Homogeneous ligand-centered hydrogen evolution and hydrogen oxidation : exploiting redox non-innocence to drive catalysis.

Hydrogen is a promising carbon-free fuel / energy carrier and is an essential building block for many industrial and agricultural processes. Rising energy demands have ignited interest in the development of carbon-free and carbon neutral energy sources. In this context, hydrogen is an attractive candidate—being energy-dense, carbon-free—and easily accessible through a two-electron reduction of water. Accordingly, many electrochemical homogeneous catalyst systems have been studied, with a focus on understanding the mechanism of hydrogen evolution proceeding through metal-hydride intermediates. However, there has been a renaissance in hydrogen evolution reaction (HER) catalyst design, with many groups implicating ligand redox non-innocence as a crucial driving force for catalysis rather than metal-hydride formation. In this dissertation, using characterization techniques including, cyclic voltammetry, controlled potential coulometry, UV-visible spectroscopy, 1H NMR, cyclic voltammetry modeling, x-ray crystallography, kinetic isotope effect studies, and density functional theory, we investigate ligand-centered electrocatalysts, which function without the generation of metal-hydride intermediates, for the production and oxidation of dihydrogen. Chapter three expands upon the previous work in the Grapperhaus Lab, and focus on ReL3 (L = diphenylphosphinobenzenethiolate). ReL3 reduces acids to H2 in dichloromethane with an overpotential of 0.708 V and a turnover frequency (TOF) of 32 s-1, and also oxidizes H2 in the presence of base with an overpotential of 0.970 V and a TOF of 4 s-1. The mechanism is supported by kinetic isotope effect (KIE) studies and density functional theory calculations (DFT). Chapters four and five will build on Chapter three, aiming to develop sustainable approaches for ligand-centered catalysis. The non-transition metal complex, ZnL1, the metal-free complex, H2L1, and the transition metal complex, CuL1 (L1 = diacetyl-bis(N4-methyl-3-thiosemicarbazonato)), function as electrocatalysts for hydrogen evolution (ZnL1, H2L1 and CuL1) and hydrogen oxidation (ZnL1 and H2L1). H2L1and ZnL1 display TOF’s of 1,320 s-1 and 1,170 s-1 at overpotentials of 1.43 and 0.756 V, respectively, while the CuL1 complex demonstrates a TOF of 10,000 s-1. H2L1 and ZnL1 also display TOF values for H2 oxidation of 32 s-1 and 72 s-1 at overpotentials of 0.328 and 0.315 V, respectively. Mechanisms for the HER were modeled using digital simulations and are further supported by DFT calculations. ReL3, ZnL1, H2L1, and CuL1 represent a fundamentally new class of electrocatalysts. Contrary to traditional molecular electrocatalysts that employ a metal-hydride as the key mechanistic intermediate, this approach facilitates H2 evolution through ligand-centered proton and electron-transfer events resulting in the evolution of H2 through either ligand-centered H● radical coupling or ligand-centered hydride proton coupling

Student Learning Styles And Performance In An Introductory Finance Class

Many academic disciplines have examined the role that variation in Jungian personality types plays in the academic performance of college students. Different personality types tend to have different learning styles, which in turn influence student performance in a variety of college courses. To measure the impact of learning styles on student performance in the introductory finance course, we administered an online Myers-Briggs Type Indicator (MBTI) test to students and then used regression analysis to measure the effects of different learning styles on course performance. We found several significant effects, which have implications for the teaching of introductory finance

Acetabular components in total hip arthroplasty: is there evidence that cementless fixation is better?

BACKGROUND: The use of cementless acetabular components in total hip arthroplasty has gained popularity over the past decade. Most total hip arthroplasties being performed in North America currently use cementless acetabular components. The objective of this systematic review and meta-analysis was to compare the survivorship and revision rate of cemented and cementless acetabular components utilized in total hip arthroplasty. METHODS: A primary literature search in PubMed identified 3488 articles, of which 3407 did not meet the inclusion criteria and were excluded. Only English-language articles on either the survivorship or revision rate of primary total hip arthroplasty at a minimum of ten years of follow-up were included. The present study analyzed forty-five articles reporting the long-term outcome of cementless acetabular components, twenty-nine reporting the outcome of cemented acetabular components, and seven comparing cemented and cementless acetabular components. Meta-analysis (with a random-effects model) was performed on the data from the seven comparative studies, and study-level logistic regression analysis (with a quasibinomial model) was performed on the pooled data on the eighty-one included articles to determine a consensus. The studies were weighted according to the number of total hip arthroplasties performed. RESULTS: The meta-analysis did not reveal any effect of the type of acetabular component fixation on either survivorship or revision rate. The regression analysis revealed the estimated odds ratio for survivorship of a cemented acetabular component to be 1.60 (95% confidence interval, 1.32 to 2.40; p = 0.002) when adjustments for factors including age, sex, and mean duration of follow-up were made. CONCLUSIONS: The preference for cementless acetabular components on the basis of improved survivorship is not supported by the published evidence. Although concerns regarding aseptic loosening of cemented acetabular components may have led North American surgeons toward the nearly exclusive use of cementless acetabular components, the available literature suggests that the fixation of cemented acetabular components is more reliable than that of cementless components beyond the first postoperative decade

Formation of tungsten oxide nanostructures by laser pyrolysis: stars, fibres and spheres

In this letter, the production of multi-phase WO3 and WO3-x (where x could vary between 0.1 and 0.3) nanostructures synthesized by CO2-laser pyrolysis technique at varying laser wavelengths (9.22-10.82 mm) and power densities (17-110 W/cm2) is reported. The average spherical particle sizes for the wavelength variation samples ranged between 113 and 560 nm, and the average spherical particle sizes for power density variation samples ranged between 108 and 205 nm. Synthesis of W18O49 (= WO2.72) stars by this method is reported for the first time at a power density and wavelength of 2.2 kW/cm2 and 10.6 μm, respectively. It was found that more concentrated starting precursors result in the growth of hierarchical structures such as stars, whereas dilute starting precursors result in the growth of simpler structures such as wires

Solvent Accessibility Promotes Rotamer Errors during Protein Modeling with Major Side-Chain Prediction Programs

Side-chain rotamer prediction is one of the most critical late stages in protein 3D structure building. Highly advanced and specialized algorithms (e.g., FASPR, RASP, SCWRL4, and SCWRL4v) optimize this process by use of rotamer libraries, combinatorial searches, and scoring functions. We seek to identify the sources of key rotamer errors as a basis for correcting and improving the accuracy of protein modeling going forward. In order to evaluate the aforementioned programs, we process 2496 high-quality single-chained all-atom filtered 30% homology protein 3D structures and use discretized rotamer analysis to compare original with calculated structures. Among 513,024 filtered residue records, increased amino acid residue-dependent rotamer errors─associated in particular with polar and charged amino acid residues (ARG, LYS, and GLN)─clearly correlate with increased amino acid residue solvent accessibility and an increased residue tendency toward the adoption of non-canonical off rotamers which modeling programs struggle to predict accurately. Understanding the impact of solvent accessibility now appears key to improved side-chain prediction accuracies.OA-hybri

Thermal receptivity of free convective flow from a heated vertical surface: linear waves

Numerical techniques are used to study the receptivity to small-amplitude thermal disturbances of the boundary layer flow of air which is induced by a heated vertical flat plate. The fully elliptic nonlinear, time-dependent Navier–Stokes and energy equations are first solved to determine the steady state boundary-layer flow, while a linearised version of the same code is used to determine the stability characteristics. In particular we investigate (i) the ultimate fate of a localised thermal disturbance placed in the region near the leading edge and (ii) the effect of small-scale surface temperature oscillations as means of understanding the stability characteristics of the boundary layer. We show that there is a favoured frequency of excitation for the time-periodic disturbance which maximises the local response in terms of the local rate of heat transfer. However the magnitude of the favoured frequency depends on precisely how far from the leading edge the local response is measured. We also find that the instability is advective in nature and that the response of the boundary layer consists of a starting transient which eventually leaves the computational domain, leaving behind the large-time time-periodic asymptotic state. Our detailed numerical results are compared with those obtained using parallel flow theory