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| 2. |
- Elg Christoffersson, Kristina, et al.
(author)
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Reactivity of dissolving pulp: characterisation using chemical properties, NMR spectroscopy and multivariate data analysis
- 2002
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In: Cellulose. ; 9:2, s. 159-70
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Journal article (peer-reviewed)abstract
- The reactivity of dissolving pulp was experimentally determined in termsof residual cellulose in viscose. The correlations between 11 chemicalproperties of pulp and filter values and residual cellulose contents of viscosewere then investigated by multivariate data analysis. Both the viscose filtervalue and the residual cellulose were well modelled from the 11 propertiesby partial least squares regression. The results show that pulps with highacetone extractable fractions, high magnesium contents, low alkali resistanceand low viscosity, gave low viscose filter values and low residual cellulosecontents. Pulps with low residual cellulose contents also had low carboxylgroupcontents and low polydispersity. The results are interpreted as that in pulpwith high reactivity, the hemicellulose content is low and that the cellulosechains are shorter and more soluble in alkali. An explanation of the positiveeffect from the high extractive content is that the extractives facilitate thediffusion of carbon disulfide. A principal component analysis of CP/MAS13C-NMR spectral data of six pulp samples showed that differences inreactivity between the pulps could be explained by variations in the hydrogenbonds in the cellulose and/or changes in the glucosidic bonds. In a separatestudy electron beam processing enhanced the reactivity, i.e. lowered theresidual cellulose content, of the investigated pulps. The magnitude of theelectron dose, within the tested range (5.4–23.7 kGy), didnotseem to be important, but the reactivity within pulp sheets tended to be ratherinhomogeneous.
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| 3. |
- Gromov, Sergey P, et al.
(author)
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Novel Photoswitchable Receptors: Synthesis and Cation-Induced Self-Assembly into Dimeric Complexes Leading to Stereospecific [2+2]-Photocycloaddition of Styryl Dyes Containing a 15-Crown-5 Ether Unit
- 2003
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In: The Journal of Organic Chemistry. - : American Chemical Society (ACS). - 0022-3263 .- 1520-6904. ; 68:16, s. 6115-25
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Journal article (peer-reviewed)abstract
- Styryl dyes 4a-e containing a 15-crown-5 ether unit and a quinoline residue with a sulfonatoalkyl or sulfonatobenzyl N-substituent were synthesized. The relationship between the photochemical behavior of these dyes and their aggregates derived from complexation with Mg2+ in MeCN was studied using 1H NMR and absorption spectroscopy. The E-isomers of 4a-e were shown to form highly stable dimeric (2:2) complexes with Mg2+. Upon irradiation with visible light, the dimeric complexes undergo two competing photoreactions, viz., geometric E Z isomerization, resulting in an anion-capped 1:1 complex of the Z-isomer with Mg2+ and stereospecific syn-head-to-tail [2+2]-cycloaddition, affording a single isomer of bis-crown-containing cyclobutane. The N-substituent in the dye has a dramatic effect on the photochemical behavior of the dimeric complex. Molecular dynamics and semiempirical quantum-chemical calculations were carried out to interpret the observed photocycloaddition in the dimer. Conformational equilibria for the dimer of (E)-4b were analyzed using 1H NMR spectroscopy.
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| 4. |
- Gromov, Sergey P, et al.
(author)
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Synthesis, Structure, Spectroscopic Studies, and Complexation of Novel Crown Ether Butadienyl Dyes
- 2002
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In: Helvetica Chimica Acta. ; 85:1, s. 60-81
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Journal article (peer-reviewed)abstract
- Butadienyl dyes of the benzothiazole series with various fragments of benzocrown ethers 1a-c were synthesized for the first time. The structures and spectral properties of crown-containing butadienyl dyes and their complexes with alkali and alkaline-earth metal cations were studied by X-ray diffraction analysis and 1H-NMR, UV/VIS, and resonance Raman spectroscopy. To interpret the experimental results, quantum-chemical calculations were performed. In the case of Sr2+ and Ba2+ ions, the formation of strong sandwich complexes [M(1b)2]2+ of an unusual structure involving stacking interactions was established; the dye molecules are arranged one above another in the complex according to the head-to-head' pattern.
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| 5. |
- Hauksson, Jón B, et al.
(author)
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Prediction of basic wood properties for Norway spruce. Interpretation of Near Infrared Spectroscopy data using partial least squares regression
- 2001
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In: Wood Science and Technology. - : Springer Science and Business Media LLC. - 0043-7719 .- 1432-5225. ; 35:6, s. 475-85
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Journal article (peer-reviewed)abstract
- This work was undertaken to investigate the feasibility of using near infrared spectroscopy (NIR) and partial least squares regression (PLS) as a tool to characterize the basic wood properties of Norway Spruce (Picea abies (L.) Karst.). The wood samples originated from a trial located in the province of Västerbotten in Sweden. In this trial, the effects of birch shelterwoods (Betula pendula Roth) of different densities on growth and yield in Norway spruce understorey were examined. All Norway spruce trees in each shelterwood treatment were divided into three growth rate classes based on diameter at breast height (1.3 m) over bark. Five discs were cut from each tree (i.e. from the root stem, and at 20%, 40%, 60%, and 80% of the total height). The discs from 40% tree height were used (i.e., where the largest variations in annual ring widths and wood density were found). A total of 27 discs were selected. The discs were used for measuring annual ring widths, wood density, average fiber length and the fiber length distributions. Milled wood samples prepared from the discs were used for recording NIR spectra. PLS regression was used to generate prediction models for the wood properties (Y-matrix) and NIR spectra (X-matrix) as well as between the wood properties (Y-matrix) and the fiber length distributions (X-matrix). One set of models was generated using untreated spectra and fiber length distributions. For a second set of models the structure in the X-matrix, which was orthogonal to the matrix described by the wood properties, was eliminated using a soft target rotation technique called orthogonal signal correction (OSC). The PLS model obtained using "raw" untreated NIR spectra and fiber length distributions had a poor modeling power as evidenced by the cumulative Q2 values. For the PLS models based on untreated NIR spectra the cumulative Q2 values ranged from a minimum of 16% (wood density) to a maximum of 46% (no. of annual rings). Orthogonal signal correction of the X-matrix (NIR spectra or fiber length distributions) gave PLS models with a modeling power corresponding to cumulative Q2 values well in excess of 70%. The improvement in predictive ability accomplished by the OSC procedure was verified by placing four of the 27 observations in an external test set and comparing RMSEP values for the test set observations without OSC and with OSC.
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| 7. |
- Nilsson, David, et al.
(author)
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The effect of designed wood storage on the brightness of bleached and unbleached thermo mechanical pulp
- 2003
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In: Nordic Pulp & Paper Research Journal. ; 18:4, s. 369-76
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Journal article (peer-reviewed)abstract
- 60 Norway Spruce (Picea abies) logs were stored in climate chambers for 14 weeks in order to investigate the effect of wood storage on the brightness of thermo mechanical pulp. The storage conditions were altered according to an experimental design comprised of five factors; light, watering, temperature, tree growth and debarking. Wood samples were collected during the storage period and refined into thermo mechanical pulp. ISO brightness values were measured for the unbleached, the dithionite bleached and the hydrogen peroxide bleached thermo mechanical pulp samples that were refined from the stored wood. The decrease in ISO brightness after 14 weeks of wood storage was significant for some of the samples bleached with dithionite. It was found that the interaction between watering and light had a significant negative effect on the brightness of the unbleached and dithionite bleached samples. The samples bleached with hydrogen peroxide generally showed a more consistent ISO brightness. Only watering and temperature had a significant effect on the brightness of peroxide bleached thermo, mechanical pulp.
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| 8. |
- Ushakov, Evgeny N, et al.
(author)
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Self-Organization of Highly Stable Electron Donor-Acceptor Complexes via Host-Guest Interactions
- 2002
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In: The Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 106:10, s. 2020-3
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Journal article (peer-reviewed)abstract
- Biscrown stilbene S forms complexes of 1:1 and 2:1 composition with bisammonium viologen salt V4+ in acetonitrile solution. Both of the complexes exhibit spectroscopic behavior typical of molecular electron donor-acceptor complexes. The 1:1 complex [S·V]4+ has a very high thermodynamic stability (log K = 9.08), which is due to simultaneous interaction of the two ammonium groups of V4+ with the two 18-crown-6-ether units of S. The 2:1 complex (log K = 12.28) [S·V·S]4+ likely has a sandwich-type layered structure in which the acceptor salt is located between two complexed molecules of the biscrown stilbene.
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