Presence Of Polar Solvents Research Articles

Enhanced plasmid DNA utilization in transiently transfected CHO-DG44 cells in the presence of polar solvents.

Although the protein yields from transient gene expression (TGE) with Chinese hamster ovary (CHO) cells have recently improved, the amount of plasmid DNA (pDNA) needed for transfection remains relatively high. We describe a strategy to reduce the pDNA amount by transfecting CHO-DG44 cells with 0.06 μg pDNA/10(6) cells (10% of the optimal amount) in the presence of nonspecific (filler) DNA and various polar solvents including dimethylsufoxide, dimethyl formamide, acetonitrile, dimethyl acetamide (DMA), and hexamethyl phosphoramide (HMP). All of the polar solvents with the exception of HMP increased the production of a recombinant antibody in comparison to the untreated control transfection. In the presence of 0.25% DMA, the antibody yield in a 7-day batch culture was 500 mg/L. This was fourfold higher than the yield from the untreated control transfection. Mechanistic studies revealed that the polar solvents did not affect polyethylenimine-mediated pDNA delivery into cells or nuclei. The steady-state transgene mRNA level was elevated in the presence of each of the polar solvents tested, while the transgene mRNA half-life remained the same. These results indicated that the polar solvents enhanced transgene transcription. When screening a panel of recombinant antibodies and Fc-fusion proteins for production in the presence of the polar solvents, the highest increase in yield was observed following DMA addition for 11 of the 12 proteins. These results are expected to enhance the applicability of high-yielding TGE processes with CHO-DG44 cells by decreasing the amount of pDNA required for transfection.

Accelerated Solvent Extraction Improves Efficiency of Lipid Removal from Dry Pet Food While Limiting Lipid Oxidation

AbstractAccelerated solvent extraction (ASE) was evaluated for extracting lipids from baked and extruded dry pet foods to determine factors controlling extraction efficiency and effects on lipid oxidation. Hydroperoxide decomposition and new lipid oxidation were minimal at 40 °C but increased at higher extraction temperatures without increasing yields. Maximum extraction required grinding samples to 250 µm particles, presence of polar solvents [chloroform, chloroform/methanol 2:1 (v/v) mixed, hexane/methanol 2:1 (v/v)], and a minimum of 20 min total static extraction time in repeat extraction cycles. Hexane and methanol injected into extraction cells simultaneously but separately was able to nearly duplicate extractions of chloroform/methanol, providing an option for replacing toxic chlorinated hydrocarbon solvents in ASE. However, lipid oxidation was higher in hexane. Yields were quantitative in baked biscuits but lower in extruded kibbles due to more dense, complex molecular structures. ASE extraction yields of 40 min or less were comparable to manual extraction yields of 24–48 h, with lower oxidation. Overall, one or two ASE extraction cycles with static times less than 20 min appeared to provide adequate lipid yields that accurately reflect lipid composition while inducing minimal modification when lipid oxidation products are the analytical endpoint.

Strategies to Improve the Performance of Ionic Liquid-Based Electrolytes

Ionic liquid-based electrolytes are an emerging class of electrolytes for application in electrochemical energy storage devices. Ionic liquids display negligible vapor pressure, which leads to very low flammability. Therefore, the use of these electrolytes results particularly beneficial to improve the safety of electrochemical storage devices. However, the conductivity of ionic liquid-based electrolytes is usually lower than that of conventional molecular solvent based electrolytes. Furthermore, the melting point of many ionic liquids is considerably higher than the desired lower temperature limit of use of, e.g., -30 °C. Hence, the use at and below room temperature has been limited to low currents and ionic liquid-based electrolytes found application only in niche markets.[1] Several strategies have been developed to tackle the low temperature performance issue of ionic liquid-based electrolytes. One approach is to mix several ionic liquids in order to improve the lower temperature of use and the conductivity at low temperatures by suppressing crystallization.[2]Another option is to blend molecular solvents with ionic liquids. This approach results in much improved conductivity at the expense of increased flammability. However, a good compromise between flammability and performance can be found by selecting high flash point solvents. Mixing ionic liquids with polar solvents like propylene carbonate can lead to new issues. Aluminum metal is used as current collector on the cathode side of lithium-ion batteries and for both electrodes of supercapacitors. The presence of polar solvents in some ionic liquids can lead to anodic dissolution of Al at high potentials. This problem can be solved by a proper choice of solvent, ionic liquid anion or by the use of electrolyte additives.[3-5]A third strategy to improve the low temperature performance of ionic liquid-based electrolytes is the use of alternative ionic liquids. Replacing one or both alkyl chains of the cation N-butyl-N-methylpyrrolidinium by a proton results in protic ionic liquids. Surprisingly, a better high current performance of lithium-ion batteries employing such protic ionic liquids was found. Raman measurements suggested an increased interaction between the cation and the anion of the protic ionic liquid and a weakened interaction between Li+ and the anion of the ionic liquid. This different Li+ environment seems to be the cause for the improved performance at high current rates.[6]In this work we report a comparison about the advantages and the limits related to the use of the abovementioned strategy, with particular focus on the application of ionic liquids-based electrolytes in high power electrochemical storage devices.

Iron-mediated AGET ATRP of methyl methacrylate in the presence of polar solvents as ligands

The polar solvents, N-methylpyrrolidone (NMP), N,N-dimethylformamide (DMF), and acetonitrile (CH3CN) were used as ligands for iron(III)-mediated activators generated by electron transfer atom transfer radical polymerizations (AGET ATRPs) of methyl methacrylate (MMA) with various initiators and reducing agents. Polymerizations were conducted with a molar ratio of [MMA]0/[initiator]0/[FeBr3]0/[reducing agent]0 = 100:1:1:0.5 and a volume ratio of MMA/solvent = 2:1 at 60 °C to investigate the effects of initiator, solvent and reducing agent, and most of the systems showed the typical features of “living”/controlled radical polymerization. In order to get a deeper understanding of the mechanism, the amount of the reducing agent was changed to study the polymerization behavior. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1020–1027

Solvent effects on the hydrodeoxygenation of propanoic acid over Pd(111) model surfaces

The effects of liquid water, n-octane, and n-butanol on the hydrodeoxygenation of propanoic acid over Pd(111) model surfaces have been studied from first principles. We developed a microkinetic model for the hydrodeoxygenation and studied the reaction mechanism at a temperature of 473 K. Our model predicts that for all reaction media, decarbonylation pathways are favored over decarboxylation pathways. However, in the presence of polar solvents like water, decarboxylation routes become competitive with decarbonylation routes. The activity of the Pd surface varies as a function of the environment as follows: water > n-butanol > octane ≈ gas phase. Finally, a sensitivity analysis of our models suggests that both C–OH and C–H bond cleavages control the overall rate of the catalyst in all environments and are likely to be activity descriptors for the hydrodeoxygenation of organic acids.

A correlated ab initio quantum chemical study of the interaction of the Na+, Mg2+, Ca2+ and Zn2+ ions with the tautomers of cytosine in the presence of polar solvent

The interactions of the metal ions Na(+), Mg(2+), Ca(2+) and Zn(2+) with cytosine have been investigated with inclusion of solvent effects. Computations have been performed at the density functional and Møller-Plesset levels of theory within the IEFPCM solvent model. It has been found that the inclusion of the solvent environment is essential for giving more biologically realistic results. Earlier gas-phase findings of the stabilisation of rare tautomeric forms by the metal ions have been reproduced, with the presence of the solvent further affecting the relative stabilities.

Solution structure of cadmium carboxylate and its implications for the synthesis of cadmium chalcogenide nanocrystals

Diffusion-ordered spectroscopy (DOSY) was used to investigate the solution structure of cadmium carboxylate. The molecular weights of cadmium complexes highly depend on the solvent; the complexes are polymeric in toluene but break up in the presence of polar solvents or coordinating ligands.

Degradation of polylactide in paraffin and selected protic media

The degradation of polylactide commercial films caused by selected ingredients used in the preparation of cosmetics is reported. Despite the wide application of polylactide as a food packing material, its limitation for applications in the packaging of cosmetics is observed. Gel Permeation Chromatography (GPC), Atomic Force Microscope (AFM), Electrospray Mass Spectrometry (ESI-MS) and Nuclear Magnetic Resonance (NMR) reveal that polylactide degradation occurs not only in the presence of polar solvents (ethyl alcohol, glycerine, propylene glycol) but also in the presence of paraffin. We report the applicability of this green polymeric material for cosmetic packages based on the studies of both the eroded polymer and its degradation products.

Adsorption and Electronic Structure Study of Imidazole on (6,0) Zigzag Single-Walled Boron Nitride Nanotube

AbstractThe behavior of the imidazole adsorbed on the external surface of H-capped (6,0) zigzag single-walled boron nitride nanotube as a functional group was studied by using density functional calculations in gas and solvent phases. Geometry optimizations were carried out at the B3LYP/6-31G* level of theory using a locally modified version of the GAMESS electronic structure program. Our results show that the pristine boron nitride nanotubes can significantly detect the imidazole. In both phases, the binding energy for the imidazole/BNNT complex is negative and presenting characterizes an exothermic process. The increase in global hardness and energy gap due to imidazole adsorption lead to an increasing of the stability and decrease in reactivity of the complex in the both phases. Also, presence of polar solvent increases the electron donor of imidazole and electrophilicity of the nanotube. This study may provide new insight to the development of functionalized boron nitride nanotubes as drug delivery systems for virtual applications.Graphical AbstractGraphics for use in the table of contents. [IMAGE]

Spectroscopic and thermal characterization of the swelling behavior of nafion membranes in mixtures of water and methanol

AbstractThe spectroscopic and thermal properties of swollen Nafion membranes in methanol aqueous mixtures were investigated to understand the behavior of commercial electrolytes in the presence of polar solvents. Several differences were observed in the absorption processes depending on the composition of the solvent. Deconvolution methods were applied to study specific contributions of solvents and polymer groups based on Fourier transform infrared spectroscopy and thermogravimetric analysis. The results evidence compositional effects on the interactions between solvents and Nafion. A major influence of the nonpolar domains (hydrophobic regions) in the absorption of methanol together with a reduction of the interactions with sulfonate groups was observed. Such changes are accompanied by a modification of the cluster morphology of the equilibrated membranes evaluated by differential scanning calorimetry. These findings can be useful to improve the knowledge on Nafion's microstructure in the presence of polar solvents. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Ambient temperature rapid ATRP of methyl acrylate, methyl methacrylate and styrene in polar solvents with mixed transition metal catalyst system

Ambient temperature atom transfer radical polymerization (ATRP) of methyl acrylate (MA), methyl methacrylate (MMA) and styrene (Sty) in the presence of polar solvents (dimethyl sulfoxide: DMSO, dimethylformamide: DMF and acetonitrile: MeCN) with a mixed transition metal catalyst system (Fe(0) as initial activator and CuBr 2/Me 6TREN complex as deactivator) provides a rapid synthesis of polymers with very low polydispersity (PDI) values and predetermined molecular weights. The polymethylacrylate (PMA) prepared using this novel approach contains the Br-terminated chain ends (functionality ∼100%) and can be successfully used for block copolymer synthesis (as demonstrated on the chain extension experiment performed using the PMA–Br macroinitiator). The key elementary reactions involved in this novel ATRP system and some preliminary mechanistic aspects of the process are also discussed.

Polymorphs from supramolecular gels: four crystal forms of the same silver(i) supergelator crystallized directly from its gels

A new silver(I) complex with 1-phenyl-3-(quinolin-5-yl)urea has been prepared, acting as a supramolecular supergelator in the presence of polar solvents. In open vials temperature dependent, reversible gel-to-xerogel transition is observed, while in sealed vials direct crystallization of four polymorphs of the same gelling compound is achieved, depending on the gelling solvent.

A kinetic investigation of the oxidative addition reactions of the dimeric Bu 4N[Ir 2(μ-Dcbp)(CO) 2(PCy 3) 2] complex with iodomethane

The IR and UV/visible kinetic results of the oxidative addition of iodomethane to Bu 4N[Ir 2(μ-Dcbp)(CO) 2(PCy 3) 2] (Dcbp = 3,5-dicarboxylatepyrazolate anion) showed three time separable reactions. The first, very fast reaction corresponds to the a Ir(I)–Ir(III) alkyl species formation within 10 −3 s. The second, relative fast reaction corresponds to Ir(III)–Ir(III) alkyl formation with a rate constant of 3.25(4) × 10 −2 M −1 s −1 while the third and slowest reaction corresponds to Ir(III)–Ir(III) acyl formation with a rate constant of 1.42 × 10 −5 s −1. The IR data clearly show the existence of a number of equilibria with the formation of an Ir(I)–Ir(III) alkyl product which then react to form the Ir(III)–Ir(III) which then slowly react to form the Ir(III)–Ir(III) acyl product. A solvent study indicated increased oxidative addition activity in the presence of polar solvents, which is indicative of a polar transition state. The large negative entropy of activation for the Ir(III)–Ir(III) alkyl formation step ( k 2) of −178(23) JK −1 mol −1 is indicative of an associative process. DFT calculations successfully identified the stereochemistry of the starting complex, [Ir 2(μ-Dcbp)(CO) 2(PCy 3) 2] − as well as that of the Ir-alkyl and acyl isomers. A reaction pathway, using the IR data and DFT calculations, is proposed for the reaction.

Effect of Environment on Photo-detachment Dynamics of Halide Ions: A Model Approach

A two dimensional model approach for the photodetachment dynamics of closed shell anionic systems in presence of external light field have been proposed in the context of polar environmental media. The effects of strong coupling between the solvent polarization and the extra charge in the system were studied by a simple model. The electronic states of concerned halide ions are represented by a two dimensional model Hamiltonian with a potential V(x, y) = −V0e−σ(x2 + y2). The time dependent Fourier grid Hamiltonian method have been used to follow the detachment process with fairly high intensities of light. The environmental effects on the dynamics are sought to be modeled by two different ways. The first one was the presence of polar solvents which perturb the energy levels of anionic systems by changing the effective potential surface and the second one was allowing the fluctuation of the well depth randomly to mimic the system in a more realistic view point. The average detachment rate constant is calculated as a function of important parameters of the used light field to explain the effects of solvent field on the dynamical behavior of dipole bound anionic system at least in a qualitative way.

Vibrational circular dichroism of amylose carbamate: structure and solvent-induced conformational changes

The conformational changes of amylose tris-(dimethylphenylcarbamate) (ADMPC) in the presence of polar solvents were investigated by VCD spectroscopy for the first time. The conformation of ADMPC was monitored using this technique in the solid film state and in the presence of different concentrations of alcohols, such as ethanol, n-propanol, and isopropanol in mixtures with hexane. The VCD results revealed that in the presence of these solvents, the polymer undergoes a drastic conformational change.

A Density Functional Theory Study of the Stille Cross‐Coupling via Associative Transmetalation. The Role of Ligands and Coordinating Solvents

AbstractAn associative mechanism has been computationally characterized for the Stille cross‐coupling of vinyl bromide and trimethylvinylstannane catalyzed by PdL2 (L=PMe3, AsMe3) with or without dimethylformamide as coordinating ligand. All the species along the catalytic cycles that start from both the cis‐ and the trans‐PdL(Y)(vinyl)Br complexes (Y=L or S; L=PMe3, AsMe3 or PH3; S=DMF) have been located in the gas phase and in the presence of polar solvents. Computations support the central role of species trans‐PdL(DMF)(vinyl)Br which react by ligand dissociation and stannane coordination in the rate‐limiting transmetalation step via a puckered four‐coordinate (at palladium) transition state comprised of Pd, Br, Sn and sp2 C atoms. A donating solvent may enter the catalytic cycle assisting isomerization of cis‐PdL2(vinyl)Br to trans‐PdL(DMF)(vinyl)Br complexes via a pentacoordinate square pyramidal Pd intermediate. In keeping with experimental observations, the activation energies of the catalytic cycles with arsines as Pd ligands are lower than those with phosphines. Polytopal rearrangements from the three‐coordinate T‐shaped Pd complexes resulting from transmetalation account for the isomerization and the CC bond formation on the reductive elimination step.

Acid/Base Properties and Adsorption of an Azo Dye on Coating Pigments

Adsorption of an anionic disazo dye, Food Black 2 on coating pigments from polar solvents was studied. Pigments (kaolin, precipitated CaCO3, amorphous SiO2, TiO2, Al2O3, and talc) were chosen to be representative of those used in paper for ink‐jet printing. The predominating driving force for the adsorption was electrostatic interactions for all the pigments except talc, for which hydrophobic interactions were dominant. Lewis acid‐base properties of the pigments were studied by measuring adsorption of Lewis acid‐probe molecules from both polar and nonpolar media. The pigments studied were found to be amphoteric, containing both acidic and basic surface groups. However, in the presence of polar solvents, the adsorption of acid‐base probe molecules was greatly reduced, which indicates that Lewis acid‐base interactions have only a small influence on the adsorption of azo dyes from polar media such as water.

Rearrangement of Epoxides to Carbonyl Compounds in the Presence of Reusable Acidic Zeolite Catalysts under Mild Conditions

Rearrangement of 4-substituted styrene oxides with acidic zeolite catalysts in the presence of polar solvents at room temperature gives the corresponding 4-substituted phenylacetaldehydes in high yields. The procedure has been applied successfully to the rearrangement of disubstituted epoxides. The zeolite can be easily recovered, regenerated by heating and reused.

Stereoselective Enolizations Mediated by Magnesium and Calcium Bisamides: Contrasting Aggregation Behavior in Solution and in the Solid State

The reactions of magnesium and calcium bis(hexamethyldisilazide) with propiophenone have been studied with a view to determine the utility of these bases in the stereoselective enolization of ketones and to uncover the nature of the metal enolate intermediates produced. Both base systems are highly Z-selective when the reactions are conducted in the presence of polar solvents. However, in situ monitoring of the magnesium system in arene solution revealed a preference for E-enolate formation, which was confirmed by silyl enol ether trapping studies. Solution NMR studies of the magnesium system in toluene-d8 show the presence of a monomer-dimer equilibrium for the intermediate amidomagnesium enolates. This assignment is supported by the characterization of a disolvated amidomagnesium enolate dimer by crystallographic analysis. Comparative studies of the calcium system show distinctly different behavior. This is exemplified by the characterization of a novel solvent-separated ion pair complex and a monomeric amidocalcium enolate in the solid state. Solution NMR studies of the calcium system in pyridine-d5 reveal the co-existence of the heteroleptic amidocalcium enolate, the bisamide, the bisenolate and the ion pair complex.

Photoelectron anisotropy and channel branching ratios in the detachment of solvated iodide cluster anions

Photoelectron spectra and angular distributions in 267 nm detachment of the I(-)Ar, I(-)H(2)O, I(-)CH(3)I, and I(-)CH(3)CN cluster anions are examined in comparison with bare I(-) using velocity-map photoelectron imaging. In all cases, features are observed that correlate to two channels producing either I((2)P(3/2)) or I((2)P(1/2)). In the photodetachment of I(-) and I(-)Ar, the branching ratios of the (2)P(1/2) and (2)P(3/2) channels are observed to be approximately 0.4, in both cases falling short of the statistical ratio of 0.5. For I(-)H(2)O and I(-)CH(3)I, the (2)P(1/2) to (2)P(3/2) branching ratios are greater by a factor of 1.6 compared to the bare iodide case. The relative enhancement of the (2)P(1/2) channel is attributed to dipole effects on the final-state continuum wave function in the presence of polar solvents. For I(-)CH(3)CN the (2)P(1/2) to (2)P(3/2) ratio falls again, most likely due to the proximity of the detachment threshold in the excited spin-orbit channel. The photoelectron angular distributions in the photodetachment of I(-), I(-)Ar, I(-)H(2)O, and I(-)CH(3)CN are understood within the framework of direct detachment from I(-). Hence, the corresponding anisotropy parameters are modeled using variants of the Cooper-Zare central-potential model for atomic-anion photodetachment. In contrast, I(-)CH(3)I yields nearly isotropic photoelectron angular distributions in both detachment channels. The implications of this anomalous behavior are discussed with reference to alternative mechanisms, affording the solvent molecule an active role in the electron ejection process.