Browsing by Author "Lovikka, Ville"

The aim of this Master's Thesis was to broaden the understanding of formation of binary agglomerations in aqueous solutions. The central topic was supramolecular interactions and methods controlling the interactions in order to tailor the properties of nanocomposites. Specific attention was paid to catalytic activity, the responsivity to a magnetic field and controlling the catalytic activity of agglomerations by magnetic means. The results could be utilized in bottom up material applications. In the literature section of the thesis several topics are introduced, such as nanomagnetism, electrostatic interactions, diffusion and the formation mechanisms of agglomerations. Magnetoferritin and PAMAM-dendrimer are presented with their potential applications, which are magnetically stabilized reactors, noninvasive in situ imaging, sensing in optically thick media, spintronics and nanoelectronics, magnonic metamaterials and other applications that require high ordering and controllability of nanocomposites. In the experimental section the focus is on the agglomeration between the magnetoferritin of Pyrococcus furiosus archaea and PAMAM G3 dendrimer in aqueous solutions. The properties of the agglomerations were studied as a function of solution parameters. The parameters were pH, ionic strength, the generation of the dendrimer and the existence of the magnetoferritin mineral core. The effects of agglomeration on magnetic field responsivity and catalytic activity for the peroxidase reaction between 3,3',5,5'-tetramethylbenzidine and hydrogen peroxide were studied. The agglomeration sizes were monitored by dynamic light scattering and the proceeding of the indicator reaction by UV–VIS spectroscopy. The structures of the agglomerations were studied by small angle x-ray diffractometry. TEM was utilized to confirm the size, shape and structure of the agglomerations. The average electrokinetic potentials of the magnetoferritin and PAMAM were studied by zetapotential measurements. The catalytic activity of magnetoferritin diminished when it was agglomerated by PAMAM-dendrimer. The effect of precipitation could not be well studied with the current setup. A possible sidereaction was detected between mobile PAMAM and the product of the H2O2–TMB indicator reaction. Increase in the ionic strength resulted in faster agglomeration, which was against the expectations and differed from results of otherwise rather similar research projects. The addition of salt was expected to weaken the agglomeration by shadowing the electrostatic potentials. The effective mechanism is speculated to be caused by the size differences of the components and the shortening of Debye length as the ionic strength is increased. In that case the addition of salt might weaken more ferritin–ferritin repulsions than ferritin–PAMAM attractions. Increase in ionic strength also weakens the ordering in agglomerations. The electrokinetic potentials were shown to have varying effects on supramolecular behavior. Further studies are needed to understand better how such effects change the effective catalytic activity and the magnetic field responsivity of nanocomposites.