Showing papers on "Solvent published in 1997"

Pore Structure Control of Silica Gels Based on Phase Separation

Abstract: In the alkoxy-derived sol-gel system, various macroporous morphologies can be obtained by inducing the phase separation parallel to the sol-gel transition. This principle of macroporous morphology control can be best applied to pure silica and silica-based multicomponent oxide systems. The earlier the phase separation takes place than the sol-gel transition, the larger the characteristic sizes of pores and gel skeletons become. The time resolved light scattering measurements revealed that the morphology formation process exhibits the features of spinodal decomposition and that the final gel morphology is determined by the competitive kinetics between the domain coarsening and the structure freezing by sol-gel transition. The mesopore structure of such macroporous gel skeletons could be easily tailored by the solvent exchange procedures. Silica gels with controlled macropores and mesopores were successfully applied as a material for the continuous rod type column for high performance liquid chromatography.

Method of applying drug-release coatings

Abstract: The invention is directed to a method of applying drug-release coatings whereby a polymer can be dissolved in a first solvent (solvent A) to form a polymer system and a drug can be dissolved or suspended in a second solvent (solvent B) to form a drug system. The coating or layer of coating so formed comprises a substantially uniform combination of the drug and polymer. Solvent B can be the same as or different than solvent A. The coating can be applied on a stent body by separately spraying or dipping the polymer system and the drug system onto the devices. The coating can be accomplished by either applying the polymer and drug systems sequentially or simultaneously. In certain embodiments, a drug can be suspended in solvent B. In some cases, three or more systems can be utilized. For instance, a third system containing pure solvent A or B can smooth the coating surface, if the solvent of the third spraying system is compatible with the polymer matrix.

Extraction of a hydrophilic compound from water into liquid CO2 using dendritic surfactants

Abstract: Dendrimers are well defined, highly branched polymers1,2,3,4,5 that adopt a roughly spherical, globular shape in solution. Their cores are relatively loosely packed and can trap guest molecules5,6,7, and by appropriate functionalization of the branch tips the macromolecules can act as unimolecular micelle-like entities6. Here we show that dendrimers with a fluorinated shell are soluble in liquid carbon dioxide and can transport CO2-insoluble molecules into this solvent within their cores. Specifically, we demonstrate the extraction of a polar ionic dye, methyl orange, from water into CO2 using these fluorinated dendrimers. This observation suggests possible uses of such macromolecules for the remediation of contaminated water, the extraction of pharmaceutical products from fermentation vessels, the selective encapsulation of drugs for targeted delivery6,7 and the transport of reagents for chemical reactions (such as polymerization8,9,10,11) in liquid and supercritical CO2 solvents.

Personal care compositions

Abstract: Aerosolized compositions including a cyclic oligosaccharide; a fragrance; a volatile solvent; and a propellant; wherein the aerosolized composition is free of nonvolatile solvents are described herein. The aerosolized compositions and methods disclosed herein may provide a longer lasting fragrance.

Self-Assembly of Bisurea Compounds in Organic Solvents and on Solid Substrates

Abstract: New low molecular weight gelators based on the structure R-NHCONH-X-NHCONH-R have been synthesized and tested for their ability to cause gelation of organic solvents. Compounds 2 (R = n-dodecyl, X = -(CH2)(9)-), 3 (R = n-dodecyl, X = -(CH2)(12)-), 4 (R = n-dodecyl, X = 4,4'-biphenyl), and 5 (R = benzyl, X = -(CH2)(9)-) form thermoreversible gels with a wide range of organic solvents, at concentrations well below 10 mg mL(-1). Depending on the nature of the R and X groups, the solvents that undergo gelation include hexadecane, p-xylene. 1-octanol, n-butyl actetate, cyclohexanone, and tetralin. The gels are stable up to temperatures well above 100 degrees C, but are easily disrupted by mechanical agitation. Light microscopic investigations revealed that compounds 2-5 spontaneously aggregate to form thin flat fibers, which can be several hundreds of micrometers long and only 2-10 mu m wide. Depending on the solvent, multiple twists in the fibers are observed. In the gels, these fibers form an extended three-dimensional network, which is stabilized by multiple mechanical contacts between the fibers. Electron microscopy and X-ray powder diffraction revealed that the fibers consist of stacks of sheets. The thickness of the sheets is 3.65 and 3.85 nm for 2 and 3, respectively. Scanning tunneling microscopic investigations of 2 absorbed on graphite showed that 2 forms ion ribbons with a width of 5.0 nm. In the ribbons the molecules have a parallel arrangement, with the long molecular axis perpendicular to the long ribbon axis. The two urea groups within a given molecule are each part of mutually parallel extended chains of hydrogen bonds, Based on these observations a model is proposed for the arrangement of the molecules in the fibers, In this model the bisurea molecules aggregate through hydrogen-bond formation into long ribbons, which assemble into sheets. In these sheets the ribbons are tilted. Finally, the sheets stack to form lone thin fibers. This model is supported by molecular dynamics simulations.

Extracting Information from the Temperature Gradients of Polypeptide NH Chemical Shifts. 1. The Importance of Conformational Averaging

Abstract: A detailed analysis of backbone amide NH chemical shift temperature gradients (Δδ/ΔT values) for proteins and highly cross-linked peptides reveals that hydrogen-bonded exchange-protected NHs are characterized by Δδ/ΔT values of −2.0 ± 1.4 ppb/°C while exposed NHs typically display gradients of −6.0 → −8.5 ppb/°C; however, numerous exceptions to these generalizations occur. For partially folded peptides (rather than proteins), exceptions are more common than concordance with this rule; Δδ/ΔT values ranging from −28 to +12 ppb/°C have been observed. In the case of the peptide systems for which exchange protection data is available, the common practice of assuming that a Δδ/ΔT value less negative than −4 ppb/°C indicates that the NH is sequestered from solvent is shown to have zero predictive validity. The analysis of the data for partially folded peptides, protein fragments, and other peptides which are expected to display minimal structuring reveals a significant correlation between Δδ/ΔT and the deviation...

Macrocycle Based Membrane Sensors for the Determination of Cobalt(II) Ions

Abstract: Poly(vinyl chloride) (PVC) based membranes of macrocycles, 5,7,7,12,14,14-hexamethyl-1,4,8,11- tetraazacyclotetradeca-4,11-diene diperchlorate (I), 3,5,7,7,10,12,14,14-octamethyl-1,4,8,11-tetraazacyclo- tetradeca-4,11-diene diperchlorate (II) and 5,10,15,20-tetraphenylporphyrin(III) with sodium tetraphenylborate (STB) as an anion excluder and dibutyl phthalate (DBP), dioctyl phthalate (DOP), dibutyl butylphosphonate (DBBP) and 1-chloronaphthalene (CN) as plasticizing solvent mediators were prepared and investigated as Co 2 + -selective electrodes. The best performance was observed with the membrane having the composition III–PVC–STB–DBP in the ratio 3:8:1:8, which works well over a wide concentration range (8.0 × 10 - 6 –1.0 × 10 - 1 mol l -1 ) with a Nernstian slope of 29.0 mV per decade of activity between pH 2.8 and 7.3. This electrode shows a fast response time of 20 s and was used over a period of 4 months with good reproducibility (s = 0.4 mV). The selectivity coefficient values of the order of 0.01 for mono-, di- and trivalent cations indicate excellent selectivity for Co 2 + over a large number of cations. Anions such as Cl - and SO 4 2 - do not interfere and the electrode also works satisfactorily in a partially non-aqueous medium. The sensor has been used as an indicator electrode in the potentiometric titration of Co 2 + with EDTA.

Spectroscopy and structure of solvated alkali-metal ions

Abstract: Vibrational pre-dissociation spectroscopy combined with mass spectrometry has been used to obtain the infrared spectra of mass-selected cluster ions. The onset of new spectroscopic features, as a function of solvent number, has been shown to correspond to specific structural changes such as the filling of solvent shells and the formation of hydrogen bonds. These small finite systems offer a number of advantages over traditional solution-based measurements and perhaps are the most useful way to test current theoretical calculations and models. Whereas thermodynamic properties, derived from high-pressure mass spectrometry measurements, give some indication of solvent shell size, vibrational spectra suggest a more complex picture. When combined with recent infrared studies of size-selected neutral clusters, considerable detail of the solvent structure about the ion can be obtained. The solvation of the alkali-metal ions Na and Cs by a number of solvents, including water, will be discussed. Future directions ...

Effect of Solvent on Titania Particle Formation and Morphology in Thermal Hydrolysis of TiCl4

Abstract: Titania powders were synthesized by the thermal hydrolysis of titanium tetrachloride with the yield of above 85% in a mixed solvent of n-propanol and water. The morphology of the precipitates was controlled by adjusting the volume ratio of n-propanol to water (RH ratio) of the mixed solvent. Precipitates obtained with an RH ratio of 0 were fine, and highly agglomerated. In contrast, an RH ratio of 3 resulted in precipitates consisting of uniform and discrete particles. According to observations of the zeta potentials of precipitates and the dielectric constants of solvents, the discrete particles obtained with an RH ratio of 3 resulted from the low zeta potential and dielectric constant. The result of Fourier transform infrared (FTIR) spectroscopy showed the chemical interaction of particle surface with the solvent alcohol, which decreased the zeta potential of precipitates with an increase of RH ratio. Adding hydroxypropyl cellulose (HPC) as a steric dispersant made it possible to reduce the size of particles to the submicrometer range. Effects of the solvent on the formation and morphology of the resulting particles were investigated.

Hydrogen Atom Abstraction by Permanganate: Oxidations of Arylalkanes in Organic Solvents.

Abstract: Oxidations of arylalkanes by nBu4NMnO4 have been studied in toluene solvent: toluene, ethylbenzene, diphenylmethane, triphenylmethane, 9,10-dihydroanthracene, xanthene, and fluorene. Toluene is oxidized to benzoic acid and a small amount of benzaldehyde; other substrates give oxygenated and/or dehydrogenated products. The manganese product of all of the reactions is colloidal MnO2. The kinetics of the reactions, monitored by UV/vis spectrometry, show that the initial reactions are first order in the concentrations of both nBu4NMnO4 and substrate. No induction periods are observed. The same rate constants for toluene oxidation are observed in neat toluene and in o-dichlorobenzene solvent, within experimental errors. The presence of O2 increases the rate of nBu4NMnO4 disappearance. The reactions of toluene and dihydroanthracene exhibit primary isotope effects: kC7H8/kC7D8 = 6 (±1) at 45 °C and kC14H12/kC14D12 = 3.0 (±0.6) at 25 °C. The rates of oxidation of substituted toluenes show only small substituent...

Novel Reverse Micelles Partitioning Nonaqueous Polar Solvents in a Hydrocarbon Continuous Phase

Abstract: Reverse microemulsions have been characterized in isooctane and decane using the surfactant Aerosol-OT (AOT) and the polar solvents formamide, ethylene glycol, acetonitrile, methanol, N,N-dimethylformamide, and 1,2-propanediol. Dynamic light scattering (DLS) experiments show that reverse micelles form in these solutions. The DLS data and steady-state absorption spectra of Coumarin 343 in these solutions reveal that the character of these reverse micelles depends partially upon the solubility of the polar solvent in the hydrocarbon. For formamide and ethylene glycol, which are highly immiscible in the hydrocarbon solvents, changes in micellar size occur for variations in the volume fraction φ of the polar solvent and surfactant in the continuous phase as well as for the traditional changes in w. These reverse micelles with w = 1.1 and φ = 0.006−0.051 exhibit diameters ranging from 5.0 to 26.1 nm. For the solvents acetonitrile, methanol, N,N-dimethylformamide, and 1,2-propanediol, which are slightly miscibl...

Solvent-assisted proton transfer in catalysis by zeolite solid acids

Abstract: Intermolecular proton transfer in the gas phase is usually strongly disfavoured because the charged products are highly unstable. It is promoted in aqueous solution, however, because the high dielectric constant (e = 78.3) of water allows efficient stabilization of the corresponding cations and anions. Zeolites—microporous catalysts used in petroleum refining and the synthesis of chemical feedstocks—provide another medium for proton-transfer reactions1,2,3, because their anionic aluminosilicate frameworks are highly acidic. The low dielectric constant of zeolites (e ≈ 1.6; ref. 3) suggests, however, that such processes in the zeolite channels should involve concerted action rather than strong charge separation, and thus resemble gas-phase reactions. Here we demonstrate that solution-like proton-transfer behaviour can be induced in zeolites. We find that the co-injection of nitromethane into a catalytic flow reactor clearly enhances the conversion of methanol, isopropanol and acetone over the zeolite catalyst HZSM-5. Conservation of nitromethane during the course of reaction and its effects on the reactant–zeolite interaction complex seen by solid-state NMR indicate that nitromethane behaves in a manner similar to polar solvents: it promotes proton transfer by stabilizing ion-pair structures. These findings suggest that rationally selected solvents might provide a simple means to increase the efficiency of these industrially important catalysts.

Solution behavior of polyethylene oxide in water as a function of temperature and pressure

Abstract: A model of the solution behavior for hydrosoluble polymers [based on a model of Matsuyama and Tanaka, Phys. Rev. Lett. 65, 341 (1990)] is introduced that accounts for hydrogen bonding of solvent molecules onto polymer chains. In the limit of small volume fraction of H-bonded solvent molecules, the resulting free energy has the standard Flory-Huggins form with a good solvent contribution to the effective \ensuremath{\chi} parameter coming from the fraction of solvents H bonded to the chain. This simple theory is capable of semiquantitatively explaining the experimental temperature-concentration (T-\ensuremath{\varphi}) and temperature-pressure (T-P) phase diagrams of polyethylene oxide in water.

A Generalized Solvent Acidity Scale: The Solvatochromism of o-tert-Butylstilbazolium Betaine Dye and Its Homomorph o,o′-Di-tert-butylstilbazolium Betaine Dye†

Abstract: A total of 121 organic solvents were studied and classified by means of the solvatochromic comparison method of Kamlet and Taft, to give a solvent acidity scale for hydrogen-bond donor solvents based on the parameter SA. This parameter can readily be evaluated from the visible spectrum of a suitable basic probe (o-tert-butylstilbazolium betaine dye, TBSB) and its non-basic homomorph (o,o′-di-tert-butylstilbazolium betaine dye, DTBSB). The proposed scale has many advantages when compared to the more widely used acidity scales such as that based on Gutmann's acceptor number (AN) and the Taft-Kamlet α scale. Whilst data for the proposed scale are derived from electronic transitions only, they do provide an accurate description for solvent acidity effects in spectroscopy and other chemical areas, including thermodynamics and kinetics.

A Chloride Ion-Selective Solvent Polymeric Membrane Electrode Based on a Hydrogen Bond Forming Ionophore

Abstract: A chloride-selective solvent polymeric membrane electrode based on a neutral hydrogen bond forming ionophore, poly(vinyl chloride) (PVC), the plasticizer 2-nitrophenyl octyl ether (o-NPOE), and cationic sites (50 mol %, relative to the ionophore) is described. At pH 7.0 (HEPES buffer), this electrode responds to chloride in a linear range from 10-5 to 10-2 M with a slope of (−54.0 ± 1.0) mV/decade and a detection limit of (6.5 ± 3.0) × 10-6 M. As compared to conventional anion-exchanger electrodes, the interference of SCN-, Br-, NO3-, I-, and even salicylate is considerably reduced, as shown by the selectivity coefficients determined with the matched potential method (MPM) in the chloride concentration range 10-2.34−10-2.04 M (log (MPM): Sal-, +1.8; SCN-, +1.6; NO3-, +0.7; I-, +0.5; Br-, +0.4). Because the discrimination of the more hydrophilic anions SO42-, HSO3-/SO32-, OAc-, HCO3-, and H2PO4-/HPO42- is too large for a determination of accurate selectivity coefficients in this high chloride concentratio...

Polarity of Liquid Interfaces by Second Harmonic Generation Spectroscopy

Abstract: A spectroscopic method, based on the interface selectivity of second-harmonic generation, is used to obtain the polarity of liquid interfaces. In this paper the second-harmonic measurement of the spectrum of the polarity indicator molecule N,N‘-diethyl-p-nitroaniline (DEPNA) at the air/water interface demonstrates the method. Two different approaches are used to measure the intramolecular charge transfer (CT) absorption band position of DEPNA at the air/water interface. The DEPNA CT band blue-shifts from 429 nm in bulk water (polar solvent) to 359 nm in bulk hexane (nonpolar solvent) and 329 nm in the gas phase (no solvent). At the air/water interface, the charge transfer peak band maximum occurs at 373 nm, which indicates that the polarity of the air/water interface is similar to those of the bulk solvents carbon tetrachloride and butyl ether. The DEPNA results together with the results from another solvatochromic polarity indicator molecule, ET(30), which will be reported elsewhere, show that the polari...

Biodegradation of phenol at high initial concentrations in two-phase partitioning batch and fed-batch bioreactors

Abstract: A two-phase organic-aqueous system was used to degrade phenol in both batch and fed-batch culture. The solvent, which contained the phenol and partitioned it into the aqueous phase, was systematically selected based on volatility, solubility in the aqueous phase, partition coefficient for phenol, biocompatibility, and cost. The two-phase partitioning bioreactor used 500 mL of 2-undecanone loaded with high concentrations of phenol to deliver the xenobiotic to Pseudomonas putida ATCC 11172 in the 1-L aqueous phase, at subinhibitory levels. The initial concentrations of phenol selected for the aqueous phase were predicted using the experimentally determined partition coefficient for this ternary system of 47.6. This system was initially observed to degrade 4 g of phenol in just over 48 h in batch culture. Further loading of the organic phase in subsequent experiments demonstrated that the system was capable of degrading 10 g of phenol to completion in approximately 72 h. The higher levels of phenol in the system caused a modest increase in the duration of the lag phase, but did not lead to complete inhibition or cell death. The use of a fed-batch approach allowed the system to ultimately consume 28 g of phenol in approximately 165 h, without experiencing substrate toxicity. In this system, phenol delivery to the aqueous phase is demand based, and is directly related to the metabolic activity of the cells. This system permits high loading of phenol without the corresponding substrate inhibition commonly seen in conventional bioreactors.

Hydrogen-transfer hydrodehalogenation of aromatic halides with alcohols in the presence of noble metal catalysts

Abstract: Catalytic hydrodehalogenation of aromatic halides was carried out in an alcohol solution containing base compounds in the presence of carbon-supported noble metal catalysts. It was found that dechlorination of 1,2,4-trichlorobenzene to benzene effectively occurred in a 2-propanol solution of a base compound such as NaOH or KOH in the presence of Rh/C or Pd/C at temperatures below 65°C. When deuorium-labeled 2-propanol, CD3CD(OD)CD3, was used as a solvent, 1,2,4-trichlorobenzene was dechlorinated to give benzene containing D atoms with high yield, indicating that the hydrodechlorination reaction includes hydrogen-transfer from 2-propanol to chlorobenzenes. Iodo-, bromo- and fluoro-benzenes were also readily dehalogenated in the catalytic system.

Cell surface properties of organic solvent-tolerant mutants of Escherichia coli K-12.

Abstract: In this study, we examined cell surface properties of mutants of Escherichia coli for which organic solvent tolerance levels were elevated. The cell surface of each mutant was less hydrophobic than that of the parent, probably due to an increase in lipopolysaccharide content. OmpF synthesis was repressed in the mutants. Organic solvent bound readily to viable E. coli cells in response to the polarity of the solvent. The mutants were bound less abundantly with the organic solvent than was the parent.

How many water molecules are actively involved in the neutral hydration of carbon dioxide

Abstract: The detailed reaction pathways for the hydration of carbon dioxide by water and water clusters containing two, three, and four water molecules (CO2 + nH2O → H2CO3 + (n − 1)H2O, n = 1−4) have been investigated in both gas phase and aqueous solution using ab initio molecular orbital (MO) theory up to the quadratic configuration interaction QCISD(T)/6-31G(d,p)//MP2/6-31G(d,p) level, both SCRF and PCM models of continuum theory, and a mixed approach based on MO calculations in conjunction with Monte Carlo and reaction field simulations. It is confirmed that the CO2 hydration constitutes a case of active solvent catalysis where solvent molecules actively participate as a catalyst in the chemical process. In aqueous solution the hydration mechanism is multimolecular, where geometric parameters of the solvent fully intervene in the reaction coordinate. The hydration reaction was found to proceed through an attack of a water oxygen to the CO2 carbon in concert with a proton transfer to a CO2 oxygen. The proton tr...