Department of Chemistry

Permanent URI for this communityhttps://hdl.handle.net/10217/100367

These digital collections include honor theses, theses, dissertations, faculty publications, and datasets from the Department of Chemistry.

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Open Access
Applications of inorganic nanoparticles in biological electron microscopy
(Colorado State University. Libraries, 2016) Ni, Thomas Wentung, author; Ackerson, Christopher, advisor; Prieto, Amy, committee member; Finke, Richard, committee member; Peersen, Olve, committee member
Electron microscopy is an immensely powerful for imaging at the cellular level. However, many of the macromolecules of interest are difficult to image due to low electron density. There has been an immense body of work in order to visualize these macromolecules. In the past, many of the methods of visualization revolved around staining samples with heavy metals, however these stains are non-specific. In order to develop more specific methods of tagging macromolecules, there are two different methods to consider: the first being a top-down approach, in which electron dense tags, in this case inorganic nanoparticles, are given specific ligands to take advantage of different chemistries to attach these nanoparticles to macromolecules of interest. The second method is through a bottom-up approach where biomolecules are given the specific ability to form inorganic nanoparticles. Inorganic nanoparticles have been investigated with various ligands in order to enhance binding capability to macromolecules. The chief method of functionalizing these inorganic nanoparticles comes from ligand exchange; much has been studied regarding ligand exchange, but there are still many unanswered questions. Herein, we endeavor to reveal both the mechanism of exchange and the functional unit of exchange. We also report progress towards understanding an enzyme that is capable of forming inorganic nanoparticles, which could be cloned onto proteins as well. This bottom up style has been studied in several other groups; however, none of the previously reported methods have seen much use. Herein, we report a potential NADPH-dependent enzyme that forms selenium nanoparticles.
Open Access
Biogenic nanoparticles and their application in biological electron microscopy
(Colorado State University. Libraries, 2018) Nemeth, Richard S., author; Ackerson, Christopher, advisor; Yao, Tingting, committee member; Bjostad, Louis, committee member; Peersen, Olve, committee member
Interest in nanomaterials has seen a dramatic increase over the past twenty years. In recent years many have turned toward proteins to aid in developing novel materials due to the mild reaction conditions, functionalization, and novel synthetic control of the resulting inorganic structures. Proteins have the ability to direct aggregation of inorganic nanostructures, while some enzymes are able to perform oxio/reductase activity to synthesize the materials as well. These two general properties are not always mutually exclusive and the dual function of certain proteins in nanoparticle synthesis is at the core of this work. Of all the applications for biogenic nanoparticles, generating tools for biological electron microscopy is one of the most appealing. The contrast issue, specifically with in vivo biological sample in the electron microscope has drastically limited the information obtainable by this method. An ideal biogenic nanoparticle would operate analogously to GFP in optical microscopy and contain the dual function characteristics stated above. More specifically it would have to fulfill three criteria: i) reduction of a metal precursor, ii) product size control, iii) product retention. To discover such a clonable contrast tag we must deepen our understanding of biogenic nanoparticle formation in tandem with discovering and developing novel dual function enzymes. This work encapsulates both aspects necessary for the development of a successful clonable nanoparticle for biological electron microscopy. Current biogenic synthetic methods produce nanomaterials with less desirable properties than their inorganic counterparts. Conducting fundamental research and establishing a set of rules and guidelines for biogenic methods will ultimately get us closer to mimicking the control nature has already developed. This dissertation contains 3 chapters. Chapter 2 focuses on the use of protein crystals as scaffolds for nanomaterial synthesis. Herein porous protein crystals were used to control the gold nanocluster seeded growth of gold nanorods in an attempt to help establish guidelines for biogenic nucleation controlled nanomaterial synthesis. High aspect gold nanorod products were generated from within the crystal pores. Subsequent dissolving of the crystals allowed for release of these rods from their template. The following two chapters focus on metalloid reductase nanoparticle synthesis in which we have discovered and characterized a novel selenophile bacteria. Through purification and mass spectrometry we found a glutathione reductase like enzyme to be responsible for Se nanoparticle formation. A commercially available glutathione reductase from yeast was used for Se nanoparticle formation in vitro. This mechanism was characterized and the system was assessed for potential use as a clonable tag. The native enzyme was sequenced and isolated, followed by its own characterization. Our kinetic findings suggest this enzyme is the first documented metalloid reductase due to its specificity for selenium substrates. The enzymes transportability to foreign organisms demonstrates its potential use as a clonable contrast tag for electron microscopy.
Open Access
Does orientation matter? Controlling laccase orientation on planar gold electrodes
(Colorado State University. Libraries, 2024) Perry, Collin, author; Ackerson, Christopher, advisor; Snow, Christopher, committee member; Dandy, David, committee member; Neale, Nathan, committee member
Enzyme electronics are becoming more common in modern life. Even though these technologies have been integrated into everyday life, the fundamental understanding of how an enzymes' orientation at the electrode surfaces affects the enzymes catalysis is still unknown. To understand this more we designed a library of laccase mutants, all with a single solvent exposed cysteine. These cysteine residues are used to bind to a gold electrode modified with a monolayer of sulfhydryl molecules capped with a maleimide binding group. Each mutants' single cysteine will bind to the maleimide group orienting each mutant differently at the electrode surface. The wild type enzyme (WT) and all the mutants, D113C, N264C, H470C all show activity toward a common substrate 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS). Although each mutant does show catalytic activity in solution, we were unable to obtain an electrochemical response from the laccase library using the maleimide capped electrodes for either ABTS or oxygen. Modification of the electrodes via the deposition gold clusters makes the electrode surface more topographically complex. The cluster modified electrodes bound with WT laccase displayed an electrochemical response for the reduction of oxygen to water. The increased topography from using gold clusters allows for electron transfer with laccase enzymes, while the planar electrodes modified with the laccase enzymes in which we achieved an electrochemical response.
Open Access
Radiofrequency heating of nanoclusters and nanoparticles for enzyme activation
(Colorado State University. Libraries, 2018) Collins, Christian Blake, author; Ackerson, Christopher, advisor; Van Orden, Alan, committee member; Finke, Rick, committee member; Collins, George, committee member
Radiofrequency (RF) fields heat magnetic nanoparticles. Applications include remote drug delivery and noninvasive cancer therapy. The underlying objective is to increase temperatures precisely where desired without heating the surroundings. Before our work, the replicable limit of this precision has been in the micrometer range. To investigate the lower limit of this concept of local heat, we explored the RF remote activation of a thermophilic enzyme, thermolysin, covalently attached to gold coated iron oxide nanoparticles (6.1 nm in core diameter). Thermolysin activity was a function of applied radiofrequency power, independent of bulk solution temperature. Besides iron oxides, many other inorganic nanomaterials have been investigated for RF heating. One of the more interesting and controversial material choices is gold nanoparticles, primarily investigated for cancer treatment. Early reports of gold nanoparticle heating conflated the heating of supporting electrolytes with the heating of nanoparticles. Multiple mechanisms were proposed to account for the observed heat of gold nanoparticle suspensions. There was no consensus among specialists on how gold nanoparticles heat, if they heat at all. To investigate this, a critical review of the RF heating of gold nanoparticles field was performed with new experimental results presented to elucidate the confounding results. Following this, Au25(SR)18 gold nanoclusters were used as a model system to investigate the controversial heating rates reported for gold nanoparticles. For the first time the observed rates were explained entirely with a single mechanism: electrophoretic heating. The success of this reconciliation of theory and experiment considered the screened charge of the particle in addition to the contribution of the counterions. To enable deconvolution of possible contributions to gold nanoparticle heating by cluster decomposition products, an investigation of the practical stability of gold nanoclusters was conducted. It was found that organo-soluble particles with large ligands possessed over one month long lifetime in air-free non-polar solvents.

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Browsing Department of Chemistry by Author "Ackerson, Christopher, advisor"