| 1. |
- MARTINELLE, M, et al.
(författare)
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ON THE INTERFACIAL ACTIVATION OF CANDIDA-ANTARCTICA LIPASE-A AND LIPASE-B AS COMPARED WITH HUMICOLA-LANUGINOSA LIPASE
- 1995
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Ingår i: BIOCHIMICA ET BIOPHYSICA ACTA-LIPIDS AND LIPID METABOLISM. - ROYAL INST TECHNOL,DEPT BIOCHEM & BIOTECHNOL,S-10044 STOCKHOLM,SWEDEN. : ELSEVIER SCIENCE BV. - 0005-2760. ; 1258:3, s. 272-276
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Tidskriftsartikel (refereegranskat)abstract
- The interfacial activation of Candida antarctica lipase A (CALA) and B (CALB) has been investigated and compared with that of Humicola lanuginosa lipase (HLL). CALB displayed no interfacial activation towards p-nitrophenyl butyrate (PNPB) when exceeding the solubility limit of the substrate. No activation was observed towards p-nitrophenyl acetate (PNPA) at the addition of sodium dodecyl sulfate (SDS) nor in the presence of a solid polystyrene surface. The catalytic action of CALB was very different from that of Humicola lanuginosa lipase, which showed a pronounced interfacial activation with the same substrates. The basis for the anomalous behaviour of CALB is proposed to be due to the absence of a lid that regulates the access to the active site. in contrast to CALB, CALA expressed interfacial activation, but the activation was not as prominent as for Humicola lanuginosa lipase (HLL). The structural basis for the activation of CALA is unknown.
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| 2. |
- Martinelle, M, et al.
(författare)
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The role of Glu87 and Trp89 in the lid of Humicola lanuginosa lipase
- 1996
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Ingår i: Protein Engineering. - : Oxford University Press (OUP). - 0269-2139 .- 1460-213X. ; 9:6, s. 519-524
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Tidskriftsartikel (refereegranskat)abstract
- The importance of Glu87 and TRp89 in the lid of Humicola lanuginosa lipase for the hydrolytic activity at the water/lipid interface was investigated by site-directed mutagenesis. It was found that the effect on the hydrolytic activity upon the replacement of Trp89 with Phe, Leu, Gly or Glu was substrate dependent, The Trp89 mutants displayed an altered chain length specificity towards triglycerides, with a higher relative activity towards triacetin and trioctanoin compared with tributyrin, Trp89 was shown to be less important in the hydrolysis of vinyl esters compared with ethyl esters and triglycerides. An exclusive effect on the acylation reaction rate by the mutation of Trp89 was consistent with the data, It is suggested that Trp89 is important in the process of binding the acyl chain of the substrate into the active site for optimal acylation reaction rate, The Trp89Phe mutation resulted in an increased hydrolytic activity towards 2-alkylalkanoic acid esters. This is suggested to be due to reduction of unfavourable van der Waals contacts between Trp89 and the 2-substituent of the substrate, Thus, in contrast to natural substrates, Trp89 has a negative impact on the catalytic efficiency when substrates with bulky acyl chains are used, In contrast to the Trp89 mutations, the effect on the hydrolytic activity of the Glu87Ala mutation was almost substrate independent, 35-70% activity of wild-type lipase, A reduction of both the acylation and deacylation reaction was consistent with the data.
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| 3. |
- Trollsas, M, et al.
(författare)
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Highly branched radial block copolymers via dendritic initiation of aliphatic polyesters
- 1998
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Ingår i: Journal of Polymer Science Part A. - 0887-624X .- 1099-0518. ; 36, s. 2793-2798
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Tidskriftsartikel (refereegranskat)abstract
- Living ring opening polymerization of epsilon-caprolactone initiated from the numerous chain-end hydroxymethyl groups of the analogous dendrimeric and hyperbranched polyesters derived from 2,2-bis(hydroxymethyl) propionic acid is described. By controlling the size of the dendritic macromolecule and the molar ratio of epsilon-caprolactone, a variety of highly branched radial block copolymers are obtained. Comparison of the results obtained for the dendrimeric and hyperbranched initiators demonstrates that the reactivity of the chain-end hydroxymethyl groups in the dendrimer are significantly greater than in the isomeric hyperbranched case. (C) 1998 John Wiley & Sons, Inc.
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| 4. |
- Trollsås, M., et al.
(författare)
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The influence of the molecular structure on the second-order nonlinear optical properties of pyroelectric liquid crystalline polymers
- 1998
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Ingår i: American Chemical Society Symposium Series (ACS). - Washington, DC : American Chemical Society. - 0097-6156 .- 1947-5918. ; 695, s. 315-327
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Tidskriftsartikel (refereegranskat)abstract
- Pyroelectric Liquid Crystal Polymers (PLCP), a novel class of material with intrinsic polar order developed in our laboratory, are discussed. Thin films (2-4µm) of PLCP were prepared by photopolymerization of ferroelectric liquid crystalline monomers in the chiral smectic C (SmC*) phase. The poly(acrylate) materials have been structurally modified in order to improve their nonlinear optical and thermal properties. Further are their longterm nonlinear optical properties discussed based on results from second harmonic generation (SHG), spontaneous polarization (Ps), and dielectric spectroscopy.
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| 5. |
- Berglund, P., et al.
(författare)
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Alcohols as enantioselective inhibitors in a lipase catalysed esterification of a chiral acyl donor
- 1995
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Ingår i: Biotechnology Letters. - 0141-5492. ; 17:1, s. 55-60
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Tidskriftsartikel (refereegranskat)abstract
- Increased reaction rates and increased enantioselectivities were observed with decreased concentrations of n-alkanols when resolving 2-methyldecanoic acid by esterification catalysed by immobilised lipase from Candida rugosa at controlled water activities in cyclohexane. The enantioselectivity was found to be independent of the water activity in the reaction medium at the n-heptanol concentrations investigated. However, when n-decanol was used as the acyl acceptor, not only the alcohol concentration but also the water activity in the reaction medium, influenced the enantioselectivity. The results obtained showed that the low enantioselectivity seen at a high alcohol concentration could be explained by the alcohol influencing the apparent V(max)(S) and V(max)(R) differently.
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| 6. |
- Ekström, Lars, 1959, et al.
(författare)
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Intervertebral disc response to cyclic loading--an animal model.
- 1996
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Ingår i: Proceedings of the Institution of Mechanical Engineers. Part H, Journal of engineering in medicine. - 0954-4119. ; 210:4, s. 249-58
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Tidskriftsartikel (refereegranskat)abstract
- The viscoelastic response of a lumbar motion segment loaded in cyclic compression was studied in an in vivo porcine model (N = 7). Using surgical techniques, a miniaturized servohydraulic exciter was attached to the L2-L3 motion segment via pedicle fixation. A dynamic loading scheme was implemented, which consisted of one hour of sinusoidal vibration at 5 Hz, 50 N peak load, followed by one hour of restitution at zero load and one hour of sinusoidal vibration at 5 Hz, 100 N peak load. The force and displacement responses of the motion segment were sampled at 25 Hz. The experimental data were used for evaluating the parameters of two viscoelastic models: a standard linear solid model (three-parameter) and a linear Burger's fluid model (four-parameter). In this study, the creep behaviour under sinusoidal vibration at 5 Hz closely resembled the creep behaviour under static loading observed in previous studies. Expanding the three-parameter solid model into a four-parameter fluid model made it possible to separate out a progressive linear displacement term. This deformation was not fully recovered during restitution and is therefore an indication of a specific effect caused by the cyclic loading. High variability was observed in the parameters determined from the 50 N experimental data, particularly for the elastic modulus E1. However, at the 100 N load level, significant differences between the models were found. Both models accurately predicted the creep response under the first 800 s of 100 N loading, as displayed by mean absolute errors for the calculated deformation data from the experimental data of 1.26 and 0.97 percent for the solid and fluid models respectively. The linear Burger's fluid model, however, yielded superior predictions particularly for the initial elastic response.
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| 7. |
- Glauser, T, et al.
(författare)
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Electron-beam curing of thick thermoset composite matrices
- 1999
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 40, s. 5297-5302
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Tidskriftsartikel (refereegranskat)abstract
- Electron-beam (EB) curing of two epoxy resins, one acrylated and one methacrylated, has been investigated. The change in thermomechanical properties, such as T-g, and the change of residual unsaturation have been studied as a function of dose. These results, in combination with in situ measurements of the temperature during cure, have shown the importance of sample geometry for the final properties of the thermoset. The thermal history of the sample during cure greatly affects the properties of the cured resin. (C) 1999 Elsevier Science Ltd. All rights reserved.
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| 8. |
- HULT, A, et al.
(författare)
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DENDRITIC RESINS FOR COATING APPLICATIONS
- 1995
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Ingår i: Macromolecular Symposia. - : Wiley. - 1022-1360 .- 1521-3900. ; 98, s. 1159-1161
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Tidskriftsartikel (refereegranskat)abstract
- Hyperbranched, aliphatic polyesters of theoretically calculated molar masses 1 200-44 300 (2-7 generations) were synthesized in the molten state from 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) (repeating unit of AB(x)-type) and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (TMP) (core molecule) using acid catalysis. The synthetic procedure was a pseudo-one-step divergent reaction. The degree of branching was found to be near 80 %. A study has also been made with respect to the theological properties of the hyperbranched aliphatic polyesters. The polymers exhibit an almost newtonian behaviour in the molten state. They also exhibit a lower increase in viscosity with molecular weight than linear polymers. The surface functionality is shown to greatly affect the viscosity of the polymers.
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| 9. |
- Hult, A, et al.
(författare)
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Hyperbranched polymers
- 1999
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Ingår i: BRANCHED POLYMERS II. - : SPRINGER-VERLAG BERLIN. ; , s. 1-34
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Polymers obtained from the statistical polymerization of A(x)B monomers by means of condensation or addition procedures are referred to as hyperbranched polymers. The paper aims to give a brief historical background and to give a survey of hyperbranched polymers in the literature. Polymerization of A(x)B monomers yields highly branched polymers, with a multitude of end groups, which are less prone than linear polymers to form entanglements and undergo crystallization. Hyperbranched polymers are phenomenologically different from linear polymers; for example, the lack of entanglements results in lower viscosity than in linear polymers of the same molecular weight. The thermal properties of hyperbranched polymers have been shown to depend on the nature of the chain ends. The lower the polarity, the lower the glass transition temperature since it is suggested that the glass transition of hyperbranched polymers is due to translational motions. Hyperbranched polymers are unique in that their properties ape easily tailored by changing the nature of the end groups. For some areas, such as coating resins and tougheners in epoxy-resins, hyperbranched polymers are foreseen to play an important role. Various applications have been suggested, even though only a few have been commercialized at this time.
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| 10. |
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| 11. |
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| 12. |
- Johansson, M, et al.
(författare)
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On the synthesis and characterization of new low temperature curing powder coatings cured with radiation
- 1998
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Ingår i: JCT. - 0361-8773. ; 70, s. 57-62
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of a new type of low temperature curing powder coating is described. The type of materials used were mixtures of an amorphous methacrylate-functional prepolymer and crystalline acrylate and methacrylate monomers. The introduction of a crystalline component in an amorphous resin mixture was shown to markedly reduce the melt viscosity and thus enhance the flow properties of the powder coating. Curing experiments showed the advantage of using photoinitiation compared to thermal initiation. The reaction was much faster and the problem with oxygen inhibition could be avoided.
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| 13. |
- JOHANSSON, M, et al.
(författare)
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SYNTHESIS, CHARACTERIZATION, AND UV CURING OF ACRYLATE FUNCTIONAL HYPERBRANCHED POLYESTER RESINS
- 1995
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Ingår i: JCT. - 0361-8773. ; 67, s. 35-39
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Tidskriftsartikel (refereegranskat)abstract
- A series of different hyperbranched aliphatic polyester resins with acrylate functionality have been synthesized, characterized, and UV cured. The terminal groups have been either benzoates, propionates, or hydroxyls. The glass transition (T-g) and viscosity of the resins have been shown to depend on the polarity of the end groups. The increase in viscosity, while the propionate functional resin has the lowest T-g and viscosity. The acrylates are all free radically UV cured with little or no oxygen inhibition found. The residual unsaturation in the cured films is not detectable with Raman spectroscopy, i.e., less than five percent. The cured films are all hard with a T-g difference varying with the structure of terminal groups in the resins.
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| 14. |
- Johansson, M, et al.
(författare)
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The synthesis and properties of hyperbranched polyesters
- 1996
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Ingår i: TRENDS IN POLYMER SCIENCE. - 0966-4793. ; 4, s. 398-403
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Tidskriftsartikel (refereegranskat)abstract
- Hyperbranched polyesters are a group of materials within the family of dendritic polymers (dendrimers and hyperbranched polymers) that have enjoyed increased attention in recent years. The backbone architecture induces new and intriguing properties for the polymers, such as low viscosity and high solubility in various solvents. Hyperbranched polymers also have a large number of endgroups, which allows them to be tailored for very different applications. Hyperbranched polymers have been presented as thermoplastics, thermosets and in blends with conventional linear polymers. A general background to hyperbranched polymers and dendrimers and a more detailed survey of hyperbranched polyesters is presented, together with some speculations on future developments.
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| 15. |
- MALMSTROM, E, et al.
(författare)
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HYPERBRANCHED ALIPHATIC POLYESTERS
- 1995
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 28, s. 1698-1703
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Tidskriftsartikel (refereegranskat)abstract
- Hyperbranched, aliphatic polyesters of theoretically calculated molar masses 1200-44 300 were synthesized in the molten state from 2,2-bis(hydroxymethyl)propionic acid (repeating unit of AB(x) type) and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (core molecule) using acid catalysis. The synthesis procedure was a pseudo-one-step reaction where stoichiometric amounts corresponding to each generation were added successively. The resulting polymers were glassy, slightly yellow solids at room temperature with hydroxyl groups as terminal groups. The degree of branching of the polyesters was determined with the help of model compounds using C-13-NMR and was found to be near 80%. The material exhibited good thermal stability as analyzed with TGA in a nitrogen atmosphere. Glass transition temperatures were determined using DSC and were found to be about 40 degrees C and to be relatively insensitive to variations in molar mass.
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| 16. |
- Malmstrom, E, et al.
(författare)
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The effect of terminal alkyl chains on hyperbranched polyesters based on 2,2-bis(hydroxymethyl)propionic acid
- 1996
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Ingår i: Macromolecular Chemistry and Physics. - : Wiley. - 1022-1352 .- 1521-3935. ; 197, s. 3199-3207
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Tidskriftsartikel (refereegranskat)abstract
- A hyperbranched hydroxyfunctional polyester based on 2,2-bis(hydroxymethyl)propionic acid as AB(2)-monomer and a tetrafunctional polyol as core was end-capped with five different alkylacyl chlorides. Alkyl chain lengths ranging from three to sixteen carbons were used. Short alkyl chains (3-6 carbons) decrease the glass transition temperature from around 30 degrees C for the hydroxyterminated polyester to temperatures well below zero. With a sufficiently long alkyl chain (12-16 carbons) the polymers tend to crystallize. The polyesters with C-16-chains as terminal groups exhibit several different crystalline phases as revealed by differential scanning calorimetry. From X-ray data it was possible to suggest that the crystallization for the C-16-terminated samples occurs in a non-interpenetrating fashion for the larger sample and in an interpenetrating way for the smaller polymers.
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| 17. |
- MARTINELLE, M, et al.
(författare)
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KINETICS OF ACYL TRANSFER-REACTIONS IN ORGANIC MEDIA CATALYZED BY CANDIDA-ANTARCTICA LIPASE-B
- 1995
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Ingår i: Biochimica et Biophysica Acta - Protein Structure and Molecular Enzymology. - ROYAL INST TECHNOL,DEPT BIOCHEM & BIOTECHNOL,S-10044 STOCKHOLM,SWEDEN. : ELSEVIER SCIENCE BV. - 0167-4838 .- 1879-2588. ; 1251:2, s. 191-197
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Tidskriftsartikel (refereegranskat)abstract
- The acyl transfer reactions catalysed by Candida antarctica lipase B in organic media followed a bi-bi ping-pong mechanism, with competitive substrate inhibition by the alcohols used as acyl accepters. The effect of organic solvents on V-m and K-m was investigated. The V-m values in acetonitrile was 40-50% of those in heptane. High K-m values in acetonitrile compared to those in heptane could partly be explained by an increased solvation of the substrates in acetonitrile. Substrate solvation caused a 10-fold change in substrate going from heptane to acetonitrile. Deacylation was the rate determining specificity, defined as (V-m/K-m)(ethyl) (octanoate)/(V-m/K-m)(octanoic) (acid), step for the acyl transfer in heptane with vinyl- and ethyl octanoate as acyl donors and (R)-2-octanol as acyl acceptor. With I-octanol, a rate determining deacylation step in heptane was indicated using the same acyl donors. Using I-octanol as acceptor in heptane, S-ethyl thiooctanoate had a 25- to 30-fold lower V-m/K-m value and vinyl octanoate a 4-fold higher V-m/K-m value than that for ethyl octanoate. The difference showed to be a K-m effect for vinyl octanoate and mainly a K-m effect for S-ethyl thiooctanoate. The V-m values of the esterification of octanoic acid with different alcohols was 10-30-times lower than those for the corresponding transesterification of ethyl octanoate. The low activity could be explained by a low pH around the enzyme caused by the acid or a withdrawing of active enzyme by nonproductive binding by the acid.
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| 18. |
- Oppermann, U, et al.
(författare)
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Regulatory factors and motifs in SDR enzymes
- 1999
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Ingår i: Advances in experimental medicine and biology. - Boston, MA : Springer US. - 0065-2598. ; 463, s. 365-371
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Tidskriftsartikel (refereegranskat)
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| 19. |
- Skagerlind, P, et al.
(författare)
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Binding of Rhizomucor miehei lipase to emulsion interfaces and its interference with surfactants
- 1995
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Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 4, s. 129-135
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Tidskriftsartikel (refereegranskat)abstract
- Interactions between Rhizomucor miehei lipase and emulsion droplets were studied in oil-in-water emulsions. The emulsions were stabilised by either the cationic surfactant didodecyldimethylammonium bromide, the anionic surfactant sodium bis (2-ethylhexyl) sulfosuccinate or the non-ionic surfactant, 1-(2-ethylhexyl)-3-(2-ethylbutyl)-2-hexaethylene glycerol ether. By measuring the mobility of emulsion droplets it was shown that the lipase bound to droplets stabilized by the nonionic surfactant, but not to those stabilized by the negatively charged surfactants. It was experimentally impossible to show any adsorption of the lipase to the emulsion droplet surfaces consisting of the non-ionic surfactant. From Langmuir measurements it was decuced that the lipase adsorbed to positively but not negatively charged surfaces. Only a small change of the break point of the isotherm was observed in the non-ionic system. Eicosanoic acid disappeared from the air/water interface at pH4, when Rhizomucor miehei lipase was dissolved in teh subsolution. The lipase-catalyzed hydrolysis of the oil-soluble model substrate, o-nitrophenyl palmitate, was studied in emulsions stabilized by the different surfactants. The highest reaction rate was observed in systems with the non-ionic surfactant and also with the cationic surfactant, while in the anionic system almost no reaction was observed. In all three tests, i.e. the mobility of emulsion droplets, Langmuir measurements and enzymatic activity measurements, an increased salt concentration from 1μM to 1 mM sodium phosphate decreased the affinity of the lipase to the surfaces stabilized by the cationic surfactant. With a lipase-stabilized oil-in-water emulsion, displacement of the lipase from the emulsion droplet surface occurred with the cationic surfactant, but not with the anionic surfactant. Again with the non-ionic system, it was not possible to show any displacement of the lipase since the mobility value for the lipase system was almost the same as for the non-iopnic system. From each set of experiment it could be concluded independently that the lipase from Rhizomucor miehei prefers positively charged surfaces over negatively charged surfaces.
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| 20. |
- Skagerlind, P, et al.
(författare)
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Glucoside ester synthesis in microemulsions catalyzed by Candida antarctica component B lipase
- 1997
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Ingår i: Journal of the American Oil Chemists Society. - 0003-021X .- 1558-9331. ; 74, s. 39-42
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Tidskriftsartikel (refereegranskat)abstract
- The surfactant, ethyl 6-O-decanoyl glucoside, was synthesized in microemulsion systems by lipase catalysis. The microemulsions were based on the two substrates for the reaction, ethyl glucoside and fatty acid, and either the sodium salt of the fatty acid or the glucoside ester was used as surfactant. The lipase used was component B from Candida antarctica. Reduced pressure was employed to eliminate the water of condensation. The reaction yield was good, with conversion of fatty acid and ethyl glucoside reaching 77 and 96%, respectively.
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| 21. |
- Thurfjell, L., et al.
(författare)
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Automatic Detection of Hypoperfused Areas in SPECT Brain Scans
- 1998
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Ingår i: IEEE Transactions on Nuclear Science. - : Institute of Electrical and Electronics Engineers (IEEE). - 0018-9499 .- 1558-1578. ; 45:4, s. 2149-2154
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Tidskriftsartikel (refereegranskat)abstract
- Describes a method for automatic identification of areas with perfusion changes in SPECT brain images. An intersubject registration technique is used to stereotactically register images from a selected control group allowing for reference images to be created by averaging the subjects image data. An individual SPECT brain scan can be brought into registration with the reference image and comparison to the normal reference group can be made by subtracting the two volumes. Furthermore, since the variance in the reference group is known, a z-score image or an image coded in standard deviations, can be computed. The SPECT reference volume is defined in the same coordinate system as a brain atlas, and anatomical labeling of areas of interest is possible. The authors show results from the creation of an average image based on 11 individuals and from its comparison with pathological cases
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| 22. |
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| 23. |
- Uppenberg, J, et al.
(författare)
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Crystallographic and molecular-modeling studies of lipase B from Candida antarctica reveal a stereospecificity pocket for secondary alcohols.
- 1995
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Ingår i: Biochemistry. - 0006-2960. ; 34:51, s. 16838-51
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Tidskriftsartikel (refereegranskat)abstract
- Many lipases are potent catalysts of stereoselective reactions and are therefore of interest for use in chemical synthesis. The crystal structures of lipases show a large variation in the shapes of their active site environments that may explain the large variation in substrate specificity of these enzymes. We have determined the three-dimensional structure of Candida antarctica lipase B (CALB) cocrystallized with the detergent Tween 80. In another crystal form, the structure of the enzyme in complex with a covalently bound phosphonate inhibitor has been determined. In both structures, the active site is exposed to the external solvent. The potential lid-forming helix alpha 5 in CALB is well-ordered in the Tween 80 structure and disordered in the inhibitor complex. The tetrahedral intermediates of two chiral substrates have been modeled on the basis of available structural and biochemical information. The results of this study provide a structural explanation for the high stereoselectivity of CALB toward many secondary alcohols.
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