Nonpolar Organic Solvents Research Articles

P‐70: The Effect of Orthogonal Solvent of Colloidal Quantum Dots on QD‐LED device

AbstractWe investigated the orthogonal solvent of CdSe/ZnS quantum dots in order to deposit poly‐TPD hole transport layer without damages and enhance the performances of QD‐LEDs. Using hexane and heptane as nonpolar organic solvent of QDs does not affect poly‐TPD layer has found. 3 mg/ml in hexane shows highest luminance and current efficiency but creates non‐uniform QD‐layer because lower boiling point of hexane. The last we found that even different concentration of QDs in heptane show similar device performance.

Influence of the lipid environment on valinomycin structure and cation complex formation

Carrier-type molecular ionophores, such as the cyclic dodecadepsipeptide valinomycin, often must undergo structural changes during the binding and transport of a cation across the lipid membrane. Observing the structural fluctuations that occur during this process experimentally has proven extremely difficult due to the complexities of spectroscopic analysis of protein structure/dynamics in native lipid bilayer environments. Currently, our understanding of how valinomycin selectively transports ions across membranes is derived from atomic structures solved of the cyclic macromolecule solvated in various organic solvents and complimentary in silico dynamics experiments. We have shown recently that deep-UV excited resonance Raman spectroscopy (DUVRR) has a unique ability to characterize secondary structure content and simultaneously provide information about the relative solvation of the probed peptide backbone C.M. Halsey, J. Xiong, O. Oshokoya, J.A. Johnson, S. Shinde, J.T. Beatty, G. Ghirlanda, R.D. JiJi, J.W. Cooley, Simultaneous observation of peptide backbone lipid solvation and a-helical structure by deep-UV resonance Raman spectroscopy, ChemBioChem 12 (2011) 2125–2128, [16]. Interpretation of DUVRR spectra of valinomycin in swelled lipid and unilamellar lipid bilayer environments indicate that the uncomplexed valinomycin molecule dynamically samples both the open and closed conformations as described for the structures derived from polar and non-polar organic solvents, respectively. Upon introduction of potassium, the structure of valinomycin in swelled lipid environments resembles more closely that of the open conformation. The shift in structure upon complexation is accompanied by a significant decrease in the valinomycin DUVRR spectral amide I intensity, indicating that the open conformation is more water solubilized and is seemingly “trapped” or predominantly located close to the lipid–water interface. The trapping of the valinomycin in the act of complex of potassium at the bilayer-solvent interface and its analysis by DUVRR represents the first spectroscopic description of this state. Conversely, an opposite trend is observed in the amide I intensity upon potassium complexation in unilamellar (or extruded) vesicles, implying the predominant conformation upon potassium binding in native bilayers is one where the peptide backbone of valinomycin is desolvated as would be expected if the molecule were more readily able to traverse a bilayer interior. Interpretation of the DUVRR spectral features is also consistent with the loss or formation of hydrogen bonds observed in the open and closed structures, respectively. Valinomycin must then sample several conformations in the absence of appropriate ions depending upon its locale in the lipid bilayer until potassium causes a greater degree of closure of the open conformer and an increased residency within the more non-polar interior. The potassium induced decreased solubility enables diffusion across the membrane where potassium release can occur by equilibration at the opposite lipid water interface.

Optically Active, Amphiphilic Poly(meta-phenylene ethynylene)s: Synthesis, Hydrogen-Bonding Enforced Helix Stability, and Direct AFM Observation of Their Helical Structures

Optically active, amphiphilic poly(meta-phenylene ethynylene)s (PPEa) bearing L- or D-alanine-derived oligo(ethylene glycol) side chains connected to the backbone via amide linkages were prepared by microwave-assisted polycondensation. PPEa's exhibited an intense Cotton effect in the π-conjugated main-chain chromophore regions in various polar and nonpolar organic solvents due to a predominantly one-handed helical conformation stabilized by an intramolecular hydrogen-bonding network between the amide groups of the pendants. The stable helical structure was retained in the bulk and led to supramolecular column formation from stacked helices in oriented polymer films as evidenced by X-ray diffraction. Atomic force microscopy was used to directly visualize the helical structures of the polymers in two-dimensional crystalline layers with molecular resolution, and, for the first time, their absolute helical senses could unambiguously be determined.

Three-Dimensionally Macroporous Fe/C Nanocomposites As Highly Selective Oil-Absorption Materials

In this study, three-dimensionally macroporous Fe/C nanocomposites were investigated as highly selective absorption materials for removing oils from water surface. The macroporous nanocomposites were synthesized by sintering a mixture of closely packed polystyrene microspheres and ferric nitrate precursor. These nanocomposites exhibited superhydrophobic and superoleophilic properties without the modification of low-surface-energy chemicals. And the pore size of the nanocomposites, which is crucial for the oil-absorption capacity, was tuned by varying the diameter of polystyrene microspheres. The macroporous nanocomposites fast and selectively absorbed a wide range of oils and hydrophobic organic solvents on water surface, and the removal of the absorbed oils from the water surface was readily achieved under a magnetic field. Moreover, the nanocomposites still kept highly hydrophobic and oleophilic characteristics after repeatedly removing oils from water surface for many cycles. Because of frequently occurring environmental pollution arising from oil spills and chemicals leakage, the results of this study might offer a kind of efficient and selective absorbent materials for removing oils and nonpolar organic solvents from the surface of water.

Oleic-acid-coated CoFe2O4 nanoparticles synthesized by co-precipitation and hydrothermal synthesis

Oleic-acid-coated CoFe2O4 nanoparticles were synthesized by co-precipitation and hydrothermal synthesis. The coprecipitation of the nanoparticles was achieved by the rapid addition of a strong base to an aqueous solution of cations in the presence of the oleic acid surfactant, or without this additive. The nanoparticles were also synthesized by a hydrothermal treatment of suspensions of the precipitates, coprecipitated at room temperature in the presence of the oleic acid, or without it. The influence of the synthesis conditions, such as the valence state of the iron cation in the starting aqueous solution, the temperature of the treatment and the presence of oleic acid, on the particles size was systematically studied. X-ray powder diffractometry (XRD) and transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS) revealed that, although spinel forms at room temperature, a substantial amount of Co was incorporated within the secondary, feroxyhyte-like phase when the iron cation was in the 2+ state. In contrast, when iron was in the 3+ state, the spinel forms at elevated temperatures of approximately 60°C. The presence of the oleic acid further increased the formation temperature for the stoichiometric spinel. Moreover, the oleic acid impeded the particles’ growth and enabled the preparation of colloidal suspensions of the nanoparticles in non-polar organic solvents. The nanoparticles’ size was successfully controlled by the temperature of the synthesis in the region where superparamagnetism dominates to the region where mono-domain ferrimagnetism dominates the magnetic properties.

Novel HTPB/MWNTs-COOH PU Conductive Polymer Composite Films for Detection of Hazardous Organic Solvent Vapors

A novel polyurethane (PU) conducting composite film was developed by a simple coupling reaction route. The morphologies and structural characterization were conducted by means of FTIR, UV-vis, XRD, TEM, TGA and POM. The influence of the MWNTs-COOH loading amount and curing temperature on response was investigated. The results indicated that the films displayed strong and selective response to some non-polar organic solvent vapor, and have long-term stability. The film loading 15.5 wt% conductive filler exhibited higher response. As the curing temperature is increased, the response is increased, demonstrating the potential for developing a new class of stable and sensitive sensors.

Production and Characterization of Violacein by Locally Isolated Chromobacterium violaceum Grown in Agricultural Wastes

The present work highlighted the production of violacein by the locally isolated Chromobacterium violaceum (GenBank accession no. HM132057) in various agricultural waste materials (sugarcane bagasse, solid pineapple waste, molasses, brown sugar), as an alternative to the conventional rich medium. The highest yield for pigment production (0.82 g L⁻¹) was obtained using free cells when grown in 3 g of sugarcane bagasse supplemented with 10% (v/v) of L-tryptophan. A much lower yield (0.15 g L⁻¹) was obtained when the cells were grown either in rich medium (nutrient broth) or immobilized onto sugarcane bagasse. Violacein showed similar chemical properties as other natural pigments based on the UV-Vis, Fourier transform infrared spectroscopy, thin-layer chromatography, nuclear magnetic resonance, and mass spectrometry analysis. The pigment is highly soluble in acetone and methanol, insoluble in water or non-polar organic solvents, and showed good stability between pH 5-9, 25-100 °C, in the presence of light metal ions and oxidant such as H₂O₂. However, violacein would be slowly degraded upon exposure to light. This is the first report on the use of cheap and easily available agricultural wastes as growth medium for violacein-producing C. violaceum.

Bent-Core and Nematic Liquid Crystal Functionalized Gold Nanorods

Gold nanorods (GNRs) functionalized with trimethoxysilane terminated nematic or bent-core liquid crystals (LCs) are described. In the first step, cetyltrimethylammonium bromide (CTAB) surfactant-stabilized GNRs were prepared using a single step, non-seeding method. The CTAB capping on the GNRs was then replaced in a two-step process first by binding of mercaptopropyltrimethoxysilane followed by immobilization of the nematic or bent-core LC silane by a dehydration condensation. The final LC-decorated GNRs were characterized by UV-vis-NIR spectrophotometry, IR spectroscopy and transmission electron microscopy (TEM). The functionalized nanorods were found to be stable, well dispersible in non-polar organic solvents. The bent-core LC-capped GNRs exhibited only short-range self-assembly after slow evaporation of the solvent on TEM grids. However, the nematic LC-decorated rods displayed regular patterns of self-assembled GNRs on TEM grids after annealing the sample in the presence of an external magnetic field.

Phase-Transfer Assisted Self-Assembly of Noble Metal Nanoparticles

A phase-transfer assisted experimental procedure has been developed for the self-assembly of noble metal nanoparticles prepared by wet-chemistry methods. The protocol calls for firstly the mixing of the metal hydrosol with an ethanol solution of alkylamine, and then the extraction of the alkylamine-stabilized metal nanoparticles into a non-polar organic solvent (such as toluene, hexane, or chloroform). This method offers an effective approach to assemble metal nanoparticles on a substrate. It is therefore an attractive alternative for the preparation of self-assembled nanoparticle layers.

Insight into peptide self-assembly from anisotropic rotational diffusion derived from 13C NMR relaxation

The NMR heteronuclear relaxation rate's dependency on the anisotropy of rotational diffusion motions can be exploited to investigate the supramolecular organization that results from reversible peptide self-assembly in solution. The measurement of longitudinal (R1) and transverse (R2) 13C relaxation rates for several peptide concentrations provides insight both into the orientation of individual molecules within the supramolecular assembly and its growth. The methodology was applied on the pore forming cyclic lipodepsipeptide pseudodesmin A, which reversibly assembles into supramolecular structures of indefinite size in non-polar organic solvents. The information extracted by correlating the 13C R1 and R2 relaxation rates—obtained at natural abundance and at multiple peptide concentrations—with the orientation of the C–H bonds in the monomer conformation demonstrates the existence of an axially symmetric assembly that exhibits unidimensional growth upon increased peptide concentrations. The orientation of the pseudodesmin A peptide within this assembly could be determined accurately and is consistent with the suggested model for the pore forming function and the peptide-peptide interactions within the oligomer.

Supramolecular graphene oxide-alkylamine hybrid materials: variation of dispersibility and improvement of thermal stability

Supramolecular hybrid materials of graphene oxide (GO) with octadecylamine or dodecylamine have been fabricated by a simple self-assembly technique at room temperature. Many characterization methods have been used to research the micelle-like nanostructures. Compared to unmodified GO, the alkyl-functionalized graphene hybrids could be easily dispersed in various nonpolar organic solvents, such as petroleum ether, n-heptane, isooctane, dimethylbenzene etc., rather than in polar solvents. It was found that alkylamine plays a key role during such preparation. Octadecanol (ODO) produced hardly any modification of GO under the conditions, because the so-called product (GO-ODO) exhibits a high degree of similarity to GO in solvent dispersion behaviour and the Fourier transform infrared spectroscopy. The addition of alkylamine significantly improves the thermal stability of the nanomaterials. The improved thermal degradation temperatures can be obtained for polyethylene glycol and polymethyl methacrylate after filling it with as little as 1 wt% of the hybrid, suggesting their great potential as novel nanofillers in industry.

Tuning redox potentials of bis(imino)pyridine cobalt complexes: an experimental and theoretical study involving solvent and ligand effects

The structure and electrochemical properties of a series of bis(imino)pyridine Co(II) complexes (NNN)CoX(2) and [(NNN)(2)Co][PF(6)](2) (NNN = 2,6-bis[1-(4-R-phenylimino)ethyl]pyridine, with R = CN, CF(3), H, CH(3), OCH(3), N(CH(3))(2); NNN = 2,6-bis[1-(2,6-(iPr)(2)-phenylimino)ethyl]pyridine and X = Cl, Br) were studied using a combination of electrochemical and theoretical methods. Cyclic voltammetry measurements and DFT/B3LYP calculations suggest that in solution (NNN)CoCl(2) complexes exist in equilibrium with disproportionation products [(NNN)(2)Co](2+) [CoCl(4)](2-) with the position of the equilibrium heavily influenced by both the solvent polarity and the steric and electronic properties of the bis(imino)pyridine ligands. In strong polar solvents (e.g., CH(3)CN or H(2)O) or with electron donating substituents (R = OCH(3) or N(CH(3))(2)) the equilibrium is shifted and only oxidation of the charged products [(NNN)(2)Co](2+) and [CoCl(4)](2-) is observed. Conversely, in nonpolar organic solvents such as CH(2)Cl(2) or with electron withdrawing substituents (R = CN or CF(3)), disproportionation is suppressed and oxidation of the (NNN)CoCl(2) complexes leads to 18e(-) Co(III) complexes stabilized by coordination of a solvent moiety. In addition, the [(NNN)(2)Co][PF(6)](2) complexes exhibit reversible Co(II/III) oxidation potentials that are strongly dependent on the electron withdrawing/donating nature of the N-aryl substituents, spanning nearly 750 mV in acetonitrile. The resulting insight on the regulation of redox properties of a series of bis(imino)pyridine cobalt(II) complexes should be particularly valuable to tune suitable conditions for reactivity.

Spectroscopic Insights into the Structural Dynamics and Mechanism of Ionophore Function of Valinomycin in Lipid Membranes

The ionophore valinomycin has been well studied as a model carrier depsipeptide, whose proposed mechanism involves the selective complexation of a monovalent cation in solution which is carried across the membrane and released. However, the proposed mechanisms of transport rely primarily on studies done in non-polar organic solvent. Here we present the first spectroscopic studies of valinomycin aimed at structural information done in the presence of a model lipid membrane without the need for sample or solvent modification. Deep-UV resonance Raman spectroscopy with a 197-206 nm excitation range is ideally suited to probe the secondary structure without interference from the lipid moiety. Two lipid environments were investigated, micelles and single unilamellar vesicles, which induce different conformations of valinomycin. Complexation of valinomycin with potassium was also investigated, both with and without competing sodium ions present. Implications for the mechanism of ion transport are discussed.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Solution Processable Phosphorescent Red Luminescent Polymer for OLED Devices

This study reports on the synthesis of red phosphorescent, solution processable chain-end functional, mid-chain- and three-arm star polymers from a functionalized styryl monomer host and a RAFT agent contain- ing a tris-cyclometalated Ir(III) complex phosphorescent group (dopant). The polymerization was carried out in toluene at 120 ˚C, and the resulting polymers showed a narrow molecular weight distribution (- D<1.3) and con- tained approximately 6-11 mol% of the Ir(piq)3 complex. All polymers showed good solubility in non-polar organic solvents and exhibited red emission. Of these polymers, the three-arm star polymer showed better energy trans- fer (in film) compared to the midchain functional and end chain functional polymers. No significant difference in optical properties and energy levels was found for the end functional vs the mid-chain and three-arm star poly- mers. Preliminary device evaluation of the end functional Ir(piq)3 poly(host) showed a current efficiency of 0.4 cd/A at 10 mA/cm 2 and a voltage of 10.5 V with color CIE 1931 coordinate (0.68, 0.31).

Toward the design of superabsorbent materials for non-polar organic solvents and oils: ionic content dependent swelling behaviour of cross-linked poly(octadecyl acrylate)-based lipophilic polyelectrolytes

Oil spills and other industrial chemical leaks to natural environments can cause long-term impact on ecosystems, and the use of polymer-based absorbent materials for such media is a promising technique for cleaning up contaminated sites. Here, we prepared a set of poly(octadecyl acrylate)-based lipophilic polyelectrolyte gels bearing tetraalkylammonium tetrakis(3,5-bis(trifluoromethyl)phenyl) borate (TFPB) with different contents of the ionic groups from 1.0 mol% (EG18(1%)) to 10 mol% (EG18(10%)), and investigated their swelling behaviours in organic solvents and oils. The swelling degrees of the polymer gels in non- or less-polar media (3 < ε < 14) increased both with increasing the contents of TFPB salt on the polymer chain and increasing the dielectric constants of the solvents. The swelling degrees of EG18(10%) in dichloromethane and 1,2-dichloroethane showed over 300 times as much as its dry weight. In nonpolar media (ε < 3) such as toluene and hexane, however, EG18(10%) collapsed and showed low swelling degrees owing to their low dielectric constants. But, the addition of ethanol (ε = 24.6) to them increased the solvent polarities as mixtures, resulting in the high swelling degrees over 100 times by polyelectrolyte effects. The lipophilic polyelectrolyte gels could find applications as protective barriers for volatile organic compounds (VOCs) spilled in the environment and as absorbents for waste oil.

Ultrasonic cavitation induced water in vegetable oil emulsion droplets – A simple and easy technique to synthesize manganese zinc ferrite nanocrystals with improved magnetization

In the present investigation, synthesis of manganese zinc ferrite (Mn 0.5Zn 0.5Fe 2O 4) nanoparticles with narrow size distribution have been prepared using ultrasound assisted emulsion (consisting of rapeseed oil as an oil phase and aqueous solution of Mn 2+, Zn 2+ and Fe 2+ acetates) and evaporation processes. The as-prepared ferrite was nanocrystalline. In order to remove the small amount of oil present on the surface of the ferrite, it was subjected to heat treatment at 300 °C for 3 h. Both the as-prepared and heat treated ferrites have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IR), TGA/DTA, transmission electron microscopy (TEM) and energy dispersion X-ray spectroscopy (EDS) techniques. As-prepared ferrite is of 20 nm, whereas the heat treated ferrite shows the size of 33 nm. In addition, magnetic properties of the as-prepared as well as the heat treated ferrites have also been carried out and the results of which show that the spontaneous magnetization ( σ s) of the heat treated sample (24.1 emu/g) is significantly higher than that of the as-synthesized sample (1.81 emu/g). The key features of this method are avoiding (a) the cumbersome conditions that exist in the conventional methods; (b) usage of necessary additive components (stabilizers or surfactants, precipitants) and (c) calcination requirements. In addition, rapeseed oil as an oil phase has been used for the first time, replacing the toxic and troublesome organic nonpolar solvents. As a whole, this simple straightforward sonochemical approach results in more phase pure system with improved magnetization.

Self-Organization of Gold Nanoparticles Coated with a Monolayer of Azobenzene Liquid Crystals

A gold nanoparticle having a monolayer of azobenzene liquid crystal (LC) was synthesized. The size of the gold nanoparticle obtained was 4.7 nm in average diameter, and it was soluble in common non-polar organic solvents such as toluene and dichloromethane. We confirmed that the reversible photochemical and thermal isomerization of the azobenzene could take place on the surface of the gold nanoparticles in analogy with free azobenzenes in solutions. Furthermore, a 1-dimensional self-organization of the nanoparticle was observed by transmission electron microscopy. However, a gold nanoparticle without LC molecules never showed such self-organization. Therefore, we conclude that the self-organization of the gold nanoparticle is based on the liquid crystallinity of the organic ligands attached on their surface.

Synthesis of NaYF4:Yb3+, Er3+ upconversion nanoparticles in normal microemulsions

An interface-controlled reaction in normal microemulsions (water/ethanol/sodium oleate/oleic acid/n-hexane) was designed to prepare NaYF4:Yb3+, Er3+ upconversion nanoparticles. The phase diagram of the system was first studied to obtain the appropriate oil-in-water microemulsions. Transmission electron microscopy and X-ray powder diffractometer measurements revealed that the as-prepared nanoparticles were spherical, monodisperse with a uniform size of 20 nm, and of cubic phase with good crystallinity. Furthermore, these nanoparticles have good dispersibility in nonpolar organic solvents and exhibit visible upconversion luminescence of orange color under continuous excitation at 980 nm. Then, a thermal treatment for the products was found to enhance the luminescence intensity. In addition, because of its inherent merit in high yielding and being economical, this synthetic method could be utilized for preparation of the UCNPs on a large scale.

Preparation, structure, and a coarse-grained molecular dynamics model for dodecanethiol-stabilized gold nanoparticles

Thiol-stabilized metal nanoparticles possess unique properties in the comparison with larger-scale materials, which enable their use in many promising chemical and biological applications. We have synthesized thiol-coated colloidal gold nanoparticles (AuNP) soluble in non-polar organic solvents by a simplified procedure, in which AuCl 4 - was initially reduced in aqueous phase and then coated with thiol residues and transferred to organic phase. Using the transmission electron micrograph (TEM) imaging, the average diameter of a dodecanethiol-stabilized AuNP was estimated to be 3.75 ± 0.06 nm. Based on the experimental TEM data, a new coarse-grained molecular dynamics model of AuNP was developed. The model was applied for studying self-assembly of AuNPs on a flat graphite surface, enabling further elucidating the structure and packing of the ligand shell around the spherical nanoparticle core.

Neutron and synchrotron radiation scattering by nonpolar magnetic fluids

The complex approach (which comprises different physical methods, including neutron and synchrotron radiation scattering) is justified in the structural analysis of magnetic fluids (MFs). Investigations of MFs based on nonpolar organic solvents with magnetite nanoparticles (2–20 nm in size) coated by various monocarboxylic acids have been performed. It is shown that the use of saturated linear acids with various alkyl chain (C12–C18) lengths instead of unsaturated oleic acid (alkyl chain C18 with a kink in the middle due to the double bond in the cis-configuration) in the classical stabilization procedure for the given type of magnetic fluids leads to a decrease in the mean size and polydispersity of nanoparticles in the final systems.