| 51. |
- Johansson, Mats H., et al.
(författare)
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Reducing end groups in brich xylan and their alkaline degradation
- 1977
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Ingår i: Wood Science and Technology. - 1432-5225 .- 0043-7719. ; 11:4, s. 251-263
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Tidskriftsartikel (refereegranskat)abstract
- The structure of the reducing end group in xylan can be written: -β-D-Xylp-(1→4)-β-D-Xylp-(1→3)-α-L-Rhap-(1→2)--α-D-GalpA-(1→4)-D-XylIn alkaline media the reducing xylose group is easily isomerized and removed by a β-elimination which leads to a reducing galacturonic acid end group. The 1, 2-linkage between rhamnose and the galacturonic acid explains the retarding effect on the alkaline peeling. Even under fairly mild conditions the galacturonic acid group is converted to other groups which are very stable in alkaline media. Model experiments permit the conclusion that OH-3 in the reducing group is subjected to β-hydroxyelimination. The 3-deoxy-2-O-α-L-rhamnopyranosyl-D-threo-hex-2-enuronic acid group formed is unstable in acid medium and escapes observation by the techniques employed for determination of the end groups.Upon prolonged alkaline treatment and increased proportion of these groups is lost and a rapid peeling proceeds until a xylose group with a 4-O-methylglucuronic acid substituent is liberated. The consecutive reactions of this group are similar to those of the galacturonic acid groups.The formation of 3-deoxyaldonic acid end groups, an important stopping reaction in cellulose, is of minor importance in xylan.The financial support from the 1959 Års Fond för Teknisk och Skoglig Forskning samt Utbildning is gratefully acknowledged.
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| 52. |
- Jonas, I., et al.
(författare)
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Circular dichroism and absolute configuration of tris(acetyl-acetonato) cobalt(III)
- 1976
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Ingår i: Inorganic and Nuclear Chemistry Letters. - : Elsevier BV. - 0020-1650. ; 12:1, s. 43-47
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Tidskriftsartikel (refereegranskat)abstract
- Efficient optical resolution of Co(acac)3 was obtained chromatographically in isopentane/ether solution by the use of a 30 cm D-lactose/Al2O3 column. The absolute configuration of (−)546Co(acac)3 was found to be by correlation with the chromatographic behaviour of other M(acac)3 complexex. The circular dichroism (CD) spectrum was scaled to molar unity by assuming perfect optical purity. The assignments of important bands in the UV and visible ranges are discussed with reference to available theoretical work.
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| 53. |
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| 54. |
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| 55. |
- Jonas, I., et al.
(författare)
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Orientation Studies of Probe Molecules in Lamellar Liquid Crystalline Lipid Systems by Linear Dichroism
- 1977
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Ingår i: Spectroscopy Letters. - : Informa UK Limited. - 1532-2289 .- 0038-7010. ; 10:6, s. 501-506
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Tidskriftsartikel (refereegranskat)abstract
- The LD-method of inclined incidence was found useful in the study of the orientations of probe chromophores (carotene, anthracene) solubilized in lamellar mesophases of the systems sodium octanoate/decanol/water and sodium di-2-ethylhexylsulphosuccinate/water, respectively. The results suggest the existence of two competing molecular orientation mechanisms aligning the longest axis of the probe molecule either parallel with the lamellar surface or perpendicular to it.
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| 56. |
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| 57. |
- Jonson, Björn, 1941, et al.
(författare)
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Decay of (86)Rn-210(124) to Levels in (85)at-210(125)
- 1973
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Ingår i: Physica Scripta. - : IOP Publishing. - 1402-4896 .- 0031-8949. ; 7:4, s. 147-159
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Tidskriftsartikel (refereegranskat)abstract
- The decay of 210Rn to 210At has been investigated. Gamma rays were recorded in singles and coincidence using Ge(Li) detectors. Conversion electrons were studied with a Si(Li) detector and a double focusing magnetic spectrometer. Internal conversion coefficients have been deduced and several transition multipolarities have been determined. A decay scheme is presented and spin assignments are made.The electron capture decay from 210Rn has been found to proceed mainly to three levels in 210At: 2 280.8 keV (0-, (1-)), 1 525.5 keV (1+) and 1 488.6 keV (1+), with log ft values
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| 58. |
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| 59. |
- Kubat, J., et al.
(författare)
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Internal stresses and activation volumes from the stress relaxation behavior of polyethylene at low deformations
- 1976
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Ingår i: Journal of Applied Polymer Science. - : Wiley. - 1097-4628 .- 0021-8995. ; 20:10, s. 2799-2809
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Tidskriftsartikel (refereegranskat)abstract
- Internal stress levels and values of the activation volume have been evaluated from the kinetics of stress relaxation in annealed samples of LD and HD polyethylene. The initial deformation of the samples was varied, the maximum values amounting to ca. 1%. The temperature of the experiments was 24°C for LDPE, and 24°, 50°, and 69°C for HDPE. The internal stress level was found to be approximately proportional to the initial deformation and independent of the temperature used. Such internal stresses appear to be introduced upon deformation, since permanent stresses had been removed by careful annealing. The activation volume (v) was found to satisfy the relation vσ* ≈ 10kT, where σ* is the effective stress, i.e., the difference between the applied and internal stress, k is Boltzmann's constant, and T is the absolute temperature. This is in good agreement with results reported elsewhere for a wide variety of materials. This relation applies primarily to the exponential flow portion of the relaxation curves, but by a simple transformation the power‐law region can also be encompassed. Copyright © 1976 John Wiley & Sons, Inc.
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| 60. |
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