R-3 Repository :: Browsing by Author "Marti, Angel A."

Browsing by Author "Marti, Angel A."

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Carbon Nanomaterials for Fibers, Photonics and Composites
(2014-04-21) Xiang, Changsheng; Tour, James M.; Pasquali, Matteo; Marti, Angel A.
This thesis investigates various carbon nanomaterials from the basic synthesis to the characterizations and applications in fibers, photonics and composites. The carbon nanomaterials we studied include graphene, graphene oxide, graphene nanoribbons, functionalized graphene nanoribbons, graphene oxide nanoribbons, graphene quantum dots and carbon nanotubes. With all these chemical approaches, these carbon nanomaterials’ mechanical, electrical, photonic and gas barrier properties were carefully studied and demonstrated.
Carbon Nanotubides: an Alternative for Dispersion, Functionalization and Composites Fabrication
(2016-04-14) Jiang, Chengmin; Marti, Angel A.; Pasquali, Matteo; Wilson, Lon J.
Negatively charged single-walled carbon nanotube (SWCNT), also called SWCNT polyelectrolytes and single-walled carbon nanotubides (SWCNTDs), are formed by the reduction (either chemical or electrochemical) of the SWCNT wall by alkali metals (or an electrode) to form negative charged SWCNTs surrounded by an alkali metal counter ions. SWCNT polyelectrolytes can spontaneously dissolve in a variety of polar aprotic solvents without assistance of sonication and will readily react with alkyls and aryls halides to functionalize the walls of SWCNTs. Although SWCNT polyelectrolytes present a good alternative for achieving high concentration of SWCNTs in solution, the condensation of the counter ions on the surface of negatively charged SWCNTs partially shield their charge, limiting the solubility of SWCNT polyelectrolytes. For HiPco SWCNT polyelectrolytes, the highest solubility reported before this work was only 0.4 mg/mL in DMSO. However, we developed a method that greatly improve the solubility of SWCNTs by adding crown ether into the system to coordinate the potassium cation and thus separate the negatively charged SWCNTs from counter ions. This new method produces a high concentration of SWCNT polyelectrolytes up to 9.2 mg/mL in DMSO. In addition, we were able to observe the formation of liquid crystalline phases at highly concentrated solutions, which has been proved to be an essential factor for manufacturing highly ordered robust macroscopic materials. After applying a more efficient dispersion method, speed-mixing, the concentration of SWCNT polyelectrolytes can be further improved up to 52 mg/mL. Compared with previous reported results, the increase in solubility is more than 100 times. As mentioned above, we achieved high concentration of SWCNT polyelectrolytes by adding crown ether to the mixture and using speed-mixing. The SWCNTs in these solutions spontaneously align forming liquid crystalline solutions that can be manufactured into strong and conductive carbon nanotubes fibers by spinning the SWCNT dispersions into aqueous coagulation solutions. The best fibers we have obtained by this method have tensile strength up to 124 MPa, which compares to HiPco SWCNT fibers spun from superacid solutions, and conductivity 2 × 104 S/m. Our method provides an acid-free alternative towards high performance carbon nanotube fibers, which can be expanded for the production of other materials such as films. Also, we expanded our methodology to disperse graphite intercalation compounds (GICs) into graphene polyelectrolytes. Graphene polyelectrolytes, when mixed with SWCNT polyelectrolytes were spun onto SWCNT/Graphene hybrid fibers, which maintains a similar tensile strength (as for HiPco SWCNT fibers) while the Young’s modulus increases by 70% and conductivity increases 2 times.
Design, Synthesis, and Monitoring of Light-Activated Motorized Nanomachines
(2013-09-16) Chiang, Pinn-Tsong; Tour, James M.; Marti, Angel A.; Verduzco, Rafael
Our group has developed a family of single molecules termed nanocars, which are aimed at performing controllable motion on surfaces. In this work, a series of light-activated motorized nanomachines incorporated with a MHz frequency light-activated unidirectional rotary motor were designed and synthesized. We hope the light-activated motor can serve as the powering unit for the nanomachines, and perform controllable translational motion on surfaces or in solution. A series of motorized nanovehicles intended for scanning tunneling microscopy (STM) imaging were designed and synthesized. A p-carborane-wheeled motorized nanocar was synthesized and monitored by STM. Single-molecule imaging was accomplished on a Cu(111) surface. However, further manipulations did lead to motor induced lateral motion. We attributed this result to the strong molecule-surface interactions between the p-carborane-wheeled nanocar and the Cu(111) surface. To fine-tune the molecule-surface interactions, an adamantane-wheeled motorized nanocar and a three-wheel nanoroadster were designed and synthesized. In addition, the STM substrates will be varied and different combinations of molecule-surface interactions will be studied. As a complimentary imaging method to STM, single-molecule fluorescence microscopy (SMFM) also provides single-molecule level resolution. Unlike STM experiment requires ultra-high vacuum and conductive substrate, SMFM experiment is conducted at ambient conditions and uses non-conductive substrate. This imaging method allows us to study another category of molecule-surface interactions. We plan to design a fluorescent motorized nanocar that is suitable for SMFM studies. However, both the motor and fluorophore are photochemically active molecules. In proximity, some undesired energy transfer or interference could occur. A cyanine 5- (cy5-) tagged motorized nanocar incorporated with the MHz motor was designed and synthesized in order to minimize the potential energy transfer or interference between the motor and the fluorophore. The SMFM study of this cy5-tagged motorized nanocar is currently undergoing. The design of light-activated motorized nanocar inspired the design of nanosubmarines. We used fluorescence quenching and fluorescence correlation spectroscopy (FCS) to study the diffusion of single molecules. The fluorescence quenching experiments of Ru(bpy)3+2 by a quenching nanosubmarine was conducted, but no motor induced acceleration of the molecule were observed. Another fluorescent nanosubmarine was monitored by FCS, and no increase of diffusion coefficient was found. Finally, a 1-D channel approach was adopted for decreasing the effects of Brownian motion, and acceleration of nanosubmarine was observed.
Developing Dirhodium-Complexes for Protein Inhibition and Modification & Copper-Catalyzed Remote Chlorination of Alkyl-Hydroperoxides
(2013-09-16) Kundu, Rituparna; Ball, Zachary T.; Marti, Angel A.; Biswal, Sibani Lisa
The work describes the development of a new class of protein-inhibitors for protein-protein interactions, based on metallopeptides comprised of a dirhodium metal center. The metal incorporation in the peptide sequence leads to high increase in binding affinity of the inhibitors. The source of this strong affinity is the interaction of histidine on the protein surface with the rhodium center. In addition to this work, rhodium-based small molecule inhibitors for FK-506 binding proteins are investigated. Also, methodology for rhodium-catalyzed modification of proteins containing surface cysteine has been developed where a simple rhodium(II) complex catalyzes cysteine modification with diazo reagents. The reaction is marked by clean cysteine selectivity and mild reaction conditions. The resulting linkage is significantly more stable in human plasma serum, when compared to common maleimide reagents. Apart from this body of work in chemical-biology, the thesis contains the discussion of development of copper-catalyzed remote chlorination of alkyl hydroperoxides. The atom transfer chlorination utilizes simple ammonium chloride salts as the chlorine source and the internal redox process requires no external redox reagents.
Engineering Single Walled Carbon Nanotube Assemblies: From Ruthenium Complexes Assisted Dispersions to Networks on Different Platforms
(2013-08-07) Saha, Avishek; Marti, Angel A.; Tour, James M.; Pasquali, Matteo
Manufacturing large area networks have potential applications in electronic devices such as thin film transitors, transparent conductive electrodes, and organic photovoltaics among others. The design of two-dimensional SWCNT networks necessitates addressing the challenges of nanotube individualization and organization of networks on different scaffolds. Chapter 1 describes a comprehensive overview of ongoing research in the field of nanotube networks on different platforms. Efficient individualization of SWCNTs in chlorosulfonic acid (CSA) has been reported earlier but preparation of networks on suitable scaffolds still requires attentions. To address that, we have demonstrated a simple solution based technique to produce SWCNTs networks. Chapter 2 describes the deposition of protonated SWCNTs (p-SWCNTs) on the external surface of porous materials. SWCNTs are dispersed in CSA via protonation before the deposition and placed in contact with mesoporous and microporous silicates. Furthermore, the nanotubes are deprotonated using vinyl pyrrolidone, while immobilized resulting in a network of mostly individual pristine SWCNTs on the surface of microporous and mesoporous materials. In chapter 3, we applied a solution-based approach to design thin films on the surface of non-porous silica. SWCNTs networks were formed on fused silica using a simple, efficient dip coating technique. We found the properties of these networks could be tuned by changing the density of SWCNTs in the network. For example, when we prepared low-density films, NIR photoluminescence from individual SWCNTs was observed on the surface of fused silica after deprotonation with diethyl ether. Our findings also support the arguments of reversible protonation of sidewall of SWCNTs during dispersion by CSA. Finally, for high-density films, we achieved sheet resistance of 471 Ω/Sq with 86% transparency. The opto-electronic performance of our films was compared with other recent works reported in literature. Chapter 4 presents the aqueous dispersion of SWCNTs using non-photoluminescent ruthenium polypyridyl complexes with extended -systems by non-covalent dispersion. We further used photoluminescent complexes, which cannot only disperse SWCNTs but can also be monitored in photo-excited state to achieve photo-excited electron transfer processes with potential applications to light harvesting. In the final chapter, a study was reported on the vapoluminescence of encapsulated rhenium metal complexes in zeolite supercages. Upon exposure to solvent vapors, the hybrid materials show characteristic emission maxima, intensity and lifetime decay. This work shows detection of solvent vapors in a simple unambiguous way, which may find applications in the area of sensing.
Grb2 monomer–dimer equilibrium determines normal versus oncogenic function
(Macmillan Publishers Limited, 2015) Ahmed, Zamal; Timsah, Zahra; Suen, Kin M.; Cook, Nathan P.; Lee, Gilbert R. IV; Lin, Chi-Chuan; Gagea, Mihai; Marti, Angel A.; Ladbury, John E.
The adaptor protein growth factor receptor-bound protein 2 (Grb2) is ubiquitously expressed in eukaryotic cells and involved in a multitude of intracellular protein interactions. Grb2 plays a pivotal role in tyrosine kinase-mediated signal transduction including linking receptor tyrosine kinases to the Ras/mitogen-activated protein (MAP) kinase pathway, which is implicated in oncogenic outcome. Grb2 exists in a constitutive equilibrium between monomeric and dimeric states. Here we show that only monomeric Grb2 is capable of binding to SOS and upregulating MAP kinase signalling and that the dimeric state is inhibitory to this process. Phosphorylation of tyrosine 160 (Y160) on Grb2, or binding of a tyrosylphosphate-containing ligand to the SH2 domain of Grb2, results in dimer dissociation. Phosphorylation of Y160 on Grb2 is readily detectable in the malignant forms of human prostate, colon and breast cancers. The self-association/dissociation of Grb2 represents a switch that regulates MAP kinase activity and hence controls cancer progression.
Investigating the Synthesis, Structure, and Catalytic Properties of Versatile Au-Based Nanocatalysts
(2013-09-16) Pretzer, Lori; Wong, Michael S.; Marti, Angel A.; Hafner, Jason H.
Transition metal nanomaterials are used to catalyze many chemical reactions, including those key to environmental, medicinal, and petrochemical fields. Improving their catalytic properties and lifetime would have significant economic and environmental rewards. Potentially expedient options to make such advancements are to alter the shape, size, or composition of transition metal nanocatalysts. This work investigates the relationships between structure and catalytic properties of synthesized Au, Pd-on-Au, and Au-enzyme model transition metal nanocatalysts. Au and Pd-on-Au nanomaterials were studied due to their wide-spread application and structure-dependent electronic and geometric properties. The goal of this thesis is to contribute design procedures and synthesis methods that enable the preparation of more efficient transition metal nanocatalysts. The influence of the size and composition of Pd-on-Au nanoparticles (NPs) was systematically investigated and each was found to affect the catalyst’s surface structure and catalytic properties. The catalytic hydrodechlorination of trichloroethene and reduction of 4-nitrophenol by Pd-on-Au nanoparticles were investigated as these reactions are useful for environmental and pharmaceutical synthesis applications, respectively. Structural characterization revealed that the dispersion and oxidation state of surface Pd atoms are controlled by the Au particle size and concentration of Pd. These structural changes are correlated with observed Pd-on-Au NP activities for both probe reactions, providing new insight into the structure-activity relationships of bimetallic nanocatalysts. Using the structure-dependent electronic properties of Au NPs, a new type of light-triggered biocatalyst was prepared and used to remotely control a model biochemical reaction. This biocatalyst consists of a model thermophilic glucokinase enzyme covalently attached to the surface of Au nanorods. The rod-like shape of the Au nanoparticles made the thermophilic-enzyme complexes responsive to near infrared electromagnetic radiation, which is absorbed minimally by biological tissues. When enzyme-Au nanorod complexes are illuminated with a near-infrared laser, thermal energy is generated which activates the thermophilic enzyme. Enzyme-Au nanorod complexes encapsulated in calcium alginate are reusable and stable for several days, making them viable for industrial applications. Lastly, highly versatile Au nanoparticles with diameters of ~3-12 nm were prepared using carbon monoxide (CO) to reduce a Au salt precursor onto preformed catalytic Au particles. Compared to other reducing agents used to generate metallic NPs, CO can be used at room temperature and its oxidized form does not interfere with the colloidal stability of NPs suspended in water. Controlled synthesis of different sized particles was verified through detailed ultraviolet-visible spectroscopy, small angle X-ray scattering, and transmission electron microscopy measurements. This synthesis method should be extendable to other monometallic and multimetallic compositions and shapes, and can be improved by using preformed particles with a narrower size distribution.
Investigation of the amyloid-beta aggregation and oxidation using photoluminescent metal complexes
(2021-12-03) Jiang, Bo; Marti, Angel A.
Amyloid-β (Aβ), a short peptide of 39 to 42 amino acids, is formed by the cleavage of the amyloid precursor protein by proteases in the membrane of neurons, and self-assembles into aggregated species. These aggregates take oligomeric (soluble) and fibrillar (insoluble) forms, which have been proven to be toxic to our brain, playing a key role of the onset of Alzheimer’s disease. In the past few decades, many groups have taken on the task of investigating the aggregation process of Aβ. Previous work in our lab has shown that metal complexes can be used as a new family of photoluminescent probes for the detection of Aβ aggregates. More specifically, we have shown that [Re(CO)3(dppz)(Py)]+ can photooxidize Aβ, providing a new way to investigate the interaction between metal complexes and these species. This thesis covers different topics related to the interaction of Aβ and metal complexes including probing Aβ oligomerization using ruthenium complexes, investigating the interactions between Aβ species and rhenium complexes, and exploring the inhibition effect and degradation of Aβ aggregates. Chapter 1 is a review of the photoluminescent metal complexes that have been developed for detection of Aβ aggregates. In the last few years this area of research has exploded making available photoluminescent metal complexes of ruthenium, iridium, rhenium and platinum for the study of Aβ aggregates. In chapter 2, I reported using the photoluminescence anisotropy of [Ru(bpy)2(dpqp)]2+ for the detection in real time of Aβ oligomers. Aβ oligomers are believed to form immediately following monomers, however they are invisible to fluorescence sensors such as Thioflavin T. Given that photoluminescence anisotropy is sensitive to the rotational correlation time of molecules, it is useful for monitoring the formation of biomolecule aggregates. We found that Aβ oligomers start to form from time zero with a steady increase in anisotropy that plateaus after 48 hours. The real-time monitoring of Aβ oligomers is of great importance for understanding the kinetics of aggregation, the forces that bring peptides together and study their inhibition. The formation of Aβ oligomers was supported by various characterization techniques including Western Blot analysis, SDS-PAGE analysis, dynamic light scattering analysis, transmittance electron microscopy and atomic force microscopy. Chapter 3 details the interactions between Aβ fibrils and [Re(CO)3(dppz)(Py)]+. Job plot and binding assay were used to determine the dissociation constant (Kd) as 4.2 ± 0.6 μM. Molecular dynamics simulations were used to propose a binding site for [Re(CO)3(dppz)(Py)]+ on Aβ fibrils at a hydrophobic cleft between Val18 and Phe20. Due to the fact that Aβ fibrils are oxidized by [Re(CO)3(dppz)(Py)]+ after UV irradiation, the binding site was studied using the oxidation site as a chemical footprint. In addition, the study of the photooxidation of Aβ monomers showed that after UV irradiation His14 is the most likely oxidized residue by [Re(CO)3(dppz)(Py)]+. In order to further study the secondary light-switching behavior of [Re(CO)3(dppz)(Py)]+, functional groups were used to simulate the amino acids of Aβ. We found that the photoluminescence of [Re(CO)3(dppz)(Py)]+ was enhanced in the presence of imidazole and dimethyl sulfide, indicating potential photochemical reaction was occurred . In addition, the quantum yield of singlet oxygen produced by [Re(CO)3(dppz)(Py)]+ upon UV irradiation, power flux of the irradiation source, and the quantum yields of photooxidation were determined. In chapter 4, we used [Ru(bpy)2(dpqp)]2+ in conjunction with time-resolved photoluminescence spectroscopy to assess Aβ aggregation. The added information available in the time-decay curves can be mathematically deconvoluted to obtain specific information about [Ru(bpy)2(dpqp)]2+ bound to Aβ. By considering a two sites non-cooperative binding model, the existence of two different binding sites on Aβ was discovered: one that affects the lifetime of [Ru(bpy)2(dpqp)]2+ and one that shows not affect its lifetime. These binding sites were further studied using MD simulations. The formation of Aβ aggregates was monitored in real-time using time-resolved photoluminescence spectrosocopy and confirmed using AFM. Chapter 5 investigated the inhibition of Aβ aggregation using a real-time assay. The results indicate that upon UV irradiation of [Re(CO)3(dppz)(Py)]+ with Aβ monomers, fibrillar aggregates are not produced. Further studies indicated that the photooxidized Aβ monomers play an important role for the inhibition effect. More investigations including MD simulation and other characterization are needed to explore the mechanism of this inhibition effect which could provide a unique method for the therapeutics of AD. In addition, we studied the photo-degradation of Aβ fibrils using rhenium complexes upon UV irradiation. The spectroscopic results and AFM images confirmed degradation of fibrillar species into small fragments and oligomers. This project is not yet done and needs more detailed and fundamental studies, but will be extremely helpful for the development of therapeutic strategies of AD.
Long-lived Luminescent Metal Complexes for Molecules Sensing and Nanotube Dispersion
(2014-09-19) Huang, Kewei; Marti, Angel A.; Wilson, Lon J; Diehl, Michael
Phosphorescent heavy-metal complexes are one class of excellent photoluminescent materials. The heavy metal-induced spin–orbit coupling leads to singlet–triplet state mixing, thus decreases the “spin-forbidden” component of the radiative relaxation of the triplet state, and consequently improves the phosphorescence quantum eﬃciency and radiative emission lifetime. Moreover, the emission wavelength of metal complexes can be easily tuned through the ligand modification and the change of central metals. Ruthenium(II) and Iridium(III)-based complexes have d6 electronic structures. The advantageous photophysical properties including long lifetime, large Stokes shift and long wavelength excitation provide them to be good candidates for chemosensors. This thesis focuses on the development of novel iridium and ruthenium complexes for small molecules sensing. Their long-lived photoluminescence lifetime allows detecting analytes even in the presence of short-lived background fluorescence by using time-gating techniques. An overview of the developing trends in molecular beacon design and applications will be introduced in Chapter 1. In Chapter 2, the long-lived emission of Ir(III) and Ru(II) complexes are combined with time-resolved spectroscopic techniques for optimizing the sensitivity of molecular beacons. A novel iridium complex with long-lived photoluminescence will be discussed in Chapter 3, which can be used for the detection of thiol-containing amino acids in the presence of strong background fluorescence. In Chapter 4, pre-exponential factors derived from time-resolved experiments will be applied for quantifying free histidine in mixtures with histidine-containing proteins. The last Chapter is the development of the new application of Ruthenium complexes as a media for dispersion nanotubes in aqueous solution.
RF heating of ultra-short single-walled carbon nanotubes and gadonanotubes for non-invasive cancer hyperthermia
(2014-01-30) Phounsavath, Sophia; Wilson, Lon J.; Marti, Angel A.; Grande-Allen, K. Jane; Curley, Steven A.
An emerging field of nanoparticle-mediated cancer therapy is based on the interaction of nanoparticles with radiofrequency (RF) energy to induce hyperthermia or thermal cytotoxicity within cancer cells. In this work, the heating properties of ultra-short single-walled carbon nanotubes (US-tubes) and gadonanotubes (GNTs) were assessed in an external radiofrequency field (900 W, 13.56 MHz). Surfactant (Pluronic F-108) suspensions of US-tubes (carbon-based nanocapsules that are 20-80 nm in length and 1.4 nm in diameter) and GNTs (US-tubes loaded internally with Gd3+ ions) heated in a concentration dependent manner when the RF field was applied. The observed bulk heating of the sample suspensions have been attributed to the nanomaterial itself and not the background surfactant solution. The efficacy of these remotely triggered heating agents to produce thermal cytotoxicity was then investigated in vitro in three different hepatocellular cancer cell lines (Hep3B, HepG2, and Snu449). In all cases, cancer cells that were treated with either US-tubes or GNTs in conjunction with RF had lower viabilities than those treated with RF alone. The ability of GNTs to induce thermal cytotoxicity in vivo was then investigated using subcutaneous tumor models in nude mice. Histopathological analysis of treated tumors demonstrated more pronounced and widespread cell damage in tumors treated with GNTs and RF than in the control tumors. It is anticipated that these results will aid in the future development of nanoparticle-mediated cancer therapy by hyperthermia.
Sensing amyloid aggregation using photoluminescent ruthenium(II) probes
(2014-04-24) Cook, Nathan Patrick; Marti, Angel A.; Ball, Zachary T.; Segatori, Laura
Amyloid proteins are a broad class of proteins that are implicated in a wide number of diseases. This thesis explores the use of photoluminescent ruthenium(II) complexes for the detection of amyloid aggregation. Furthermore, we report the detection of amyloid aggregates from test tube to cell culture using photoluminescent and lifetime measurements.
Surface Functionalization of Graphene-based Materials
(2013-09-16) Mathkar, Akshay; Ajayan, Pulickel M.; Barrera, Enrique V.; Marti, Angel A.
Graphene-based materials have generated tremendous interest in the past decade. Manipulating their characteristics using wet-chemistry methods holds distinctive value, as it provides a means towards scaling up, while not being limited by yield. The majority of this thesis focuses on the surface functionalization of graphene oxide (GO), which has drawn tremendous attention as a tunable precursor due to its readily chemically manipulable surface and richly functionalized basal plane. Firstly, a room-temperature based method is presented to reduce GO stepwise, with each organic moiety being removed sequentially. Characterization confirms the carbonyl group to be reduced first, while the tertiary alcohol is reduced last, as the optical gap decrease from 3.5 eV down to 1 eV. This provides greater control over GO, which is an inhomogeneous system, and is the first study to elucidate the order of removal of each functional group. In addition to organically manipulating GO, this thesis also reports a chemical methodology to inorganically functionalize GO and tune its wetting characteristics. A chemical method to covalently attach fluorine atoms in the form of tertiary alkyl fluorides is reported, and confirmed by MAS 13C NMR, as two forms of fluorinated graphene oxide (FGO) with varying C/F and C/O ratios are synthesized. Introducing C-F bonds decreases the overall surface free energy, which drastically reduces GO’s wetting behavior, especially in its highly fluorinated form. Ease of solution processing leads to development of sprayable inks that are deposited on a range of porous and non-porous surfaces to impart amphiphobicity. This is the first report that tunes the wetting characteristics of GO. Lastly as a part of a collaboration with ConocoPhillips, another class of carbon nanomaterials - carbon nanotubes (CNTs), have been inorganically functionalized to repel 30 wt% MEA, a critical solvent in CO2 recovery. In addition to improving the solution processability of CNTs, composite, homogeneous solutions are created with polysulfones and polyimides to fabricate CNT-polymer nanocomposites that display contact angles greater than 150o with 30 wt% MEA. This yields materials that are inherently supersolvophobic, instead of simply surface treating polymeric films, while the low density of fluorinated CNTs makes them a better alternative to superhydrophobic polymer materials.
Synthesis and Tracking of Fluorescent and Polymerization-Propelled Single-Molecule Nanomachines
(2013-07-24) Godoy Vargas, Jazmin; Tour, James M.; Wong, Michael S.; Marti, Angel A.
This dissertation describes the synthesis of molecular machines designed to operate on surfaces (nanocars) or in the solution phase (nanosubmarines), and the study of their diffusion using fluorescence techniques. The design of these molecular machines is aimed to facilitate monitoring of their movement and incorporation of a source of energy for propulsion. To complement previous scanning tunneling microscopy studies of the translation of nanocars on surfaces, chapter 1 describes the synthesis of a family of fluorescently tagged nanocars. The nanocars were functionalized with a tetramethylrhodamine isothiocyanate (TRITC) fluorescent dye. Single-molecule fluorescence microscopy (SMFM) studies of one of these nanocars revealed that 25% of the nanocars moved on glass. The SMFM results also suggested that the dye hindered the mobility of the nanocars. Seeking to improve the mobility, chapter 2 presents the synthesis of a new set of fluorescent nanocars, featuring a 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) dye embedded in their axles. The mobility of these inherently fluorescent nanocars on glass was nearly double than that of their TRITC-tagged predecessors. Their diffusion was also studied on reactive-ion-etched glass, and amino-functionalized glass. The results showed that the mobility is affected by the substrate. To equip the nanocars with an energy input for propulsion, two nanocars functionalized with an olefin metathesis catalyst were synthesized, as described in chapter 3. The catalytic activity of these nanocars toward ring-opening metathesis polymerization (ROMP) in solution was similar to that of their parent catalysts. As an alternative approach to investigate if chemical propulsion through a ROMP process can be achieved at the molecular level, chapter 4 presents the synthesis of a fluorescent ROMP catalyst, termed a nanosubmarine, and the study of its diffusion using fluorescence correlation spectroscopy (FCS). FCS results showed an increase of 20 ± 7% in the diffusion constant of this nanosubmarine in presence of its fuel, cis,cis-1,5-cyclooctadiene. Overall, the work accomplished in this dissertation constitutes a step forward toward development of easily tracked and highly mobile nanocars, and paves the way for the synthesis of truly nanosized chemically propelled molecular machines that operate in the solution phase.
The catalytic growth of single walled carbon nanotubes
(2013-12-05) Orbaek, Alvin; Barron, Andrew R.; Hauge, Robert H.; Adams, Wade; Tour, James M.; Marti, Angel A.
Single walled carbon nanotubes were synthesized using a variety of transition metal catalyst nanoparticles under a variety of reaction conditions. The degree of control for the growth procedure was qualitatively and quantitatively assessed using a variety of characterization techniques including resonance Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, thermogravimetric analysis, and atomic force microscopy. It was found that doping the catalysts with a second metal, also from the first row transition series, would alter both the rate of growth, and the diameters of the nanotubes that were produced. Further to this, work conducted using a bimetallic FeCo catalyst was found to exhibit two distinct growth stages, where each stage required careful selection of reaction conditions to maximize product output. By this method the design of a ‘catalyst activity map’ is proposed such that optimal conditions for nucleation and growth are determined. As a corollary to this work the synthesis of multi walled nanotubes was also carried out and it was found that the affect of the reaction conditions also greatly influenced the product outcome. Whereby products ranged from long thin multi walled nanotubes, to making carbon nano fibers instead. In this manner a ‘process map’ was developed according to the carbon nanomaterials that were created, as a function of the reaction conditions that were employed.
Water purification and monitoring
(2014-03-11) Maguire-Boyle, Samuel J.; Barron, Andrew R.; Marti, Angel A.; Li, Qilin
The purification of water for the next century is paramount. As global demand for energy increases new ways of generating energy have been discovered and exploited. However, with the diversification of energy sources one thing remains constant, the water energy nexus. The water energy nexus is the intimate connection of water generation to energy generation and visa-versa. In other words, to have energy clean water is needed and to have clean water energy is needed. Because of this, new methods of water purification and monitoring have been investigated and developed.Herein the author describes new water purification methods using zwitterionic surfaces which have been used to purify various types of water including to date the most difficult waters such as ‘oilfield brines’. The author also describes techniques developed to monitor the chemical content of the oilfield brine which may be adapted for use at on-site wells as well as techniques which may be utilized to monitor for aquifer contamination by oilfield operations via nanoparticle sensors.

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