聚乙二醇/十二烷基硫酸钠对碳酸钙晶体形貌的调控作用

研究了水溶性聚乙二醇-6000(PEG-6000)、十二烷基硫酸钠(SDS)及PEG-6000/SDS复合物对CaCO3晶体形貌的调控作用;采用傅立叶变换红外光谱仪、扫描电子显微镜和X射线衍射仪分析了CaCO3微观形貌及晶体结构.研究表明,SDS和PEG-6000之间产生协同效应,有利于调控形成特定形貌的CaCO3晶体;利用这种复合体系制备CaCO3晶体,可以有效地模拟生物矿化过程中阳离子的摄取或富集.     

Preparation of hemispherical hollow silica microcapsules with different affinity surface by using spherical vaterite calcium carbonate as template

We developed a method to prepare hemispherical hollow silica microcapsules (HHSM) with different affinity surfaces using spherical vaterite calcium carbonate (SVCC) as a template. The preparation process composed of the adhesion of calcium carbonate onto the surface of methyl methacrylate (MMA) droplets followed by suspension polymerization, the partial etching of calcium carbonate on the polymethyl methacrylate (PMMA) mother particle, the formation of silicon dioxide powder by sol–gel reaction and their deposition onto the etched flat surface of calcium carbonate, the surface modification of deposited silicon dioxide with silane coupling agent, the removal of the mother particle with acetone, the formation of silicon dioxide powder by sol–gel reaction and deposition onto the exposed hemispherical surface of calcium carbonate, and the surface modification of deposited silicon dioxide with silane coupling agent. The synthesized microcapsules had a complete hemispherical structure and both hydrophilic and hydrophobic surfaces. Copyright © 2007 John Wiley & Sons, Ltd.     

Quantitative calibration of a TPD-MS system for CO and CO2 using calcium carbonate and calcium oxalate

A method is described for calibrating quantitatively a temperature-programmed decomposition, mass-spectrometric (TPD-MS) system by monitoring the gases evolved during the thermal decomposition of a chemical within the TPD reactor. A method for calibrating for evolved CO and CO₂ is described using the thermal decompositions of calcium carbonate and calcium oxalate. The method takes into account the production of CO⁺ ions from CO₂⁺ ions and secondary reactions in the thermal decomposition of calcium oxalate.     

SERS detection of ceftriaxone and sulfadimethoxine using copper nanoparticles temporally protected by porous calcium carbonate

The authors describe a new composite based on SERS-active copper nanoparticles (CuNPs; 10?±?2 nm) incorporated into calcium carbonate microspheres (CaCO₃-CuNPs; 3.4?±?0.3 μm). The CaCO₃ coating acts as a temporal protector of CuNPs against oxidation. Incorporated CuNPs have significantly improved stability during storage and a month-long shelf lifetime. The composite was used for SERS detection of rhodamine 6G and two antibacterial drugs (ceftriaxone and sulfadimethoxine). Two analytical formats, one with and one without solid phase extraction, are introduced to demonstrate the flexibility of the method. Both formats imply the dissolution of CaCO₃ matrix before SERS analysis to release CuNP used as SERS substrate. The study of the influence of pH value and acid nature on the SERS signal demonstrated that HCl is the most efficient candidate to release the CuNPs. Sensitivity (expressed as LOD) is shown to be improved by more than one order when solid phase extraction is used. The average SERS enhancement factor is 10^7 which makes the material efficiency comparable to the one of silver nanoparticles. The LOD (<5 μM), precision (RSDs between 20 and 24% at LOD levels), and trueness (apparent recoveries 84–113%) for the two antibiotics (ceftriaxone and sulfadimethoxine) make the method quite useful for quantitative analysis and therapeutic drug monitoring at physiologically relevant concentrations.

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Graphical abstract A composite with temporally stable copper nanoparticles was synthesized, studied, and used for SERS detection of two antibacterial drugs. The analytical efficiency of the composite was found appropriate for quantitative analysis due to Raman enhancement comparable with silver nanostructures.

     

Synthesis of hydroxyapatite by using calcium carbonate and phosphoric acid in various water-ethanol solvent systems

The purpose of the present study is to synthesize hydroxyapatite by using CaCO₃ and H₃PO₄ in various water-ethanol solvent systems. It was observed from experiments that formation of ammonium phosphate compounds hindered the formation of calcium phosphates in ethanol medium. Although the reactivity was better in aqueous medium, the carbonate contents of the products obtained were above 8.5%. Best results with a carbonate content as low as 3.82% was obtained in 50% ethanol containing mixed-aqueous medium at 80°C and the FTIR analysis showed that the product was a carbonated apatite with a calculated composition of 14CaO·4.2P₂O₅·CO₃·7.2H₂O. The amorphous and porous phosphate compound obtained with a BET surface area of 106.6 m² g⁻¹ seems to be useful as adsorbent in wastewater treatment. Upon sintering of the amorphous product at 750°C, crystalline hydroxyapatite with a BET surface area of 25.9 m² g⁻¹ is obtained that may be used in biomedical applications.      

Palladium-catalyzed oxyarylation of olefins using silver carbonate as the base. Probing the mechanism by electrospray ionization mass spectrometry

The Pd(OAc)₂-catalyzed oxyarylation of electron-rich (8 and 12) and electron-poor (10) olefins by ortho-iodophenols (3a-d) was studied using Ag₂CO₃ as the base, in acetone, and in the presence and absence of PPh₃. The corresponding adducts of oxyarylation were obtained in moderate yields. The reaction mechanism was examined by electrospray ionization mass spectrometry (ESI-MS). Cationic arylpalladium intermediate (14), formed by the oxidative insertion of Pd(0) into 3a, and the cationic palladacycles (15), obtained by reaction of 14 with olefins 8 and 12, were intercepted by ESI-MS and characterized by ESI-MS/MS.     

Control of calcium carbonate particle size and shape by precipitation from CTAB/alcohol/hexadecane mixtures

 When used as a precipitation media, emulsified mixtures of cetyltrimethylammonium bromide/n-butanol (E), hexadecane (O) and water (W), controls the size and shape of calcium carbonate particles. Monodisperse 2-micron spherical-calcite particles were obtained in a water-rich region of the mixture, while 2-micron rhombohedral-calcite particles with an aspect ratio near one were obtained in the middle region of the mixture. Replacing n-butanol with i-butanol led to consistent formation of monodisperse spherical particles, while using n-propanol in place of n-butanol limited the number of spherical particles produced in the water-rich region. Received: 17 March 1997 Accepted: 2 May 1997     

Preparation of ZnS/CdS composite nanoparticles by coprecipitation from reverse micelles using CO2 as antisolvent

The possibility of simultaneously recovering ZnS and CdS particles from reverse micelles by dissolving antisolvent CO2 into the micellar solution was investigated by high-pressure UV-Vis spectra. It was found that all the ZnS and CdS particles in the reverse micelles could be precipitated by compressed CO2 at suitable pressures. The phase structures and morphologies of the obtained composites were characterized by X-ray diffraction and transmission electronic micrographs. The results illustrate that the smaller molar ratio of water to surfactant of the reverse micelles and higher pressure of CO2 are favorable for producing smaller particles. This method has many potential advantages for the production of composite nanoparticles.     

W/0乳化法制备明胶/β-磷酸三钙多孔复合微球及其物化性能表征

采用乳液、离子缔合法制备得到明胶（Gel）/β-纳米磷酸三钙(β-TCP)复合多孔微球,其尺寸可通过控制反应的搅拌速度进行调节。 SEM和光学显微镜观察表明,明胶/β-TCP复合微球尺寸在20～40 μm之间,被包敷的磷酸三钙为200 nm左右,微球内部呈多孔结构。 当m（磷酸三钙）∶m（明胶）＞0.4∶1时,有大量花瓣状晶体附着于复合微球的表面,是磷酸三钙溶解和明胶分子诱导重结晶所致。 XRD与IR图谱表明,磷酸三钙纳米粒子与明胶之间存在化学键合,明胶/β-纳米磷酸三钙复合微球的微观结构与自然骨相似。 DSC-TGA结果显示,90%的TCP在乳化过程中与明胶复合。 本文所制备的复合微球,为添加各种药物和促骨生长因子并实现缓释提供了优良的载体。     

Experimental studies on the chemiluminescence reaction mechanism of carbonate/bicarbonate and hydrogen peroxide in the presence of cobalt(II)

Chemiluminescence (CL) phenomena of carbonates or bicarbonates of potassium, sodium, or ammonium with hydrogen peroxide in the presence of cobalt sulfate were reported. After cobalt(II) solution was injected into the mixture of carbonate/bicarbonate and hydrogen peroxide, a CL signal was given out briefly. The CL conditions of these systems were optimized. The CL reaction mechanisms were studied experimentally by examining the spectrum emitted by the CL system and the effect of various free radical scavengers on CL emission intensity. The results showed that the maximal emission wavelengths of the CO32--H2O2-Co2+ and HCO3--H2O2-Co2+ systems were 440 and 490 nm, respectively. As a result, a radical scavenger of ascorbic acid, thiourea, and superoxide dismutase exhibited different effects on these CL systems. The different CL mechanisms involving the carbon dioxide dimer and the oxygen dimer were revealed, respectively.     

Transport of carbonate ions through supported liquid membrane by using Alamine 336 and trioctylphosphine oxide as carriers

Abstract

Transport studies were carried out for carbonate ions through supported liquid membrane (SLMs) by using Alamine 336 and trioctylphosphine oxide (TOPO) as carriers. Experimental variables were investigated, such as concentration of carbonate ion (10^?5 to 4×10^?2 M), carriers (10^?5 to 10^?1 M), and alkali (0.01–0.5); and stirring speed (50–150 rpm) of bulk solutions. The use of combined carriers Alamine 336 and TOPO shows a synergic transport of carbonate ions. The stability of the SLM system in relation to the transport of carbonate ions has been studied. The enrichment of carbonate ions (10^?6 to 4×10^?2 M) from the dilute solution was explored. The different combinations of amines with TOPO show synergic permeability of the carbonate ions through SLM system.     

Contributions to the mechanism of water glass hardening by using thermal analysis methods and X-ray diffractometry

Thermal analysis methods and X-ray diffractometry provided data on and permitted practical use of the eutectic mixture between Na₂O·2SiO₂ and SiO₂, which melts at 790°C. Based on this, water glass was used as a binder to obtain artificial cluster granules, ceramically hardened by heating at 800°C. The process of water glass hardening in the presence of hardening reagents such as Na₂SiF₆, NH₄Cl, silica gel and ultra-fine silica was studied by thermal analysis. In the first stage, gelification of the SiO₂ sol takes place by neutralization of the NaOH deflocculant, while the second stage involves tridimensional cross-linking by polycondensation, promoted by powders rich in SiO₂.

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Zusammenfassung Die durch Thermoanalyse und Röntgendiffraktion gewonnenen Daten ermöglichten die Nutzung eines eutektischen Gemisches aus Na₂O·2SiO₂ und SiO₂ mit einem Schmelzpunkt von 790°C. Auf dieser Basis wurde Wasserglas als Bindemittel zur Herstellung von künstlichen Cluster-Granulaten genutzt, die bei 800°C keramisch gehärtet wurden. Dieser Härtungsprozess von Wasserglas in Gegenwart von Härtemitteln wie z.B. Na₂SiF₆, NH₄Cl, Silikagel und ultrafeiner Kieselerde wurde mittels Thermoanalyse untersucht. Im ersten Schritt der Gelbildung aus dem SiO₂-Sol erfolgt die Neutralisation des NaOH-Deflokulanten, während der zweite Schritt durch Polykondensation eine dreidimensionale Vernetzung umfaßt, die durch SiO₂-reiche Pulver unterstützt wird.

     

Electrochemical study of Cu2O/CuO composite coating produced by annealing and electrochemical methods

The electrochemical behavior of a copper oxide electrode produced by annealing and electrochemical methods was studied in an acetonitrile solvent by means of the cyclic voltammetry method. The presence of different peaks of oxidation and reduction produced by repeating the potential scans, numerous variations in the current, and shifts of peak potentials in consecutive cycles have been justified. Voltammograms proved that various oxidation species can be produced in solid-deposited forms of Cu₂O_s and CuO_s and dissolved forms of Cu(II)_sol and Cu(I)_sol ions. The experimental results indicated that higher amounts of Cu₂O_s than CuO_s can be produced in the process of copper electrode annealing. Also, the nature of copper species is responsible for different peak currents in the cyclic voltammograms, characterized by UV–Vis and XRD spectrometric methods.

     

Reaction mechanism of CO methanation on nickel catalysts,as studied by isotopic and nonstationary methods

Kinetic isotope effects were measured upon the replacement of hydrogen by deuterium in the reaction of carbon monoxide methanation on nickel catalysts supported on TiO₂ and γ-Al₂O₃. Data on the mechanism of the process were obtained with the use of a nonstationary method. A step-scheme was proposed, in which the interaction of oxygen-containing compounds with hydrogen is a slow step of the process.     

Systematic investigation of simultaneous removal of phosphate/nitrate from water using Ag/rGO nanocomposite: Development,characterization, performance and mechanism

Research on Chemical Intermediates - The primary purpose of this study is to create a method for removal of nitrate and phosphate utilizing adsorption-based technique. To this end, the adsorption...     

Paramagnetic cobalt(II) as a probe for kinetic and NMR relaxation studies of phosphate binding and the catalytic mechanism of Streptomyces dinuclear aminopeptidase

Phosphate was proposed to be a bridging ligand in the structure 1xjo.pdb of Streptomyces dizinc aminopeptidase (sAP), which prompted further studies of phosphate binding to this enzyme. Phosphate inhibits sAP and its Co(2+)-substituted derivatives in a noncompetitive manner from pH 6.0 to 9.0, with strongest inhibition observed at lower pHs (K(i) = 0.6, 8.2, and 9.1 mM for ZnZn-, CoCo-, and CoZn-sAP, respectively, at pH 6.0), which indicates that phosphate does not compete with substrate binding to the dinuclear active site and that monobasic phosphate has a higher binding affinity. The inhibition K(i)-pH profiles for phosphate inhibition of both the native and the Co(2+)-substituted derivatives reveal a similar pK(a) around 7.0, reflecting that phosphate binding is not affected by the metal centers of different Lewis acidities. Modification of ZnZn- and CoCo-sAP with the arginine-specific reagent phenylglyoxal reveals a significant weakening in phosphate and substrate binding by showing approximately a 10-fold increase in the dissociation constant K(i) for phosphate binding and approximately 4-8-fold increase in K(m). The catalysis is also influenced by the modification as reflected by a significant decrease in k(cat) in both cases. Furthermore, phosphate and the transition-state inhibitor 1-aminobutyl phosphonate can protect arginine from the modification, strongly suggesting that Arg202 near the active site is involved in phosphate binding and in stabilizing the transition state. The effect on (31)P NMR relaxation of phosphate caused by the paramagnetic metal center in Co(2+)-substituted derivatives of sAP has been measured, which reveals that only one phosphate is bound to sAP with the Co(2+)-(31)P distance in the range of 4.1-4.3 A. The (1)H NMR relaxation of the bulk water signal in the CoCo-sAP sample remains unchanged in the presence of phosphate, further indicating that phosphate may not bind to the active-site metals to displace any metal-bound water/hydroxide. These results strongly support that the phosphate binding site is Arg202 and that this residue plays an important role in the action of sAP.     

Comparative studies on hydrolysis of bis(p-nitrophenyl) phosphate catalyzed by short- and long-alkyl-multiamine metallomicelles

Four short- and long-alkyl-multiamine ligands L¹–L⁴ have been synthesized and characterized. The catalytic efficiency of complex CuL¹ and functional metallomicelles CuL²–CuL⁴ were comparatively investigated for the hydrolysis of bis(p-nitrophenyl) phosphate (BNPP) in buffered solution at 30 °C. The ternary kinetic model for metallomicellar catalysis was suggested to analyze the experimental data. The kinetic and thermodynamic parameters k^′_N, K_T and pK_a were obtained. The results indicated that the complexes with 1:1 ratio of ligands L²–L⁴ to copper(II) ion were the kinetic active catalysts, and the deprotonized Cu(II) complex formed by activated water molecule was the real active species for BNPP catalytic hydrolysis. The real rate constant of the reaction catalyzed by CuL¹–CuL⁴ was 4.00 × 10⁻⁶, 7.44 × 10⁻⁵, 1.42 × 10⁻⁴ and 4.10 × 10⁻⁴ s⁻¹, respectively. The effects of ligand and microenvironment on the hydrolytic reaction of BNPP have been discussed in detail.     

Assembled structures of nanocrystals in polymer/calcium carbonate thin-film composites formed by the cooperation of chitosan and poly(aspartate)

Assembled structures of calcium carbonate (CaCO₃) nanocrystals have been examined for polymer/CaCO₃ thin-film composites synthesized through a self-organization process inspired by biomineralization. For the crystallization of CaCO₃, a thin-film matrix of chitosan has been used as a polymeric substrate. When the matrix is immersed into a supersaturated aqueous solution of CaCO₃ containing 1.4 × 10⁻³ wt % poly(aspartate) (PAsp), thin-film crystals of CaCO₃ are formed spontaneously. Three kinds of disklike films have been observed under a polarizing optical microscope. Electron diffraction analyses of each film have revealed that one is aragonite, displaying radial orientation of the c axes, and the others are vaterite, exhibiting different orientations. Detailed observation by scanning electron microscopy has clarified that these films are assemblies of crystalline particles 10–20 nm in size. The thin-film composites have been obtained over a PAsp concentration range of 4.4 × 10⁻⁴ to 1.0 × 10⁻² wt %. Vaterite formation becomes dominant when the concentration of PAsp is increased. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5153–5160, 2006     

Hydrogen bonding: A molecular orbital treatment by the EHT and the CNDO/2 methods of methanol and of formic acid

By both the EHT and the CNDO/2 calculations, the linear dimer of methanol is found to be more stable than the cyclic dimer. The hydrogen bonds in the trimer are stronger than those in linear dimers. The proton potential function, charge densities, and overlap populations in the linear dimer of methanol have been obtained. The CNDO/2 calculations show that the cis-form of formic acid is more stable than the trans-form, in agreement with experimental data. The cyclic dimer of formic acid is more stable than the open dimer. The -form of formic acid trimer is more stable than the -form. The proton potential function and the charge densities in the cyclic dimer of formic acid have been obtained. The CNDO/2 method gives more realistic proton potential functions for the dimers of methanol and formic acid. The O ... O stretching force constant in the dimers of methanol and formic acid have been estimated to be 0.13 × 10⁵ dynes/cm and 0.27 × 10⁵ dynes/cm, respectively, in agreement with experimental data.     

An examination of intermolecular and intramolecular hydrogen bonding in biomolecules by AM1 and MNDO/M semiempirical molecular orbital studies

The recent NMDO/M modification and parameterization of the MNDO molecular orbital method has been used to analyze intermolecular hydrogen bonding between amino acids and water, and intramolecular hydrogen bonding in monosaccharides. The results have been compared to AM1 calculations on the same systems. The MNDO/M calculations gave values which were similar to ab initio calculations with respect to the intermolecular interactions, but yielded significantly poorer results for the intramolecular interactions. The AM1 procedure performed better on the intramolecular interactions than the MNDO/M procedure, but frequently provided unfavorable three-centered hydrogen bonding geometries for the intermolecular interactions.