Master Degree / Yüksek Lisans Tezleri

Permanent URI for this collectionhttps://hdl.handle.net/11147/3008

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Author: search.filters.author.Emrullahoğlu, MustafaSubject: search.filters.subject.DOPA

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  • Master Thesis
    Studying Dopa Adhesion on Polystyrene Under Water
    (Izmir Institute of Technology, 2021) Yıldız, Remziye; Akdoğan, Yaşar; Emrullahoğlu, Mustafa
    Mussels wet adhesive performance has been arousing curiosity for a long time. It is found that 3,4-dihydroxyphenylalanine (DOPA) is responsible for adhesive properties of mussels. Despite a large body of research characterizing the interactions DOPA with hydrophilic surfaces, relatively few works have addressed the mechanism of interactions with hydrophobic surfaces. The benzene ring of DOPA is the main attributor to the adhesion on hydrophobic polystyrene (PS) surface. However, here we showed that two hydroxyl groups of catechol have also effects on wet adhesion. We studied wet adhesive properties of DOPA, tyrosine and phenylalanine functionalized PEG polymers, PEG-(N-Boc-L-DOPA)4, PEG-(N-Boc-L-Tyrosine)4, PEG-(N-Boc-L-Phenylalanine)4, on spin labeled PS nanobeads (SL-PS) by electron paramagnetic resonance (EPR) spectroscopy. Surface coverage ratio of SL-PS upon additions of PEG-(N-Boc-L-DOPA)4, PEG-(N-Boc-L-Tyrosine)4 and PEG-(N-Boc-L-Phenylalanine)4 showed that SL-PS was covered with 70%, 50% and 0%, respectively. This showed that spontaneous wet adhesion on PS increases with the number of amino acids hydroxyl groups. This is also supported with the density functional theory (DFT) energy calculations and ab-initio molecular dynamics (AIMD) simulations. In water, interactions between water molecules and hydroxyl groups on the catechol induce catechol adhesion via π-π stacking between the catechol and double styrene rings which were already tilted out with water.
  • Master Thesis
    Adhesion of Dopa Functionalized Gels To Spin Labeled Surfaces
    (Izmir Institute of Technology, 2017) Göksel, Yaman; Akdoğan, Yaşar; Emrullahoğlu, Mustafa
    This study investigates the force free adhesive properties of synthetic polymer in aqueous media using electron paramagnetic resonance (EPR) spectroscopy. Due to poor performance of commercial adhesives in wet environments, scientists are interested in different types of adhesives to overcome this difficulty. On this context, mussels attract attention because of their versatile properties to adhere different types of surfaces from rocks to ship hulls underwater. Adhesion occurs when mussel secretes mussel foot proteins (MFPs) in order to form threads and plaques. Seven types of MFPs are unique in plaque contains high amount of L-3,4-dihydroxyphenylalanine (DOPA) amino acid which is reputed to be responsible for adhesion. In this research, branched polyethylene glycol (PEG) based polymers functionalized with DOPA were synthesized and their force-free adhesive properties to hydrophobic polystyrene and hydrophilic silica nanobeads were investigated in solution. These nanobead surfaces were conjugated with spin label molecules to probe adhesion dynamics using EPR spectroscopy. In addition, gel forms of polymers obtained using NaIO4, FeCl3 and Cr2O7 were used as adhesive materials for EPR measurements. All of these adhesive materials showed adhesion to spin labeled polystyrene (SL-PS) surface. However, non-DOPA containing PEG showed no indication of adhesion thus, demonstrating the importance of DOPA in wet adhesion. In addition, EPR results showed that DOPA based PEG polymers were unable to adhere to spin labeled silica (SL-SiO2) surface. This behavior was attributed to hydration layers around silica nanobeads. These layers formed around hydrophilic SiO2 surface prevent interaction between nanobead surface and polymeric material.