presence of bands due to the PO₄ ^3?ions in apatite further bands at 875 cm^?1characteristic of HPO₄ ^2?in apatite deficient with respect to calcium ions are observed. Similarly, the powders synthesized by heat treatment at 1000°C showed that nonstoichiometric apatites are formed. Chemical analyses show, that when the atomic ratio Ca/P of the initial mixture is less than 1.50, the apatite formed has an atomic Ca/P ratio of 1.58. When the initial Ca/P ratio is greater than 1.50, the product formed is biphasic and has an atomic ratio Ca/P of 1.62. This result is mainly due to the presence of an excess of CaCO₃in the original mixture (XRD, IR).     

Investigation of entrance effects on particle electrophoretic behavior near a nanopore for resistive pulse sensing

Resistive pulse sensing using solid-state nanopores provides a unique platform for detecting the structure and concentration of molecules of different types of analytes in an electrolyte solution. The capture of an entity into a nanopore is subject not only to the electrostatic force but also the effect of electroosmotic flow originating from the charged nanopore surface. In this study, we theoretically analyze spherical particle electrophoretic behavior near the entrance of a charged nanopore. By investigating the effects of pore size, particle–pore distance, and salt concentration on particle velocity, we summarize dominant mechanisms governing particle behavior for a range of conditions. In the literature, the Helmholtz–Smoluchowski equation is often adopted to evaluate particle translocation by considering the zeta potential difference between the particle and nanopore surfaces. We point out that, due to the difference of the electric field inside and outside the nanopore and the influence from the existence of the particle itself, the zeta potential of the particle, however, needs to be at least 30% higher than that of the nanopore to allow the particle to enter into the nanopore when its velocity is close to zero. Accordingly, we summarize the effective salt concentrations that enable successful particle capture and detection for different pore sizes, offering direct guidance for nanopore applications.     

Perimidine-based synthetic receptors for determination of copper(II) in water solution

Perimidine-based chelators 1 and 2 were prepared, and their structures were confirmed by ¹H and ¹³C NMR, MS spectroscopy and elemental analysis. These compounds were studied as specific synthetic receptors for the recognition of transition metal ions. They exhibited high affinity and selectivity towards Cu(II) ions. The conditional binding constants, linear dynamic range and detection limit were determined by UV–vis spectroscopy. These parameters demonstrated high potential of the prepared synthetic receptors for the recognition and determination of Cu(II) ions. The minimum detectable concentrations of Cu(II) ions for the synthetic receptors 1 and 2 were 270 and 75 nM (R ² = 0.9915 and 0.9964) in aqueous medium (water/DMSO; 99:1 (v/v)), respectively.     

Viscometric Estimation of Unperturbed Chain Dimensions of Polymers

A new expression is proposed to determine the unperturbed dimensions of coil-like polymers viscometrically by use of the Flory and Kratky expression. The unperturbed dimensions so estimated are compared with the results obtained by using different expressions available in the literature. The results are comparable even for stiff chain polymers. The data obtained under theta conditions also fit this expression very well. The effect of molecular weight, its distribution, and that of the solvent has also been studied. It is concluded that the unperturbed dimensions are independent of molecular weight and solvent but depend on the heterogeneity of the system.     

Synthesis,photophysical and NMR evaluations of thiourea-based anion receptors possessing an acetamide moiety

The synthesis and photophysical evaluation of three diaryl thiourea-based anion receptors (4–6) for comparison with their urea counterparts (1–3) is outlined. These anion receptors posses an acetamide functionality on one of the aryl groups and an electron-withdrawing CF₃ group on the other. By varying the position of the acetamide group, in the o-, m- and p-positions of 4–6, respectively, the anion binding ability was both tuneable and found to be, in some cases, significantly different from that seen for the urea analogues 1–3. The binding affinities of the receptors 4–6, as well as the binding stoichiometries, were evaluated using UV–vis absorption spectroscopy in MeCN. However, these receptors were not sufficiently emissive to quantify the anion recognition using fluorescence. The results confirmed strong binding of these receptors to anions such as fluoride, acetate, phosphate, pyrophosphate and chloride. Nevertheless, the overall results obtained did not conform to the anticipated trends seen for 1–3, which is most likely due to the enhanced binding affinity of the thiourea analogues 4–6. The binding interactions were also investigated by using ¹H NMR which confirmed that these receptors interacted with the anions in a stepwise manner, where the primary anion binding interaction occurred at the thiourea side, which led to an activation of the acetamide moiety towards the second anion binding interaction, an example of an allosteric activation mode.     

Fe（C5H4-CH2-Trp-OMe）2的合成、晶体结构及金属离子识别性能

摘要： 以优化的两步一锅反应法合成了生物金属有机化合物Fe（C₅H₄-CH₂-Trp-OMe）₂（FcL）,通过NMR、HRMS及IR等对其结构进行了表征,利用X射线单晶衍射测定了分子结构。循环伏安法研究表明FcL在0.00~0.90 V电位范围内,给出一稳定的、形态良好的氧化还原峰,这归于化合物中Fc/Fc⁺电对的氧化还原过程。电化学金属离子识别研究显示FcL在过渡金属离子Zn²⁺和Cu²⁺的存在下,导致了配体Fc/Fc⁺式量电位的显著阳极移动,其△E^0''对Zn²⁺和Cu²⁺分别为342和335 mV,表明了FcL对Zn²⁺和Cu²⁺具有良好的识别能力。