Survey of ligand field parameters of strong field d complexes obtained from the g matrix

Using a newly proposed approach involving an internally consistent set of equations, the ligand field parameters Δ/ξ, V/ξ and k are obtained from literature values of the g matrix for strong field d⁵ systems of various conformations in which |Δ/ξ|≤10. Qualitative analysis of the observed results is done using the Angular Overlap Model, AOM.     

Transport phenomenon as a function of counter and co-ions in solution: chronopotentiometric behavior of anion exchange membrane in different aqueous electrolyte solutions

Anion exchange membrane has been investigated in different electrolyte solutions by chronopotentiometry to explore the influence of co-ion and counterion of the exchange group of the membrane, on the transport phenomena. Chloride, nitrate, sulfate and acetate in sodium salts were used as counterions and sodium, potassium, calcium and ammonium in chloride salts were used as co-ions. The membrane showed a potential drop (E₀) in all these electrolytes when a constant current was applied across it, which remained constant for a period less than τ, called the transition time and rose gradually to a maximum (E_max) value. The parameters such as τ, E₀ and E_max and the potential jump (ΔE) and τ and the inflection zone (Δt) along the time axis have been measured and compared at an applied current density (I) of 10 mA cm⁻² in 10 mM solutions. The values of τ^1/2/z_A[A₀] or τ^1/2/z_C[C₀], with or , E₀ and ΔE with or (where r_A and r_C are the ionic radii of counter and co-ions, respectively) have been correlated. Permselectivity (P) and transference number of the membrane with respect to each one of the above electrolytes have been evaluated and discussed.     

The formula of anchoring energy for a nematic liquid crystal

The interface energy for a nematic liquid crystal (NLC) is considered as the sum of potential energy between LC molecules and molecules of the substrate surface, and a formula for anchoring energy is derived by elementary principles. The anchoring energy for a NLC should have two terms, the first term is the same as the Rapini-Papoular expression, the second is related to the normal of interface and resultes from the biaxial property of a NLC induced by interface. Hence there are two anchoring coefficients, W₁ and W₂. We demonstrate that W₁ is equal to the tilt angle strength A_θ, and W₂ corresponds to the difference between A_θ and the azimuthal strength A_ϕ. Thus A_θ-A_ϕ is due to the biaxial property of the NLC near the interface. Applying this formula to the twisted NLC cell, we discuss the threshold and saturation field, as well as the maximal tilt angel θ_m with respect to A_θ/A_ϕ. Previously proposed formulae are discussed from our point view.     

Enantioseparation of various amino acid derivatives on a quinine based chiral anion-exchange selector at variable temperature conditions. Influence of structural parameters of the analytes on the apparent retention and enantioseparation characteristics

The influence of temperature on the performance of an enantioselective anion-exchange type chiral selector (SO) was systematically investigated. The resolution of the enantiomers of 23 N-acylated amino acids (selectands, SAs) on a covalently immobilized quinine tert.-butylcarbamate chiral stationary phase (CSP) was studied under linear chromatographic conditions over a temperature range of 0–85 °C with hydro–organic buffers (pH_a 6.0) as mobile phases. The apparent enantioseparation factors increased considerably at low column temperatures, indicating that enthalpic contributions are the dominating thermodynamic driving force for chiral recognition for all investigated SAs. Retention factors gave non-linear van’t Hoff plots, while the corresponding apparent enantioseparation factors showed linear van’t Hoff behavior. Correlations between magnitude and sign of the relative thermodynamic parameters of enantioselective adsorption (ΔΔG, ΔΔH and ΔΔS) and specific structural features of the analytes, i.e., steric and electronic nature of the various side chains and the N-acyl groups, are discussed with the aim to rationalize their possible contributions to the overall chiral recognition.     

The lipid-mediated hypothesis of fumonisin B1 toxicodynamics tested in model membranes

The disruption of lipidic metabolism was considered a good candidate to explain FB1 toxicity mechanism. In the present work we investigated molecular organizational changes induced by FB1–biomembrane interaction possibly involved in mycotoxic effects.

FB1 was self-aggregated with a critical micellar concentration of 1.97 mM. FB1 (0–81.4 μM), decreased in a dose-dependent manner, the fluorescence anisotropy of TMA-DPH (from 0.349 ± 0.003 to 0.1720 ± 0.0035) in dpPC bilayers, whilst no differences were registered with DPH. At 5.6 μM in the subphase, FB1 increased the lateral surface pressure (π) of a Langmuir film to an extent that depended on the monolayer composition (Δπ_{dpPC:DOTAP 3:1} > Δπ_dpPC:dpPA3:1 > Δπ_dpPC), the molecular packing (Δπ decreased linearly as a function of the initial π) and the subphase pH (Δπ_{pH 2.6} > Δπ_{pH 7.4} and maximal π allowing the drug penetration π_cut-off was 34.3 and 27.7 mN/m at pH 2.63 and 7.4, respectively). FB1 increased the surface potential of dpPC and dpPC:DOTAP monolayers and decreased that of dpPC:dpPA. This suggested that FB1 acquired different orientations and/or foldings depending on the surface electrostatics and the toxin charge state. Moreover, FB1–lipid interactions were transduced into long-range effects at the mesoscopic level affecting the lipidic self-separated lateral domains shape and density.     

On the non-symmetric planar aligned NLC cell

The planar aligned nematic liquid crystal cell with different anchoring for the two substrates (i.e. a non-symmetric NLC cell) is investigated by an analytical method. We deduce the basic equations and the boundary conditions of the tilt angle θ of the LC director. Expressions for threshold and saturation magnetic field are obtained, and numerical results of these two quantities with variation in anchoring parameters of the two substrates are given. A symmetry breaking parameter Δ is introduced and the relations between Δ and applied field, as well as the two sets of anchoring parameters are discussed in detail. A feasible experimental plan for measurement of anchoring strengths of a series of different substrates is proposed.     

Broadband dielectric studies of weakly polar and non-polar liquid crystals

Complex dielectric permittivities, for two orientations of the director n, parallel (E || n) and perpendicular (E ⊥ n) to the probing electric field E, of the weakly polar liquid crystals (LCs) 4,4'-dihexylazoxybenzene (D6AOB) and 4,4'-diheptylazoxybenzene (D7AOB) as well as the non-polar LC diheptylazobenzene (D7AB) have been measured in the frequency range 75 kHz to 1 GHz. The measurements were performed in the nematic, smectic and isotropic phases of the LCs. The dielectric anisotropies Δε (=ε_||-ε_⊥) obtained from the values of dielectric permittivities at 100 kHz in the nematic phase were found to increase with decreasing temperature. However, for the DnAOBs, the Δε values are somewhat smaller than that for D7AB which does not have a permanent dipole moment. In the nematic phase two molecular relaxation processes were observed for both DnAOBs in each of the orientations—parallel and perpendicular. The four processes merge into two separate processes in the isotropic phase. For D7AB no orientational relaxations were observed in the experimental frequency range.     

The optical properties of polymethylmethacrylate polymer dispersed liquid crystals

The effect of the addition of polymer liquid crystals as dispersed molecules to polymethylmethacrylate (PMMA) on the optical properties in the UV-visible and near infrared regions is investigated. From transmission, absorption and reflection spectra the absorption coefficient (ω) and refractive index (n) at angular frequency of radiation (ω) have been calculated at room temperature. The values of the optical band gap (E_opt) have been obtained from the direct allowed transitions in k-space. The width of the tails of localized states in the band gap (ΔE) was evaluated from Urbach edges. Both the parameters (E_opt) and (ΔE) vary with the mixing ratio of dispersed liquid crystals.     

Anomalous electric birefringence behavior of sonicated DNA fragments as observed in reversing-pulse transients and steady-state sign reversal: a multicomponent approach

Anomalous electric birefringence signals of a sonicated and column-fractionated medium-size calf thymus DNA sample (bp  =  570) in Na⁺ solutions were measured at 7 °C. The reversing-pulse electric birefringence (RPEB) signal pattern was theoretically calculated in the low electric field region for two axially symmetric models coexisting in equilibrium in solution. The RPEB theory is based on the electric dipole moment due to ion-fluctuation along the longitudinal direction and the electric polarizability anisotropy (Δ′), together with various electric and optical parameters assigned to the models. An analytical method was developed for the steady-state birefringence of the two-component system in a wide range of electric fields. The NaDNA samples exhibit complex RPEB patterns mixed with negative- and positive-going profiles. An experimental RPEB signal of NaDNA at an absorbance (A₂₆₀) of 8 was fitted to theoretical curve at weak electric fields. The anomalous RPEB signal was attributed to the component 2, which shows a dip in the buildup and another in the reverse processes with a positive sign and a larger relaxation time. For the component 1, a normal DNA profile with negative sign is associated with a narrow dip in the reverse and a faster relaxation time in the decay signal. The field-strength dependence of observed steady-state birefringence δ(∞) could be fitted for NaDNA at A₂₆₀  =  8 by the SUSID orientation function with saturated ionic and electronic moments. An apparent positive maximum and the sign reversal in δ(∞) at weak electric fields is an interplay between the positive component 2 with positive optical factor Δg and negative Δ′ and the negative component 1 with negative Δg and positive Δ′. Possible conformation of two DNA components involved in solution was estimated.     

Surface properties of ω-perfluorooctyl-alkyl polyacrylates: odd–even effect

A series of ω-perfluorooctyl-alkyl polyacrylates has been prepared and analysed. The odd–even effect, already observed in the case of liquid crystalline polymers has been exhibited for perfluorinated ones. Values of the contact angles to advanced (θ_a), with withdrawal (θ_r), as well as the contact angle hysteresis (Δθ) of various ω-perfluorooctyl-alkyl polyacrylates in water at 20 °C are described. Contrary to the advancing contact angle which is almost independent of spacer length, the receding one varies strongly with it.     

The melt elastic behavior of polypropylene/glass bead composites in capillary flow

The melt extrudate swell and entry pressure losses are important characteristics of elastic properties during die extrusion of polymeric fluids. They are usually expressed with die-swell ratio (B) and entry pressure drop (ΔP_o). In the present paper, the die-swell behavior and entrance pressure drop of a polypropylene (PP) filled with A-glass beads were investigated by using a Rosand capillary rheometer to identify the effects of the filler contents and extrusion rate on the elastic behavior of the sample melts. The experiments were carried out under the conditions with an apparent shear rate range of 50–10⁴ s⁻¹ and a temperature of 190 °C. The results showed that B increased nonlinearly with increasing shear rate at the wall (γ_w), and increased linearly with the increase of shear stress at the wall (τ_w). With the increase of the volume fraction of the fillers B decreased nonlinearly. Similarly, the entry pressure drop increased linearly with the increase of τ_w, whereas the influence of the filler concentration on ΔP_o was insignificant in this case. Furthermore, B increased as a linear function of ΔP_o, and extension stress (σ_e) increased nonlinearly with increasing γ_w.     

Determination of concentration-dependent transport coefficients in nanofiltration: Defining an optimal set of coefficients

The currently used equation for solute transport in nanofiltration contains two parameters (ω and 1 – σ) that may be concentration-dependent. A force balance equation allows interpretation of these parameters (as well as L_p) in terms of distribution and friction coefficients, as was demonstrated for a neutral solute and a single 1:1 salt. It is generally assumed in model calculations that it is the distribution coefficient that determines the concentration dependence of ω and 1 – σ. This suggests that a more practically convenient form of the equation may be proposed, in which only one concentration-dependent parameter, ω, appears, while the other is replaced with the ratio of the two, A, which has the meaning of the membrane Peclét number divided by the volume flux and may be assumed to be constant. This may facilitate the analysis of flux–rejection curves and parameter evaluation including concentration dependence, which is a crucial and unavoidable step towards predictive NF modeling. The direct connection between transport parameters and distribution coefficients also suggests that experimentally measured concentration dependence may help to discriminate between different exclusion mechanisms. An approximate analysis based on the connection between A and solute–water friction shows that for presently used NF membranes and realistic fluxes the expected contribution of convection to solute flow cannot become dominant so that the limiting value for salt rejection, R = σ, cannot be reached.     

Kinetic analysis of thermogravimetric data obtained under linear temperature programming—a method based on calculations of the temperature integral by interpolation

A new technique, called interpolation method, with general application in the kinetic analysis of processes studied by thermogravimetry (TG) under linear temperature programming is developed. It is based on the linear relationship, with slope 1, between log g() and log I(γ, θ) for the appropriate kinetic function, where I(γ, θ) is the normalized temperature integral, θ the normalized temperature (θ=T/T₀) and γ a dimensionless activation energy (γ=E/RT₀). Values of log I(γ, θ) are calculated by linear interpolations in a pre-built table. This method can easily be programmed and implemented in a personal computer, where the results (kinetic parameters and quality of regressions for the kinetic functions considered) are typically obtained in a very short time. The method is validated by analyzing different simulated thermogravimetric curves and comparing the results with those determined with some classic methods taken from the literature. In addition, the results are compared with the values obtained by a similar method, also developed and explained in this paper, which involves the evaluation of all the values of the temperature integral by numerical integration, therefore, demanding a much larger calculation time. The interpolation method is found to be more accurate than other published methods, particularly in the case of thermogravimetric curves corresponding to processes with low activation energies. The results obtained are always similar to those determined by the integration method, which is taken as reference. Application of the technique to experimental data for various types of reactions shows that the results are in agreement with the published parameters and kinetic laws.     

Critical coagulation concentration for a suspension of cation-absorptive biocolloids

Critical coagulation concentration (CCC) of a biocolloidal suspension is investigated theoretically by taking into account the influences of cationic absorption in particulate membrane phase, variation in dielectric constant, size of charged species and nonuniform distribution of fixed membrane groups. Here, an increase in both valence and effective radius of the original functional group (OFG) via absorption of electrolyte cation(s) is especially considered. The simulated results indicate that stronger membrane electricity yields a larger electrostatic repulsion and a higher potential energy, which generates a higher CCC. A lower CCC can be resulted from a larger (1) cation-functional group complex (CFGC) for a fixed difference between the radius of CFGC and that of OFG, Δ, (2) number of OFG(s) involved in the formation of a CFGC, (3) Δ for a positively charged CFGC, (4) dielectric constant of main membrane phase, in general, (5) membrane thickness for a constant amount of space-average functional groups, and (6) effective radius of anions. CCC decreases with the following parameters: (1) Δ for a negatively charged CFGC, (2) equilibrium constant of the reaction of cationic absorption, (3) nonuniform feature index of fixed groups, and (4) effective radius of cations.     

Reducing power losses caused by ionic shortcut currents in reverse electrodialysis stacks by a validated model

Both in electrodialysis and in reverse electrodialysis ionic shortcut currents through feed and drain channels cause a considerable loss in efficiency. Model calculations based on an equivalent electric system of a reverse electrodialysis stack reveal that the effect of these salt bridges could be reduced via a proper stack design. The critical parameters which are to be optimized are ρ/r and R/r, where ρ is the lateral resistance along the spacers, R is the resistance of the feed and drain channels between two adjacent cells, and r is the internal resistance of a cell. Because these two parameters are dimensionless, different stacks can be easily compared. The model is validated with two experimental stacks differing in membrane type and spacer thickness, one with large ionic shortcut currents and one where this effect is less. The loss in efficiency decreased from 25 to 5% for a well-designed stack. The loss of efficiency in reverse electrodialysis and in electrodialysis can be reduced with the aid of the design parameters presented in this paper.     

宏观均相多孔电极电化学阻抗谱基础

电化学阻抗谱可用于诊断多孔电极内电荷转移反应,即界面电荷集聚和电荷传导,以及反应物质输运。本文采用复相量方法,在同态假设条件下,重新推演多孔电极阻抗谱模型,厘清传统多孔电极阻抗谱模型中的模糊性表述。(1) 定义多孔电极表征输入参数,包括电极基体电子电导率σ₁ 、电解质离子电导率σ₂、界面电荷传递电导率g_ct、单位面积界面电容C、固相扩散系数D、速度常数k、电极厚度d、特征孔深L_p 和单位体积表面积S_c;(2) 解析阻抗谱特征输出参数,包括场扩散常数K,特征频率ω₀、ω₁、ω₂、ω₃和 ω_max,它们分别相关于界面传导反应、有限场扩散、氧化还原反应、孔内扩散和最小特征孔尺寸,以及分别对应于从传导到扩散和从扩散到饱和的转折频率f_k1 和f_k2;(3) 当参数X和Z同时变化时(X = σ₁和Z = d,S_c,L_p,C,g_ct,D,k),通过阻抗谱特征参数的演变规律,分析了电荷转移反应中X和Ζ参数耦合竞争;(4)为深入分析电荷转移反应中参数X和Z的耦合竞争,引入了分叉频率f_XZ和f_ZX 。f_XZ和f_ZX所处位置可以用于表征参数X和Z影响电荷转移反应的深度和广度。当分叉频率f_XZ和f_ZX不存在时,表明电荷转移反应中参数X和Z在全频率范围内存在耦合竞争。总之,借助于特征频率和分叉频率,本文一方面研究了动力学参数和微观结构参数对多孔电极中电荷转移反应的影响,另一方面分析谱图的变化及其背后的阻抗谱特征演化规律。本文研究结果可为阻抗谱的系统仿真和辨识提供理论基础,可为多孔电极内电荷转移反应的竞争分析提供技术支撑,还可为电化学储能系统的优化设计提供诊断工具。     

Evaluation of antitubercular drug insertion into preformed dipalmitoylphosphatidylcholine monolayers

Insertion profiles of antitubercular drugs isoniazid (INH), rifampicin (RFM) and ethambutol (ETH) into dipalmitoylphosphatidylcholine (DPPC) membrane models were evaluated by Langmuir monolayer technique. Maximum drug insertion into DPPC monolayer was observed with rifampicin with a surface pressure increase (Δπ_max) in the range of 21–33 mN/m depending upon rifampicin concentration. Isoniazid had minimal insertion resulting in a lower Δπ_max of about 2–3 mN/m, suggestive of minimal interactions between INH and DPPC. Ethambutol surface pressure increment on insertion resulted in an intermediate rise in the Δπ_max (6–10 mN/m). Antitubercular drug combination in the ratio of 2 mM:0.7 mM:4.5 mM for INH:RFM:ETH, attained Δπ_max between 25 and 33 mN/m. Insertion profiles similar to rifampicin were exhibited by the antitubercular drug mixture suggestive of predominant rifampicin insertion into the DPPC monolayer. The extent of drug insertion into the DPPC monolayer is suggestive of the drug penetration potential into biological membranes in vivo. Higher RFM Δπ_max is suggestive of excellent cell membrane penetration, which explains broad reach of the drug to all the organs including the cerebrospinal fluid while lower Δπ_max of INH suggests poor membrane penetration restricting the entry of the drug in different biological membranes. DPPC membrane destabilization was observed at higher antitubercular drug concentrations indicated by the negative slopes of the surface pressure–time curves. This may correlate with the dose related toxic effects observed in tuberculosis affected patients. Drug insertion studies offer a potential tool in understanding the pharmacotoxicological behavior of the various pharmacological agents.     

Interaction of Bauhinia monandra lectin (BmoLL) with lipid monolayers

The interfacial behavior of the hypoglycemia lectin BmoLL purified from the leaves of Bauhinia monandra, and its ability to interact with lipid monolayers has been studied by surface tension (γ) measurements. The results of these experiments revealed that in the solution concentration range comprised between 0.2 and 1.0 mg/ml, there was an extremely pronounced increase in the BmoLL adsorption at the interface with the air phase. This adsorption at the higher studied BmoLL concentrations gave rise to a more gradual increase in the surface pressure (π = γ₀−γ). The results showed also that the surface pressure of adsorbed films was pH dependent and it substantially increased at low pHs (between pH 4.0 and pH 2.5). Independently carried out ξ potential measurements demonstrated that BmoLL was negatively charged at all pHs and borne the highest charge at the pH around 5.5. The penetrant ability of BmoLL into the two different in chemical nature monolayers: (dioleoylphosphatidylcholine and octadecylamine) have been assessed measuring Δπ increments at constant area. It was observed that, whereas the monolayers of either pure dioleoylphosphatidylcholine (DOPC) or pure octadecylamine (ODA) stimulated BmoLL adsorption, the lectin adsorption within their mixtures strongly depended on both the content of positively charged octadecylamine in a mixture and on the monolayer compressibility. These findings are discussed in terms of both the electrostatic interaction involved in adsorption of BmoLL and of changes in monolayer compressibilities brought up by the addition of ODA molecules to the phospholipid. The relevance of this work to liposome preparations is indicated in the concluding remarks.     

Structural ordering and molecular-optical properties of a discotic liquid crystal (Colho)

The infrared absorbance and the dispersion of the refractive indices in the region 0.49-0.63 µm of the discotic mesogen 2,3,6,7,10,11-hexaheptyloxytriphenylene were studied for the columnar and isotropic phases. The temperature dependence of the orientational order parameter S and the local field parameters of a light wave acting on the sample have been evaluated. It is shown that the mixing of molecular excitations modifies the behaviour of S as a function of temperature. Molecular-optical properties of the triphenylene derivative, such as the anisotropy of the polarizability, Δγ and the mean polarizability, &gammatilde; were investigated on the basis of the generalized Lorenz-Lorentz relation for uniaxial liquid crystals. The experimentally observed changes of these properties in the columnar phase seem to be affected by the induction mechanism of the change in the molecular polarizability with increasing S.