Model for Reaction Between CaO Particles and Portland Cement Clinker

The reaction of CaO particles in a cement clinker is described by a simple model for diffusion-controlled dissolution of spheres. The experimental results agree well with those predicted from data obtained in independent diffusion experiments. Under certain conditions it is possible to determine the maximum size of CaO particles which can react with C₂S to give C₂S within a given reaction time; further, for a given size distribution of CaO particles, the content of free CaO in the clinker after a given burning time can be estimated.     

Effects of Sulfate, Pyrophosphate, and Citrate Ions on the Physicochemical Properties of Cements Made of β-Tricalcium Phosphate-Phosphoric Acid-Water Mixtures

Several additives were selected to increase the setting time of calcium phosphate cements made of β-tricalcium phosphate (β-TCP; β-Ca₃(PO₄)₂)-phosphoric acid-water mixtures. The effects of the additives, i.e., sulfate, pyrophosphate, and citrate ions, are presented in this study. The results show that they all increased the setting time of the cement. Their effectiveness at increasing the setting time is in the order pyrophosphate > citrate > sulfate. The effect of sulfate ions on the setting time is increasingly large below a concentration of 0.1 M . Above that concentration, calcium sulfate dihydrate (CSD; CaSO₄-2H₂O) crystals nucleate and act as nuclei for dicalcium phosphate dihydrate (DCPD; CaHPO₄-2H₂O) crystals, which are the normal product of the setting reaction. This decreases the setting time and decreases the DCPD crystal size, resulting in an increase of the tensile strength of the cement.     

New Approach to the β→α Polymorphic Transformation in Magnesium-Substituted Tricalcium Phosphate and its Practical Implications

The transformation β→α in Mg-substituted Ca₃(PO₄)₂ was studied. The results obtained showed that, contrary to common belief, there is, in the system Mg₃(PO₄)₂–Ca₃(PO₄)₂, a binary phase field where β+α-Ca₃(PO₄)₂ solid solutions coexist. This binary field lies between the single-phase fields of β- and α-Ca₃(PO₄)₂ solid solution in the Ca₃(PO₄)₂-rich zone of the mentioned system. In the light of the results and the Palatnik–Landau's Contact Rule of Phase Regions, a corrected phase equilibrium diagram has been proposed. The practical implications of these findings with regard to the synthesis of pure α- and β- Mg-substituted Ca₃(PO₄)₂ powders and to the sintering of related bioceramics with improved mechanical properties are pointed out.     

Conduction and Dielectric Loss Mechanisms in β-Alumina and Glass: A Discussion Based on the Paired Interstitialcy Model

A paired interstitialcy model is used as a basis for qualitative comparisons of conductivity and dielectric phenomena in β-alumina crystals and in glass. Thus, the increase in the conductivity of sodium silicate glasses with increasing Na₂O activity can be explained if the concentration of (Na₂*)²⁺ interstitial pairs increases with increased polarizability of O^2- ions, expressed in terms of the optical basicity parameter, Δ. Similarly, the occurrence of the pronounced minima in conductivity isotherms (the mixed-alkali effect in glass) is attributed to disappearance of mobile interstitial pairs, e.g. (Li₂*)²⁺ or (K₂*)²⁺, and the stabilization (by polarization interactions) of apparently immobile mixed-alkali pairs, (LiK*)²⁺. The phenomenon of coionic conduction in certain β-alumina crystals is an interesting departure from this general pattern. The orientation dependence of the electrical modulus spectrum of monocrys-talline β-alumina highlights the presence of a bimodal distribution of relaxation times, in which the low-frequency component ( v ₀=10¹¹ Hz) may arise from the rearrangement of interstitial pairs and the high-frequency component ( v ₀=2×10¹² Hz) may arise from less hindered ionic motions. It is suggested that the motions of interstitial pairs and surrounding cations are mutually catalytic and that some form of combined motion is responsible for both the electrical and mechanical relaxations in β-alumina and glass.     

A “Clickable” MTX Reagent as a Practical Tool for Profiling Small‐Molecule–Intracellular Target Interactions via MASPIT

We present a scalable synthesis of a versatile MTX reagent with an azide ligation handle that allows rapid γ‐selective conjugation to yield MTX fusion compounds (MFCs) appropriate for MASPIT, a three‐hybrid system that enables the identification of mammalian cytosolic proteins that interact with a small molecule of interest. We selected three structurally diverse pharmacologically active compounds (tamoxifen, reversine, and FK506) as model baits. After acetylene functionalization of these baits, MFCs were synthesized via a CuAAC reaction, demonstrating the general applicability of the MTX reagent. In analytical mode, MASPIT was able to give concentration‐dependent reporter signals for the established target proteins. Furthermore, we demonstrate that the sensitivity obtained with the new MTX reagent was significantly stronger than that of a previously used non‐regiomeric conjugate mixture. Finally, the FK506 MFC was explored in a cellular array screen for targets of FK506. Out of a pilot collection of nearly 2000 full‐length human ORF preys, FKBP12, the established target of FK506, emerged as the prey protein that gave the highest increase in luciferase activity. This indicates that our newly developed synthetic strategy for the straightforward generation of MFCs is a promising asset to uncover new intracellular targets using MASPIT cellular array screening.     

A New "Incipient-Wetness" Method for the Synthesis of Chemically Stabilized β-Cristobalite

A new "incipient-wetness" method is proposed for the synthesis of chemically stabilized β-cristobalite (CSC) that avoids the need to handle liquid phases as required by the sol-gel routes proposed in the literature. Stoichiometric compounds with the composition Si_1–xAl_*xCa_1/2O₂ have been investigated. ×= 0.07 represents the optimal composition for obtaining an extremely well-crystallized material consisting of a single β-cristobalite phase. XRD, FTIR, DSC, and differential dilatometry have been used for the physicochemical characterization of the samples.     

A Molecular Perspective on the d-Band Model: Synergy Between Experiment and Theory

The d-band model of Hammer and Nørskov (Nature 376:238, 1995 [3]) relating adsorption energies to the d-band position, and the adsorption energies to barriers in catalytic reactions, has been extremely successful in predicting reactivities and catalysts. In the present contribution we review recent combined experimental and theoretical work on chemical bond-formation at surfaces. We focus on the adsorbate and how the adsorbate electronic structure can be rehybridized through mixing with unoccupied states to generate the radical state, real or virtual, that can then form electron pairs with the metal d-states, as described by the d-band model. We discuss five important bonding situations: (i) atomic radical, (ii) diatomics with unsaturated π-systems (Blyholder model), (iii) unsaturated hydrocarbons (Dewar–Chatt–Duncanson model), (iv) lone–pair interactions, and (v) saturated hydrocarbons (physisorption). Where the d-band model predicts trends along the series of transition metals, the present work provides intuitive tools for predicting trends among different adsorbates.     

A Practical NMR‐Based High‐Throughput Assay for Screening Enantioselective Catalysts and Biocatalysts

Two NMR‐based approaches for high‐throughput screening of enantioselective catalysts and biocatalysts are described. One version makes use of pseudo‐enantiomers or pseudo‐meso‐compounds based on ¹³C‐labeling. A throughput of at least 1400 ee determinations per day is possible by using an appropriate flow‐through cell and an autosampler. The other approach is based on traditional diastereomer formation using a chiral reagent or complexing agent. The ee values are accurate to within ±2% and ±5% of the true values.     

A Thermo‐Chemo‐Mechanical Model for the Oxidation of Zirconium Diboride

A thermo‐chemo‐mechanical model was proposed, which couples the oxidation rate of ZrB₂ between 1000°C and 1800°C with the induced mechanical stress in the oxide scale. The model includes the mechanism for the coupling effect. Due to the special porous microstructure of the oxide, the diffusivities of the oxidation reactants and products through the columnar pores dominate the oxidation kinetics. The pores in the oxide shrink under the compressive stress generated during the oxidation due to the constraint from the substrate to the lateral growth of the oxide. And the shrinkage reduces the Knudsen diffusivities of both the molecular oxygen coming inward and the liquid boria evaporating outward. Consequently, the oxidation rate is reduced, which also affects the stress state. Mechanical approaches, such as Mori–Tanaka homogenization method and laminate theory were adopted in the model to quantitatively describe the coupled effect. The evolutions of oxide thickness, pore diameter, and stresses in both the oxide and the substrate were predicted with the model, which showed that the oxidation rate can be significantly altered by the stress‐diffusion coupling during isothermal oxidation, especially at higher temperatures in the range 1000°C–1800°C.     

Evolutionary Interactions Between Visual and Chemical Signals: Chemosignals Compensate for the Loss of a Visual Signal in Male <Emphasis Type="Italic">Sceloporus</Emphasis> Lizards

Animals rely on multimodal signals to obtain information from conspecifics through alternative sensory systems, and the evolutionary loss of a signal in one modality may lead to compensation through increased use of signals in an alternative modality. We investigated associations between chemical signaling and evolutionary loss of abdominal color patches in males of four species (two plain-bellied and two colorful-bellied) of Sceloporus lizards. We conducted field trials to compare behavioral responses of male lizards to swabs with femoral gland (FG) secretions from conspecific males and control swabs (clean paper). We also analyzed the volatile organic compound (VOC) composition of male FG secretions by stir bar extraction and gas chromatography-mass spectrometry (GC-MS) to test the hypothesis that loss of the visual signal is associated with elaboration of the chemical signal. Males of plain-bellied, but not colorful-bellied species exhibited different rates of visual displays when exposed to swabs of conspecific FG secretions relative to control swabs. The VOC composition of male Sceloporus FG secretions was similar across all four species, and no clear association between relative abundances of VOCs and evolutionary loss of abdominal color patches was observed. The emerging pattern is that behavioral responses to conspecific chemical signals are species- and context-specific in male Sceloporus, and compensatory changes in receivers, but not signalers may be involved in mediating increased responsiveness to chemical signals in males of plain-bellied species.     

Interactions between Artemisinins and other Antimalarial Drugs in Relation to the Cofactor Model—A Unifying Proposal for Drug Action

Artemisinins are proposed to act in the malaria parasite cytosol by oxidizing dihydroflavin cofactors of redox‐active flavoenzymes, and under aerobic conditions by inducing their autoxidation. Perturbation of redox homeostasis coupled with the generation of reactive oxygen species (ROS) ensues. Ascorbic acid–methylene blue (MB), N‐benzyl‐1,4‐dihydronicotinamide (BNAH)–MB, BNAH–lumiflavine, BNAH–riboflavin (RF), and NADPH–FAD–E. coli flavin reductase (Fre) systems at pH 7.4 generate leucomethylene blue (LMB) and reduced flavins that are rapidly oxidized in situ by artemisinins. These oxidations are inhibited by the 4‐aminoquinolines piperaquine (PPQ), chloroquine (CQ), and others. In contrast, the arylmethanols lumefantrine, mefloquine (MFQ), and quinine (QN) have little or no effect. Inhibition correlates with the antagonism exerted by 4‐aminoquinolines on the antimalarial activities of MB, RF, and artemisinins. Lack of inhibition correlates with the additivity/synergism between the arylmethanols and artemisinins. We propose association via π complex formation between the 4‐aminoquinolines and LMB or the dihydroflavins; this hinders hydride transfer from the reduced conjugates to the artemisinins. The arylmethanols have a decreased tendency to form π complexes, and so exert no effect. The parallel between chemical reactivity and antagonism or additivity/synergism draws attention to the mechanism of action of all drugs described herein. CQ and QN inhibit the formation of hemozoin in the parasite digestive vacuole (DV). The buildup of heme–Fe^III results in an enhanced efflux from the DV into the cytosol. In addition, the lipophilic heme–Fe^III complexes of CQ and QN that form in the DV are proposed to diffuse across the DV membrane. At the higher pH of the cytosol, the complexes decompose to liberate heme–Fe^III. The quinoline or arylmethanol reenters the DV, and so transfers more heme–Fe^III out of the DV. In this way, the 4‐aminoquinolines and arylmethanols exert antimalarial activities by enhancing heme–Fe^III and thence free Fe^III concentrations in the cytosol. The iron species enter into redox cycles through reduction of Fe^III to Fe^II largely mediated by reduced flavin cofactors and likely also by NAD(P)H–Fre. Generation of ROS through oxidation of Fe^II by oxygen will also result. The cytotoxicities of artemisinins are thereby reinforced by the iron. Other aspects of drug action are emphasized. In the cytosol or DV, association by π complex formation between pairs of lipophilic drugs must adversely influence the pharmacokinetics of each drug. This explains the antagonism between PPQ and MFQ, for example. The basis for the antimalarial activity of RF mirrors that of MB, wherein it participates in redox cycling that involves flavoenzymes or Fre, resulting in attrition of NAD(P)H. The generation of ROS by artemisinins and ensuing Fenton chemistry accommodate the ability of artemisinins to induce membrane damage and to affect the parasite SERCA PfATP6 Ca²⁺ transporter. Thus, the effect exerted by artemisinins is more likely a downstream event involving ROS that will also be modulated by mutations in PfATP6. Such mutations attenuate, but cannot abrogate, antimalarial activities of artemisinins. Overall, parasite resistance to artemisinins arises through enhancement of antioxidant defense mechanisms.     

泥浆性能与离子溶出关系实验总结

通过测定外加不同量电解质的泥浆离子溶出量的方法．揭示了泥浆的各种阳离子值与泥浆性能之间的关系。     

Practical Method for the Rhodium‐Catalyzed Addition of Aryl‐ and Alkenylboronic Acids to Aldehydes

The arylation or alkenylation of aldehydes with boronic acids is conveniently effected by a catalyst system comprising RhCl₃⋅3 H₂O (1 mol %), the sterically hindered imidazolium salt 2 (1 mol %), and a base. The N‐heterocyclic carbene 6 derived from 2 is believed to be the actual ligand to the catalytically active rhodium species formed in situ. The method is compatible with various functional groups in both reaction partners and follows a non‐chelation controlled pathway in additions to the Garner aldehyde 23 .     

研究G-四链体与其配体相互作用的技术方法概述

近年来以G-四链体DNA为药物靶点的研究引起了人们的广泛关注,G-四链体与其配体相互作用的研究方法也多种多样.本文对研究G-四链体形成的结构,配体与G-四链体结合能力,配体与G-四链体结合模式等三个方面的技术方法进行了综述.     

Study on Si-P-Fe and Si-P-Al ternary System Interactions Applied by MIVM Model for the Process of Specific Actual Production

Silicon - The content of P in industrial silicon affects the photoelectric conversion efficiency of solar-grade silicon. Based on a large amount of actual production data, this paper uses...     

Substitution Model of Monovalent (Li, Na, and K), Divalent (Mg), and Trivalent (Al) Metal Ions for β-Tricalcium Phosphate

The maximum substitution of monovalent, divalent, and trivalent metal ions for β-tricalcium phosphate (β-TCP) was investigated, and a substitution model of these metal ions for β-TCP was proposed. Monovalent metal ions (M^I) could replace Ca(4) site and vacancy ( V _Ca(4)) in β-TCP as 2M^I=Ca²⁺+ V _Ca(4) and the maximum substitution was about 9.1 mol%. In the case of divalent metal ions (M^II), Ca(4) and Ca(5) sites were replaced by divalent metal ions as M^II=Ca²⁺, and the maximum substitution was about 13.6 mol%. Trivalent metal ions (M^III) could be substituted for Ca(4) site and vacancy as 3M^III=2Ca²⁺+ V _Ca(4), and the maximum substitution was about 9.1 mol%.