Optimising oxygen-sensitivity of optical sensor using pyrene carboxylic acid by myristic acid co-chemisorption onto anodic oxidized aluminium plate

Optical oxygen-sensitivity using pyrene carboxylic acid with long alkyl chain (1-pyrenedecanoic acid and 1-pyrenedodecanoic acid) and myristic acid co-chemisorption layer was controlled by varying the molar ratio of myristic acid to pyrene carboxylic acid. The ratio I₀/I₁₀₀, where I₀ and I₁₀₀ represent the detected fluorescence intensities from a substrate exposed to 100% argon and 100% oxygen, respectively, is used as an indicator of the sensitivity of the sensing film. At a composition ratio of 1 pyrene carboxylic acid to 10 myristic acids, the I₀/I₁₀₀ attained its maximum value and then the ratio decreased with increase in the molar ratio of myristic acid to pyrene carboxylic acid. The Stern-Volmer constant (K_SV) also attained its maximum value at a composition ratio of one pyrene carboxylic acid to ten myristic acids and then the ratio decreased with increase in the molar ratio of myristic acid to pyrene carboxylic acid. The oxygen-sensitivity of optical sensor using pyrene carboxylic acid is optimized by myristic acid co-chemisorption.     

The extraction of copper(I), lead(II) and tin(IV) from hydrochloric acid by solutions of tetra-n-hexylammonium chloride in ethylene dichloride

Copper(I) is strongly extracted from chloride media as the ion-pair NR₄+CuCl₃-by solutions of tetra-n-hexylammonium chloride (NR₄+Cl-) in ethylene dichloride. The distribution coefficient decreases from ca. 100 in 1 M chloride but is still as high as 13 in 10 M chloride. The extraction of lead(II) is shown to be due to the partition of the ion-pair (NR₄+PbCI₃-). The percentage of 0.0018 M lead extracted is 98% from 0.58 M hydrochloric acid and falls to 38% from 7.8 M acid. The distribution coefficient decreases rapidly with the total lead concentration. The extractions of tin(IV) increased to a maximum of 99.5% in ca. 5 M hydrochloric acid but decreased rapidly above 6 M acid. It proved impossible to identify the extractable species.     

The extraction of niobium (V) and Tantalum (V) by Octylarsinic acid in chloroform

Dioctylarsinic acid (HDOAA) in chloroform solution extracts Nb(V) and Ta(V) efficiently from solutions containing oxalate and oxalic acid at hydrochloric acid concentrations greater than 1M.The extraction coefficients are 92.5 at 7M hydrochloric acid and 251 at 6M hydrochloric acid for niobium and tantalum, respectively. These metals can be extracted even more efficiently from sulfuric acid solutions. The results of the reagent- and pH-dependence studies suggested that a trimeric, monobasic oxoacid of niobium, associated with ten HDOAA molecules, is extracted. Tantalum appears to be present in the organic phase as (H₂DOAA)⁺ [Ta(C₂O₄)₃ (HDOAA_n] (n=l or 2).     

The luminescent properties of polyethylene films with admixtures of luminophores based on europium compounds

Polyethylene films activated with europium(III) complexes with carboxylic acids and Eu(L)₃ · nD · xH₂O + ANT compositions, where L is the trifluoroacetic, toluyl, or cinnamic acid anion and ANT is anthranilic acid, were prepared. The intensity of luminescence of the polymeric compositions depended on the content of luminophores (molar ratio between europium compounds and anthranilic acid). An analysis of the excitation spectra showed that, in polymer—Eu(L)₃ · nPhen · xH₂O + ANT compositions, there was effective energy transfer from phenanthroline to anthranilic acid levels.     

The acidity of superacidic media derived from fluorosulfuric acid and trifluoromethanesulfonic acid

The acidity level of superacidic media derived from fluorosulfuric acid and trifluoromethanesulfonic acid (TFMS) was determined by using the potentiometric indicators tetrachloroquinone and tetrafluoroquinone. A voltammetric and potentiometric study of these indicators was conducted to evaluate their pH indicator range, from the strongest acid media (SbF₅ solution) to the strongest base media (H₂O or KF solution). The R₀ function in 1 M strong base medium was found to be R₀ = ?17.2 (fluorosulfuric acid) and R₀ = ?16 (TFMS). The autoprotolysis constant (pK_i) was evaluated in both solvents; pK_i = 6.1 (fluorosulfuric acid) and pK_i = 6 (TFMS).     

Hydrogen bonding of catechol groups in the crystal structure of dihydrocaffeic acid

Dihydrocaffeic acid C₉H₁₀O₄ is a natural antioxidant. The crystal structure of dihydrocaffeic acid is determined; the crystallographic data at 100 K are: a = 11.3189(4) Å, b = 5.5824(1) Å, c = 13.8431(4) Å, β = 109.248(4)°, and V = 825.80(4) ų; the space group is P2₁/c, Z = 4. In addition to the formation of hydrogen bonds that are typical of acids, the compound has features that are important from the viewpoint of reactivity of dihydrocaffeic acid molecules. The position of one of the hydroxyl hydrogen atoms in the catechol group is disordered even at 100 K. The crystal structure of caffeic acid does not show such a disordering.     

Synthesis of ACAT inhibitors through substitution using allylic picolinate and copper reagent

Amide of an octanoic acid possessing an aryl group at C3 position is a highly potent ACAT inhibitor. In this paper, we describe a synthetic access to this class of compounds as optically active forms. The key reaction is substitution of the allylic picolinate of (S,Z)-8-(benzyloxy)oct-5-en-4-ol with a copper reagent derived from (benzo[d][1,3]dioxol-4-yl)MgBr and CuBr·Me₂S to produce anti S_N2′ product regio- and stereo-selectively. The product was hydrogenated to afford (S)-3-benzo[d][1,3]dioxol-4-yloctan-1-ol, which upon oxidation furnished the octanoic acid. Finally, the acid was converted with 2,6-(i-Pr)₂C₆H₃NH₂ to the target amide via acid chloride. In a similar way, the one-carbon long homolog was synthesized.     

Chelation of manganese(II) with quinaldic acids. An NMR relaxation study

Manganese(II) enhanced spin-lattice relaxation rates (1/T_1p) of ¹H and ¹³C nuclei in quinoline-2-carboxylic acid, 8-methoxyquinoline-2-carboxylic acid, 8-hydroxyquinoline-2-carboxylic acid, 8-aminoquinoline-2-carboxylic acid, and 6-(hydroxymethyl)pyridine-2-carboxylic acid were measured in aqueous solution at various temperatures. Relative metal-nucleus distances were calculated from the r^?6 dependence of 1/T_1p. The results indicate that the Mn²⁺ ion in the 8-methoxyquinaldic acid chelate is coordinated to the carboxyl oxygen atom and the nitrogen atom but not t the methoxyl oxygen atom.     

Plutonium extraction from mixed aqueous media. Plutonium—Uranium separation

A systematic study is presented on Pu IV extraction with tri-n-butyl phosphate and trilaurylamine from binary mixtures of H₂SO₄ with HCl and HBr. The addition of sulfuric acid to the mentioned mineral acid solutions, was found to affect appreciably D_Pu, which recommended some useful purification procedures. The effect of water-miscible alcohols on the extraction of plutonium from HCl and HNO₃ solutions was also investigated.     

Dichromate dosimetry: The effect of acetic acid on the radiolytic reduction yield

The radiation chemical yield for the reduction of dichromate, Cr(VI) → Cr³⁺, in an acidic aqueous perchloric acid solution of potassium dichromate, may be increased from 0.04 to >0.2 μ mol J^-1 by adding acetic acid. The increased yield, G[-(Cr₂O₇)^2-] is about the same in N_2- and O₂-saturated solutions. The molar linear absorption coefficient at 350 nm also is the same in both solutions (ϵ_m = 2800 M^-1cm^-1) at pH 0.4. The proposed mechanism to explain the enhanced response in N₂-saturated solutions involves the efficient reaction of acetic acid with hydroxyl radicals by the abstraction of H from the methyl group; the resulting acid radicals react with relatively high yield to reduce Cr(VI). In O₂-saturated solution, the acetic acid radical apparently goes through an acetic acid peroxyl radical by a bimolecular reaction to the tetroxide intermediate of acetic acid, which releases H₂O₂ with relatively high yield by a Bennett-type reaction. This additional H₂O₂, as a reducing agent, reacts slowly with dichromate and boosts the value of G[-(Cr₂O₇)^2-]. The negative slope of the response (ΔA vs dose) continues to increase during the period immediately after irradiation of oxygenated solution, due to slow reaction of radiolytically-produced H₂O₂ with dichromate. There is also in both O₂- and N₂-saturated solution a long-term slow reaction involving oxidation of the organic substrate (in this case, acetic acid). Because of these instabilities, the solutions cannot readily be used for dosimetry without the presence of silver ions, which in the oxidized state, Ag²⁺, act to stabilize the solution after irradiation. The addition of silver dichromate at a concentration of 0.1 mM decreases the yield to G[-(Cr₂O₇)^2-] = 0.17 μmolJ^-1, but greatly improves the stability of the solution after irradiation. The absorbed dose range for the modified dichromate dosimeter when analyzed spectrophotometrically at 350 nm wavelength is approx. 2 × 10²-2 × 10³ Gy.     

Synthesis and characterization of aliphatic unsaturated polyesters from trans-4-octene-1,8-dioic and trans-3-hexene-1,6-dioic acids

The influence of the double bond on the thermodynamic parameters, T_m, ΔH_m and ΔS_m of some unsaturated aliphatic polyesters has been found to depend on the number of —CH₂— groups separating the double bond from the ester linkage. Thus, T_m's of the polyesters derived from trans-4-octene-1,8-dioic acid (OD) are lower than those for the corresponding saturated polyesters; no such effect has been observed by comparing T_m's of polyesters derived from trans-3-hexene-1,6-dioic acid (HD) and adipic acid respectively. X-ray investigation has shown, for polyesters of the OD series, the presence of the two polymorphic forms.     

Separation of fuel additive levulinic acid using toluene,xylene, and octanol from water stream

Levulinic acid is an important fuel additive due to its multifunctionality with keto and carboxylic functional groups. It also carries the potential to produce some other fuel additives viz. γ-valerolactone, ethyl levulinate, and 2-methyl tetrahydrofuran. These substances can be combined with petroleum-derived transportation fuels similarly to bioethanol without modifying in engines. The wastewater and solid wastes from various industries contain organic acids in the downstreams. The recovery and separation of organic acids from wastewater is challenging due to its dilute concentrations and other issues. The presented study involves the separation of levulinc acid from the waste-water stream using various solvents such as toluene, xylene, and octanol at 25°C. The experimental results were described in terms of the partition constant (P_c), dimerization constant (D_c), distribution coefficients (K_D), and extraction efficiency (E_η). The present study can significantly contribute to the recovery of levulinic acid as fuel additive levulinic with low-cost process.     

Determination of oxygen content in YBa2Cu3O6.5+x

A method for determining the oxygen content of the high-temperature superconductor YBa₂Cu₃O_6.5+x is described. The superconductor is dissolved in 4.4 M hydrobromic acid, forming bromine. The mixture is then diluted with hydrochloric acid to obtain a solution of bromine and Cu(II) in 0.44 M hydrobromic acid and 1.1 M hydrochloric acid. As(III) is added in slight excess of that required to react with the bromine and the unreacted As(III) is determined by titration with potassium bromate. Oxygen does not interfere. The results of this method are in agreement with those of other iodimetric procedures. The dissolution of the superconductor in 4.4 M hydrobromic acid is much faster than in hydrochloric acid, the medium used in one iodimetric technique. YBa₂Cu₃O_6.5+x sintered fibers and powder samples weighing from ca. 0.5 to 200 mg were analyzed for oxygen content.     

The quantitative separation of calcium from magnesium,aluminium and other elements by cation-exchange chromatography in ethanol-hydrochloric acid

Magnesium can be separated from calcium by elution with 3.0 M hydrochloric acid containing 60% ethanol from a column of AG₅₀W-X8 cation-exchange resin. Calcium is retained and can be eluted with 3.0 M hydrochloric acid or 2.0 M nitric acid. The separation factor of (α_Mg^ca=5.6 is considerably higher than that in aqueous hydrochloric acid and comparable to those obtained with organic complexing reagents. Separations are sharp and quantitative; up to 10 mmol of magnesium can be separated from 0.01 mmol of calcium and vice versa on a 60-ml column. Al, Fe(III), Mn, Ni(II), Co(II), Zn, Cd, Cu(II), Pb(II), U(VI), Be, Ga, Ti(IV) in the presence of H₂O₂ and many other elements accompany magnesium and can be separated from calcium quantitatively. Sr, Ba, Zr, Hf, Th, Sc, La and the rare earths are retained together with Ca, but can be separated by other methods.     

LC-DAD-ESI-MS Characterization of Carbohydrates Using a New Labeling Reagent

A novel labeling reagent 1-(2-naphthyl)-3-methyl-5-pyrazolone (NMP) coupling to liquid chromatography with electrospray ionization mass spectrometry for the detection of carbohydrates from the derivatized rape bee pollen samples is reported. Carbohydrates are derivatized to their bis-NMP-labeled derivatives. Derivatives showed an intense protonated molecular ion at m/z [M+H]⁺ in positive-ion detection mode. The mass-to-charge ratios of characteristic fragment ions at m/z 473.0 could be used for the accurately qualitative analysis of carbohydrates. This characteristic fragment ion is from the cleavage of C2–C3 bond in carbohydrate chain giving the specific fragment ions at m/z [MH-C _m H_2m+1O _m -H₂O]⁺ for pentose, hexose and glyceraldehydes and at m/z [MH-C _m H_2m-1O _m+1-H₂O]⁺ for alduronic acids such as galacturonic acid and glucuronic acid (m = n ? 2, n is carbon number of carbohydrate). No interferences for all aliphatic and aromatic aldehydes presented in natural environmental samples were observed due to the highly specific parent mass-to-charge ratio and the characteristic fragment ions. The method, in conjunction with a gradient elution, offered a baseline resolution of carbohydrate derivatives on a reversed-phase Hypersil ODS-2 column. The carbohydrates such as mannose, galacturonic acid, glucuronic acid, rhamnose, glucose, galactose, xylose, arabinose and fucose can successfully be detected.     

Optical constants of electrochemically synthesized polyindole and poly(5-carboxilic acid indole)

The optical properties and optical constants of the polyindole and poly(5-carboxilic acid indole) conductive polymers synthesized and doped electrochemically with ClO ₄ ^? in acetonitrile solution were investigated by means of transmittance and reflectance spectra, in the wavelength range of 300–800 nm. Absorption band centered at 425 nm assigned to the direct allowed electron transition (π → π*) from valence band to the conduction band. The optical band gap, E _g , was determined out of the optical absorption spectra. The E _g increases from 2.17 eV for polyindole film to 2.40 eV for poly(5-carboxilic acid indole) polymer thin film, which is attributed to the effect of electron withdrawing carboxylic acid functional group on the growth of chain length of the polymer during the electropolymerization. The oscillator energy E ₀, dispersion energy E _d and other parameters were determined by the Wemple-DiDomenico method.     

Determination of the kinetic parameters for the electrothermal atomization of gold with and without chemical modifiers

The effect of various experimental parameters and the presence of chemical modifiers on the atomization kinetics of gold have been investigated. The dissipation process of the atomic vapour is also studied and the diffusion parameters calculated in the absence and in the presence of chemical modifiers. The chemical modifiers studied are ascorbic acid, rhenium, palladium and rhodium. In the absence of chemical modifiers, a two-precursor atomization mechanism is observed in distinctive different temperature regions. When a long pyrolysis step and low masses of gold are employed, an atomization from dispersed particles with low E_a value is observed in the low temperature region (LT region). At high masses of gold, a fractional order atomization from gold agglomerates with high, mass-dependent, E_a values, approaching the heat of vaporization, ΔH_vap, is observed in the high temperature region (HT region). In the presence of ascorbic acid, a high E_a value is obtained in the LT region, suggesting a fast atomization from surface particles at the active sites produced by the pyrolysis of ascorbic acid and a low E_a value is obtained in the HT region, with first-order kinetics, which indicates a desorption process through the micropores of the amorphous carbon residue of ascorbic acid. In the presence of 5 μg Re, a two-precursor mechanism is also found, with a high E_a value in the LT region, suggesting vaporization from small clusters, and a low E_a value in the HT region with a first-order kinetics, indicating vaporization of disperse particles from the graphite surface. In the presence of 0.1–1 μg Pd, a two-precursor mechanism is also observed. The first process, in the LT region, has a low E_a value, which indicates vaporization of disperse particles from the available free active sites of the graphite surface. The second process, in the HT region, begins at the appearance temperature of Pd and shows a high E_a value and first-order kinetics, which means that release of gold atoms occurs only after the vaporization of Pd has begun. In the presence of Rh, a mass-dependent E_a value is found in the LT region, suggesting atomization from gold clusters. However, in the HT region, the generation of atomic vapour of Au is kinetically controlled by the release of the Rh modifier.     

Biomimetic total synthesis of colneleic acid and its function as a lipoxygenase inhibitor

A biomimetic synthesis of colneleic acid (2) from 9(S)-hydroperoxy-10(E),12(Z)-octadecadienoic acid (1) is reported. The lipoxygenase of potato which converts linoleic acid to 1 was found to be strongly inhibited by acid 2 (K_i = 8μM).