氢氧化铝镁钠米颗粒的零电荷点及电荷密度研究

探讨了电位滴定(PT)法测定的零电荷点的物理意义, 认为是零净电荷点(ZPNC)。并对零净电荷点pH(pHZPNC), 零可变电荷点pH(pHZPVC), 永久电荷密度(σP), 可变电荷密度(σV)和净电荷密度(σT)之间的关系进行了理论分析。用PT法测定了氢氧化铝镁纳米颗粒的pHZPNC和σP, 探讨了电解质浓度和pH对各电化学性质的影响规律。另外, 还考察了CO3^2^-对PT法测定结果的影响。     

Zn-Al类水滑石结构正电荷对内禀电离平衡常数的影响

采用电势滴定(potentiometric titration,PT)法测定了Zn-Al类水滑石(HTlc)的零净电荷点(pHPZNC);利用电势滴定数据直接计算得到Zn-Al HTlc的内禀电离平衡常数(pKa2int)和质子吸附自由能(G0ads,2);研究了结构电荷密度(σp)对pKa2int 和G0ads,2的影响.结果表明,随σp增加, pKa2int 和G0ads,2数值均降低,说明σp越大,带正电荷的HTlc与H＋结合力越低,HTlc去质子能力越强,H＋游离出HTlc表面的趋势越大.研究发现，HTlc的pKa2int与pHPZNC之间符合关系式: pKa2int =1.372pHPZNC－3.328.     

Zn-Al类水滑石零净电荷点及等电点研究

用非均相共沉淀法合成了系列Zn-Al类水滑石(HTlc)样品，研究发现A1／(Zn Al)摩尔比(x)在0．31～0．52范围内可得到纯类水滑石相．用电势滴定法和显微电泳法分别测定了5个纯Zn-Al HTic样品的零净电荷点(PZNC)和等电点(IEP)，以考察结构电荷对PZNC和IEP的影响．研究发现随结构正电荷密度的增加，PZNC和IEP均降低；IEP高于PZNC，且随结构正电荷密度的降低，IEP与PZNC的差值也降低，表明IEP与PZNC的差异来自结构电荷的影响．结构正电荷对HTlc的IEP与PZNC相对大小的影响与高价阳离子特性吸附的影响一致．初步探讨了结构电荷对PZNC和IEP的影响机理．     

东北草甸棕壤的零电荷点和界面酸-碱反应特征平衡常数

分别采用电势滴定(Potentiometric titration)法, 质量滴定(Mass titration)法和惰性电解质滴定(Inert electrolyte titration)法测定了荷结构负电荷的东北草甸棕壤的零净电荷点(PZNC), 研究表明荷结构负电荷的土壤依然存在与电解质浓度无关的零净电荷点, 三种方法的实验结果分别为2.9, 5.0和3.3. 相比较而言, 电势滴定法和惰性电解质滴定法的结果相近, 而质量滴定法的结果偏高. 对文献中推算表面质子活性位密度(N_s)的方法进行了改进, 得到东北草甸棕壤样品的N_s为2.5 mmol•g^－1. 根据实验测定的pH_PZNC, N_s和结构电荷密度(σ_st)值直接计算得出东北草甸棕壤样品的界面反应特征平衡常数即1-pK模型中的pK, 2-pK模型中pK_a1^int和pK_a2^int, 分别为3.37, 2.42和4.32, 与文献报道的沉积物和蒙脱土的值相吻合.     

净电荷对螺旋型抗癌肽生物活性的影响

以高活性两亲性α-螺旋型阳离子抗癌肽A12L/A20L(多肽P)为模板, 在其亲水面进行氨基酸定点取代, 获得了一系列带有不同净电荷的多肽类似物, 研究了净电荷对螺旋型抗癌肽生物活性的影响. 结果表明, 抗癌肽净电荷的改变对其溶血活性影响较小(最大差异为2倍), 而对抗癌活性和选择性的影响显著(最大差异为10倍). 抗癌肽P的净电荷最适范围为+7到+8, 分子间静电排斥作用的最佳数目为3~5个, 高于或低于此范围, 其抗癌活性和选择性均明显降低. 与人的正常细胞相比, 负电性的癌细胞膜对于抗癌肽的净电荷变化更敏感, 表明两亲性螺旋型抗癌肽针对癌细胞与正常细胞表现出良好的选择特异性.     

取代1-氯蒽醌中分子内卤键的电子密度拓扑分析

运用量子化学密度泛函B3LYP方法,在6-311＋＋G（d,p）基组水平上对邻位和间位取代1-氯葸醌的分子内卤键进行了研究．用电子定域函数和“分子中的原子,,理论对分子内卤键的性质进行了电子密度拓扑分析．通过对计算得到的密度矩阵进行σ-π兀分离,得到了π-键的键径和分子图,并讨论了。电荷密度和兀电荷密度对卤键的影响．结果表明,键鞍点和环鞍点处的电子密度拓扑性质均可作为衡量分子内卤键强度的量度．键鞍点和环鞍点处的电荷密度P越大,键鞍点与环鞍点的距离越大,卤键强度越大．除σ电荷密度外,π电荷密度对分子内卤键的性质也有明显影响．     

十六烷基三甲基溴化铵修饰P型沸石吸附水中直链烷基苯磺酸钠的研究

通过使用碱液对天然斜发沸石(Z)进行处理制得P型沸石(PZ), 再用十六烷基三甲基溴化铵(CTMAB)对Z和PZ进行修饰, 制得有机改性沸石ZC和PZC, 对比考察了ZC和PZC对直链烷基苯磺酸钠(LAS)的吸附性能. 实验结果表明, 制得的PZ硅/铝比为2, 比Z(4.85)降低58.8%; PZ的零净电荷点、 比表面积、 孔径和孔容均高于Z; 吸附平衡时间为4 h. 当pH=2时, ZC和PZC对LAS吸附量达到最高, 吸附数据符合Langmuir准二级动力学方程和Langmuir等温吸附方程, 饱和吸附量(q_m)分别为12.658和27.100 mg/g, 吸附过程主要为单分子层的化学吸附, PZC的吸附速率常数大于ZC, 具有更好的动力学性能.     

蛋白质在离子交换色谱上选择性和非吸附特性

对蛋白质在离子交换柱上选择民性和非吸附特性进行了研究。蛋白质在有机磷酸锆阳离子色谱柱上,其保留作用随流动相ｐＨ值在离子强度的增加而减小;蛋白质在强阳离子和强阴离子色谱柱上的保留作用,即是流动相中的ｐＨ值等于蛋白质的等当点,其净电荷为零。不册蛋白质仍有不同程度的保留,这主要是由于蛋白质的三维结构使电荷 密度的大小和分布的不均匀以及离子交换填料表面性质的影响。     

对成键时电子几率密度分布的改变的讨论

对N电子波函数Ψ, ρ(q)=N∫|Ψ|~2dσ_1dν_2dσ_2…dν_Ndσ_N表示在q处发现一个任意自旋(σ_i是自旋变量)的电子的几率密度,称为电子几率密度(电子密度、电荷密     

双电层相互作用时胶体表面电位的分布及电荷密度的计算

本文以实验为基础,运用计算机数值解解出双电层相互作用时平面胶体表面电位ψ随距离X的分布,依据作者导出的双电层相互作用时胶体表面阴离子负吸附方程,计算出胶体表面外Hclmhotz面(OHP)处的表面电荷密度σ_δ;讨论了双电层相互作用程度(ψ_d/ψ_δ)对胶体表面电位分布及其表面电荷密度的影响。     

Studies on Zero Point of Charge and Permanent Charge Density of Mg-Fe Hydrotalcite-like Compounds

The theoretical analysis on the zero point of charge (ZPC) and charge density of colloidal particle possessing permanent charges indicates that ZPC determined directly by means of potentiometric titration (PT) should be zero point of net charge (ZPNC) and the permanent charge density (σ_P) can be obtained from the adsorption amount of H⁺ and OH^-(Γ_OH--Γ_H+) at ZPNC. ZPNC does not change with the electrolyte concentration while the zero point of variable charge (ZPVC) changes with the electrolyte concentration. When σ_P is zero, ZPNC equals to ZPVC, and only under this condition is ZPC measured directly by PT equal to ZPVC. The relationship between ZPNC, ZNVC, σ_P, the variable charge density (σ_V)5 or the total net surface charge density (σ_T) with pH or electrolyte concentration is derived.     

Mg-Al-NO_3层状双金属氢氧化物电性质研究

采用电泳法和电势滴定法测定出不同电解质（LiCl,NaCl和KCl）溶液中Mg-Al- NO_3层状双金属氢氧化物（Mg-Al-NO_3LDH）颗粒的ξ电位、等电点、永久电荷密 度以及零电荷点等电化学物理量，探讨了电解质、pH和样品化学组成对Mg-Al- NO_3LDH电性质的影响，研究发现一价阳离子Li~+,Na~+,K~+对Mg-Al-NO_3LDH颗粒 的等电点有影响，电荷点依次增大，而等电点依次降低。     

On derivatives of surface charge curves of minerals

Surface titrations of minerals in aqueous electrolyte solutions are used as building blocks for surface complexation modelling. However, these potentiometric data may contain less model relevant information than previously and presently assumed. In the literature, derivative analyses have been applied to experimental surface charge versus pH curves and four or more pK values were extracted for goethite or aluminium oxide. Derivative analysis of specific surface charge versus pH curves calculated for various published model variants for goethite shows that not more than the net-zero proton surface charge condition can be extracted from computer generated data. Generated data can be produced in density and precision superior to experimental data, but yield only relatively little output from such derivative analysis compared to what has previously been extracted from derivatives of experimental data. For the generated goethite data and for all model variants only the point of zero could be extracted. For the various goethite model variants tested a nearly symmetrical peak appeared at the point of zero charge in the derivative curve. A different pattern could be obtained for generic models, for which two sites with unequal sites densities and different pK values were assumed. Variation of these parameters could result in derivatives of the charging curves with two maxima or one maximum and a broad tailing. In the literature, curves with features nearly identical to these generated curves have been interpreted by up to four pK values (i.e., four different sites within a 1-pK model). It is concluded that the interpretation of the generated data is in all cases hampered by the overwhelming electrostatic contributions to the free energy of proton ad/desorption. In no case except for the one-site 1-pK model was it possible to extract the input pK value(s) from the derivatives. Plausible explanations for the discrepancy between generated data and published experimental data are discussed.     

Study on electric property at interface of positive sol of magnesium aluminum hydroxide

The isoelectric point (IEP) and zero point of charge (ZPC) of magnesium aluminumhydroxide were studied by electrophoresis method,potentiometric titration method,and elemental analysis.Results showed that the charge of magnesium aluminum hydroxide was composed of variable charge and permanent positive charge.Because of the permanent positive charge,the IEP and ZPC obtained were higher than calculated.The IEP decreased and ZPC increased as X increased.     

The use of the pH at the point of zero charge for characterizing the properties of oxide hydroxides

The modern theoretical views on the point of zero charge of the oxide hydroxide surface are considered. Methods for determination of the pH of the point of zero charge and the use of this value to characterize the properties of oxide hydroxides are described. Examples of using the pH of the point of zero charge in studies of oxide anodes and amorphous oxide hydroxide sorbents are presented. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1029–1035, June, 1999.     

Point of zero charge/isoelectric point of exotic oxides: Tl2O3

The pristine point of zero charge of Tl(2)O(3) determined in the presence of NaNO(3) using the inert electrolyte titration method and confirmed by microelectrophoresis is at pH 7.9.     

Studies on zero point of charge and intrinsic ionization constant of Zn−Mg−Al hydrotalcite-like compounds

The zero point of charge (ZPC) and the intrinsic ionization constant ( % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr % 0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8 % frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaadaaakeaacqWG % lbWsdaqhaaWcbaGaeeyyaegabaGaeeyAaKMaeeOBa4MaeeiDaqhaaa % aa!304C! K_a^int K_{\rm a}^{{\rm int}} ) of Zn-Mg-Al hydrotalcite-like compounds (HTlc) with the general formula [(Zn,Mg) _{1- x} Al _x (OH) ₂] ^{x +} [(OH,Cl) _x] ^{x -} were determined by potentiometric titration (PT). The variation of the ZPC and % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr % 0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8 % frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaadaaakeaacqWG % lbWsdaqhaaWcbaGaeeyyaegabaGaeeyAaKMaeeOBa4MaeeiDaqhaaa % aa!304C! K_a^int K_{\rm a}^{{\rm int}} with xwas investigated. For the colloidal particles possessing permanent charges, the ZPC determined by the PT method is the zero point of net charge (ZPNC). The ZPNC ( pH _ZPNC) values were 9.63 {[Zn _0.27Mg _0.36Al _0.37 (OH) ₂]Cl _0.13 (OH) _0.24 }, 9.68 {[Zn _0.13Mg _0.58Al _0.29 (OH) ₂]Cl _0.12 (OH) _0.17 }, 9.67 {[Zn _0.17Mg _0.54Al _0.29 (OH) ₂]Cl _0.16 (OH) _0.12 },10.16 {[Zn _0.08Mg _0.67Al _0.25 (OH) ₂]Cl _0.17 (OH) _0.08}, 10.33 {[Zn _0.16Mg _0.60Al _0.24 (OH) ₂] Cl _0.16 (OH) _0.08} and 10.60 {[Zn _0.19Mg _0.60Al _0.21 (OH) ₂] Cl _0.15 (OH) _0.06}; the intrinsic ionization constants % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr % 0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8 % frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaadaaakeaacqqG % WbaCcqWGlbWsdaqhaaWcbaGaeeyyaeMaeeOmaidabaGaeeyAaKMaee % OBa4MaeeiDaqhaaaaa!329E! pK_a2^int {\rm p}K_{{\rm a2}}^{{\rm int}} of the same HTlc samples were 10.31, 10.44, 10.44, 11.02, 11.19 and 11.54. With decreasing x, ZPNC and % MathType!MTEF!2!1!+- % feaaeaart1ev0aaatCvAUfKttLearuavTnhis1MBaeXatLxBI9gBae % bbnrfifHhDYfgasaacH8srps0lbbf9q8WrFfeuY-Hhbbf9v8qqaqFr % 0xc9pk0xbba9q8WqFfea0-yr0RYxir-Jbba9q8aq0-yq-He9q8qqQ8 % frFve9Fve9Ff0dmeaabaqaciGacaGaaeqabaWaaeaadaaakeaacqWG % lbWsdaqhaaWcbaGaeeyyaeMaeeOmaidabaGaeeyAaKMaeeOBa4Maee % iDaqhaaaaa!3137! K_a2^int K_{{\rm a2}}^{{\rm int}} of HTlc increased, and the acidity of the HTlc samples decreased.     

Novel properties from experimental charge densities: an application to the zwitterionic neurotransmitter taurine

The charge distribution of taurine (2-aminoethane-sulfonic acid) is revisited by using an orbital-based method that describes the density in a fixed molecular orbital basis with variable orbital occupation numbers. A new neutron data set is also employed to explore whether this improves the deconvolution of thermal motion and charge density. A range of molecular properties that are novel for experimentally determined charge densities are computed, including Weinhold population analysis, Mayer bond orders, and local kinetic energy densities, in addition to charge topological analysis and quantum theory of atoms-in-molecules (QTAIM) integrated properties. The ease with which a distributed multipole analysis can be performed on the fitted density matrix makes it straightforward to compute molecular moments, the lattice energy, and the electrostatic interaction energies of molecules removed from the crystal. Results are compared with high-level (QCISD) gas-phase calculations and band structure calculations employing density functional theory. Finally, the avenues available for extending the range of molecular properties that can be calculated from experimental charge densities still further using this approach are discussed.     

Determination of Point of Zero Charge of Tunisian Kaolinites by Potentiometric and Mass Titration Methods

This paper deals with determining points of zero charge of natural and Na⁺‐saturated mineral kaolinites using two methods: (1) acid‐base potentiometric titration was employed to obtain the adsorption of H⁺ and OH^? on amphoteric surfaces in solutions of varying ionic strengths in order to determinate graphically the point of zero net proton charge (PZNPC) defined equally as point of zero salt effect (PZSE); (2) mass titration curve at different electrolyte concentrations in order to estimate PZNPCs by interpolation and to compare with those determined by potentiometric titrations. The two methods involved points of zero charge approximately similar for the two kaolinites between 6.5‐7.8, comparable to those reported previously and were in the range expected for these clay minerals. The comparison of potentiometric surface titration curves obtained at 25 °C and those published in the literature reveals significant discrepancies both in the shape and in the pH of PZNPCs values.