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.     

Electroabsorption study of metal-to-ligand charge transfer in an organic complex of iridium (III)

The dipole moment and polarizability changes have been determined from electroabsorption (EA) spectroscopy of solid films of fac tris(2-(phenyl)pyridinato,N,C^2′)iridium (III) [Ir(ppy)₃]. The maximum changes in the dipole moment |Δμ|_S=(5.0±0.5) D/f (f is the local field correction factor: 1.3–1.7) accompany ground state to the lowest singlet, and |Δμ|_T=(1.7±0.5) D/f ground state to the lowest triplet metal-to-ligand charge transfer (MLCT) excited states formation, while the average polarizability change ų/f² follows from the fitting procedure throughout the visible absorption spectrum range. The experimental values of |Δμ| as well as energy positions of the MLCT states correlate with the literature results of time-dependent density functional theory.     

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 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.     

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.     

A simple method for predicting the frequency of the infrared inactive carbonyl stretching mode in LM(CO)5 molecules with C4V symmetry

The paper presents a new method for predicting the frequency of the b₁ mode, which is infrared-inactive, in complexes of the type LM(CO)₅ belonging to C_4V point group. The method was based on the relation λ₃=λ₄+[(1−δ/δ)](λ₁−λ₂), where δ=(λ₁−λ₂)/(λ₁−λ₂+λ₃−λ₄), λ₁, λ₂, λ₃ and λ₄ are the λ parameters of the , , b₁ and e modes, respectively. For a large numbers of complexes of the type LM(CO)₅ the average value of δ was found to be 0.80, with a standard deviation of 0.02. With the use of average value of δ, the frequencies of b₁ mode were estimated. The result obtained indicated that there exists a rather good fit between observed and calculated frequencies, with a mean error of 2.7 cm⁻¹. In addition, it was shown that the δ parameter can be used as a criterion of the correct band assignment for the complexes understudy.     

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.     

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.     

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.     

Reaction force constant and projected force constants of vibrational modes along the path of an intramolecular proton transfer reaction

We have explored the relationships between the reaction force F(ξ), the reaction force constant κ(ξ) and the projected force constants of the intramolecular proton transfer HO−NS → ON−SH along the intrinsic reaction coordinate ξ. The structural changes and energetics associated with the reaction are analyzed in terms of the three regions defined by F(ξ): reactant, transition and product. The significance of the similarity between κ(ξ) and the variation of the force constant associated to the reaction coordinate mode, k_ξ(ξ), is discussed in detail.     

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.     

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.     

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.     

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.     

Electron transfer from cresols to N3, BrO2, ClO2, NO2 and SO4 radicals: correlation between rate constants and one-electron reduction potentials

The rate constants of oxidation of phenol and the cresol isomers to phenoxyl or methylphenoxyl radicals by inorganic radicals (R√) were studied in aqueous solutions at pH=5.8 and 11.5 using pulse radiolysis. The oxidation was due to electron transfer. Using the Marcus theory the electron transfer data were evaluated on the basis of the energy difference, ΔE, between the one-electron reduction potential of the inorganic couple and the mid-point potential of the half-cell of the phenoxyl/phenolate(phenol) couple. The standard reduction potentials of (o-CH₃PhO√/o-CH₃PhO⁻) and (m-CH₃PhO√/m-CH₃PhO⁻) couples (vs. NHE) were determined as 760 and 800 mV, respectively. The electron transfer was found to be diffusion limited when ΔE500 mV independently of the inorganic radical, type of phenol or pH. Between 0ΔE500 mV the rate constants showed good correlation with ΔE. The rate constants were dependent on the isomeric position of the methyl substituent.     

Thermogravimetric study on perovskite-like oxygen permeation ceramic membranes

The oxygen permeation properties of mixed-conducting ceramics SrFeCo_0.5O_3−δ (SFCO), Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCFO), La_0.2Sr_0.8Co_0.8Fe_0.2O_3−δ (LSCFO) and Ba_0.95Ca_0.05Co_0.8Fe_0.2O_3−δ (BCCFO) were studied by thermogravimetric method in the temperature range 600–900 °C. The results show that the oxygen adsorption rate constants k_a of all material are larger than oxygen desorption rate constants k_d and both k_a and k_d are not strongly dependent on temperature in the studied temperature range. The oxygen vacancy contents δ(N₂) and δ(O₂) in nitrogen and oxygen and their difference Δδ = δ(N₂) − δ(O₂) play an important role in determining the temperature behavior of oxygen permeation flux J_O2.     

FTIR studies of the CH3CN–BF3 complex in solid Ar, N2, and Xe: Matrix effects on vibrational spectra

FTIR spectra of the four isotopically substituted 1:1 complexes of acetonitrile and boron trifluoride were recorded in Ar, N₂ and Xe matrices. In Ar, previously unreported three vibrational modes of the complex were clearly observed. Several significant vibrational bands were also observed in N₂ and Xe. The observed frequency shifts on complexation, Δν, were qualitatively in good agreement with the computational results, which were calculated at the B3LYP/6-311++G(d,p) level using the optimized geometry of the C_3v eclipsed conformation. The observed magnitudes of Δν for most of the complex bands were larger than the calculated values. The BF₃ symmetric deformation mode is an exception. The observed frequency shits for this mode were smaller than the calculated values, especially in N₂. This suggests that even an inert matrix can significantly affect the vibrational spectrum of the complex.     

Impact of bulk and surface properties of some biocompatible hydrophobic polymers on the stability of methylene chloride-in-water mini-emulsions used to prepare nanoparticles by emulsification-solvent evaporation

The emulsifying and stabilizing ability of several hydrophobic (insoluble in water and soluble in volatile organic solvents) polymers, such as Eudragit RL, Eudragit RS, PLGA, PCL, and their mixtures, with regard to the methylene chloride (MC)-in-water mini-emulsions, has been compared to the viscosity of MC solutions and to the properties of adsorption and spread monolayers of these polymers.

Eudragits RS and RL contain 2.5 and 5 mol% of pendent cationic trimethylammonium (TMA) groups per 164 g/mol segments, whereas PLGA and PCL contain 1 and 2 polar carbonyl groups per 130 and 114 g/mol, respectively. The electrostatic attraction between the dipoles, formed by TMA groups and the condensed counter ions in the MC solutions, leads to the contraction of macromolecular coils of Eudragits, whereas the PLGA and PCL macromolecules, interacting by low polar carbonyl groups (with dipole moment μ = 2.7 D) retain more extended conformation in MC. This explains why the characteristic viscosities [η] of MC solutions are much lower for the former polymers (0.1 dL/g) with regard to PLGA and PCL solutions whose [η] is equal to 0.3 and 0.6 dL/g, respectively.

The ionization of TMA groups in contact with the water phase leads to the irreversible adsorption of Eudragits at the MC/water interface and to high decrease of the interfacial tension γ (down to 4 mN/m for the 5% MC solutions). Whereas PLGA and PCL possessing low polar carbonyl groups adsorb poorly at the MC/water interface exhibiting γ  28 mN/m. Higher stability of spread monolayers of Eudragits (π*  40 mN/m) with regard to PLGA and PCL (π* < 20 mN/m) correlates well with higher interfacial activity of the former with regard to the later. The higher surface potential ΔV of Eudragits (0.9 V) with regard to PLGA (0.3 V) and PCL (0.4 V) is explained by the formation of electric double layer (DL) by the former, whereas the later contribute to the ΔV only by cumulative dipole moments of carbonyl groups. The experimental values of surface potentials correlate well with the Gouy–Chapman model of the DL and the Helmholtz model of the monolayer.

The ensemble of experimental results leads to the conclusion that higher emulsifying and stabilizing ability of Eudragits with regard to PLGA and PCL is due to higher adsorption activity of the former which form the corona of polymeric chains with ionized TMA groups around the droplets. It can be postulated that Eudragit polymers have good surface active properties which may allow manufacturing of biocompatible nanoparticles by emulsification–solvent evaporation method without surfactants.     

α,β,γ,δ,ε,η-Bi2O3电子结构和光学性质的第一性原理研究

基于密度泛函理论的CASTEP模块研究了α, β, γ, δ, ε和η-Bi₂O₃晶型, 计算分析了其几何结构、 能带结构、 电子态密度和光学性质. 结果表明, α, ε和η相均为层状结构, 其中, α和ε相为单层—Bi—O—结构, 而η相为双层—Bi—O—结构; β, γ和δ相为—Bi_m—O_n—交错结构, 其中δ相交错尤为密集, 呈现导体特性. 各晶相的导带均由Bi 6p态构成, 价带由O_2p态起主导作用. 电势电位分析结果表明, 6种晶相价带电位均在H₂O/O₂之下, 具有强氧化能力, 与实验报道的光催化氧化能力大小顺序γ-Bi₂O₃>β-Bi₂O₃>α-Bi₂O₃>δ-Bi₂O₃一致, 而导带还原电位低于H₂/H₂O, 预测纯Bi₂O₃很难具备催化产氢能力. 光学性质分析发现, γ和δ相的起始响应波长较大, 说明其应具备红外激发的性质. 这些结果可为获得偏红外激发和较宽光谱响应的Bi₂O₃材料研究提供理论基础, 为研发和应用Bi₂O₃及其复合物提供重要的指导.