1.
Larsson, Mikael, 1982
(författare)
Heterogeneities in polymer gels: Effects on swelling and mechanical properties
2010
Licentiatavhandling (övrigt vetenskapligt/konstnärligt) abstract
Polymeric hydrogels is a class of scientifically interesting materials that are being extensively studied. They are found in numerous applications within; drug delivery, hygiene products, food industry, analytical chemistry, etc. In addition, polymeric hydrogels have promising future applications as; cell scaffolds, implants, sensors, etc.One of the critical parameters for the performance of hydrogels in different applications is their structure. One such structural feature is the heterogeneity of the material, where the term heterogeneity applies to many different types of structural variations.The aim of this thesis was to investigate how different kinds of heterogeneities can be introduced into hydrogels, and how the presence of the different heterogeneities can be related to swelling and mechanical properties of such materials. The materials investigated were; polyacrylic acid neutralized with calcium hydroxide, polysodium acrylate superabsorbents with microfibrillated cellulose utilized as a filler and hydroxypropyl methylcellulose with heterogeneous distribution of the substituents.It was found that the presence of calcium ions during the synthesis of crosslinked polyacrylic acid introduces heterogeneities, both in network structure and in the form of phase separation, with dramatic impact on gel properties. Microfibrillated cellulose was found to even in small amounts cause significant changes to the swelling and shear modulus of crosslinked polysodium acrylate superabsorbents. The effect of the microfibrillated cellulose was similar as if an equivalent mass of covalent crosslinker had been used, but with improved resistance to fracture. For hydroxypropyl methylcellulose it was found that a heterogeneous distribution of the substituents causes increased interactions within the material, as determined from the glass transition temperature. Those increased interactions are coherent with earlier reports on solution behaviour for heterogeneously substituted hydroxypropyl methylcellulose.Hopefully the results presented in this thesis can contribute to the field of gel science, and in particular to the design of new multi-component soft materials.
2.
Blissing, Annica
(författare)
Thiopurine S-methyltransferase - characterization of variants and ligand binding
2017
Licentiatavhandling (övrigt vetenskapligt/konstnärligt) abstract
Thiopurine S-methyltransferase (TPMT) belongs to the Class I S-adenosylmethionine-dependent methyltransferase (SAM-MT) super family of structurally related proteins. Common to the members of this large protein family is the catalysis of methylation reactions using S-adenosylmethionine (SAM) as a methyl group donor, although SAM-MTs act on a wide range of different substrates and carry out numerous biologically important functions. While the natural function of TPMT is unknown, this enzyme is involved in the metabolism of thiopurines, a class of pharmaceutical substances administered in treatment of immune-related disorders. Specifically, methylation by TPMT inactivates thiopurines and their metabolic intermediates, which reduces the efficacy of clinical treatment and increases the risk of adverse side effects. To further complicate matters, TPMT is a polymorphic enzyme with over 40 naturally occurring variants known to date, most of which exhibit lowered methylation activity towards thiopurines. Consequently, there are individual variations in TPMTmediated thiopurine inactivation, and the administered dose has to be adjusted prior to clinical treatment to avoid harmful side effects.Although the clinical relevance of TPMT is well established, few studies have investigated the molecular causes of the reduced methylation activity of variant proteins. In this thesis, the results of biophysical characterization of two variant proteins, TPMT*6 (Y180F) and TPMT*8 (R215H), are presented. While the properties of TPMT*8 were indistinguishable from those of the wild-type protein, TPMT*6 was found to be somewhat destabilized. Interestingly, the TPMT*6 amino acid substitution did not affect the functionality or folding pattern of the variant protein. Therefore, the decreased in vivo functionality reported for TPMT*6 is probably caused by increased proteolytic degradation in response to the reduced stability of this protein variant, rather than loss of function.Also presented herein are novel methodological approaches for studies of TPMT and its variants. Firstly, the advantages of using 8-anilinonaphthalene-1-sulfonic acid (ANS) to probe TPMT tertiary structure and active site integrity are presented. ANS binds exclusively to the native state of TPMT with high affinity (KD ~ 0.2 μm) and a 1:1 ratio. The stability of TPMT was dramatically increased by binding of ANS, which was shown to co-localize with the structurally similar adenine moiety of the cofactor SAM. Secondly, an enzyme activity assay based on isothermal titration calorimetry (ITC) is presented. Using this approach, the kinetics of 6-MP and 6-TG methylation by TPMT has been characterized.
