Predicting the selectivity of imprinted polymers

Summary Imprinted polymers as stationary phases for HPLC separations have been the subject of extensive investigations in recent years. In order to aid the rational design of synthetic protocols for the preparation of imprinted polymers, a series of calculations were made to assess the equilibrium concentration of templatemonomer complexes as a function of association constant (K) for the functional groups involved in the interactions and initial concentrations of reactants. This data was then used to predict the selectivity of polymers prepared under different reaction conditions and the model was tested using an experimentally determined value ofK and separation factors taken from the literature.     

Heat transfer to nonspherical particles in a rarefied plasma flow

The interaction of a nonspherical metallic or nonmetallic particle with a rarefied thermal plasma flow is considered. Heat transfer to a particle of arbitrary shape with an extremely thin plasma sheath due to, respectively, gas molecules, electrons, and ions is described. Analytical expressions are derived for charge and heat fluxes in the particular case of a spheroidal metallic or nonmetallic particle in a subsonic plasma flow. It has been shown that the intensity of heat exchange is greatly influenced by gas ionization, charge transfer processes, and particle shape, velocity, and orientation in the plasma flow.     

LnSrNiO4-λ系列复合氧化物的物化性质与对NO分解的催化性能

用柠檬酸络合法合成了Ｋ２ＮｉＦ４结构的ＬｎＳｒＮｉＯ４－λ（Ｌｎ＝Ｌａ，Ｐｒ，Ｎｄ，Ｓｍ，Ｇｄ）系列稀土取代类钙钛石型复合氧化物催化剂，对该系列催化剂的固态物理、化学性质及其对ＮＯ分解的催化性能进行研究。结果表明，该系列复合氧化物催化剂对ＮＯ分解活性都很高，在此基础上对该系列复合氧化物中稀土元素对ＮＯ分解反应的取代效应进行了探讨。     

Surface chemistry of nanoscale Fe_3O_4 dispersed in magnetic fluids

The interaction between stabilizers and nanoparticles is one of the important factors to prepare stable magnetic fluids. The magnetic nano-size Fe3O4 core with single domain and the average grain size around 8-12 nm were prepared by chemical precipitation method. The O/Fe molar ratio of the particle surface was measured by X-ray photoelectron spectroscopy (XPS). The heat effects of stabilizers ad- sorption on nanoparticles were measured by solution calorimetry. The excess amount of oxygen was possibly the result of the hydroxygen formed on the surface of the nanoparticles. The heat effects showed that compounds containing carboxyl groups can be adsorbed chemically on magnetite by forming chemical bonds. The other stabilizers involving NH-groups, such as polyethylene-imine, can be adsorbed physically. The exothermic value is about half of the former case.     

A statistical model for the optimization of dsc performance in the evaluation of drugs for preformulation studies

Differential scanning calorimetry (DSC) is a thermal analytical tool for preformulation studies. Extrapolated melting temperature (T_P) and heat of fusion (ΔH_f) can be used as parameters for optimizing the DSC performance. Two model pharmaceuticals acetaminophen and nicotinamide are used in this study. Using a factorial design for the experimental model and matrix analysis the results, the effect of sample mass, heating rate and the nitrogen flow rate were evaluated on the ΔH_f values and T_P values. Two levels for each of the procedural variables were used as a balanced experimental design with two sample sizes, two heating rates and two nitrogen flow rates. It was found that the change in the heating rate caused significant changes in the ΔH_f values but not the T_p values for acetaminophen. However, no significant effect was found for the T_p value but ΔH_f value was affected to a certain extent for nicotinamide.     

Influence of the heating conditions on the thermal and chemical behaviour of solid particles undergoing a fast endothermic decomposition

This paper deals with models describing the thermal and chemical behaviour of solid particles undergoing fast endothermic reactions under the influence of an external heat flux. The heat source temperature is supposed to be constant, to increase with time, or to deliver a simple thermal flash. It is shown that the pyrolysis conditions (reaction temperature, conversion, etc.) depend on the chemical characteristics of the reaction and also to a large extent on the external heating conditions. Relationships are proposed to take into account these parameters. The results are applied to the thermal decomposition of NaHCO₃. The pyrolysis of cellulose is finally chosen in order to show how these operating parameters can also affect the selectivity of a more complex reaction.     

热导式热量计特征热谱方程的建立

Based on the interfacial model of a conduction calorimeter, a characteristic thermogram equation is suggested in this paper. Measurements of only two quantities such as the maximum peak height △m and its time tm, enables us to calculate the peak height at any interval by using this model. Thermograms of alkaline hydrolysis of ethyl propionate and ethyl acetate have been measured at 25℃, respectively. The themographic data calculated by using the characteristic thermogram equation are in reasonable agreement with those read from the thermograms.     

联苯甲酰双缩氨基脲硫氰酸根硝酸根混合阴离子配位钕(Ⅲ)配合物的合成与结构

合成了联苯甲酰双缩氨基脲硫氰酸根、硝酸根混合配位的钕(Ⅲ)配合物。在此配合物中只有1个链状配体,另有2个硫氰酸根、1个硝酸根和1个水分子参与配位。总配位数是9。晶体结构分析表明,该配合物晶体属三斜晶系,P空间群。晶胞参数a=10。866(2),b=13.687(3),c=15.433(3),α=98.75(4)°,β=107.64(5)°,γ=112.14(5)°。最终偏差因子R=0.075。用INDO方法计算结果表明:NCS对Nd(Ⅲ)的配位比=C基对Nd(Ⅲ)的配位强。     

Crystal structure of a new high-pressure phase, K0.82Mg1.68(Cr2.84Fe0.84Ti2.11Zr0.08)O12, with one-dimensional tunnels

The crystal structure of a new complex Ti-Cr oxide phase, K_0.82Mg_1.68(Cr_2.84Fe_0.84Ti_2.11Zr_0.08)O₁₂, synthesized at 13 GPa and 1400 °C, has been determined with single-crystal X-ray diffraction. It has a hexagonal symmetry with the space group P6₃/m and unit-cell parameters a=9.1763(13) and , , Z=1. The structure is characterized by the hollandite-type double chains of edge-shared M2 octahedra occupied by trivalent and tetravalent cations (Ti+Cr+Fe+Zr); these double chains are linked to one another through shared octahedral apexes to form a framework structure containing two types of tunnels running parallel to the c-axis. One type of tunnels has a hexagonal cross-section and is occupied by large K⁺, whereas the other has a triangular cross-section and is occupied by Mg²⁺. The K⁺ cation is disordered between two crystallographically equivalent (2a) sites in the tunnels and displays a U₃₃ displacement parameter that is significantly greater than U₁₁. The new high-pressure phase reported in this study possesses many structural features similar to those for the hollandite compounds, making it a candidate for the 1-D fast ionic conductors.     

Chemical equilibrium model for the thermodynamic properties of mixed aqueous micellar systems: Application to thermodynamic functions of transfer

Mixed micelles can be formed in water between various pairs of hydrophobic solutes such as surfactants, alcohols and hydrocarbons. These systems can often be studied through the thermodynamic functions of transfer of one of the solutes, usually kept near infinite dilution, from water to an aqueous solution of the other solute. When mixed micelles are formed, these functions change significantly, and often go through extrema, in the region where the binary system micellizes or undergoes some microphase transition.Three main effects are responsible for the observed trends: pair-wise interactions between both solutes in the monomeric form, a distribution of the reference solute between the aqueous and micellar phases and a shift in the monomer-micelle equilibrium in the vicinity of the reference solute. Simple equations can be derived for these three effects which can account for the sign and magnitude of the observed trends using parameters which are derived for the most part from the two binary systems.