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- All Subjects: Chemistry
- Creators: Ghirlanda, Giovanna
- Resource Type: Text
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Non-canonical amino acids (NCAAs) can be used in protein chemistry to determine their structures. A common method for imaging proteins is cryo-electron microscopy (cryo-EM) which is ideal for imaging proteins that cannot be obtained in large quantities. Proteins with indistinguishable features are difficult to image using this method due to the large size requirements, therefore antibodies designed specifically for binding these proteins have been utilized to better identify the proteins. By using an existing antibody that binds to stilbene, NCAAs containing this molecule can be used as a linker between proteins and an antibody. Stilbene containing amino acids can be integrated into proteins to make this process more access able. In this paper, synthesis methods for various NCAAs containing stilbene were proposed. The resulting successfully synthesized NCAAs were E)-N6-(5-oxo-5-((4-styrylphenyl) amino) pentanoyl) lysine, (R,E)-2-amino-3-(5-oxo-5-((4-styrylphenyl)amino)pentanamido)propanoic acid, (E)-2-amino-5-(5-oxo-5-((4-styrylphenyl) amino) pentanamido) pentanoic acid. A synthesis for three more shorter amino acids, (R,E)-2-amino-3-(3-oxo-3-((4-styrylphenyl) amino) propanamido) propanoic acid, (E)-2-amino-5-(3-oxo-3-((4-styrylphenyl) amino) propanamido) pentanoic acid, and (E)-N6-(3-oxo-3-((4-styrylphenyl) amino) propanoyl) lysine, is also proposed.
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In the first study, a new chemical approach to functionalize the AFM tip in a simple and user-friendly way has been described. Copper-free click chemistry and a vinyl sulfone PEG linker have been utilized during the process. Using this technique, human thrombin and integrin were detected in separate experiments. Then a novel tri-arm linker with two recognition molecules on it was designed and two proteins (human thrombin and integrin) were detected simultaneously in the same experiment using recognition imaging. This technique can be applied to understand many multivalent interactions taking place in nature. Using the same tri-arm linker functionalized with two biotin molecules, the interaction of streptavidin with mono-biotin and bis-biotin ligands were investigated. The thermal stability of streptavidin-biotin complex was also studied using SDS-PAGE analysis.
In the final study, structure of native chromatin extracted from normal and cancer cell lines were analyzed using AFM imaging and agarose gel electrophoresis. Different salt fractions were used to extract chromatin region depending on their solubility. Mnase sensitivity of the chromatin sample was used to understand the open and closed structures of chromatin from different sources. The amount of chromatin in different salt fractions could act as an indicator of amount of open and condensed chromatin in normal and cancer cells. Eventually this ratio of closed and open structure of chromatin could be an indicator of tumorigenic nature of particular cell lines.
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Additionally, two different approaches to incorporate non-natural organometallic catalysts into protein matrix are discussed. First, cobalt protoporphyrin IX was incorporated into cytochrome b562 to produce a water-soluble proton and CO2 reduction catalyst that is active upon irradiation in the presence of a photosensitizer. The effect of the porphyrin axial ligands provided by the protein environment has been investigated by introducing mutations into the native scaffold, indicating that catalytic activity of proton reduction is dependent on axial coordination to the porphyrin. It is also shown that effects of the protein environment are not directly transferred when applied to other reactions, such as CO2 reduction.
Inspired by the active site of [FeFe]-hydrogenases, the second approach is based on the stereoselective preparation of a novel amino acid bearing a 1,2-benzenedithiol side chain. This moiety can serve as an anchoring point for the introduction of metal complexes into protein matrices. By doing so, this strategy enables the study of protein interactions with non-natural cofactors and the effects that it may have on catalysis. The work developed herein lays a foundation for furthering the study of the use of proteins as suitable environments for tuning the activity of organometallic catalysts in aqueous conditions, and interfacing these systems with other supporting units into supramolecular assemblies.
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To evaluate size dependent stability of metal nanoparticles using electrochemical techniques in aqueous media, a synthetic route was designed to produce water soluble Pd nanoparticles. Also, a purification technique was developed to obtain monodisperse metal nanoparticles to study size dependent stability using electrochemical methods. Chapter 2 will describe in detail the synthesis, characterization and size dependent anodic dissolution studies of water soluble palladium nanoparticles.
The cost associated with using expensive metal catalysts can further decreased by using the underpotential deposition (UPD) technique, in which one metal is electrodeposited in monolayer or submonolayer form on a different metal substrate. Electrochemically, this process can be detected by the presence of a deposition peak positive to the bulk deposition potential in a cyclic voltammetry (CV) experiment. The difference between the bulk deposition potential and underpotential deposition peak (i.e. the UPD shift), which is a measure of the energetics of the monolayer deposition step, depends on the work function difference between the metal pairs. Chapter 3 will explore how metal nanoparticles of different sizes will change the energetics of the UPD phenomenon, using the UPD of Cu on palladium nanoparticles as an example. It will be shown that the UPD shift depends on the size of the nanoparticle substrate in a way that is understandable based on the Plieth model.
High electrocatalytic activity of palladium towards ethanol oxidation in an alkaline medium makes it an ideal candidate for the anode electrocatalyst in direct ethanol based fuel cells (DEFCs). Chapter 4 will explore the poisoning of the catalytic activity of palladium in the presence of halide impurities, often used in synthesis of palladium nanoparticles as precursors or shape directing agents.