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- Maliniak, Arnold, et al.
(author)
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NUCLEAR-SPIN RELAXATION STUDY OF HYDROGEN-BONDING IN SOLUTIONS OF QUINUCLIDINE
- 1984
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In: Journal of Physical Chemistry. - 0022-3654. ; 88:23, s. 5628-5631
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Journal article (peer-reviewed)abstract
- The intermolecular hydrogen bonds formed by quinuclidine together with different solvents (benzene, chloroform, methanol, trifluoroacetic acid) are studied by using NMR relaxation measurements. The carbon-1 3 and nitrogen-I4 relaxation rates are determined and Woessner's model for dipole relaxation in a symmetric rotor is applied. The different values for the ratio between the rotational diffusion constants RII and R, in different solvents and at different temperatures are discussed in terms of molecular reorientation anisotropy due to hydrogen bonds formed by quinuclidine and the solvent. From the nitrogen-14 relaxation rates the quadrupole coupling constants (QCC) are evaluated and compared with the results of quantum-chemical calculations of electric field gradients performed on model systems.
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- Agnemo, Roland, 1944-
(author)
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Ligniners reaktioner med alkalisk väteperoxid
- 1981
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Doctoral thesis (other academic/artistic)abstract
- Under alkaline conditions hydrogen peroxide can be used either as a 1ignin-degrading or a 1ignin-preserving bleaching agent. If heavy metal ions are present and/or silicate is absent in the reaction medium, hydrogen peroxide decomposes via hydroxyl radicals and superoxide ions to oxygen and water. These decomposition products are able to react for example with phenolic lignin structures and thereby cause a partial degradation of lignin. In such a system peroxide could act as a bleaching and delignifying agent at the same time and these properties can be utilized for the bleaching of chemical pulps.In order to elucidate the factors which influence the degradation of phenolic structures by oxidation with alkaline hydrogen peroxide the lignin model compounds-methylsyringyl alcohol was studied.By determining the first order reaction rate constants for the oxidation, the main results which were obtained indicate that phenolic lignin structures can be efficiently degraded especially if:A. The pH in the bleaching liquor is close to the pK -valueàfor hydrogen peroxide.B. The ionic strength in the bleaching medium is as high as possible.C. A fixed amount of heavy metal ions (manganese) is added to the bleaching liquor.In the presence of silicate and diethylentriaminepenta-acetic acid (DTPA) hydrogen peroxide is stabilized against decomposition. Under these conditions alkaline hydrogen peroxide is able to react only with lignin units containing conjugated carbonyl groups such as quinone, aryl-oe-carbonyl and cinnamaldehyd structures, leading to an elimination of the chromophoric structures without any substantial dissolution of lignin. In this part of work we have elucidated the kinetic behavior and the reaction products from lignin model compounds of the aryl-of- carbonyl and cinnamaldehyde types.1,2-Diarylpropan-1,3,-diol structures constitute an important building unit in native lignins. We have demonstrated that under hydrogen peroxide bleaching conditions the model compound 2,3--bis(4-hydroxy-3-methoxyphenyl)-3-ethoxy-propanol was converted to stilbenes, ûe. structures which when present in pulps may contribute to a rapid yellowing. The results obtained with model compounds under simulated lignin retaining bleaching conditions demonstrate that there are possibilities to improve the bleaching of mechanical pulps with hydrogen peroxide if:A. The remaining heavy metal ions complexed with DTPA are present in their lowest valence states.B. The concentration of hydroperoxy ions can be maintained at a high level at the lowest possible pH-value.
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- Allard, Bert, et al.
(author)
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Actinide Sorption on Rock Minerals
- 1981
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In: Proceedings of the International Seminar on Chemistry and Process Engineering for High Level Liquid Waste. ; Jül Conf 42
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Conference paper (other academic/artistic)
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- Andersson, Barbro, 1940-
(author)
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Analysis of plant growth regulating substances
- 1982
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Doctoral thesis (other academic/artistic)abstract
- Natural plant growth regulators (phytohormones) are a group of organic compounds which, in very small amounts, act as regulators of physiological processes in plants.Methods were developed for the analysis of phytohormones in samples from Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris (L.) Karst»). Identification of abscisic acid, 3-indoleacetic acid, gibbe-rellin Ag and the conjugate N-(3-indoleacetyl)aspartic acid was performed by GC-MS as their methyl esters. A quantitative determination of abscisic acid was made by GC-ECD and this method was also applied to anther samples of Anemone canadensis. 3-Indole-acetic acid and N-(3-indoleacetyl)aspartic acid were quantified by reversed-phase HPLC and spectrofluorimetric detection. Dichlorophene, used as a growth regulator in containerized seedlings of pine and spruce, was analysed by GC-MID in peat and paper.
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