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In an effort to further the understanding of ligand-surface interactions, a combination of multi-nuclear (1H, 29Si, 31P) and multi-dimensional solid-state NMR techniques were utilized to characterize the phosphonic acid functionalization of fumed silica nanoparticles using methyl phosphonic acid (MPA) and phenyl phosphonic acid (PPA). Quantitative 31P MAS solid-state NMR measurements indicate that ligands favor a monodentate binding mode. Furthermore, 1H-1H single quantum-double quantum (SQ-DQ) back-to-back (BABA) 2D NMR spectra of silica functionalized with MPA and PPA indicate that the MPA and PPA are within 4.2±0.2 Å on the surface of the nanomaterial.
The ligand capping of phosphonic acid (PA) functionalized CdSe/ZnS core-shell quantum dots (QDs) was investigated with a combination of ligand exchange, solution and solid-state 31P NMR spectroscopy. In order to quantify the ligand populations on the surface of the QDs, ligand exchange facilitated by PPA resulted in the displacement of the PAs, and allowed for quantification of the free ligands using 31P liquid state NMR.
In addition to characterizing nanomaterials, the ionicity and transport properties of a series of diethylmethylamine (DEMA) based protic ionic liquids (PILs) were characterized, principally utilizing NMR. Gas phase proton affinity was shown to be a better predictor for the extent of proton transfer, and in turn the ionicity of the PIL, than using ∆pKa. Furthermore, pulsed field gradient (PFG) NMR was used to determine that the exchangeable proton diffuses with the cation or the anion based on the strength of the acid used to generate the PILs.
Despite the great strides being made in the areas of alternative energy and solar-energy conversion, consumption of fossil fuels for energy generation will likely continue into the foreseeable future. This is primarily motivated by economic factors inasmuch as fossil fuels are a proven resource base with robust harvesting and distribution infrastructure.2 Presently, there are more than 8,000 stationary CO2 emission sources with an annual output of 13,466 megatons of CO2 per year.2 In this context, development of systems that ameliorate the output of greenhouse gasses from stationary CO2 sources, such as coal and natural gas burning power plants, is urgently needed.
In this document the utility of sulfur nucleophiles for CCS schemes is explored. The main thrust of the research has been utilizing electrogenerated sulfur nucleophiles to capture CO2, which can be electrochemically recovered from the resulting thiocarbonates while concomitantly regenerating the masked capture agent. Further, a temperature swing CO2 capture scheme that employs benzylthiolate as the CO2 sorbent is proposed and methods of manipulating the release temperature and kinetics were investigated. These reports represent the first application of organosulfur compounds toward CCS technologies and there are a number of newly reported compounds. The appendix deviates from the theme of the first four chapters to describe the functionalization of poly(2,6-dimethyl-1,4-phenylene oxide) with ferrocene moieties by the copper catalyzed azide-alkyne coupling reaction. This material is discussed within the context of anion recognition and sensing applications.
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.
Human Papillomavirus, or HPV, is a viral pathogen that most commonly spreads through sexual contact. HPV strains 6 and 11 normally cause genital warts, while HPV strains 16 and 18 commonly cause cervical cancer, which causes cancerous cells to spread in the cervix. Physicians can detect those HPV strains, using a Pap smear, which is a diagnostic test that collects cells from the female cervix.
Johann Gregor Mendel studied patterns of trait inheritance in plants during the nineteenth century. Mendel, an Augustinian monk, conducted experiments on pea plants at St. Thomas’ Abbey in what is now Brno, Czech Republic. Twentieth century scientists used Mendel’s recorded observations to create theories about genetics.
In the 1930s, George Beadle and Boris Ephrussi discovered factors that affect eye colors in developing fruit flies. They did so while working at the California Institute of Technology in Pasadena, California. (1) They took optic discs (colored fuchsia in the image) from fruit fly larvae in the third instar stage of development. Had the flies not been manipulated, they would have developed into adults with vermilion eyes. (2) Beadle and Ephrussi transplanted the donor optic discs into the bodies of several types of larvae, including those that would develop with normal colored eyes (brick red), and those that would develop eyes with other shades of red, such as claret, carmine, peach, and ruby (grouped together and colored black in the image). (3a) When implanted into normal hosts that would develop brick red eyes, the transplanted optic disc developed into an eye that also was brick red. (3b) When implanted into abnormal hosts that would develop eyes of some other shade of red, the transplanted optic discs developed into eyes that were vermilion. Beadle and Ephrussi concluded that there was a factor, such as an enzyme or some other protein, produced outside of the optic disc that influenced the color of the eye that developed from the disc.
This illustration shows George Beadle and Edward Tatum's experiments with Neurospora crassa that indicated that single genes produce single enzymes. The pair conducted the experiments at Stanford University in Palo Alto, California. Enzymes are types of proteins that can catalyze reactions inside cells, reactions that produce a number of things, including nutrients that the cell needs. Neurospora crassa is a species of mold that grows on bread. In the early 1940s, Beadle and Tatum conducted an experiment to discover the abnormal genes in Neurospora mutants, which failed to produce specific nutrients needed to survive. (1) Beadle and Tatum used X-rays to cause mutations in the DNA of Neurospora, and then they grew the mutated Neurospora cells in glassware. (2) They grew several strains, represented in four groups of paired test tubes. For each group, Neurospora was grown in one of two types of growth media. One medium contained all the essential nutrients that the Neurospora needed to survive, which Beadle and Tatum called a complete medium. The second medium was a minimal medium and lacked nutrients that Neurospora needed to survive. If functioning normally and in the right conditions, however, Neurospora can produce these absent nutrients. (3) When Beadle and Tatum grew the mutated mold strains on both the complete and on the minimal media, all of the molds survived on the complete media, but not all of the molds survived on the minimal media (strain highlighted in yellow). (4) For the next step, the researchers added nutrients to the minimal media such that some glassware received an amino acid mixture (represented as colored squares) and other glassware received a vitamin mixture (represented as colored triangles) in an attempt to figure out which kind of nutrients the mutated molds needed. The researchers then took mold from the mutant mold strain that had survived on a complete medium and added that mold to the supplemented minimal media. They found that in some cases the mutated mold grew on media supplemented only with vitamins but not on media supplemented only with amino acids. (5) To discover which vitamins the mutant molds needed, Beadle and Tatum used several tubes with the minimal media, supplementing each one with a different vitamin, and then they attempted to grow the mutant mold in each tube. They found that different mutant strains of the mold grew only on media supplemented with different kinds of vitamins, for instance vitamin B6 for one strain, and vitamin B1 for another. In experiments not pictured, Beadle and Tatum found in step (4) that other strains of mutant mold grew on minimal media supplemented only with amino acids but not on minimal media supplemented only with vitamins. When they repeated step (5) on those strains and with specific kinds of amino acids in the different test tubes, they found that the some mutated mold strains grew on minimal media supplemented solely with one kind of amino acid, and others strains grew only on minimal media supplemented with other kinds of amino acids. For both the vitamins and amino acid cases, Beadle and Tatum concluded that the X-rays had mutated different genes in Neurospora, resulting in different mutant strains of Neurospora cells. In a cell of a given strain, the X-rays had changed the gene normally responsible for producing an enzyme that catalyzed a vitamin or an amino acid. As a result, the Neurospora cell could no longer produce that enzyme, and thus couldn't catalyze a specific nutrient.
The Southern Gastric Brooding Frog (Rheobotrahcus silus) was a frog species that lived in Australia. It was declared extinct in 2002. Once adult males fertilized the eggs of females, the females swallowed their eggs. The stomachs of the females then functioned somewhat like wombs, protecting the eggs while they gestated. Once the eggs developed into juveniles, female frogs performed oral birth and regurgitated their young.
Mechanism of Notch Signaling: The image depicts a type of cell signaling, in which two animal cells interact and transmit a molecular signal from one to the other. The process results in the production of proteins, which influence the cells as they differentiate, move, and contribute to embryological development. In the membrane of the signaling cell, there is a ligand (represented by a green oval). The ligand functions to activate a change in a receptor molecule. In the receiving cell, there are receptors; in this case, Notch proteins (represented by orange forks). The Notch proteins are embedded in the receiving cell membrane, and they have at least two parts: an intracellular domain (inside the cell) and the receptor (outside the cell). Once the ligand and receptor bind to each other, a protease (represented by the dark red triangle) can sever the intracellular domain from the rest of the Notch receptor. Inside the nucleus of the receiving cell (represented by the gray area) are the cellês DNA (represented by the multi-colored helices) and its transcription factors (blue rectangles). Transcription factors are proteins that bind to DNA to regulate transcription, the first step in gene expression, which eventually yields proteins or other products. Initially, repressor proteins (represented by a red irregular hexagon) prevent transcription factors from allowing transcription. When the severed Notch receptor intracellular domain reaches the nucleus, it displaces the repressor. The transcription factor can then signal for transcription to occur. 1) There is a Notch receptor protein in the membrane of a receiving cell, and a ligand for this receptor (for example, Delta) in the membrane of the signaling cell. When the ligand binds to the receptor, the intracellular domain of the receptor changes shape. 2) Inside the receiving cell, there are proteases. Once the intracellular domain of the receptor changes shape, the protease can bind to it and shear the intracellular domain away from the rest of the receptor molecule. 3) The severed intracellular domain is shuttled to the receiving cell nucleus. Here, the intracellular domain displaces a repressor protein. This allows a transcription factor to initiate DNA transcription. During transcription, DNA is used as a template to create RNA. Following transcription, the process of translation occurs, which uses RNA as a template to create proteins. These proteins influence the behavior, fate, and differentiation of cells, which contribute to normal embryonic development