Showing papers on "Solvent published in 2005"

Green chemistry: Reversible nonpolar-to-polar solvent

Abstract: Imagine a smart solvent that can be switched reversibly from a liquid with one set of properties to another that has very different properties, upon command. Here we create such a system, in which a non-ionic liquid (an alcohol and an amine base) converts to an ionic liquid (a salt in liquid form) upon exposure to an atmosphere of carbon dioxide, and then reverts back to its non-ionic form when exposed to nitrogen or argon gas. Such switchable solvents should facilitate organic syntheses and separations by eliminating the need to remove and replace solvents after each reaction step.

Effect of Mesoscale Crystalline Structure on the Field‐Effect Mobility of Regioregular Poly(3‐hexyl thiophene) in Thin‐Film Transistors

Abstract: Regioregular poly(3-hexyl thiophene) (RR P3HT) is drop-cast to fabricate field-effect transistor (FET) devices from different solvents with different boiling points and solubilities for RR P3HT, such as methylene chloride, toluene, tetrahydrofuran, and chloroform. A Petri dish is used to cover the solution, and it takes less than 30 min for the solvents to evaporate at room temperature. The mesoscale crystalline morphology of RR P3HT thin films can be manipulated from well-dispersed nanofibrils to well-developed spherulites by changing solution processing conditions. The morphological correlation with the charge-carrier mobility in RR P3HT thin-film transistor (TFT) devices is investigated. The TFT devices show charge-carrier mobilities in the range of 10 - 4 ∼10 - 2 cm 2 V - 1 s - 1 depending on the solvent used, although grazing-incidence X-ray diffraction (GIXD) reveals that all films develop the same π-π-stacking orientation, where the -axis is normal to the polymer films. By combining results from atomic force microscopy (AFM) and GIXD, it is found that the morphological connectivity of crystalline nanofibrils and the -axis orientation distribution of the π-π-stacking plane with respect to the film normal play important roles on the charge-carrier mobility of RR P3HT for TFT applications.

Surface Modification of Magnetic Nanoparticles with Alkoxysilanes and Their Application in Magnetic Bioseparations

Abstract: A versatile and inexpensive method for the introduction of amine groups onto the surface of silica-coated magnetite composite nanoparticles has been established based on the condensation of (aminopropyl)triethoxysilane (APTS). The process was observed to be sensitive to a range of variables, and a range of silane surface-modified nanoparticles was synthesized under various reaction conditions, that is, solvent systems [water, tetrahydrofuran (THF), ethanol, or 1:1 mixtures of them], reaction times (from 1 to 24 h), and temperatures (18, 50, and 70 degrees C), with water as the catalyst and silane at either 0.2% or 2% (w/v) in an attempt to optimize the process. The products of the various reactions were characterized in terms of their possession of surface -NH2 groups, morphologies, and properties with respect to DNA binding and elution before being modified with a single-stranded oligonucleotide capture sequence. It was observed that careful manipulation of temperature, time, and solvent conditions was important for optimal silanization of the nanoparticles, and in our experiments best results were obtained when silanization of the particles in suspension involved use of water as the solvent and APTS at 0.2% (w/v) and when the reaction was conducted at room temperature for 5 h and was preceded by ultrasonication of the particle suspension. The materials produced were used in experiments to selectively capture complementary nucleic acid sequences by hybridization after grafting with an oligonucleotide. The efficiency of the oligonucleotide-modified particles in the capture experiments was observed to be directly related to the original density of amine groups present at the surface of the support. The results indicate that surface engineering of the nanoparticles was possible by silanization under defined, optimized conditions. This approach could be extended to the activation of such surfaces and other materials with other functional groups.

Effect of Solvent and pH on the Structure of PAMAM Dendrimers

Abstract: We report various structural and conformational properties of generations 4, 5, and 6 PAMAM (polyamidoamine) dendrimer [EDA (ethylenediamine) core)] at various protonation levels through extensive molecular dynamics (MD) simulations in explicit solvent. The presence of solvent leads to swelling of the dendrimer (by 33% for G5 compared to the case of no solvent). We find that decreasing the solution from high pH (∼10, no protonation) to neutral (∼7, only primary amines protonated) to low pH (∼4, tertiary amines also protonated) changes the radius of gyration of G5 from 21 to 22 to 25 A, respectively. We also report such other structural quantities as radial density, distribution of terminal groups, solvent accessible surface area and volume, shape, and structure factors (to compare with SAXS and SANS experiments) at various pH conditions. We find significant back-folding of the outer subgenerations in the interior of the molecules at all levels of pH, contrary to original expectations and some SANS experiments but in agreement with other SANS experiments. We find significant water penetration inside the dendrimer, with ∼3 water/tertiary amine for high pH and ∼6 water/tertiary amine for low pH (all for G5). This indicates that the interior of the dendrimer is quite open with internal cavities available for accommodating guest molecules, suggesting using PAMAM dendrimer for guest−host applications. This estimate of internal waters suggests that sufficient water is available to facilitate metal ion binding.

Solvent Effects on the Two-Photon Absorption of Distyrylbenzene Chromophores

Abstract: A series of organic- and water-soluble distyrylbenzene-based two-photon absorption (TPA) fluorophores containing dialkylamino donor groups at the termini was designed, synthesized, and characterized. The central core was systematically substituted to modulate intramolecular charge transfer (ICT). These molecules allow an examination of solvent effects on the TPA cross section (delta) and on the TPA action cross section. In toluene, the delta values follow the order of ICT strength. The effect of solvent on delta is nonmonotonic: maximum delta was measured in an intermediate polarity solvent (THF) and was lowest in water. We failed to find a correlation between the observed solvent effect and previous theoretical predictions. Hydrogen bonding to the donor groups and aggregation of the optical units in water, which are not included in calculational analysis, may be responsible for the discrepancies between experimental results and theory.

Polar Attributes of Supercritical Carbon Dioxide

Abstract: Supercritical carbon dioxide (scCO2) is increasingly promoted as an environmentally benign alternative to conventional organic solvents. The supercritical state bridges the gap between liquid and gaseous states by offering gaslike diffusion rates and liquidlike solvent densities, thereby enabling potential opportunities as a reaction and separation medium in chemical industry. Understanding the solvent behavior of liquid and scCO2 is of critical importance to enable the design of CO2-philic molecular systems and to expand the use of these solvent systems to a wider range of chemical processes. Historically CO2 was treated as a nonpolar solvent, primarily because of its low dielectric constant and zero molecular dipole moment. CO2 has also been described as a quadrupolar solvent because of its significant quadrupole moment. Recent studies suggest that, as far as the microscopic solvent behavior of CO2 is concerned, CO2 has the potential to act as both a weak Lewis acid and Lewis base. Also, strong theoreti...

Comparison of Electrokinetic Properties of Colloidal Fullerenes (n-C60) Formed Using Two Procedures†

Abstract: In this study we report on the electrokinetic behavior of colloidal aggregates of C60fullerenes (n-C60) produced through two different techniques: solvent exchange and extended mixing with water. In the first technique, used to produce colloidal materials in several recent toxicity and transport studies, an organic solvent such as tetrahydrofuran (THF) is used to dissolve the C60 before mixing with water. The second technique is more indicative of conditions that might occur in natural aquatic systems. Both types of n-C60 were observed to be negatively charged under a variety of solution chemistries; however, the n-C60 formed using THF was more strongly charged. We conclude that n-C60 likely acquires charge through charge transfer from the organic solvent (when present) and surface hydrolysis reactions. Nevertheless, C60 is capable of acquiring charge and becoming dispersed as n-C60 in water without the aid of organic solvents, a pathway that may be important in determining the mobility of fullerenes in ...

Solvent hydrolysis and templating effects in the synthesis of metal-organic frameworks

Abstract: Hydrolysis of the DMF or DEF solvent influences the nature of the product observed in the reaction between zinc(II) nitrate and 1,4-benzenedicarboxylic acid, with dialkylammonium cations able to template the formation of anionic networks.

Electrolyte and battery

Abstract: PROBLEM TO BE SOLVED: To provide a battery capable of enhancing high temperature characteristics. SOLUTION: A separator is impregnated with an electrolyte. The electrolyte contains a solvent and an electrolyte salt. The solvent contains halogenated ethyl carbonate such as 4-fluoro-1,3-dioxolane and a phosphorus-containing compound such as trimethyl phosphate. Thereby, chemical stability at high temperature can be increased. By furthermore containing vineylene carbonate as the solvent, higher effect can be obtained. COPYRIGHT: (C)2007,JPO&INPIT

Proteomic Analysis Reveals the Participation of Energy- and Stress-Related Proteins in the Response of Pseudomonas putida DOT-T1E to Toluene

Abstract: Pseudomonas putida DOT-T1E is tolerant to toluene and other toxic hydrocarbons through extrusion of the toxic compounds from the cell by means of three efflux pumps, TtgABC, TtgDEF, and TtgGHI. To identify other cellular factors that allow the growth of P. putida DOT-T1E in the presence of high concentrations of toluene, we performed two-dimensional gel analyses of proteins extracted from cultures grown on glucose in the presence and in the absence of the organic solvent. From a total of 531 spots, 134 proteins were observed to be toluene specific. In the absence of toluene, 525 spots were clearly separated and 117 proteins were only present in this condition. Moreover, 35 proteins were induced by at least twofold in the presence of toluene whereas 26 were repressed by at least twofold under these conditions. We reasoned that proteins that were highly induced could play a role in toluene tolerance. These proteins, identified by matrix-assisted laser desorption ionization-time of flight mass spectrometry, were classified into four categories: 1, proteins involved in the catabolism of toluene; 2, proteins involved in the channeling of metabolic intermediates to the Krebs cycle and activation of purine biosynthesis; 3, proteins involved in sugar transport; 4, stress-related proteins. The set of proteins in groups 2 and 3 suggests that the high energy demand required for solvent tolerance is achieved via activation of cell metabolism. The role of chaperones that facilitate the proper folding of newly synthesized proteins under toluene stress conditions was analyzed in further detail. Knockout mutants revealed that CspA, XenA, and Tuf-1 play a role in solvent tolerance in Pseudomonas, although this role is probably not specific to toluene, as indicated by the fact that all mutants grew more slowly than the wild type without toluene.

Hydrogen Production from Hydrolytic Oxidation of Organosilanes Using a Cationic Oxorhenium Catalyst

Abstract: We describe herein the novel application of a transition metal oxo complex, a cationic oxorhenium(V) oxazoline, in the production of molecular hydrogen (H2) from the catalytic hydrolytic oxidation of organosilanes. The main highlights of the reaction are quantitative hydrogen yields, low catalyst loading, ambient conditions, high selectivity for silanols, water as the only co-reagent, and no solvent requirement. The amount of hydrogen produced is proportional to the water stoichiometry. Thus, reaction mixtures of polysilyl organics such as HC(SiH3)3 and water contain potentially >6 wt % hydrogen. Kinetic and isotope labeling experiments have revealed a new mechanistic paradigm for the activation of Si−H bonds by oxometalates.

Solvothermal Synthesis of CdS Nanowires in a Mixed Solvent of Ethylenediamine and Dodecanethiol

Abstract: CdS nanowires with an average diameter of 25 nm and lengths of 20−40 μm have been solvothermally synthesized in a mixed solvent of ethylenediamine and dodecanethiol at 180 °C. The time-dependent examinations reveal that the formation process of CdS nanowires involves two sequential processes: a short-period solid−solid transformation process in the initial stage and a long-period Ostwald ripening process. The effect of both the volume ratios between the two components of the solvent and the reaction temperatures on the nanowire growth has also been investigated in detail. The results of the photoluminescence and UV−vis spectroscopy measurements reveal that the as-prepared CdS nanowires show a quantum confinement effect.

Noncrystalline phases in poly(9,9-di-n-octyl-2,7-fluorene).

Abstract: Selective formation of amorphous, nematic (N), and β phases in poly(9,9-di-n-octyl-2,7-fluorene) (PFO) films was achieved via judicious choice of process parameters. Phase structure and film morphology were carefully examined by means of X-ray diffraction as well as electron microscopy. “Amorphous” thin films were obtained by quick evaporation of solvent. Slow solvent removal during film formation or extended treatment of the amorphous film with solvent vapor resulted in predominantly the β phase, which corresponds to a frozen (due to decreased segmental mobility upon solvent removal) and intrinsically metastable state of transformation midway between a solvent-induced clathrate phase and the equilibrium crystalline order in the undiluted state. The frozen transformation process is reactivated upon an increase in temperature beyond 100 °C. Compared to the amorphous film, extended backbone conjugation in the β phase is evidenced from the emergence of a characteristic absorption peak around 430 nm near the ...

Investigation on Aggregate Formation of Ionic Liquids

Abstract: Understanding the behavior of ionic liquids on the molecular level is essential for explaining solubilizing or reaction processes, including catalytic reactions in ionic liquids or with ionic liquids as co-solvent. Using mass spectrometry techniques it is possible to characterize their aggregate formation behavior, which depends on the used solvent. With increasing polarity of the solvent and decreasing ionic liquid concentration, the size of the formed aggregates decreases. From conductivity measurement curves “critical aggregate concentrations” were calculated, which confirm the results of mass spectrometry measurements. Addition of ionic liquids increases the solubility of acetophenone in water. This effect can be explained by the aggregate formation ability of ionic liquids. The findings can be used to explain the outstanding solubility and solvation properties of ionic liquids.

1H-1,2,4-Triazole: An Effective Solvent for Proton-Conducting Electrolytes

Abstract: We report 1H-1,2,4-triazole as an actived group to enhance proton conduction in liquid electrolytes and in polymer electrolyte membreanes (PEMs) 1H-1,2,4-triazole and PEMs containing 1H-1,2,4-triazole are stable in a wide potential range, implying excellent electrochemical stability under fuel cell operating conditions

Spectroelectrochemical Investigations of Soluble Polyaniline Synthesized via New Inverse Emulsion Pathway

Abstract: A new inverse emulsion protocol has been developed for the synthesis of polyaniline (PANI), which can be dissolved completely in common organic solvents such as chloroform. Benzoyl peroxide is used as the oxidizing agent and toluene + 2-propanol−water is used as the solvent. Dodecylbenzenesulfonic acid (DBSA) has been selected as the dopant because it also functions as the surfactant. Cyclic voltammetry and spectroelectrochemical investigations were carried out to study the electroactivity, UV−Vis response, and metal-to-insulator transition of the chemically synthesized PANI as a function of applied electrode potential. At more positive potentials, cyclic voltammograms of PANI in aqueous acids show two oxidation waves caused by redox processes of PANI as observed with electrochemically prepared PANI. Peak position and shape are influenced by the slow anion exchange rate. Electrical conductivity of the material is relatively high as the minimum resistance value is nearly 10 Ω. SEM investigations show that ...

Influence of composition and heat-treatment on the charge transport properties of poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester blends

Abstract: Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends have been demonstrated to form highly efficient polymer photovoltaic devices. In this letter, the time-of-flight technique is used to investigate the influence of composition and heat treatment on charge transport properties of P3HT and PCBM blends. The transport of electrons and holes both display a transition from dispersive to nondispersive and return to dispersive again as the percentage of PCBM increases. A balanced mobility of both electron and hole is obtained at a composition of 1:1 weight ratio, and it is nearly independent of the electrical field in the range of our test. The increase in carrier mobility is attributed to the formation of a more-ordered structure in the blend. This structural ordering is further enhanced by slowly evaporating the solvent during film formation which results in additional increase in carrier mobility. However, no such effect is observed in thick films (∼200nm), indicating the...

An explicit quantum chemical method for modeling large solvation shells applied to aminocoumarin C151.

Abstract: The absorption spectra of aminocoumarin C151 in water and n-hexane solution are investigated by an explicit quantum chemical solvent model. We improved the efficiency of the frozen-density embedding scheme, as used in a former study on solvatochromism (J. Chem. Phys. 2005, 122, 094115) to describe very large solvent shells. The computer time used in this new implementation scales approximately linearly (with a low prefactor) with the number of solvent molecules. We test the ability of the frozen-density embedding to describe specific solvent effects due to hydrogen bonding for a small example system, as well as the convergence of the excitation energy with the number of solvent molecules considered in the solvation shell. Calculations with up to 500 water molecules (1500 atoms) in the solvent system are carried out. The absorption spectra are studied for C151 in aqueous or n-hexane solution for direct comparison with experimental data. To obtain snapshots of the dye molecule in solution, for which subsequent excitation energies are calculated, we use a classical molecular dynamics (MD) simulation with a force field adapted to first-principles calculations. In the calculation of solvatochromic shifts between solvents of different polarity, the vertical excitation energy obtained at the equilibrium structure of the isolated chromophore is sometimes taken as a guess for the excitation energy in a nonpolar solvent. Our results show that this is, in general, not an appropriate assumption. This is mainly due to the fact that the solute dynamics is neglected. The experimental shift between n-hexane and water as solvents is qualitatively reproduced, even by the simplest embedding approximation, and the results can be improved by a partial polarization of the frozen density. It is shown that the shift is mainly due to the electronic effect of the water molecules, and the structural effects are similar in n-hexane and water. By including water molecules, which might be directly involved in the excitation, in the embedded region, an agreement with experimental values within 0.05 eV is achieved.