| 1. |
- Dario, Mårten, et al.
(author)
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Sorption of Cd to colloidal ferric hydroxides : impact of pH and organic acids
- 1997
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In: Chemical speciation and bioavailability. - 0954-2299 .- 2047-6523. ; 9:1, s. 3-14
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Journal article (peer-reviewed)abstract
- The sorption (both ad- and desorption) of Cd to or from colloidal ferric hydroxides as a function of pH, the concentration of organic acids (acetic acid (AA), EDTA, fulvic acid (FA) and malonic acid (MA)), the precipitation procedure for the ferric hydroxide as well as the contact time were investigated in the present study. The concentrations of Cd, colloids and organic acids were chosen to be representative of natural surface waters. The ferric hydroxide were either precipitated in presence of FA or the acid was mixed with the colloids after the purification steps. The presence of FA during the precipitation of ferric hydroxide, had an impact on the size distribution of the solid phase, but it did not have any influence on the sorption behaviour of Cd. The adsorption process was found to be relatively fast and largely pH-dependent. It was fully reversible when the pH was decreased, however, with somewhat slower kinetics. The addition of up to 1 mmol L-1 AA or MA did not cause any measurable desorption of Cd, probably due to the relatively weak complexes formed between Cd(II)-ions and the anions of the acids. Thermodynamic calculations of the distribution between different soluble Cd-species indicated that EDTA and FA would form stronger complexes with Cd. This was indicated in the experiments as enhanced adsorption at low pH-values due to the adsorption of Cd(II)-organic species, and an increase in the soluble fraction at high pH-values caused by competition for Cd(II)-ions between complex forming groups on the surfaces and the soluble organic ligands.
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| 5. |
- Berger, Rolf, et al.
(author)
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Diffusion in Copper Sulphides : An experimental study of chalcocite, chalcopyrite and bornite
- 1996
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Reports (other academic/artistic)abstract
- Diffusion measurements on three copper-containing sulphides have been performed by an electrochemical potentiometric method. -- The diffusion coefficient for chalcocite is in good agreement with values found previously, and a reasonable agreement is also found for chalcopyrite and bornite when our data are compared with values acquired at much higher temperatures with a different technique. The activation energies are remarkably similar for the three sulphides, considering that their relative errors are of a 10% magnitude, which indicates that the bonding strengths and the diffusion mechanisms are similar.
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| 6. |
- Bauschlicher, C.W., et al.
(author)
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A further study of the products of scandium and dioxygen reactions
- 1999
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In: Journal of Physical Chemistry A. - 1089-5639 .- 1520-5215. ; 103:28, s. 5463-5467
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Journal article (peer-reviewed)abstract
- The products of the reaction of Sc and dioxygen have been reinvestigated. By adding the electron-trapping molecule CCl4 additional information about the IR spectra has been obtained, as well as the observation of new bands. New ab initio calculations are also performed on possible products of the Sc plus O-2 reaction. The previously observed band at 722.5 cm(-1) is assigned as the b(2) mode of ScO2-. Bands arising from ScO+, Sc(O-2)(+), and(O-2)ScO are also assigned. We are still unable to assign any bands to OScO. The problems associated with the computational study of ScO2 are discussed.
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| 7. |
- Snis, Anders, et al.
(author)
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Characterizations of (NO)(3)- and N3O2- molecular anions
- 1999
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In: Chemical Physics Letters. - 0009-2614. ; 305:3-4, s. 285-292
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Journal article (peer-reviewed)abstract
- Isomers of (NO)3− are characterized by means of B3LYP density functional theory and the wavefunction-based CASPT2 method. Stabilities, vertical electron detachment energies (VDEs), vertical electron excitation energies (VEEs), and vibration frequencies are determined. Experimental isotope shifts in the IR spectrum of (NO)3− and theory were previously employed to determine the structure of an N–N–N connected anion. Further support for this assignment is obtained in the present study by comparing experimental and theoretical VDEs and VEEs. A parallel analysis of a w-shaped N3O2− molecular anion along the above lines is performed for reference, as a comprehensive understanding of the two systems is sought.
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| 8. |
- Snis, Anders, et al.
(author)
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N2O2, N2O2- and N2O22-: structures, energetics and N-N bonding
- 1997
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In: Chemical Physics. - 0301-0104. ; 221:1-2, s. 1-10
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Journal article (peer-reviewed)abstract
- The density functional theory and the ab initio quantum chemistry methods, Becke3LYP and CASPT2, have been employed to determine structures and energetics of neutral and anionic N2O2 species. When going from a neutral NO dimer to an anionic species the N---N bond lengths decrease drastically and the corresponding N---N frequencies increase. The relative stabilities of the different N2O2− isomers suggest an ONNO structure in a Trans configuration to be the most stable mono valent anion. The formation energies of 1.4–1.7 eV relative to the NO + NO− asymptote are in agreement with experiments. Excitation energies are determined and specific formation channels for three N2O2− isomers are discussed. The hyponitrite ion, N2O22−, is also studied. Its total energy is 2.7–2.8 eV above the total energy of two NO−. In order to connect to an experimental study of NO adsorption on MgO the ability of two NO molecules to form a complex with Mg and Mg+ is investigated.
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| 9. |
- Kjellberg, Alexandra, 1970-
(author)
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Studies of oligosaccharides and carbon-13 enriched bacterial polysaccharides using NMR spectroscopy and computer simulations
- 1998
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Doctoral thesis (other academic/artistic)abstract
- The conformation and dynamics of the trisaccharide methyl β-D-Glcp-(1--> 2)[β-D-Glcp-(1 --> 3)] α-D-Manp and its constituent disaccharides methyl β-D-Glcp-(1 --> 2) α-D-Manp and methyl β-D-Glcp-(1 --> 3) α-D-Manp have been studied using computer simulations and NMR spectroscopy. The computer simulations applied were Metropolis Monte Carlo simulations employing the HSEA force field and Langevin dynamics simulations using the PARM22 and CHEAT95 force fileds. The NMR methods used were measurement of long-range heteronuclear coupling constants across the glycosidic linkages, measurement of carbon-13 nuclear relaxation rates for the determination of dynamical parameters according the Lipari-Szabo "model free" approach and measurements of homonuclear NOE and TROE cross relaxation rates for the determination of proton-proton distances. Experimental data were then compared to the corresponding parameters extracted from the various computer simulations.Studies of the carbon-13 labelled O-polysaccharides from Escherichia coli O25 and O91 have also been performed. 13C-13C TOCSY experiments, with the spin-lock on the carbon-13 nuclei, were applied to sugar residues of different geometries. This circumvented the problem of hampered magnetisation transfer encountered in residues with 3JHH < 2Hz when the spin-lock is applied on the protons.The carbon-13 labelling was also used to demonstrate the biosynthesis of one of the substituents in the Escherichia coli O91 O-polysaccharide.
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| 10. |
- Tryzell, Robert, 1969-
(author)
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Multidetection and chemometrics in flow injection analysis
- 1997
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Doctoral thesis (other academic/artistic)abstract
- An ideal method for the determination of ions in aqueous solutions should be fast, inexpensive, simple, reliable and require small sample volumes. Flow Injection Analysis (FIA) is in many respects such an ideal method but it is too often limited to the determination of one analyte at a time. In this thesis some system design aspects have been addressed. A new system for multianalyte determination has been developed which is based on the hyphenation of FIA with capillary electrophoresis (CE). Chemometrics have been used to optimise the design of this new system and further to optimise the design of a typical single analyte FIA manifold namely a gas diffusion manifold for the determination of ammonia.The second major theme in this work is the development of new signal evaluation methods for FIA and FIA-CE systems. By using a multivariate approach the simultaneous determination of ammonium and excess acid (sulphuric acid) in one single run has been made possible. For conventional two line or gas diffusion applications in FIA, peak area by triangulation was found to be the evaluation method of choice both for "normal" and extended analyte concentration ranges. For the FIA-CE system, which is based on electrokinetic injection, various evaluation methods, both univariate and multivariate, were critically examined and compared. The conductivity corrected peak area method is superior to the traditionally used evaluation principles such as peak height, peak area, standard addition and internal standard methods.
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