Effect of pulp composition on the characteristics of residuals in CMC made from such pulps

Four different spruce sulphite pulp samples were used for the preparation of carboxymethylcellulose (CMC). The characteristics of the unreacted fibre and particle residuals obtained in the CMC-preparation were used to establish a correlation between the hemicellulose in the pulp and the intrinsic viscosity, i.e.,␣cellulose chain length and the occurence of unreacted residuals. It was shown that the residual particles in the CMC consisted of fibres, fibre fractions and gel particles of different degrees of substitution. The results suggested that pulps with long cellulose chains, i.e., pulps with high intrinsic viscosities, resulted in particles that were more substituted and more swollen. These pulps also resulted in more substituted hemicelluloses in the CMC and more substituted residuals. It was also suggested that galactoglucomannan in the cellulose pulps is favourable for the swelling which results in more substituted hemicelluloses in the CMC and more swollen residuals. The amount of residuals was influenced mainly by the characteristics of the cellulose in the pulp. It is therefore believed that a combination of high viscosity and a suitable combination of hemicelluloses is the most favourable way of eliminating the occurrence of undissolved residuals in CMC.     

Preconcentration and separation of copper (II) with solvent extraction using N,N′-bis(2-hydroxy-5-bromo-benzyl)1,2 diaminopropane

Preconcentration and separation with solvent extraction of Cu(II) from aqueous solution using N,N′-bis(2-hydroxy-5-bromo-benzyl)1,2 diaminopropane (H₂L) as the new extractant has been studied. Separation of Cu(II) from other metal ions such as Cd(II), Ni(II), Zn(II), Pb(II), Cr(III), Co(II) and Mn(II) at aqueous solutions of various pH values and complexing agent H₂L, has been described. The possible extraction mechanism and the compositions of the extracted species have been determined. The separation factors for these metals using this reagent are reported while efficient methods for the separation of Cu(II) from other metal ions are proposed. From the loaded organic phase, Cu(II) stripping was carried out in one stage with different mineral acid solutions. The stripping efficiency was found to be quantitative in case of HNO₃ and HCl. From quantitative evaluation of the extraction equilibrium data, it has been deduced that the complex extracted is the simple 1:1 chelate, CuL. The extraction constant has a value of logK_ex=−4.05±0.04.     

Determination of microcystins in fish by solvent extraction and liquid chromatography

A liquid chromatography electrospray mass spectrometry (LC/ESI/MS) method has been developed to identify and quantify microcystins in fish liver and intestine. Microcystins (MCs) were extracted from 500 mg sample with methanol-water (85:25, v/v) and the extracts concentrated to 250 microl. The parameters were optimized by a full factorial 2(3) design. Neither laborious pre-treatment nor clean up were necessary. MCs were separated using conventional C18 column and an acetonitrile-acidified water (pH 3) gradient. Negative samples (without MCs) were discriminated by liquid chromatography diode array detection (LC/DAD). The limits of detection (LOD) and the limits of quantification (LOQ) resulted equal for MC-RR, MC-YR, and MC-LR and were 0.1 and 0.5 microg g(-1), respectively. MCs recoveries at three levels in spiked samples (0.5-3.0 microg g(-1)) were > 92%, with relative standards deviations (RSDs) < 16% for liver samples and > 68% with RSDs < 18% for intestine samples. The proposed method was applied to determine MC-LR in exposed fish to evaluate the bioaccumulation risk. The results showed the transference of MC-LR from cyanobacterial cells to fish tissues.     

Molecular dynamics study of the tautomeric equilibrium in the 4-nitro- and 2,4,6-trichloro derivatives of 2-(N,N-dialkyloaminomethyl)phenol

 Molecular dynamics thermodynamic integration (MDTI) method and quantum chemical calculations at the density functional theory B3LYP 6-31+(d,p) level, which included the Tomasi model of the solvent reaction field, were applied to study the tautomeric equilibrium of Mannich base in methanol solution. The values obtained for the free-energy difference are in good agreement with experimental data. However, the results from quantum mechanical calculations were not as good as the results of MDTI simulations owing to inappropriate treatment of intermolecular hydrogen bonds between the solute molecule and the first shell of solvent molecules in the Tomasi model of the solvent reaction field. The radial distribution functions between solute atoms and solvent atoms confirmed the formation of hydrogen bonds between the solute molecule and surrounding methanol molecules and indicated that the zwitterionic form is associated more with an organized solvent structure at the level of the first solvation shell than is the molecular form. Received: 26 April 2002 / Accepted: 9 September 2002 / Published online: 31 March 2003     

A new regioselective synthesis and ambient light photochemistry of quinazolin-1-oxides

Quinazolin-1-oxides were prepared by the oxidation of tetrahydroquinazolines with H₂O₂-tungstate and their ambient light photochemistry was investigated. Substituent effects on their photochemical cyclization and the reactions of the products 1aH-[1,2]oxazireno[2,3-a]quinazolines under photochemical and thermal conditions are reported. The cyclization of quinazolin-1-oxides and the reactions of 1aH-[1,2]oxazireno[2,3-a]quinazolines show pronounced solvent isotope and solvent effects.     

Solvent Sublation Using Dithizone as a Ligand for Determination of Trace Elements in Water Samples

Solvent sublation was studied as a method of separating and pre-concentrating traces of Zn(II), Cd(II) and Cu(II) as diphenylthiocarbazone (dithizone) complexes for their determination. The experimental conditions, such as pH of solution, amount of dithizone as ligand, stirring time, gas flow rate and flotation time, were optimized. Different non-ionic surfactants and types of organic solvents were optimized for efficient sublation. The analyte ions in a 350mL sample were complexed as metal-dithizone complexes by adding 10mL of 0.084% dithizone, 0.5mL of 0.1% nonylphenol polyoxyethylene ether (NP) and 10mL of pH 4.3 potassium hydrogen phthalate-sodium hydroxide buffer solution. The solution was stirred with a mechanical stirrer for 30min. It was transferred to a flotation cell, and the complexes were floated by bubbling air and extracted into 10mL of methylisobutyl ketone (MIBK) on the surface of the aqueous solution. The analytes in the organic phase were determined by flame atomic absorption spectrometry (F-AAS) for Zn(II) and by graphite furnace atomic absorption spectrometry (GF-AAS) for Cd(II) and Cu(II). The proposed method was applied to determine Zn(II), Cd(II) and Cu(II) in real water samples; the enrichment factor was more than 37, the RSD was less than 4.26%, recoveries ranged from 92.7 to 107.3%, and the detection limits were 1.0µgL^–1 for Zn(II), 0.006µgL^–1 for Cd(II) and 0.06µgL^–1 for Cu(II). The results obtained were satisfactory.     

TheT 1 state ofp-nitroaniline and related molecules: A CNDO/S study

The nature of the lowest energy triplet state (T ₁) ofp-nitroaniline (PNA), N,N-dimethyl-p-nitroaniline (DMPNA) and nitrobenzene (NB) is reexamined using the semiempirical CNDO/S-CI method with selected parameter options. The present results indicate that in the case of theunperturbed molecules the short-axis polarized * n() triplet largely localized at the acceptor end of the molecule may lie lower in energy than the triplet manifold counterpart of the intense intramolecular charge-transferD ⁺ A ^–singlet excitation. Computations suggest, however, that polar solvents strongly stabilize the PNA and DMPNA * charge-transfer triplet relative to other excitations, whereas specific solvent hydrogen-bonded interactions stabilize the * n() triplet of NB below those of * character. These assignments allow a rationalization of phosphorescence lifetime data,T _n T ₁ absorption measurements and relative photochemical behavior.     

INDO-SCPT calculations of the solvent dependence of some carbon-proton spin-spin coupling constants

Summary A theoretical study of the effects of non-specific solute-solvent interactions on the directly bonded carbon-proton couplings¹ J(C–H), in acetaldehyde, acetone and acrylonitrile is presented. The solvent induced changes in these couplings calculated by an INDO-SCPT procedure incorporating a modified solvaton model are in satisfactory agreement with experiment and show significant improvement over the INDO-FPT calculations using the Klopman-Germer solvaton model.

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INDO-SCPT-Rechnungen der Lösungsmittelabhängigkeit einiger C-H-Kopplungskonstanten

Zusammenfassung Es wird eine theoretische Studie zu den nichtspezifischen Lösungsmittelwechselwirkungen auf die Spin-Spin-Kopplungen direkt aneinander gebundener C- und H-Atome von Acetaldehyd, Aceton und Acrylnitril vorgestellt. Die vom Solvens induzierten Änderungen der Kopplungskonstanten werden von der INDO-SCPT-Methode unter Verwendung eines modifizierten Solvationsmodells zufriedenstellend wiedergegeben. Die Übereinstimmung mit den experimentellen Daten ist besser als INDO-FPT-Rechnungen mit dem Klopmann-Germer-Solvaton-Modell.

     

Concurrent solvent evaporation for on-line coupled HPLC-HRGC

A technique is proposed which allows introduction of very large volumes of liquid (10 ml were tested) into capillary columns equipped with short (1–2 m long) retention gaps. It is based on concurrent solvent evaporation, i.e. evaporation of the solvent during introduction of the sample. The technique presupposes high carrier gas flow rates (at least during sample introduction) and column temperatures near the solvent boiling point. The major limitation of the method is the occurrence of peak broadening for solutes eluted up to 30°, in some cases up to 100°, above the injection temperature. This is due to the absence of solvent trapping and a reduced efficiency of phase soaking. Therefore, use of volatile solvents is often advantageous. Application of the concurrent solvent evaporation technique allows introduction of liquids which do not wet the retention gap surface. However, the method is still not very attractive for analysis of aqueous or water-containing solutions (reversed phase HPLC).     

The influence of solvation on π *←n and π *←π transition energies in molecules containing Aza or carbonyl groups

The influence of solvation on ^*n and ^* transition energies of formaldehyde, acetaldehyde, acetone, pyridine and 1,2-, 1,3-, 1,4-diazabenzenes has been investigated through CNDO calculations.A static solvation model which distinguishes a) molecules directly involved in hydrogen bonding with solute, b) the layer of molecules in contact with the solute molecule and c) the main of molecules farther from solute, is presented.Blue and red shifts due to solvent effects are correctly predicted by calculations for each model.