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| 2. |
- Nygren, Martin, et al.
(författare)
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Identification of 2,3,7,8-substituted polychlorinated dioxins and dibenzofurans in environmental and human samples
- 1986. - 1
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Ingår i: Chlorinated dioxins and dibenzofurans in perspective. - Boca Raton : CRC Press. - 9781315891545 - 9781351070645 ; , s. 17-34
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) are two series of tricyclic, almost planar aromatic compounds that exhibit very similar physical, chemical, and biological properties. The human exposure to PCDDs and PCDFs by milk consumption is not negligible. Detection levels in ecological and human samples should be orders of magnitude below the usual detection levels obtained in pesticide analyses. One objective of the study is to identify background levels of PCDDs and PCDFs in these samples, especially those of human origin. The spectrum of toxic effects is species dependent but for humans they include chloracne and porphyria cutane tarda and for other animals edema, thymic atrophy, teratogenicity, liver lesions and a slow wasting syndrome followed by death. It is evident that it is of particular importance to identify the ultimate source or sources of the toxic 2,3,7,8-substituted PCDDs and PCDFs found as background constituents in the environmental and human samples, especially the samples of mother's milk, which are of toxicological interest.
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| 3. |
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| 4. |
- Agnemo, Roland, 1944-
(författare)
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Ligniners reaktioner med alkalisk väteperoxid
- 1981
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 5. |
- Andersson, Barbro, 1940-
(författare)
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Analysis of plant growth regulating substances
- 1982
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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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| 10. |
- Antoni, Gunnar, et al.
(författare)
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Synthesis of gamma-amino[4-11C]butyric acid.
- 1989
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Ingår i: Journal of labelled compounds & radiopharmaceuticals. - 0362-4803 .- 1099-1344. ; 27, s. 571-
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Tidskriftsartikel (refereegranskat)
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| 11. |
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| 12. |
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| 14. |
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| 15. |
- Berglin, Ewa H., MD, PhD, 1955-, et al.
(författare)
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Potentiation by sulfide of hydrogen peroxide-induced killing of Escherichia coli
- 1985
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Ingår i: Infection and Immunity. - : American Society for Microbiology. - 0019-9567 .- 1098-5522. ; 49:3, s. 538-543
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Tidskriftsartikel (refereegranskat)abstract
- L-Cysteine potentiates 100-fold the hydrogen peroxide-induced killing of a growing culture of Escherichia coli K-12 (Berglin et al., J. Bacteriol. 152:81-88). In the present study it is shown that hydrogen sulfide is formed from L-cysteine and that sodium sulfide could substitute for L-cysteine in the potentiation of hydrogen peroxide-induced killing of E. coli K-12. Addition of an amino acid, L-leucine, L-valine, or L-alanine, to an L-cysteine-containing medium with a growing culture of E. coli K-12 inhibited hydrogen sulfide formation and the potentiation of hydrogen peroxide-induced killing. These amino acids did not inhibit hydrogen sulfide formation from L-cysteine by a cell extract, and they did not inhibit the potentiation by sulfide of hydrogen peroxide-induced killing. This indicated that the amino acids protected the culture from L-cysteine-potentiated, hydrogen peroxide-induced killing by inhibiting the transport of L-cysteine into the cell. The potentiation by sodium sulfide of hydrogen peroxide-induced killing was abolished by the metal ion chelator 2,2'-bipyridyl. This indicated that metal ions, in addition to sulfide, were involved in the killing. Toxic effects of hydrogen peroxide are often presumed to be mediated by hydroxyl radicals formed in iron-catalyzed reactions. It was demonstrated that iron sulfide was more efficient than ferrous iron in catalyzing the formation of hydroxyl radicals from hydrogen peroxide. It was suggested that hydrogen sulfide formed in polymicrobial infections may play an important role in the host defense by potentiating the antimicrobial effect of hydrogen peroxide produced by phagocytic cells.
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| 16. |
- Berglin, Ewa, MD, PhD, 1955-, et al.
(författare)
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Potentiation by L-cysteine of the bactericidal effect of hydrogen peroxide in Escherichia coli
- 1982
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Ingår i: Journal of Bacteriology. - : American Society for Microbiology. - 0021-9193 .- 1098-5530. ; 152:1, s. 81-88
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Tidskriftsartikel (refereegranskat)abstract
- Under anaerobic conditions an exponentially growing culture of Escherichia coli K-12 was exposed to hydrogen peroxide in the presence of various compounds. Hydrogen peroxide (0.1 mM) together with 0.1 mM L-cysteine or L-cystine killed the organisms more rapidly than 10 mM hydrogen peroxide alone. The exposure of E. coli to hydrogen peroxide in the presence of L-cysteine inhibited some of the catalase. This inhibition, however, could not fully explain the 100-fold increase in hydrogen peroxide sensitivity of the organism in the presence of L-cysteine. Of other compounds tested only some thiols potentiated the bactericidal effect of hydrogen peroxide. These thiols were effective, however, only at concentrations significantly higher than 0.1 mM. The effect of L-cysteine and L-cystine could be annihilated by the metal ion chelating agent 2,2'-bipyridyl. DNA breakage in E. coli K-12 was demonstrated under conditions where the organisms were killed by hydrogen peroxide.
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| 17. |
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| 18. |
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| 19. |
- Ding, Yu-Shin, et al.
(författare)
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Synthesis of L-[5-11C]ornithine.
- 1989
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Ingår i: Journal of labelled compounds & radiopharmaceuticals. - 0362-4803 .- 1099-1344. ; 27, s. 1079-
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Tidskriftsartikel (refereegranskat)
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| 20. |
- Engdahl, Anders, et al.
(författare)
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Axial motion of water hydrogen halide and water halogen complexes in argon matrices
- 1986
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Ingår i: The Journal of chemical physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 84:4, s. 1981-1987
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Tidskriftsartikel (refereegranskat)abstract
- The infrared spectra of the water (H2O, HDO, D2O) complexes with HCl, HBr, HI Cl2, Br2, and I2 have been studied in argon matrices in the 11 to 25 K interval. In all cases, water acts as a lone-pair donor. The hydrogen halide complexes are effectively planar and rotate around the axis through the heavy atoms. For the water halogen complexes, the results are less clear, but a similar rotation, coupled to low wave number bending motions, seems possible.
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| 21. |
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| 22. |
- Grahn, Hans, 1954-
(författare)
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Paramagnetic relaxation reagents : nuclear magnetic resonance studies of preferential solvation
- 1986
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The interactions between neutral paramagnetic relaxation reagents (PARR's) and certain aromatic compounds have been studied by 1H and 13 C spin-lattice relaxation time measurements. In media such as cyclohexane and carbon tetrachloride, Cr(acac)3 becomes preferentially solvated by aromatic solutes. The solvation is significantly suppressed in a more interacting solvent like dichloromethane. Paramagnetic induced chemical shifts of the aromatic outer sphere ligand indicate in addition to relaxation data, a preferential orientation caused by dipole-dipole interactions. For benzene or for several alkylated benzenes which have small or no permanent dipole moments, the interaction is electrostatic, i.e. of a dipole-dipole induced type and where the easily polarizable aromatic ring is preferred in the solvation sphere.Carbon tetrachloride is shewn to have a specific PARR interaction. If co-ordination number, solution structure etc., are to be determined using weakly interacting substrates, this solvent should be avoided.A multivariate statistical approach is also reported, where 13 C electron-nuclear relaxation data and induced shifts of monosubstituted arcmatics have been related to different physical descriptors. Most of the variance in relaxation and shift data is best described by the dipole moment. The results support a dipole-dipole interaction as the preferred solvation mechanism.The preferential solvation of several organic substrates with the diamagnetic Co(acac)3 is studied by varying the substrate concentration in cyclohexane. By the use of 59 Co shift, it is shown that proton donating solutes such as chloroform and methanol have a specific solvation. The order of preference is close to that obtained in Cr(acac)3 solutions.
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| 23. |
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| 24. |
- Hellberg, Sven, 1955-
(författare)
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A multivariate approach to QSAR
- 1986
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Quantitative structure-activity relationships (OSAR) constitute empirical analogy models connecting chemical structure and biological activity. The analogy approach to QSAR assume that the factors important in the biological system also are contained in chemical model systems.The development of a QSAR can be divided into subproblems:1. to quantify chemical structure in terms of latent variables expressing analogy,2. to design test series of compounds,3. to measure biological activity and4. to construct a mathematical model connecting chemical structure and biological activity.In this thesis it is proposed that many possibly relevant descriptors should be considered simultaneously in order to efficiently capture the unknown factors inherent in the descriptors. The importance of multivariately and multipositionally varied test series is discussed. Multivariate projection methods such as PCA and PLS are shown to be appropriate far QSAR and to closely correspond to the analogy assumption.The multivariate analogy approach is applied to a beta- adrenergic agents, b haloalkanes, c halogenated ethyl methyl ethers and d four different families of peptides.
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| 25. |
- Kihlberg, Jan, et al.
(författare)
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Synthetic receptor analogues: preparation and calculated conformations of the 2-deoxy, 6-O-methyl, 6-deoxy, and 6-deoxy-6-fluoro derivatives of methyl 4-O-α-D-galactopyranosyl-β-D-galactopyranoside (methyl β-D-galabioside)
- 1988
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Ingår i: Carbohydrate Research. - : Elsevier BV. - 1873-426X .- 0008-6215. ; 176:2, s. 271-286
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Tidskriftsartikel (refereegranskat)abstract
- The 2-deoxy (7), 6-O-methyl (15), 6-deoxy (22), and 6-deoxy-6-fluoro (31) derivatives of methyl β-d-galabioside (1) have been synthesised. Thus, 7 was prepared by xanthate reduction using tributyltin hydride, whereas 22 was obtained by catalytic hydrogenation of a 6-deoxy-6-iodogalabioside. Regioselective mono-fluorination of methyl 2,3-di-O-benzoyl-β-d-galactopyranoside with Et2NSF3 and subsequent α-d-galactosylation provided 31. Molecular mechanics calculations yielded similar conformations for 1, 7, 15, 22, and 31 with differes in φH and ψH of 5°. No indications of intramolecular hydrogen bonds, as displayed by 1 in the crystal, were found for 7, 15, 22, or 31.
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