Prediction of Hansen Solubility Parameters with a New Group-Contribution Method

A group-contribution method for the estimation of Hansen solubility parameters of pure organic compounds is presented. It uses two kinds of characteristic groups: first-order groups that describe the basic molecular structure of compounds and second-order groups, which are based on the conjugation theory and improve the accuracy of predictions. A large variety of characteristic groups ensure the prediction of Hansen solubility parameters for a broad series of organic compounds, including those having complex multi-ring, heterocyclic, and aromatic structures. The predictions are exclusively based on the molecular structure of compounds, and no experimental data are needed. The predicted values permit a fairly reliable selection of solvents based on the radius of a Hansen solubility parameter sphere or on a Teas parameter ternary plot. Especially designed algorithms permit the preparation of a list of new molecular structures which, if synthesized, could be the ideally suited solvents for a series of corresponding applications.     

Porous Carrier Based Floating Granular Delivery System of Repaglinide

ABSTRACT

A floating granular delivery system consisting of calcium silicate (CS) as porous carrier; repaglinide (Rg), an oral hypoglycemic agent; and hydroxypropyl methylcellulose K4M (HPMC K4M), ethyl cellulose (EC) and carbopol 940 (CP940) as matrix forming polymers was prepared and evaluated for its gastro-retentive and controlled release properties. The effect of various formulation and process variables on the particle morphology, micromeritic properties, in vitro floating behavior, drug content (%) and in vitro drug release was studied. The transit of floating granules of optimized formulation in the gastrointestinal (GI) tract was monitored by gamma scintigraphy in albino rabbits. The optimized formulation was compared in vivo with lactose granules (RgSCLG) prepared from identical polymers with their optimized composition ratio. Repaglinide-loaded optimized formulation was orally administered to albino rabbits and blood samples collected were used to determine pharmacokinetic parameters of Rg from floating granular formulation. Results were compared with pharmacokinetic parameters of marketed tablet formulation of Rg. The optimized formulation (RgSCG₄) demonstrated favorable in vitro floating and release characteristics. Prolonged gastric residence time (GRT) of over 6 hr was achieved in all subjects for calcium silicate based floating granules of Rg. The relative bioavailability of Rg-loaded floating granules increased 3.8-fold in comparison to that of its marketed capsule. The designed system, combining excellent buoyant ability and suitable drug release pattern, offered clear advantages in terms of increased bioavailability of repaglinide.     

Kinetics of adsorption of dyes from aqueous solution using activated carbon prepared from waste apricot

Adsorbent (WA11Zn5) has been prepared from waste apricot by chemical activation with ZnCl(2). Pore properties of the activated carbon such as BET surface area, pore volume, pore size distribution, and pore diameter were characterized by N(2) adsorption and DFT plus software. Adsorption of three dyes, namely, Methylene Blue (MB), Malachite Green (MG), Crystal Violet (CV), onto activated carbon in aqueous solution was studied in a batch system with respect to contact time, temperature. The kinetics of adsorption of MB, MG and CV have been discussed using six kinetic models, i.e., the pseudo-first-order model, the pseudo-second-order model, the Elovich equation, the intraparticle diffusion model, the Bangham equation, the modified Freundlich equation. Kinetic parameters and correlation coefficients were determined. It was shown that the second-order kinetic equation could describe the adsorption kinetics for three dyes. The dyes uptake process was found to be controlled by external mass transfer at earlier stages (before 5 min) and by intraparticle diffusion at later stages (after 5 min). Thermodynamic parameters, such as DeltaG, DeltaH and DeltaS, have been calculated by using the thermodynamic equilibrium coefficient obtained at different temperatures and concentrations. The thermodynamics of dyes-WA11Zn5 system indicates endothermic process.     

梳形聚合物PAA-g-MPEG的合成及溶解度参数

首先采用甲氧基聚乙二醇单醚(MPEG)和丙烯酸(AA)合成了具有反应活性的大单体甲氧基聚乙二醇单醚丙烯酸酯(MPEGAA),然后以亚硫酸氢钠为还原荆和分子量调节剂,在水溶液中将MPEGAA与AA共聚合成了聚丙烯酸接枝甲氧基聚乙二醇梳形聚合物(PAA-g-MPEG).采用红外光谱(FT-IR)和核磁共振(1H-NMR)对...     

溶剂/非溶剂组合对聚醚砜分离膜结构与性能的影响

采用沉浸相转化法制备聚醚砜分离膜,研究了具有不同溶解度参数的溶剂/非溶剂组合对膜亚层结构与性能的影响.结果表明,溶剂/非溶剂组合是影响聚醚砜分离膜亚层结构性能的关键因素,溶剂与聚醚砜的溶解度参数越接近,即|△δ|越小,越易形成海绵状致密结构,而溶剂与非溶剂的|△δ|越大,相转化时间越短,越容易得到指状的大空腔结构;实验中异丙醇为非溶剂时膜的截留和通量效果较好,这是由于在形成致密膜的同时增加了膜的亲水性的缘故.     

基于溶解度参数分析方法的IPN密封材料研究

目的基于耐溶剂性原则选择硝酸异丙酯的密封材料。方法通过溶解度参数的计算验证丁腈橡胶(NBR)与IPN会产生溶胀效应。根据聚合物的耐溶剂性原则,选择三元乙丙橡胶(EPDM)和聚四氟乙烯(PTFE)代替丁腈橡胶,而后比较各材料与IPN的溶解度参数差值。结果 IPN在NBR的可溶球体范围内,两者的三维溶解度参数十分接近;IPN,EPDM与PTFE的一维溶解度参数分别为8.6,7.7,5.14,EPDM与IPN的溶解度参数较为接近;PTFE与IPN的溶解度参数相差较大。结论 EPDM与PTFE均比NBR更适合密封IPN,其中EPDM最适合密封IPN。     

氧化物／氧化物共晶复合陶瓷的生长机理与微观结构

本文基于国外定向凝固氧化物j氧化物共晶复合陶瓷的晶体生长动力学行为研究，阐述其动力学机制，分析动力学因素对微观结构形态的影响，探讨晶体生长动力学行为与微观结构形态之间的关系，同时结合以燃烧合成、快速凝固技术所制备的新型高强韧Al2O3／YSZ共晶复合陶瓷，探讨共晶复合陶瓷在快速凝固条件下的晶体生长动力学行为。结合定向凝固与快速凝固两种晶体生长机制，得出过冷度、凝固界面前沿的温度梯度是影响晶体生长方式的重要因素，且受二者决定的凝固速率（即晶体生长速率）决定了材料的最终微观结构与形态。     

Arsenate removal from aqueous solution by cellulose-carbonated hydroxyapatite nanocomposites

Microwave-assisted synthesis of the cellulose-carbonated hydroxyapatite nanocomposites (CCHA) with CHA nanostructures dispersed in the cellulose matrix was carried out by using cellulose solution, CaCl(2), and NaH(2)PO(4). The cellulose solution was previously prepared by the dissolution of microcrystalline cellulose in NaOH-urea aqueous solution. Study was carried out to evaluate the feasibility of synthetic CCHA for As(V) removal from aqueous solution. Batch experiments were performed to investigate effects of various experimental parameters such as contact time (5 min - 8h), initial As(V) concentration (1-50mg/L), temperature (25, 35 and 45°C), pH (2-10) and the presence of competing anions on As(V) adsorption on the synthetic CCHA. Kinetic data reveal that the uptake rate of As(V) was rapid at the beginning and equilibrium was achieved within 1h. The adsorption process was well described by pseudo-first-order kinetics model. The adsorption data better fitted Langmuir isotherm. The maximum adsorption capacity calculated from Langmuir isotherm model was up to 12.72 mg/g. Thermodynamic study indicates an endothermic nature of adsorption and a spontaneous and favorable process. The optimum pH for As(V) removal was broad, ranging from 4 to 8. The As(V) adsorption was impeded by the presence of SiO(3)(2-), followed by PO(4)(3-) and NO(3)(-). The adsorption process appeared to be controlled by the chemical process.     

Adsorption studies on ground shells of hazelnut and almond

Adsorption behaviour of Ni(II), Cd(II) and Pb(II) from aqueous solutions by shells of hazelnut and almond were investigated. The structural properties and surface chemistry of the shells were characterized using sorption of nitrogen and Boehm titration. The equilibrium time was found to be 120 min. The equilibrium adsorption capacity of shells were obtained by using linear Langmuir and Freundlich adsorption isotherms. The equilibrium adsorption level was determined to be a function of the solution contact time, concentration and temperature. The thermodynamic parameters have been determined. The negative values of free change (DeltaG) indicated the spontaneous nature of the adsorption of Ni(II), Cd(II) and Pb(II) onto shells of hazelnut and almond and the positive values of enthalpy change (DeltaH) suggested the endothermic nature of the adsorption process. The best correlation coefficients were obtained for the pseudo second-order kinetic model. Ion exchange is probably one of the major adsorption mechanisms for binding divalent metal ions to the shells of hazelnut and almond. The selectivity order of the adsorbents is Pb(II)>Cd(II)>Ni(II).     

Adsorption of methylene blue onto hazelnut shell: Kinetics, mechanism and activation parameters

The adsorption kinetics of methylene blue (MB) on the hazelnut shell with respect to the initial dye concentration, pH, ionic strength, particle size and temperature were investigated. The rate and the transport/kinetic processes of MB adsorption were described by applying the first-order Lagergren, the pseudo-second-order, mass transfer coefficient and the intraparticle diffusion models. Kinetic studies showed that the kinetic data were well described by the pseudo-second-order kinetic model. Significant increases in initial adsorption rate were observed with the increase in temperature followed by pH and initial MB concentration. The intraparticle diffusion was found to be the rate-limiting step in the adsorption process. Adsorption activation energy was calculated to be 45.6kJmol(-1). The values of activation parameters such as free energy (DeltaG(*)), enthalpy (DeltaH(*)) and entropy (DeltaS(*)) were also determined as 83.4kJmol(-1), 42.9kJmol(-1) and -133.5Jmol(-1)K(-1), respectively.     

Eutectic assisted synthesis of nanocrystalline NiO through chemical precipitation

Cubic NiO nanocrystallites with the particle size of 15-20 nm were successfully prepared through the decomposition of the precursor and eutectic as the assistant. The precursor was obtained by precipitating Ni(NO₃)₂·6H₂O with NaOH in a water solvent. The compared experiments were carried out either with the presence or absence of eutectic. It was indicated by X-ray diffraction (XRD) and transmission electron microscopy (TEM) analysis that the eutectic played an important part in overcoming the agglomerations and the prepared NiO nanocrystallites have better morphology and uniform granularity. The mechanism of eutectic during the synthesis of nanocrystalline NiO was also discussed.     

Study on the Relationship Lamellar Spacing and Growth Rate in the Regular Eutectic Growth by Monte—Carlo Simulation

A modified Monte-Carlo(MC) method to simulate the regular growth of binary eutectic alloys is presented.It is found that the growth rate has a linear dependence on the chemical potemtial difference between the solid and liquid ,the relation between the lamellar spacing λ and growth rate R accords well with the prediction of Jackson-Hunt(JH) theory unless the growth rate is very low.     

Study on the Relationship between Lamellar Spacing and Growth Rate inthe Regular Eutectic Growthby Monte-Carlo Simulation

A modified Monte-Carlo(MC) method to simulate the regular growth of binary eutectic alloys is presented. It is found that the growth rate has a linear dependence on the chemical potential difference between the solid and liquid; the relation between the lamellar spacing A and growth rate R accords well with the prediction of Jackson-Hunt(JH) theory unless the growth rate is very low.     

The Dependence of the Melting Temperature of Cobalt–Carbon Eutectic on the Morphology of its Microstructure

Fixed points provide a reliable way to realize and verify temperature scales. High-temperature fixed points are being developed based upon alloys, since single-phase materials are impractical to use above the copper freezing point. In particular, eutectic alloys have been shown to be sufficiently reproducible to warrant consideration as a way to significantly improve high-temperature metrology. However, eutectic alloys have certain characteristics requiring that they are used differently from the current ITS-90 fixed points. As their freezing temperature depends on the freezing rate, the melting temperature is preferred, though it has been shown that for some alloys, notably iron–carbon and cobalt–carbon, the apparent melting temperature can depend on the rate of the preceding freeze. This behavior will need to be explained and quantified if such fixed points are to be acceptable. The effect of varying the freezing rate on subsequent melting has been investigated for cobalt–carbon eutectic fixed points. The apparent melting temperature varies by up to 50 mK. Measurements were made of two different fixed-point blackbodies with very similar results. Optical microscopy of samples produced at different freeze rates shows a change in scale of the microstructure. Electron back-scatter diffraction (EBSD) shows evidence of high levels of residual strain in rapidly frozen samples. The effect of annealing on the melting behavior and microstructure has also been investigated. It is suggested that disordered phase boundaries and residual strain lead to changes in the melting behavior as nonequilibrium conditions may lead to a significant level of pre-melting. Whether this actually changes the liquidus temperature, or whether the melting temperature variation is due to the way the melting point is defined, is also discussed. The variation requires consideration if the highest accuracy is to be achieved, and will be a contributory factor to any uncertainty budget.     

可降解材料聚碳酸亚丙酯和聚乳酸的溶度参数与相容性

采用基团贡献法求出了聚碳酸亚丙酯(PPC)和聚乳酸(PLA)的一维溶度参数和Hansen三维溶度参数理论值,并通过溶解试验获得了PPC和PLA的三维溶度参数值,结合Teas图分析了聚合物与溶剂之间的溶度参数距离(Ri)和Flory-Huggins相互作用参数(χAB),预测和分析了PPC和PLA的相容性。结果表明,PPC和PLA的一维溶度参数理论值分别为20.37(J/cm³)1/2、19.97 (J/cm³)1/2; PPC的Hansen三维溶度参数(δd、δp、δh)和总溶度参数理论值(δ)分别为14.68 (J/cm³)1/2、7.37 (J/cm³)1/2、10.79 (J/cm³)1/2和19.65 (J/cm³)1/2,PLA的分别为15. 45 (J/cm³)1/2、8.51 (J/cm³)1/2、11.02 (J/cm³)1/2和20.80 (J/cm³)1/2;试验法得出PPC的δd、δp、δh、δ分别为16.94 (J/cm³)1/2、7.05 (J/cm³)1/2、6.75 (J/cm³)1/2、19.56 (J/cm³)1/2,PLA的则分别为16.83 (J/cm³)1/2、6.40 (J/cm³)1/2、6.70 (J/cm³)1/2、19.21 (J/cm³)1/2,且在Teas图中,所有良溶剂位于一定的溶解区域内,不良溶剂位于区域外,聚合物与良溶剂的Ri小于与不良溶剂的Ri,聚合物与良溶剂的χAB小于0.5,与不良溶剂的χAB大于0.5,表明试验结果可信;通过理论计算和试验法求出PPC和PLA都具有相近的溶度参数值,且溶度参数差值的绝对值(Δ)位于0.077～1.300 (J/cm³)1/2之间,表明两者之间为部分相容。     

The Double-Wavelength Technique—An Alternative Technique to Determine Thermodynamic Temperature

Filter radiometry provides thermodynamic temperatures traceable to a cryogenic radiometer. An alternative technique is possible which provides absolute thermodynamic temperature through a different traceability chain, with the radiometric measurements purely relative. If this technique could be experimentally realized with similar uncertainties to those associated with filter radiometry, then this would provide a metrologically valuable ‘second opinion’ that would test for systematic effects common to all filter radiometry measurements. This paper describes the theoretical analysis prior to an experimental investigation of this technique. This theoretical analysis implies that with Re-C and Cu as the two blackbodies, the Re-C temperature can be determined with an uncertainty of approximately twice that expected with filter radiometry. For higher-temperature metal-carbide/carbon eutectics, the uncertainty difference would be smaller.