Effect of helix-coil transition on association behavior of both-ends hydrophobically-modified water-soluble polypeptide

Dodecyl and dodecanoyl groups (C12) are attached at the chain ends of poly[N⁵-(2-hydroxyethyl) l-glutamine] (PHEG), and association behavior of this both-ends hydrophobically modified water soluble polypeptide (C12-PHEG-C12) has been investigated by means of light scattering measurements. Water/ethylene glycol (EG) mixed solvents were used as selective solvent for PHEG block, and PHEG changed its structure from random-coil state to α-helix with increasing EG content in the mixed solvent (W_EG). When W_EG is less than 0.5, flower-like micelle with C12 associated core and PHEG corona in loop conformation was suggested to be formed. Increase of W_EG from 0.5 to 0.6 induced drastic increase of association number and size of the associate, in which many C12 associated cores may be connected by PHEG in bridge conformation. This structure change of associate is considered to be driven by the increase of helix content of PHEG with W_EG, which enhances the possibility to form bridge conformation because of its rigidity. Solution preparation method, i.e. order of addition of solvent, was found to influence the structure of associate, although its effect on the helix content of PHEG was negligible.     

Bond formation in electrosorbates—I correlation between the electrosorption valency and pauling's electronegativity for aqueous solutions

the electrosorption valency, γ, which can be determined experimentally, is discussed in dependence on system-specific parameters. For correlation purposes, values at the potential of zero charge, ?N, and small coverages, θ ≈ 0·1, only are used, and mixed adsorption and phase formation must be excluded. Experimental data for 50 ionic systems in aqueous solutions are summarized. For homonucleus ions, a simple correlation between the ratio, γ/z, and the electronegativity difference, |χ_M?χS|, is established. This relationship can be described using a reasonable assumption on the geometric factor, g, and Pauling's formula for the charge transfer in diatomic molecules. It follows from this simple model as well as from the experimental data that covalent adsorption (γ/z ≈ 1, ? λ/z ≈ 1), takes place in the range, |Δχ| < 0·5, but ionic adsorption (γ/z < 0·2, λ ≈ 0) occurs at |Δχ| > 1·0. For 0·5 < |Δχ| < 1·0 the partial charge transfer (0 < ?λ/z < 1) with the formation of polarized bonds is important.Heteronucleus ions are discussed qualitatively. The influence of the geometric factor seems to be dominant for these ions.     

Oxygen vacancy enhanced room temperature ferromagnetism in Ar+ ion irradiated WO3 films

Room-temperature ferromagnetism in WO₃ films was enhanced by 130 keV Ar⁺ ion irradiation. The X-ray diffraction (XRD) and Raman measurements not only confirmed the monoclinic phase of the irradiated WO₃ films, but also showed that oxygen vacancy (V_O) defects were formed. The analysis of photoluminescence spectra strongly reconfirmed the presence of oxygen vacancy. X-ray photoelectron spectroscopy (XPS) measurements revealed that the contents of V_O and induced W⁵⁺ ions increase with increasing irradiation fluence and rich W⁵⁺-V_O defect complexes in the irradiated WO₃ films were formed. Further, the magnetic measurements exhibited a 2-fold enhancement in the saturation magnetization at the largest fluence of 3 × 10¹⁶ ions/cm². At lower irradiation fluence, a bound magnetic polaron model was proposed to reveal the ferromagnetic exchange coupling resulting from overlapping of V_O⁺ and V_O⁺⁺ defect states, and 5d¹ states of W⁵⁺. At high irradiation fluence, the carrier concentration reaches 1.02 × 10²⁰/cm³ and carrier-mediated exchange interactions result in the film's ferromagnetism.     

Selective oxidation of methanol to dimethoxymethane over acid-modified V2O5/TiO2 catalysts

Selective oxidation of methanol to dimethoxymethane (DMM) was conducted in a fixed-bed reactor over an acid-modified V₂O₅/TiO₂ catalyst. The influence of the acid modification on its structure, redox and acidic properties, and catalytic performance for methanol oxidation were investigated. The results indicated that the content of vanadia in the catalyst exhibits a vital influence on the dispersion of vanadium species, while the acid modification can enhance its surface acidity. Proper amounts of the acid (W() = 15%) and V₂O₅ (W(V₂O₅) = 15%) components loaded in the acid-modified V₂O₅/TiO₂ catalyst are able to build a bi-functional circumstance that is favorable for the formation of DMM with high activity and selectivity. As a result, for the selective oxidation of methanol, the H₂SO₄-modified V₂O₅/TiO₂ catalyst gives a much higher DMM yield at 150 °C than the unmodified one.     

The pH response of the InP/liquid ammonia interface at 223 K: A pure nernstian behavior

Liquid ammonia (NH₃liq.) provides an original electrochemical environment onto semiconductors electrodes (SC). Its particular interest is that water influences can be neglected in opposition to a lot of non-aqueous other solvents. Fundamentals electrochemistries of the SC are related to the energy diagram of the interface. In this paper it is established into NH₃liq., on both types, on p- and n-InP by flat band potential (V_fb) measurements. The V_fb are determined over the whole range of pH that reaches 33 pH units in this non-aqueous solvent. InP exhibits a pure nernstian behavior with a specific 44 mV/pH slope at 223 K. This is particular compare to the “under nernstian” dependency, observed in water onto InP. The actual band positions are related to the initial chemical state of the InP surface, since oxide free surfaces and thin native oxide covered surfaces differ slightly. Reproducible contrasted results from the acid-base equilibrium, which is supported by the V_fb according to the pH, for singular interfacial chemistry. This aspect is confirmed by XPS measurements performed before and after InP immersion into NH₃liq. They establish the perfect stability of the initial chemical composition of the semiconducting surface in contact with NH₃liq. whatever its pH conditions. NH₃liq. appears as an inert solvent which is able to create an acid-base equilibrium onto InP surfaces. Each InP surface chemistry support its own linear V_fbvs. pH variation. In NH₃liq., the poor water control on the building of the Helmholtz layer is well shown by the perfect V_fb alignment position from the intermediated pH buffered solution obtained from the addition of tetraethyl ammonium hydroxide ((Et)₄N⁺,OH⁻) dissolved in water (20%).     

Relationship of coal extraction with free radicals and coal macerals

Extraction and de-ashing of coals with N-methyl pyrrolidone (NMP) under mild conditions has been reported recently. In this work, we have studied about a dozen American coals, along with some of their residues and extracts after treatment with NMP using in situ ESR (Electron Spin Resonance) spectroscopy of free radicals. At room temperature, N-₈ (number of free radials/g) decreases whereas the percentage extraction increases with atomic H/C of coals. Also N₈ for extract (residue) is lower (higher) than that for coals, ESR spectra of the extract exhibits only the single broad component and the weighted average of N₈ for the extract and the residue nearly equals that of the parent coal. These results have led to the hypothesis that the treatment with NMP is an extraction process in which exinites and to a lesser degree vitrinites are favored, whereas the inertinites are nearly rejected by NMP.     

Magnetocaloric effect in La1-xSrxCoO3 undergoing a second-order phase transition

We have prepared rhombohedral La_1-xSr_xCoO_3-δ (x?=?0.2–0.5) compounds with a mass density ρ?≈?5.5?g/cm³. Their magnetocaloric (MC) effect is studied via the magnetic-entropy change (ΔS_m) and relative cooling power (RCP), which are calculated from initial magnetization data recorded at different temperatures. Results reveal that the ΔS_m magnitude is maximum (ΔS_max) around the ferromagnetic-paramagnetic phase transition and dependent on both the applied-field (H) magnitude and Sr content (x). For H =?50?kOe, |ΔS_max| can be tuned in the range of 1.6–2.7?J/kg?K, corresponding to RCP values of 89–141?J/kg. Among the studied La_1-xSr_xCoO_3-δ samples, the samples with x?=?0.3–0.5 have the largest |ΔS_max| values. If combining these samples as MC blocks in refrigeration application, the working temperature range of a cooling device could range from 204 to ~280?K, with |ΔS_max| stable at ~2.6?J/kg?K and RCP ≈?198?J/kg. We have also assessed the phase-transition type and magnetic order and found La_1-xSr_xCoO_3-δ undergoing a second-order phase transition. Magnetic order tends to change from the long-range type to the short-range one when x varies from 0.2 to 0.5. This is in good agreement with the results obtained from the analysis of critical behavior.     

Phase Equilibria in the Alkali Fluoride-Uranium Tetrafluoride Fused Salt Systems: II, The Systems KF-UF4 and RbF-UF4

Mixtures of alkali fluorides with uranium tetra-fluoride are of potential importance in molten-salt reactors and in the reprocessing of nuclear fuels. In this paper detailed phase diagrams are presented for the binary systems KF-UF₄ and RbF-UF₄. Data for the determination of phase boundaries were obtained in large part by quenching after equilibration. Thermal analysis and visual observation were used as supplementary methods. Phase identifications were made by X-ray powder diffraction and by optical microscopy. In the system KF-UF₄ four compounds have been identified. Two of these, 3KF.UF₄ and 7KF.6UF₄, melt congruently at 957°C. and at 789°C., respectively. The compound 2KF UF₄ melts incongruently to 3KF.UF₄ and liquid at 755° C., and the compound KF.2UF₄ melts incongruently to UF₄ and liquid at 765° C. There are three eutectic points in the system: 15.0 mole % UF₄, 735° C.; 38.5 mole % UF₄, 740° C.; and 54.5 mole % UF₄, 735° C. The compound 2KF.UF4 decomposes during cooling to 3KF.UF₄ and 7KF 6UF₄ at 608° C. Two other compounds, KF 3UF₄ and KF.6UF₄, have been described by another investigator. One of these, KF 3UF₄, was not obtained at all in the present investigation. The other, KF.6UF₄, was not obtained under equilibrium conditions and was found only in KF-UF₄ mixtures that had been exposed to the atmosphere while molten. Seven solid compounds are present in the system RbF-UF₄. All of these melt incongruently with the exception of 3RbF.UF₄ and RbF-UF₄, which melt at 995° C. and at 735° C., respectively. The incongruently melting compounds and their melting points, peritectic compositions, and melting products are: 2RbF UF₄, 818°C., 38 mole % UF₄, 3RbF -UF₄+ liquid; 7RbF.6UF₄, 693° C., 44 mole % UF₄, RbF.UF₄+ liquid; 2RbF.3UF₄, 722° C., 56.5 mole % UF₄, RbF.3UF₄+ liquid; RbF. -3UF₄, 73O°C., 57 mole % UF₄, RbF.6UF₄+ liquid; and RbF.6UF₄, 832°C., 70.5 mole % UF₄, UF₄+ liquid. The three eutectic temperatures and compositions in the system are: 10.0 mole % UF₄, 710°C.; 43.5 mole % UF₄, 675°C.; and 55.0 mole % UF₄, 714°C.     

Effect of CeO2 on the thermoelectric properties of WO3-based ceramics

The thermoelectric properties of tungsten trioxide (WO₃) ceramics doped with cerium dioxide (CeO₂) were investigated. The results demonstrated that the addition of CeO₂ to WO₃ could promote the grain growth and the densification. The magnitude of the electrical conductivity (σ) and the absolute value of the Seebeck coefficient (|s|) depended strongly on the CeO₂ content. The sample doped with 2.0 mol% CeO₂ yielded higher σ and |s|, resulting in a significant increase in the power factor (σs²). In addition, the power factor value of all samples increased abruptly at high temperatures, which revealed that WO₃-based ceramics could have greater thermoelectric properties at high temperatures.     

Integrated instrumental analysis of soft brown coals

A method for the simultaneous determination of calorific value Q^r, ash yieldA^r and total water content W^r_t of soft brown coals is described. The method involves instrumental analysis of brown coal samples using neutron thermalization and gamma back-scattering techniques. Over 80 coal samples (1.1 kg) were analysed, having Q^rvalues up to 15.5 MJ kg^?1,A^r ranging from 3.6 to 76.1 wt% and W^r_t ranging from 11.4 to 61.7 wt%. A comparison of the results from the instrumental method with those of standard laboratory analyses is given, followed by a discussion of the accuracy of the method and of possible ways for improving it.     

Fe/N/C non-precious catalysts for PEM fuel cells: Influence of the structural parameters of pristine commercial carbon blacks on their activity for oxygen reduction

Fifteen commercial SRCC furnace carbon blacks of various grades, ranging from N1 to N9, were used as carbon supports in the preparation of Fe/N/C type electrocatalysts for the oxygen reduction reaction (ORR) in PEM fuel cell conditions. All catalysts were prepared by loading the various carbon grades with 0.2 wt.% Fe as iron acetate and heat-treating the resulting material at 950 °C in pure NH₃. This reaction provides the nitrogen content and the microporosity necessary to synthesize and host the Fe/N/C catalytic sites that perform ORR. The maximum catalytic activity (V_pr max) for each carbon grade was determined by optimizing pyrolysis time. The aim of this study is to determine which structural characteristics of the pristine carbon black are important for maximizing catalytic activity. Three structural parameters that influenced the catalytic site density on the carbon support were identified. They are: (i) the average particle diameter of the pristine carbon black, d_particle, available from BET area measurements; (ii) the amount of disordered phase which is proportional to W_D, the width at half maximum of the D peak in the Raman spectrum of the pristine carbon; and (iii) the mean size of the graphene layers characterizing the graphitic crystallites in the carbon black, L_a. The latter is available by Rietveld analysis of the XRD spectra of the pristine carbons. The best catalytic activities are obtained for the smallest d_particle, the largest W_D, and the largest L_a. Optimizing these three parameters maximizes the fraction of the pristine carbon black that becomes microporous upon reaction with NH₃ and, therefore, enables the formation of Fe/N/C catalytic sites. A FeN₂₊₂/C structure bridging two adjacent graphitic crystallites is proposed as a potential model for most of the catalytic sites present in such Fe/N/C type catalysts.     

Temperature-dependent aggregation of bio-surfactants in aqueous solutions of galactose and lactose: Volumetric and viscometric approach

Modulation in the aggregation behavior of bio-surfactants(bile salts), sodium cholate(NaC) and sodium deoxycholate(NaDC) in aqueous solutions of carbohydrates(galactose and lactose) have been investigated by measuring the density(ρ), speed of sound(u) and viscosity(η) of the mixtures at different temperatures293.15, 298.15, 303.15, 308.15 and 313.15 K. The density and speed of sound data have been used to calculate various volumetric and compressibility parameters such as apparent molar volume(V_φ), isentropic compressibility(κ_s), apparent molar adiabatic compression(κ_(s, φ)) to get a better insight into the micellization mechanism of bile salts. Further, the viscosity data have been studied in the light of relative viscosity(η_r) and viscous relaxation time(τ). Some derived parameters such as free volume(V_f), internal pressure(πi) and molar cohesive energy(MCE) of Na C and Na DC in aqueous solution of saccharides have also been calculated from viscosity data in conjunction with density and speed of sound values. All the calculated and derived parameters provide qualitative information regarding the nature of interactions i.e. solute–solute, solute–solvent and solvent–solvent in the solution.     

Application of multilinear regression analysis to the evaluation of the standard EMF of the hydrogen—silver/silver chloride cell in methanol + water mixtures over wide ranges of temperature and composition

The one-stage multilinear regression method previously applied to the analysis of emf data for aqueous electrochemical cells as a function of temperature and solute concentration has been extended to the analysis of emf data for the cell: Pt|H₂|HCl (m), CH₃OH(x), H₂O (1 ? x) | AgCl|Ag as a function of methanol mole fraction (x) as well as solute molality (m) and temperature. In this way discrepancies between various sets of data are revealed and the consistent set of data for the standard potential of the cell so obtained can be used for the evaluation of thermodynamic acid dissociation constants and standard reference pH values in this important, much studied mixed aqueous solvent system.     

Liposome Microencapsulation for the Surface Modification and Improved Entrapment of Cytochrome c for Targeted Delivery

In this study, we established a procedure based on the microencapsulation vesicle (MCV) method for preparing surface‐modified liposomes, using polyethylene glycol (PEG) and a site‐directed ligand, with high entrapment efficiency of cytochrome c (Cyt c). For preparing a water‐in‐oil (W/O) emulsion, egg phosphatidylcholine and cholesterol were dissolved in organic solvents (O phase) and emulsified by sonication with aqueous solution of Cyt c (W₁). Although the dispersion stability of the W₁/O emulsion was low when n‐hexane was used to dissolve the lipids in the O phase, it was substantially improved by using mixed solvents consisting of n‐hexane and other organic solvents, such as ethanol and dichloromethane (DCM). The W₁/O emulsion was then added to another water phase (W₂) to prepare the W₁/O/W₂ emulsion. PEG‐ and/or ligand‐modified lipids were introduced into the W₂ phase as external emulsifiers not only for stabilizing the W₁/O/W₂ emulsion but also for modifying the surface of liposomes obtained later. After solvent evaporation and extrusion for downsizing the liposomes, approximately 50% of Cyt c was encapsulated in the liposomes when the mixed solvent consisting of n‐hexane and DCM at a volume ratio of 75/25 was used in the O phase. Finally, the fluorescence‐labeled liposomes, with a peptide ligand having affinity to the vasculature in adipose tissue, were prepared by the MCV method and intravenously injected into mice. Confocal microscopy showed the substantial accumulation of these liposomes in the adipose tissue vessels. Taken together, the MCV technique, along with solvent optimization, could be useful for generating surface‐modified liposomes with high drug entrapment efficiency for targeted delivery.     

Lipid Vesicle Preparation Using W/O/W Multiple Emulsions Via Solvent Evaporation: The Effect of Emulsifiers on the Entrapment Yield of Hydrophilic Materials

We studied the effects of emulsifiers on the entrapment yields of a hydrophilic material, calcein, in lipid vesicles formed using the multiple emulsion method. The primary emulsion (W₁/O) was prepared via sonication while the secondary emulsification that produced the W₁/O/W₂ multiple emulsions was achieved using the microchannel (MC) emulsification technique. The emulsifiers used in the continuous (W₂) phase were Tween® 80, Pluronic® F68, and bovine serum albumin (BSA). Lipid vesicles formed via solvent evaporation of the multiple emulsion droplets had an average diameter of about 180 nm, similar to the size of the water droplets in the primary W₁/O emulsions. The entrapment yields of calcein increased with decreasing concentrations of Tween® 80 but decreased with decreasing concentrations of Pluronic® F68 and BSA. The effects of type and concentration of emulsifier were considered in relation to three possible mechanisms: (i) destabilization/solubilization of lipid bilayers by emulsifiers, (ii) reversed-micellar transport of W₁ contents from internal to external water phases through the O phase, and (iii) release of inner water (W₁) contents into the continuous (W₂) phase via the instability of W₁/O/W₂ and leakage of W₁ contents. Using the food grade emulsifier Tween® 80 at a low concentration of about 0.1 or 0.05 wt%, calcein as a model hydrophilic material could be efficiently entrapped (ca. 80%) in homogenously dispersed lipid vesicles.     

Photoinitiator system and water effects on C=C conversion and solubility of experimental etch-and-rinse dental adhesives

The purpose of this study was to determine the influence of the photoinitiator system and moisture condition on the degree of C=C conversion (DC), the water sorption (W_sp), and the solubility (W_sl) of experimental two-step etch-and-rinse dental adhesives. Different photoinitiator systems were added at 0.5 mol% to an experimental adhesive blend (55:45 wt% Bis-GMA:HEMA), defining the experimental groups: camphorquinone (CQ)+ethyl-4-dimethylaminobenzoate (EDMAB), 9,10-phenanthrenequinone (PQ), PQ+EDMAB, diphenyl(2,4,6-trimethylbenzoyl)phosphine oxide (TPO), and phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide (BAPO). The adhesives were tested in two moisture conditions: neat and wet (with the addition of 10 wt% D₂O). The DC (n=6) was evaluated by Fourier-transformed infrared spectroscopy (FTIR). W_sp and W_sl were determined (n=10) after successive weighting procedures. Data were submitted to two-way ANOVA and Tukey׳s post hoc test (α=0.05). Pearson׳s correlation tests were used to analyze the correlation between DC and W_sp or W_sl. TPO and BAPO presented the highest DC in the neat condition while CQ+EDMAB presented the highest in the wet condition. W_sp and W_sl were both dependent on the photoinitiator system and moisture condition. PQ–based materials presented the highest W_sp and W_sl in both neat and wet conditions. Pearson׳s tests were not able to detect any significant correlation between DC and W_sp or DC and W_sl. Within the limitations of the present study, it can be concluded that the photoinitiator system and moisture condition influenced the DC, W_sp, and W_sl of experimental two-step etch-and-rinse adhesives.     

Optimization of Formulation Variables to Increase Antigen Entrapment in PLGA Particles

Efficient antigen entrapment is a key factor in preparation of poly (lactide-co-glycolide) acid (PLGA) vaccine formulations when the antigen is of short supply. This study presents a systematic approach in the testing of formulation variables with the objective to increase antigen entrapment in particles when the antigen stock concentration was low. Some of the experimental variables tested were poly (vinyl) alcohol (PVA) concentration in the inner (W₁) and outer (W₂) aqueous phase, W₁/oil (O) phase ratio and choice of organic solvent. The double emulsion solvent evaporation technique was applied to prepare PLGA particles with sonication as the emulsifying force. To measure antigen entrapment efficiency, the antigen (bovine serum albumin, BSA) was isotope labeled with ¹²⁵iodine (¹²⁵I). Our results demonstrated that a low PVA concentration in the inner aqueous (W₁) phase was beneficial to achieve a high encapsulation efficiency of antigen. On the contrary, in the outer aqueous (W₂) phase, a high PVA concentration favored antigen entrapment. We also demonstrated that decreasing the W₁ to O/polymer ratio contributed to increased entrapment efficiency. Testing different organic solvents (ethyl acetate, dichloromethane and chloroform), either alone or in combination, revealed that using chloroform as solvent resulted in the highest encapsulation of antigen and the highest production yield. Some of the results presented in this work are in disagreement with well-established formulation variables from previous studies.