Large Difference In Polarity Research Articles

Lithium-Ion Batteries Assembled with Electrospun Hybrid Polymer Membrane Containing Reactive Silica Nanoparticles

Lithium-ion batteries have been rapidly expanding in portable electronic devices, electric vehicles (EVs) and energy storage systems. In lithium-ion batteries, a separator is a critical component which prevents physical contact of the positive and negative electrodes while permitting free ionic transport within the cell. Most of the separators currently used in lithium-ion batteries are based on microporous polyolefin membranes. Although these separators offer excellent mechanical strength and chemical stability, they shrink, soften and even melt at high temperature, which cause short circuiting between electrodes. Furthermore, the large difference in polarity between the non-polar polyolefin separator and the polar organic electrolyte leads to poor wettability. As a result, there is a high resistance when the pores in the separator are not completely filled with liquid electrolyte. In our previous studies, we synthesized silica nanoparticles with vinyl groups, which permitted the surface reaction with vinyl monomers by radical polymerization [1-3]. With the goal of developing high performance separators with high thermal stability, good transport properties and enhanced wettability for non-aqueous liquid electrolytes, we prepared electrospun hybrid polymer membrane based on polyacrylonitrile (PAN) and reactive SiO2 nanoparticles. Due to the presence of reactive silica particles, it could be thermally cross-linked, resulting in good thermal stability and improved wettability for liquid electrolyte. Using the cross-linked electrospun hybrid polymer membranes, we assembled lithium-ion cell composed of carbon anode and LiNi0.6Co0.2Mn0.2O2 cathode. The cycling performances of the cells with cross-linked hybrid polymer membrane were evaluated, and the results were compared to those obtained with a pristine PE separator.

Multiplex liquid chromatography-tandem mass spectrometry assay for simultaneous therapeutic drug monitoring of ribavirin, boceprevir, and telaprevir.

New directly acting antivirals (DAAs) that inhibit hepatitis C virus (HCV) replication are increasingly used for the treatment of chronic hepatitis C. A marked pharmacokinetic variability and a high potential for drug-drug interactions between DAAs and numerous drug classes have been identified. In addition, ribavirin (RBV), commonly associated with hemolytic anemia, often requires dose adjustment, advocating for therapeutic drug monitoring (TDM) in patients under combined antiviral therapy. However, an assay for the simultaneous analysis of RBV and DAAs constitutes an analytical challenge because of the large differences in polarity among these drugs, ranging from hydrophilic (RBV) to highly lipophilic (telaprevir [TVR]). Moreover, TVR is characterized by erratic behavior on standard octadecyl-based reversed-phase column chromatography and must be separated from VRT-127394, its inactive C-21 epimer metabolite. We have developed a convenient assay employing simple plasma protein precipitation, followed by high-performance liquid chromatography coupled to tandem mass spectrometry (HPLC-MS/MS) for the simultaneous determination of levels of RBV, boceprevir, and TVR, as well as its metabolite VRT-127394, in plasma. This new, simple, rapid, and robust HPLC-MS/MS assay offers an efficient method of real-time TDM aimed at maximizing efficacy while minimizing the toxicity of antiviral therapy.

Mitsunobu Reaction of 1,2,3‐NH‐Triazoles: A Regio‐ and Stereoselective Approach to Functionalized Triazole Derivatives

Mitsunobu Reaction of 1,2,3‐NH‐Triazoles: A Regio‐ and Stereoselective Approach to Functionalized Triazole Derivatives

Tratamento de superfície de tubos de poliamida 11 com chama para deposição de revestimento hidrofílico biomédico

O processo para obtenção de uma camada polimérica hidrofílica sobre um componente polimérico pode ser basicamente dividido em: tratamento de superfície do substrato, aplicação e cura do revestimento. O tratamento de superfície se faz necessário em função da grande diferença de polaridade comumente apresentada entre os materiais que compõem este conjunto e da baixa energia livre de superfície inerente aos principais materiais utilizados como substrato, fatores estes que dificultam a adesão entre eles. Neste trabalho foi avaliada a influência da técnica de tratamento de superfície através de exposição à chama sobre a tentativa de aumento da energia livre de superfície de tubos de poliamida 11. Amostras foram submetidas ao tratamento durante 5, 10, 20, 30 e 60 segundos, e posteriormente caracterizadas por goniometria, microscopia eletrônica de varredura, espectroscopia de infravermelho e resistência ao risco da camada depositada. Amostras não tratadas foram analisadas como parâmetro de controle das modificações. Os resultados mostraram um aumento da molhabilidade e rugosidade da superfície, além de uma melhoria na adesão da camada hidrofílica após o tratamento.

First-principles studies of a two-dimensional electron gas at the interface in ferroelectric oxide heterostructures

The discovery of a two-dimensional electron gas (2DEG) at the interface between two insulating oxides has recently stimulated intense research activity in this field. The 2DEG has unique properties that are promising for applications in all-oxide electronic devices. For such applications it is desirable to have the ability to control 2DEG properties by external stimulus. Here we employ first-principles calculations to investigate ${\text{KNbO}}_{3}/A{\text{TiO}}_{3}(001)$ ($A=\text{Sr}$, Pb, and Ba) heterostructures where perovskites ferroelectrics, ${\text{KNbO}}_{3}$, ${\text{PbTiO}}_{3}$, and ${\text{BaTiO}}_{3}$, are used as oxide constituents to create the interface 2DEG. Our results suggest that the polar ${({\text{NbO}}_{2})}^{+}/{(A\text{O})}^{0}$ interface in these heretostructures favors the formation of 2DEG similar to that at the ${(\text{LaO})}^{+}/{({\text{TiO}}_{2})}^{0}$ interface in a ${\text{LaAlO}}_{3}/{\text{SrTiO}}_{3}$ heterostructure. We predict that the presence of spontaneous ferroelectric polarization which can be switched between two stable states allows modulations of the carrier density and consequently the conductivity of the 2DEG. The effect occurs due to the screening charge at the interface that counteracts the depolarizing electric field and depends on polarization orientation. The magnitude of the effect of polarization on the 2DEG properties strongly depends on contrast between polarizations of the two constituents of the heterostructure: the larger is the difference in the two polarizations, the bigger is the effect. For a sufficiently large polarization difference, we predict a metal-insulator transition at the interface driven by polarization reversal. This behavior is found for the ${\text{KNbO}}_{3}/{\text{PbTiO}}_{3}$ interface and for the ${\text{KNbO}}_{3}/{\text{BaTiO}}_{3}$ interface when polarizations of ${\text{KNbO}}_{3}$ and ${\text{BaTiO}}_{3}$ are antiparallel. The proposed concept of ferroelectrically controlled interface conductivity may be very interesting for memory and logic applications and we hope that our predictions will stimulate experimental studies in this field.

Simultaneous determination of OZ277, a synthetic 1,2,4-trioxolane antimalarial, and its polar metabolites in rat plasma using hydrophilic interaction chromatography

OZ277 is a synthetic 1,2,4-trioxolane antimalarial currently being evaluated in clinical trails. Biotransformation of OZ277 in rats results in the generation of metabolites with large differences in polarity which complicates the development of a method for the simultaneous analysis of all species. A simple, sensitive and selective hydrophilic interaction liquid chromatography–mass spectroscopy (HILIC/MS) method for simultaneous determination of OZ277 and its major metabolites in rat plasma was developed and validated. The method involves protein precipitation with acetonitrile followed by separation on a Waters Atlantis™ HILIC Silica column using gradient elution. The analytes were monitored using a positive electrospray ionization interface in selected ion monitoring mode. The calibration range for all of the analytes was 5–10,000 ng/mL and the lower limit of quantitation was 5 ng/mL using a 50 μL rat plasma sample. The inter- and intra-day accuracy and precision was within 12%. The recovery of all analytes from rat plasma over a wide concentration range was 90% or greater. The method has been successfully used for quantifying OZ277 and its metabolites in plasma following intravenous administration to rats.

Have the primary structures of biomacromolecules been selected in a Darwinian fashion to adapt to the surrounding environments of our planet?

Have the primary structures of biomacromolecules been selected in a Darwinian fashion to adapt to the surrounding environments of our planet?

Locally and Densely Sulfonated Poly(ether sulfone)s as Proton Exchange Membrane

New locally and densely sulfonated poly(ether sulfone)s were successfully prepared for fuel cell applications by the nucleophilic substitution of 4,4′-dichlorodiphenylsulfone with 1,2,4,5-tetrakis([1,1′-biphenyl]-2-oxy)-3,6-bis(4-hydroxyphenoxy)benzene and 2,2-bis(4-hydroxyphenyl)hexafluoropropane, followed by sulfonation using chlorosulfonic acid. The polymers gave tough, flexible, and transparent membranes by solvent casting. The large difference in polarity between the locally and densely sulfonated units and hydrophobic units of the polymers resulted in the formation of well-defined phase-separated structures, which induced efficient proton conduction in a wide range of 30−95% RH at 80 °C.

High current density InN∕AlN heterojunction field-effect transistor with a SiNx gate dielectric layer

In N ∕ Al N metal-insulator-semiconductor heterojunction field-effect transistors with a gate-modulated drain current and a clear pinch-off characteristic have been demonstrated. The devices were fabricated using high-quality InN (26nm)∕AlN (100nm) epifilms grown by plasma-assisted molecular-beam epitaxy on Si (111) substrates. The devices exhibited a current density higher than ∼530mA∕mm with a 5μm gate length. The pinch-off voltage was at ∼−7V with an associated drain leakage current less than 10μA∕mm. The observed high current density may be attributed to the high sheet carrier density due to the large spontaneous polarization difference between InN and AlN.

Analysis and stability study of myristyl nicotinate in dermatological preparations by high-performance liquid chromatography

Myristyl nicotinate is an ester prodrug under development for delivery of nicotinic acid to skin for treatment and prevention of conditions that involve skin barrier impairment such as chronic photodamage and atopic dermatitis or for mitigating skin barrier impairment that results from therapy such as retinoids or steroids. The formulation stability of myristyl nicotinate is crucial because even small amounts of free nicotinic acid cause skin flushing, an effect that is not harmful but would severely limit tolerability. We report here reversed-phase HPLC methods for the rapid analysis of myristyl nicotinate and nicotinic acid in dermatological preparations. Because of the large differences in polarity, myristyl nicotinate and nicotinic acid were analyzed by different chromatographic conditions, but they can be rapidly extracted from cream formulations using HPLC mobile phase as a solvent followed by HPLC analysis in less than 10 min. The methods were validated in terms of linearity, precision and accuracy and mean recovery of myristyl nicotinate from topical creams ranged from 97.0–101.2%. Nicotinic acid at levels of 0.01% in the formulations could be quantified. Stability studies show that myristyl nicotinate formulations are stable at room temperature for 3 years with less than 0.05% conversion to nicotinic acid. These methods will be effective for routine analysis of myristyl nicotinate stability in dermatological formulations.

Inhomogeneous broadening ofAlxGa1−xN∕GaNquantum wells

We report a low-temperature photoluminescence study of a series of ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}∕\mathrm{Ga}\mathrm{N}$ quantum wells of various widths $L$ and with $x$ ranging from 0.11 to 0.25, grown by molecular beam epitaxy on silicon (111) substrates. Such quantum wells are subject to an important Stark effect owing to the large macroscopic polarization (piezoelectric and spontaneous) difference between wells and barriers. Due to the opposite actions of carrier confinement and of the Stark effect on the quantum well transition energies, it appears that around a certain thickness ${L}_{0}\ensuremath{\sim}26\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$, these transition energies are independent of the barrier composition, at least in the $x$ range studied. This has already been reported in similar structures grown on sapphire [Grandjean et al., J. Appl. Phys. 86 3714 (1999)]. In such quantum wells, the inhomogeneous broadening originates essentially from well width fluctuations and alloy composition fluctuations. The effect of the latter is then expected to be minimum near $L={L}_{0}$. We show that it is indeed the case by studying the well width and barrier composition dependence of the linewidth of the quantum well luminescence lines, for samples grown on both Si and sapphire. The $x$ dependence of the minimum linewidth at $L\ensuremath{\sim}{L}_{0}$ allows to estimate a very small variance of the well width distribution $({\ensuremath{\sigma}}_{L}\ensuremath{\sim}1\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}})$, and this is discussed in relation with scanning tunneling microscopy images of GaN surfaces. Afterwards, using the fact that confinement energies in wide wells become nearly independent of well width, the variance of barrier composition fluctuations within the excitonic lateral extension is estimated from the $L$ dependence of linewidths at each barrier composition. The values we obtain for this excitonic lateral extension are in agreement with variationnal calculations of the in-plane exciton Bohr radius in such heterostructures.

Rapid determination of polyether marine toxins using liquid chromatography–multiple tandem mass spectrometry

The diarrhetic shellfish poisoning (DSP) toxins, okadaic acid (OA), dinophysistoxins (DTX); pectenotoxin-2 (PTX2) and pectenotoxin-2 seco acids, were determined in marine phytoplankton, Dinophysis acuta, and mussels (Mytilus edulis) collected along the southwest coast of Ireland. Liquid chromatography–multiple tandem mass spectrometry (LC–MS/MS) was employed for the simultaneous determination of a series of marine toxins with large polarity differences. Separation of five DSP toxins was achieved on a C18 column (Luna-2, 150 mm × 2.1 mm, 5 μm) using an acetonitrile–water gradient with ammonium acetate as an eluent modifier. Electrospray ionisation (ESI) in negative mode, was used to generate the molecule related ion, [M − H]−, for each toxin. To develop a multiple reaction monitoring (MRM) method, fragmentation studies were performed to determine the optimum precursor-product ion combinations: OA (803/255), DTX2 (803/255), DTX1 (817/255), PTX2SAs (875/137) and PTX2 (857/137). This highly sensitive method had detection limits better than 1 pg (on-column). Linear calibrations were obtained for shellfish extracts that were spiked with toxins, OA, 0.007–1.00 μg/ml (r2 = 0.9993, N = 3) and DTX2, 0.054–8.5 μg/ml (r2 = 0.9992, N = 3). Good reproducibility data were also achieved with %RSD values (N = 3) ranging from 3.15% (0.56 μg DTX2/ml) to 5.71% (0.14 μg DTX2/ml), for shellfish extracts. The method was sufficiently sensitive to permit the determination of DSP toxins in small numbers of picked phytoplankton cells (N = 12–40). In one sample of D. acuta the average toxin composition per cell was: OA (7.0 pg), DTX2 (11 pg) and PTX2 (7.2 pg).

Rapid determination of polyether marine toxins using liquid chromatography–multiple tandem mass spectrometry

The diarrhetic shellfish poisoning (DSP) toxins, okadaic acid (OA), dinophysistoxins (DTX); pectenotoxin-2 (PTX2) and pectenotoxin-2 seco acids, were determined in marine phytoplankton, Dinophysis acuta, and mussels ( Mytilus edulis) collected along the southwest coast of Ireland. Liquid chromatography–multiple tandem mass spectrometry (LC–MS/MS) was employed for the simultaneous determination of a series of marine toxins with large polarity differences. Separation of five DSP toxins was achieved on a C 18 column (Luna-2, 150 mm × 2.1 mm, 5 μm) using an acetonitrile–water gradient with ammonium acetate as an eluent modifier. Electrospray ionisation (ESI) in negative mode, was used to generate the molecule related ion, [M − H] −, for each toxin. To develop a multiple reaction monitoring (MRM) method, fragmentation studies were performed to determine the optimum precursor-product ion combinations: OA (803/255), DTX2 (803/255), DTX1 (817/255), PTX2SAs (875/137) and PTX2 (857/137). This highly sensitive method had detection limits better than 1 pg (on-column). Linear calibrations were obtained for shellfish extracts that were spiked with toxins, OA, 0.007–1.00 μg/ml ( r 2 = 0.9993, N = 3) and DTX2, 0.054–8.5 μg/ml ( r 2 = 0.9992, N = 3). Good reproducibility data were also achieved with %RSD values ( N = 3) ranging from 3.15% (0.56 μg DTX2/ml) to 5.71% (0.14 μg DTX2/ml), for shellfish extracts. The method was sufficiently sensitive to permit the determination of DSP toxins in small numbers of picked phytoplankton cells ( N = 12–40). In one sample of D. acuta the average toxin composition per cell was: OA (7.0 pg), DTX2 (11 pg) and PTX2 (7.2 pg).

Molecular Dynamics Study of the Folding of Hydrophobin SC3 at a Hydrophilic/Hydrophobic Interface

Hydrophobins are fungal proteins that self-assemble at hydrophilic/hydrophobic interfaces into amphipathic membranes. These assemblages are extremely stable and posses the remarkable ability to invert the polarity of the surface on which they are adsorbed. Neither the three-dimensional structure of a hydrophobin nor the mechanism by which they function is known. Nevertheless, there are experimental indications that the self-assembled form of the hydrophobins SC3 and EAS at a water/air interface is rich with β-sheet secondary structure. In this paper we report results from molecular dynamics simulations, showing that fully extended SC3 undergoes fast (∼100ns) folding at a water/hexane interface to an elongated planar structure with extensive β-sheet secondary elements. Simulations in each of the bulk solvents result in a mainly unstructured globular protein. The dramatic enhancement in secondary structure, whether kinetic or thermodynamic in origin, highlights the role interfaces between phases with large differences in polarity can have on folding. The partitioning of the residue side-chains to one of the two phases can serve as a strong driving force to initiate secondary structure formation. The interactions of the side-chains with the environment at an interface can also stabilize configurations that otherwise would not occur in a homogenous solution.

Optimization of chromatographic systems for the high-performance thin-layer chromatography of flavonoids

To characterize the retention and selectivity of separations of 23 flavonoids (aglycones and glycosides) relationships betweenRF and modifier concentration were determined for silica and diol adsorbents (with mixtures of ethyl acetate and methanol as mobile phases), for cyanopropyl silica (with mixtures of ethyl acetate and dichloromethane as mobile phases), for aminopropyl silica (with mixtures of ethyl acetate, methanol and water as mobile phases) and for octadecyl silica (with mixtures of methanol and water as mobile phases). Owing to large polarity differences between aglycones and glycosides, these groups of compounds cannot be separated other than by use of reversed-phase systems, for which the selectivity is lower. It follows from correlation plots ofRF1 againstRF2 that for some pairs of adsorbents (e. g. silica and diol) selectivity differences are small; for others the points in the plot are widely dispersed, indicating selectivity differences. The chemometric database obtained can be used to choose optimum chromatographic systems for the separation of given sets of flavonoids and for planning gradient elution programs for separation of flavonoid aglycones and glycosides in a single TLC experiment.

Optimising reversed phase separations with the aid of a spreadsheet

A separation of eight compounds by reversed phase HPLC, in methanol and water mixtures, was optimised with the aid of a spreadsheet. The eight compounds had large differences in polarity and some peaks exhibited crossover as solvent strength changed. Currently available linear gradient theory was used but all calculations and generation of chromatograms was done with a commonly used spreadsheet. Optimisation of resolution can be done visually from the chromatograms produced by the spreadsheet or semi automatically by using functions available in the spreadsheet. Using a small initial number of gradient runs it was possible to optimise isocratic, single segment, or dual segment linear gradient separations.

Determination of ten carbamate pesticides in aquatic and sediment samples by liquid chromatography-ionspray and thermospray mass spectrometry

Ten carbamate pesticides which exhibit large differences in polarity were determined simultaneously in various environmental samples, using both column liquid chromatography (LC)-thermospray (TSP) mass spectrometry (MS) and LC-ionspray (ISP) MS. For sample clean-up, column chromatography with three stationary phases, neutral aluminium oxide, Florisil and aminopropyl-bonded modified silica, were tested. The aminopropyl stationary phase showed the best results, with acetone-dichloromethane (25:75) as eluent; analyte recoveries were 76–100% for all compounds with a relative standard deviation of 2–8%. In the ISP mass spectra of eight of the ten carbamates, the sodium adduct ion, [M + Na] +, was the base peak, while the protonated molecule, [M + H] +, was the most abundant ion with carbendazim and aminocarb. An eluent flow-rate between 100 and 300 μl/min was found to be optimum, with optimized nebulizer and drying gas flow-rates of 350 and 15 l/h, respectively. A capillary voltage of 3.5 kV resulted in the largest total ion current. The optimum extraction voltage with regard to analyte detectability and confirmation purposes was between 15 and 35 V. The detection limits obtained with the LC-ISP-MS system were typically in the 10–60 pg range (10 μl of 10 μg/l standard solutions), which is 10–150-fold better than obtained with LC-TSP-MS (selected-ion monitoring mode used in both instances). Large-volume injections of tap water spiked with selected carbamates at a level of 0.1 μg/l illustrated the potential of LC-ISP-MS with respect to analyte detectability. Furthermore, carbofuran was identified at a concentration level of ca. 5 μg/l in water samples from the Ebro delta. LC-TSP-MS of oxamyl and methomyl in a sediment sample containing a high percentage of organic matter was adversely affected by the presence of co-extractives. This problem did not occur with LC-ISP-MS.

Rapid and sensitive determination of zidovudine and zidovudine glucuronide in human plasma by ion-pair high-performance liquid chromatography

A rapid, simple and sensitive method is described for the simultaneous determination in human plasma of the well known antiviral agent zidovudine (AZT) and its main metabolite, zidovudine-5′-O-glucuronide (G-AZT), using a solid-phase extraction method for sample preparation and a rapid ion-pair HPLC separation method with diode-array ultraviolet detection. The method overcomes the problems experienced in other procedures because of the large difference in polarity of the two compounds and the pH-sensitive retention of G-AZT by using n-octylamine to increase the retention of the glucuronide and improve the overall chromatographic behaviour. AZT and G-AZT are eluted at 3.6 and 5 min, respectively, with 7-ethyltheophylline used as internal standard eluting at 4.2 min. Caffeine, a good marker for the elution of related compounds present in plasma, appears well before, at 2.6 min. Quantification limits were established at 0.025 and 0.050 μg/ml for AZT and G-AZT, respectively. The improvement in method reproducibility due to the late elution of G-AZT could be observed even at the quantification limit at which an inter-assay relative standard deviation of only 6.4% was found after 3 months of routine use of the method.

Determination of fluazifop-butyl and fluazifop with the use of disposable solid phase extraction columns for selective clean-up and concentration of Soxhlet soil extracts

An analytical procedure based on the solid phase extraction technology has been developed for the clean-up and concentration of Soxhlet soil extracts containing fluazifop-butyl and fluazifop by the use of a phenyl phase cartridge. No liquid-liquid partition has been used; thus the consumption of organic solvents was limited and the use of chlorinated solvents could be avoided. Quantification has been performed by ion-pair HPLC. Despite the large difference in polarity the recoveries of both the compounds from spiked soil samples between 0.1 and 1 μg/g was higher than 90%. The solid-phase adsorption technology resulted in a very effective methodology of clean-up in the case of the polar compound fluazifop, for which a second disposable column with a cyanopropyl phase has been used, and was fairly satisfactory for fluazifop-butyl. The detection limits were less than 0.04 μg/g and 0.10 μg/g, respectively for fluazifop and fluazifop-butyl.

Improved methods for the selective isolation of the sulfide and thiophenic classes of compounds from petroleum

These methods are based on the ability to selectively oxidize the sulfur atom in the two different chemical environments and the large difference in polarity between the oxidized and unoxidized forms. The reagent tetrabutylammonium periodate in toluene/methanol will oxidize the sulfides to highly polar sulfoxides in high yield without affecting the thiophenic compounds. A subsequent chromatographic step permits the isolation of a polar fraction containing the sulfoxides. Reduction of this polar fraction regenerates the sulfides, which are isolated by chromatography. The sulfide content was found to vary from 2.6% to 16% of the heavy oils and bitumens of Alberta. A second oxidation of the remaining fraction, after removal of the sulfides, using m-chloroperbenzoic acid under anhydrous neutral conditions converts the thiophenes into their corresponding polar sulfones, which are isolated from the mixture by a subsequent chromatographic step. Reduction regenerates the thiophenic compounds, which are purified again by chromatography. The content of the thiophenic compounds was found to vary from 0.3% to 7.6% of the various conventional oils, heavy oils, and bitumens examined