No description available.

As an important part of the periodic table, metal elements have attracted widespread attention due to their special physical and chemical properties, as well as effective functionalities. Many metals at the nanoscale level exhibit a wide array of applications, ranging from catalysis to photonics, electronics, energy conversion/storage, and medicine. To obtain a more effective functionality in application, it is indispensable to synthesize uniform metal nanoparticles with well-defined size, morphology, composition, and crystal structures. In this dissertation, we will demonstrate high-boiling point solvent method for synthesizing metal nanocrystals, ranging from single metal nanocrystals (e.g., iridium (Ir), ruthenium (Ru), germanium (Ge), bismuth (Bi)) to binary metal nanocrystals (e.g., Sn-Ge), and ternary intermetallic compounds (e.g., Pt1-xPdxBi). By varying different halogen ions, we can get different morphologies of metal nanocrystals. We will further study the catalytic effect of Pd metal nanocrystals supported on silicon spheres and realize the hydrodeoxygenation reaction of vanillin under mild conditions.First, we used bismuth as an example to study the shape-controlled synthesis of metal nanocrystals by adjusting the injection temperature and the added halide ions (e.g., Cl-, Br-). Our findings indicated that due to the different electronegativities, halide ions are selectively adsorbed on specific crystal planes during the growth of Bi NCs, leading to different morphologies. Then we proposed a tungsten hexacarbonyl (W(CO)6)-assisted reduction strategy for obtaining uniform metal nanoparticles (e.g., Ir, Ru, Ge, Bi) of different metal salts. This strategy was extended to the synthesis of uniform binary metal (e.g., Sn-Ge) nanoparticles, which we can get tunable bandgap (0.51 eV to 0.72 eV) based on the controlled reaction of Ge2+ precursor solution with uniform tin (Sn) nanocrystals (NCs) as the template. Next, we realized the synthesis of intermetallic Pt1-xPdxBi nanoplates with controllable compositions, including Pt0.5Pb0.5Bi, Pt0.25Pd0.75Bi, and Pt0.75Pd0.25Bi via the sequential complexation-reduction-sorting method. Furthermore, we used palladium (Pd) metal nanoparticles (NPs) as a photocatalyst to trigger the hydrodeoxygenation reaction of vanillin. We demonstrated a model to disperse free-standing Pd NP on dielectric silica nanospheres (SiOx NSs). The spherical shape of SiOx can cause scattering resonance, thereby enhancing the local electric field on or near the surface to enhance light absorption of Pd NPs, further realizing a more effective catalyze on chemical reactions. We found that the adsorption of H2 on Pd is too strong to support the reaction effectively, but light absorption can reduce the "poisoning effect" by weakening the adsorption of hydrogen on Pd surface. Overall, we use innovative strategies to effectively synthesize a variety of high-quality metal nanomaterials. Our work shows that the Pd-NP/SiOx-NS composite nanostructure using dielectric SiOx as an optical nanoantenna is a promising photocatalyst that can drive photonic chemical conversion with high efficiency. / Chemistry

Mass spectrometry (MS) is emerging as an important tool for studying protein and protein complexes. When applying this tool, it is important to understand and investigate whether some of the intramolecular and intermolecular interactions of proteins in solution and are maintained in the gas phase. To investigate if some of these interactions are maintained in the gas phase, we develop and use a method in which the electron-transfer dissociation (ETD) spectra of native proteins are compared with spectra from ETD followed by low amplitude collisional induced dissociation (CID). From these experiments, we find that some intramolecular interactions from solution are maintained in the gas phase for ubiquitin and beta-2-microglobulin (β2m). However, using these approaches, cytochrome c’s structure in the gas phase appears to be quite different than its structure in solution. We also investigated if ETD spectra of intact protein complexes reflect contact site information in these complexes

No description available.

No description available.

Microbial-influenced corrosion (MIC) has been widely recognized as a significant economic and environmental problem in the oil and gas industry. MIC can be classified into two types based on the mechanisms: the extracellular electron transfer MIC (EET-MIC) and the metabolite MIC (M-MIC). The first includes electroactive bacteria that facilitate EET, while the latter includes bacteria that secrete corrosive metabolites. Sulfate-reducing bacteria (SRB) is believed to cause EET-MIC in carbon steel, a widely used metal in the oil and gas industry. In previous electroactive bacteria studies, nanowires have been shown to facilitate EET by acting as electron mediators. This study investigates the use of magnetite nanowires as electron mediators to accelerate EET-MIC of C1020 by Desulfovibrio vulgaris. The addition of 40 ppm (w/w) nanowires to carbon steel incubated with D. vulgaris, corrosive SRB species, for seven days resulted in 45% weight loss and 57% deeper pitting of carbon steel. Furthermore, electrochemical measurements of open circuit potential, linear polarization resistance and potentiodynamic polarization were found to be parallel with weight loss and pitting results. Therefore, these findings highlight the possibility of using magnetic nanowires as an electron mediator with high efficiency and selectivity to EET-MIC for future MIC studies and applications.

Due to the limited number of approved antioxidants for food applications, several alternative strategies to improve antioxidant performance have been developed by focusing on synergistic antioxidant interactions. Susceptibility to lipid oxidation in food systems is the result of the summation of antioxidative and prooxidative mechanisms. Understanding the sometimes paradoxical behavior of antioxidants and prooxidants is a vital key to design synergistic antioxidant systems suitable for particular foods. This research focused on 3 main strategies to improve the performance of antioxidant activity in oil-in-water emulsions. The first part of this research has been focused on inhibition of lipid oxidation by a combination of the modification of liposomal surfaces by chitosan-coating techniques along with addition of rosmarinic acid esters of varying polarity. Repelling metal ions away from the interface of positively charged liposomes can inhibit lipid oxidation (induced by Fe2+), and also reduce antioxidant loss by Fe3+ reduction. As a result, lipid oxidation can be inhibited synergistically because of a reduction in the prooxidant activity of iron. Second, understanding non-linear antioxidant behavior (the cut-off effect) of antioxidant esters in oil-in-water (O/W) emulsions was also studied to determine how the distributions and locations of antioxidants impacted their antioxidant activity. Antioxidant activity of rosmarinic acid was improved by esterification with alkyl chain lengths between 4 to 12 carbons due to increased ability to partitioning at the interface in oil-in-water emulsions. Surfactant micelles which could increase or decreased the concentration of the antioxidants at the emulsion droplet interface altered antioxidant activity. In the last part of this research, rosmarinic acid and its esters were found to be an excellent tool for studying how antioxidant location could impact its ability to interact with α-tocopherol in O/W emulsions. Synergistic, additive, and antagonistic effects were observed in the combinations between the rosmarinate esters with α-tocopherol. Increases in alkyl chain lengths of rosmarinic acid have influenced both the partitioning of the rosmarinate esters as well as their ability to they interact with α-tocopherol at the interface of oil-in-water emulsions. Fluorescence quenching and EPR studies showed that water soluble rosmarinic acid (R0) exhibited more interactions with á-tocopherol than any of the esters (R4-R20). Synergistic antioxidant interactions between rosmarinic acid and α-tocopherol could not be explained by electron transfer mechanisms, but formation of caffeic acid from rosmarinic acid. Due to the thermodynamic infeasibility and the fact that increases in α-tocopherol degradation rates, α-tocopherol could not be regenerated efficiently by rosmarinic acid. This formation of caffeic acid was proposed to be responsible of the synergistic activity of R0 and α-tocopherol since the formation of an additional antioxidant could further increase the oxidative stability of the emulsion.

This dissertation aims to understand the effect of incompatible side chains on the complexes of pi-conjugated electron-rich donors and electron-deficient acceptors in solution. The role of incompatible side chains were studied in simple mixtures of organic donor and acceptor molecules that form donor-acceptor complexes. The incompatible branched and linear alkane side chains on the acceptor and donor respectively prevented complex formation between naphthalene diimide acceptor and naphthalene ether donor. However, the incompatible hydrocarbon-fluorocarbon and polar-non polar side chain pairs did not affect complex formation between the donor and acceptor. In quaterthiophene-naphthalene diimide dyads, the incompatibility of the side chain on the acceptor with respect to the side chain on the donor do not have any influence on the donor-acceptor complex formation. Irrespective of the attached side chains, all the dyads show charge transfer absorption bands and have similar electron transfer rates. The effect of point of attachment of the acceptor to the donor in the quaterthiophene-flavin dyad is also studied.

As part of the study, photosynthetic system constructs based on BF2-chelated dipyrromethene (BODIPY), BF2-chelated azadipyrromethene (AzaBODIPY), porphyrin, phthalocyanine, oxasmaragdyrin, polythiophene, fullerene (C60), single-walled carbon nanotube and graphene are investigated. Antenna systems of BODIPY dyads and oligomers having BODIPY as an excitation energy donor connected to different acceptors including BODIPY, azaBODIPY, oxasmaragdyrin and aluminum porphyrin are studied. Different synthetic methodologies are used to afford donor-acceptor systems either directly linked with no spacer or with short spacers of varying length and orientation. The effect of donor orientation, donor optical gap as well as nature of donor-acceptor coupling on the donor-acceptor spectral overlap and hence the rate of excitation energy transfer is investigated. In all these systems, an ultrafast energy transfer followed by electron transfer is observed. In particular, in a directly connected BODIPY-azaBODIPY dyad an unusually ultrafast energy transfer (~ 150−200 f) via Förster mechanism is observed. The observation of energy transfer via Förster instead of Dexter mechanism in such closely coupled donor-acceptor systems shows the balance between spatial and electronic coupling achieved in the donor-acceptor system. Moreover, in donor-acceptor systems involving semiconducting 1D and 2D materials, covalently functionalized single-walled carbon nanotubes via charge stabilizing (TPA)3ZnP and noncovalently hybridized exfoliated graphene via polythiophene chromophores are studied for their charge transportation functions. In both cases, not only an ultrafast charge transfer in the range of (~ 2−5 p) is observed but also the charge-separated states were long lived implying the potential of these functionalized materials as efficient charge transporting substrates with organic chromophores for photovoltaic and optoelectronic applications where ultrafast intercomponent charge transfer is vital. In addition, as a final part of this dissertation, the mechanisms of electron injection and back electron transfer in heterogeneous systems involving supramolecularly anchored high potential chromophores on TiO2 film are studied by femtosecond transient absorption spectroscopy. In this study, not only are important insights gained on the utilization of supramolecular anchoring of chromophores such as porphyrins, phthalocyanines, and their perflorinated high potential analogues, chromophores currently showing promise as highly efficient sensitizers in dye sensitized solar cells, on TiO2 film but also on the effect of anchor length and sensitizer orientation on the rates of electron injection and back electron transfer at the sensitizer-TiO2 interface.

Electron-driven processes lie at the core of a large variety of physical, biological, and chemical phenomena. Despite their crucial roles in science and technology, detailed description of these processes remains a significant challenge, and there is a need for the development of accurate and efficient computational tools that enable predictive simulation. This work is focused on the development of novel software tools and methodologies aimed at two classes of electron-mediated processes: (i) electron-molecule scattering, and (ii) charge transfer in proteins. The first major focus of this thesis is the electronic structure of autoionizing electronic resonances. The theoretical description of these metastable states is intractable by means of conventional quantum chemistry techniques, and specialized techniques are required in order to accurately describe their energies and lifetimes. In this work, we have utilized the complex absorbing potential (CAP) method, and describe three developments which have advanced the applicability, efficiency, and accessibility of the CAP methodology for molecular resonances: (1) implementation and investigation of the smooth Voronoi potential (2) implementation of CAP in the projected scheme, and (3) development of the OpenCAP package, which extends the CAP methodology to popular electronic structure packages. The second major focus is the identification of electron and hole transfer (ET) pathways in biomolecules. Both experimental and theoretical inquiries into electron/hole transfer processes in biomolecules generally require targeted approaches, which are complicated by the existence of numerous potential pathways. To this end, we have developed an open-source web platform, eMap, which exploits a coarse-grained model of the protein crystal structure to (1) enable pre-screening of potentially efficient ET pathways, and (2) identify shared pathways/motifs in families of proteins. Following introductory chapters on motivation and theoretical background, we devote a chapter to each new methodology mentioned above. The open-source software tools discussed herein are under active development, and have been utilized in published work by several unaffiliated experimental and theoretical groups across the world. We conclude the dissertation with a summary and discussion of the outlook and future directions of the OpenCAP and eMap software packages.