芍药苷大孔树脂静态吸附动力学研究

目的 研究大孔树脂吸附芍药苷的静态吸附动力学特征.方法 通过静态吸附动力学实验,研究不同温度及不同浓度条件对树脂静态吸附的影响,并利用Lagergren一级速率方程和Kannan 颗粒内扩散方程对实验数据进行拟合.结果 实验数据符合Lagergren一级速率方程和Kannan颗粒内扩散方程,相关性均良好.结论 液膜扩散和树脂颗粒内扩散均是控制该吸附过程中吸附速率的因素,其中树脂颗粒内扩散起主要作用;在吸附进行的最初阶段,同浓度的提取液,高温条件下的吸附量明显大于低温条件下的吸附量;在吸附到达平衡阶段之前,浓度增大,吸附速率和吸附量也随之增大.     

Thermodynamic properties of flufenamic and niflumic acids--specific and non-specific interactions in solution and in crystal lattices, mechanism of solvation, partitioning and distribution

Temperature dependency of saturated vapour pressure and the thermochemical characteristics of the fusion process were measured for flufenamic acid and niflumic acid, and thermodynamic functions of sublimation, fusion and evaporation calculated. An approach to split specific and non-specific energetic terms in crystal lattices is developed. The melting points of the considered molecules correlate with the ratio between specific and non-specific interactions in crystal lattices. Temperature dependencies of the solubility in buffers with pH 2.0 and 7.4, in n-octanol and in n-hexane were measured. The thermodynamic functions of solubility, solvation and transfer processes were deduced. Specific and non-specific solvation terms were distinguished by the transfer from "inert"n-hexane to the other solvents. Comparison of the ratio between specific and non-specific interactions in solid state and in the solutions was carried out. A diagram to analyse energetic terms of partitioning and distribution processes is introduced.     

The effect of stereochemistry on the thermodynamic characteristics of the binding of fenoterol stereoisomers to the β2-adrenoceptor

The binding thermodynamics of the stereoisomers of fenoterol, (R,R′)-, (S,S′)-, (R,S′)-, and (S,R′)-fenoterol, to the β₂-adrenergic receptor (β₂-AR) have been determined. The experiments utilized membranes obtained from HEK cells stably transfected with cDNA encoding human β₂-AR. Competitive displacement studies using [³H]CGP-12177 as the marker ligand were conducted at 4, 15, 25, 30 and 37 °C, the binding affinities calculated and the standard enthalpic (ΔH°) and standard entropic (ΔS°) contribution to the standard free energy change (ΔG°) associated with the binding process determined through the construction of van’t Hoff plots. The results indicate that the binding of (S,S′)- and (S,R′)-fenoterol were predominately enthalpy-driven processes while the binding of (R,R′)- and (R,S′)-fenoterol were entropy-driven. All of the fenoterol stereoisomers are full agonists of the β₂-AR, and, therefore, the results of this study are inconsistent with the previously described “thermodynamic agonist-antagonist discrimination”, in which the binding of an agonist to the β-AR is entropy-driven and the binding of an antagonist is enthalpy-driven. In addition, the data demonstrate that the chirality of the carbon atom containing the β-hydroxyl group of the fenoterol molecule (the β-OH carbon) is a key factor in the determination of whether the binding process will be enthalpy-driven or entropy-driven. When the configuration at the β-OH carbon is S the binding process is enthalpy-driven while the R configuration produces an entropy-driven process.     

Structural and biochemical characterization of two binding sites for nucleation-promoting factor WASp-VCA on Arp2/3 complex

Actin-related protein (Arp) 2/3 complex mediates the formation of actin filament branches during endocytosis and at the leading edge of motile cells. The pathway of branch formation is ambiguous owing to uncertainty regarding the stoichiometry and location of VCA binding sites on Arp2/3 complex. Isothermal titration calorimetry showed that the CA motif from the C terminus of fission yeast WASP (Wsp1p) bound to fission yeast and bovine Arp2/3 complex with a stoichiometry of 2 to 1 and very different affinities for the two sites (K(d)s of 0.13 and 1.6 μM for fission yeast Arp2/3 complex). Equilibrium binding, kinetic, and cross-linking experiments showed that (i) CA at high-affinity site 1 inhibited Arp2/3 complex binding to actin filaments, (ii) low-affinity site 2 had a higher affinity for CA when Arp2/3 complex was bound to actin filaments, and (iii) Arp2/3 complex had a much higher affinity for free CA than VCA cross-linked to an actin monomer. Crystal structures showed the C terminus of CA bound to the low-affinity site 2 on Arp3 of bovine Arp2/3 complex. The C helix is likely to bind to the barbed end groove of Arp3 in a position for VCA to deliver the first actin subunit to the daughter filament.     

Competitive adsorption versus surface complexation as models for the simultaneous adsorption of metal complexes and free ligands

A statistical thermodynamical approach to the study of anion-induced adsorption of Cd(II) from halide solutions is presented. The simultaneous adsorption of metal complex and ligand is introduced in the isotherms by considering two possible mechanisms — competitive adsorption and surface complexation. These isotherms have been tested for the system Cd(II) in KBr at several ionic strengths. The experimental surface excesses of Cd(II) calculated from single-step chronocoulometry can be simulated, giving an explanation for the desorption of the metal complex at positive potentials. Also, the change in ligand adsorption promoted by the adsorption of the metal complex has been calculated. Both approaches lead to the conclusion that the anionic tricoordinate metal complex CdBr₃^? and the tetracoordinate CdBr₄^2? are the absorbed species on the electrode surface, with CdBr₄^2? dominating at higher bromide concentrations.     

Pairwise-additive hydrophobic effect for alkanes in water

Pairwise additivity of the hydrophobic effect is indicated by reliable experimental Henry's constants for a large number of linear and branched low-molecular-weight alkanes in water. Pairwise additivity suggests that the hydrophobic effect is primarily a local phenomenon and that the hydrophobic interaction may be represented by a semiempirical force field. By representing the hydrophobic potential between two methane molecules as a linear function of the overlap volume of the hydration layers, we find that the contact value of the hydrophobic potential (-0.72 kcal/mol) is smaller than that from quantum mechanics simulations (-2.8 kcal/mol) but is close to that from classical molecular dynamics (-0.5 approximately -0.9 kcal/mol).     

Physical stability of ternary solid dispersions of itraconazole in polyethyleneglycol 6000/hydroxypropylmethylcellulose 2910 E5 blends

In order to understand the influence of temperature and moisture, polymer blends of polyethyleneglycol 6000 (PEG 6000) and hydroxypropylmethylcellulose 2910 E5 (HPMC 2910 E5) and solid dispersions of itraconazole in these polymer blends were spray dried, further dried for 2 weeks and stored at three different conditions: 25 degrees C, 0% relative humidity (RH); 25 degrees C, 52% RH; 60 degrees C, 0% RH. MTDSC analysis of the polymer blends revealed that at 25 degrees C, 52% RH, PEG 6000 recrystallized to a high extent. At 60 degrees C, 0% RH the two polymers were miscible, probably due to the removal of bound water. In the ternary dispersions the polymers behaved similarly. The crystallinity degree of itraconazole in samples stored at 25 degrees C, 52% RH and at 60 degrees C, 0% RH was increased compared to the samples stored at 25 degrees C, 0% RH, probably due to the plasticizing effect of moisture at 25 degrees C, 52% RH and to an increased mobility at 60 degrees C, 0% RH. XPS analysis revealed a redistribution of itraconazole at the surface as itraconazole recrystallized from the blend. Dissolution tests revealed that a decrease in the itraconazole release was directly related to its crystallinity degree, no correlation was found with the crystallinity degree of PEG 6000.     

Activated Graphene Oxide-Calcium Alginate Beads for Adsorption of Methylene Blue and Pharmaceuticals

The remarkable adsorption capacity of graphene-derived materials has prompted their examination in composite materials suitable for deployment in treatment of contaminated waters. In this study, crosslinked calcium alginate–graphene oxide beads were prepared and activated by exposure to pH 4 by using 0.1M HCl. The activated beads were investigated as novel adsorbents for the removal of organic pollutants (methylene blue dye and the pharmaceuticals famotidine and diclofenac) with a range of physicochemical properties. The effects of initial pollutant concentration, temperature, pH, and adsorbent dose were investigated, and kinetic models were examined for fit to the data. The maximum adsorption capacities q_max obtained were 1334, 35.50 and 36.35 mg g⁻¹ for the uptake of methylene blue, famotidine and diclofenac, respectively. The equilibrium adsorption had an alignment with Langmuir isotherms, while the kinetics were most accurately modelled using pseudo- first-order and second order models according to the regression analysis. Thermodynamic parameters such as ΔG°, ΔH° and ΔS° were calculated and the adsorption process was determined to be exothermic and spontaneous.     

Interface Reaction between Molten Al99.7 Aluminum Alloy and Various Tool Steels

During the die-casting process as well as the hot forming process, the tool is subjected to complex thermal, mechanical, and chemical stresses that can cause various types of damage to different parts of the tool. This study was carried out to determine the resistance of various tool steels, i.e., UTOPMO1, HTCS-130, and W600, in molten Al99.7 aluminum alloy at a temperature of 700 °C. The formation kinetics of the interaction layer between the molten aluminum and tool steels was studied using differential scanning calorimetry. Light and field-emission scanning electron microscopy were used to analyze the thickness and nature of the interaction layers, while thermodynamic calculations using the Thermo-Calc software were used to explain the results. The stability of the HTCS-130 and W600 tool steels is better than the stability of the UTOPMO1 tool steel in the molten Al99.7 aluminum. Two interaction layers were formed, which in all cases indicate an intermetallic Al₁₃Fe₄ layer near the aluminum alloy and an intermetallic Al₅Fe₂ layer near the tool steels, containing small round carbides. It was confirmed that Ni reduces the activity of aluminum in the ferrite matrix and causes a reduction in the thickness of the intermetallic layer.     

Study on the Melting Temperature of CaF2-CaO-MgO-Al2O3-TiO2 Slag under the Condition of a Fixed Ratio of Titanium and Aluminum in the Steel during the Electroslag Remelting Process

During the process of electroslag remelting (ESR) of steel containing titanium and aluminum, the activity ratio between titania and alumina in CaF₂-CaO-MgO-Al₂O₃-TiO₂ slag must be fixed in order to guarantee the titanium and aluminum contents in the ESR ingots. Under the condition of fixed activity ratio between titania and alumina in the slag, the melting temperature of slag should be investigated to improve the surface quality of ESR ingots. Therefore, this paper focuses on finding a kind of slag with low melting temperature that can be used for producing steel containing titanium. In the current study, the thermodynamic equilibrium of 3[Ti] + 2(Al₂O₃) = 4[Al] + 3(TiO₂) between SUS321 steel and the two slag systems (CaF₂:MgO:CaO:Al₂O₃:TiO₂ = 46:4:25:(25 − x):x and CaF₂:MgO:CaO:Al₂O₃:TiO₂ = 46:4:(25 − 0.5 x):(25 − 0.5 x):x) are studied in an electrical resistance furnace based on Factsage software. After obtaining the equilibrium slag with fixed activity ratio between titania and alumina, the melting temperatures of the two slag systems are studied using slag melting experimental measurements and phase diagrams. The results show that the slag systems CaF₂:MgO:CaO:Al₂O₃:TiO₂ = 46:4:25:(25 − x):x, which consists of pre-melted slag S0 (CaF₂:MgO:CaO:Al₂O₃ = 46:4:25:25) and pre-melted slag F1 (CaF₂:MgO:CaO:TiO₂ = 46:4:25:25), can not only control the aluminum and titanium contents in steel, but also have the desired low melting temperature property.