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Thesis (Ed.M.)--Boston Universit

Bimetallic complexes of d- and f-block metals with pentalene ligands

The focus of this thesis is the synthesis and characterisation of organometallic complexes incorporating the silylated pentalene ligand, [C8H4{SiiPr3-1,4}2]2- (= Pn†), bound to more than one metal centre. In general, metals in low oxidation states from the d- and f-block of the periodic table have been selected for these bimetallic complexes, as they are potentially reactive with small molecule substrates. Chapter One introduces the pentalene molecule and its derivatives, and discusses their use as ligands in organometallic chemistry. Particular emphasis is given to the application of organometallic pentalene complexes, ranging from conducting polymers in materials chemistry to small molecule activation and catalysis. In Chapter Two the silylated pentalene ligand Pn† is used to bridge two lanthanide(II) centres in anti-bimetallic sandwich complexes of the type [Cp*Ln]2(μ-Pn†) (Ln = Yb, Eu and Sm). Magnetic measurements and electrochemical methods are used to investigate the extent of intermetallic communication in some of these systems, which show potential for the design of organometallic 'molecular-wires'. Chemical oxidation of [Cp*Yb]2(μ-Pn†) leads to dissociation into mononuclear fragments (η8-Pn†)YbCp* and [Cp*Yb]+, and reaction of [Cp*Sm]2(μ-Pn†) with CO yields (η8-Pn†)SmCp*. Rational synthetic routes to mononuclear mixed-sandwich Pn†/Cp* compounds with trivalent f-block ions (Dy, Tb and U) are also developed, and their magnetic properties are studied by SQUID magnetometry including variable-frequency ac susceptibility measurements. These studies identified (η8-Pn†)DyCp* as the first known example of a pentalene based single molecule magnet, with a closed-waist hysteresis loop observed up to 2 K. Chapter Three describes the synthesis of iron(II) complexes with silylated pentalene ligands, and efforts towards incorporating them into extended organometallic arrays and heteronuclear anti-bimetallic complexes. Six complexes have been structurally characterised including the triple-decker homobimetallic [Cp*Fe]2(μ-Pn†), and the potassium salt [Cp*Fe(η5-Pn†)][K] which is an organometallic polymer in the solid state. Chapter Four documents efforts towards the synthesis of syn-bimetallic pentalene complexes, including the first row d-block metals V, Ti and Sc. A novel synthetic route to the di-titanium bis(pentalene) 'double-sandwich' complex (Pn†)2Ti2 is developed, via chloride-bridged dimers [(η8-Pn†)Ti]2(μ-Cl)x (x = 2 and 3). The electronic and magnetic properties of the latter are investigated using EPR spectroscopy and SQUID magnetometry, and the structure and bonding in (Pn†)2Ti2 is examined using spectroscopic, crystallographic, electrochemical and computational techniques. Preliminary studies toward the synthesis of an analogous di-scandium complex were unsuccessful, however three novel complexes have been synthesised including (η8- Pn†)ScCp* which is first example of a Sc complex bearing a Pn† ligand to be characterised by X-ray diffraction. Chapter Five explores the reactivity of the double-sandwich compound (Pn†)2Ti2 prepared in Chapter Four, with small molecules which are of industrial and environmental importance. The relatively open structure of (Pn†)2Ti2 allows the formation of adducts with unsaturated small molecules CO, MeNC and CO2. In the latter case the adduct formed is unstable at room temperature and the coordinated CO2 molecule is reduced to give a bis(oxo) bridged dimer and a di-carbonyl complex. This provides the first example of small molecule activation by a di-metal bis(pentalene) double-sandwich complex. The reactivity survey of (Pn†)2Ti2 is extended in Chapter Six to other substrates; including unsaturated heteroallenes as model molecules for CO2. In the case of nonpolar heteroallenes CS2 and carbodiimide, thermally stable adducts are isolated and have been structurally characterised. Polar heteroallenes COS and organic isocyanates undergo reductive transformations to give sulfide- and carbonimidate-bridged complexes respectively. The reactivity of (Pn†)2Ti2 with organic molecules containing heteroatom-heteroatom bonds is also described; the reactions with diphenyldichalcogenides and azobenzene show the ability of the double-sandwich complex to act as a 2e- and 4e- reducing agent respectively. The rich and varied chemistry shown by (Pn†)2Ti2 is evaluated and future work is suggested

On-Line Fatigue Crack Growth Monitoring in Externally Pressurised Vessels Using the Alternating Current Potential Drop (ACPD) Technique

At ARE (Dunfermline) fatigue tests are carried out on internally stiffened, welded steel cylindrical pressure vessels. These vessels are constructed from high yield strength quenched and tempered steels with full penetration butt and T-butt welds

An Evaluation of Grain Processing and Storage Method, and Feed Level on the Performance and Meat Quality of Beef Cattle Offered Two Contrasting Grass Silages

Traditionally cereals have been dried or treated with propionic acid and processed prior to feeding to finishing beef cattle. Recently new techniques have been developed for storing and feeding grain to beef cattle. The objective of the current study was to evaluate the effects of grain storage and processing method, and grain feed level on performance and meat quality of beef cattle offered two contrasting feed value grass silages

A novel radioiodinated high affinity ligand for the D2-dopamine receptor Characterization of its binding in bovine anterior pituitary membranes

AbstractA novel high affinity dopaminergic ligand, N-(p-aminophenethyl)spiroperidol, has been synthesized and radioiodinated to a specific radioactivity of 2175 Cimmol. Binding of this ligand to bovine anterior pituitary membranes is: (i) rapid (40–60 min to equilibrium at 25°C) and reversible t12 = 1 h at 25°C); (ii) saturable and of high affinity (KD ~ 20 pM) and (iii) displays a typical D2-dopaminergic specificity. The ligand, which identifies the same number of receptor sites as other tritiated antagonist ligands, can be used in different tissues and preparations to delineate the characteristics of the D2 receptor. Thus, this high affinity, high specific radioactivity ligand (N-(p-amino-m-[125I]iodophenethyl)spiroperidol) represents a tool which until now had not been available for the characterization of the D2-dopamine receptor

Influence of case definition on incidence and outcome of acute coronary syndromes

© 2016, BMJ Publishing Group. All rights reserved. Objective: Acute coronary syndromes (ACS) are common, but their incidence and outcome might depend greatly on how data are collected. We compared case ascertainment rates for ACS and myocardial infarction (MI) in a single institution using several different strategies. Methods: The Hull and East Yorkshire Hospitals serve a population of ∼560 000. Patients admitted with ACS to cardiology or general medical wards were identified prospectively by trained nurses during 2005. Patients with a death or discharge code of MI were also identified by the hospital information department and, independently, from Myocardial Infarction National Audit Project (MINAP) records. The hospital laboratory identified all patients with an elevated serum troponin-T (TnT) by contemporary criteria ( > 0.03 μg/L in 2005). Results: The prospective survey identified 1731 admissions (1439 patients) with ACS, including 764 admissions (704 patients) with MIs. The hospital information department reported only 552 admissions (544 patients) with MI and only 206 admissions (203 patients) were reported to the MINAP. Using all 3 strategies, 934 admissions (873 patients) for MI were identified, for which TnT was > 1 μg/L in 443, 0.04-1.0 μg/L in 435, =0.03 μg/L in 19 and not recorded in 37. A further 823 patients had TnT > 0.03 μg/L, but did not have ACS ascertained by any survey method. Of the 873 patients with MI, 146 (16.7%) died during admission and 218 (25.0%) by 1 year, but ranging from 9% for patients enrolled in the MINAP to 27% for those identified by the hospital information department. Conclusions: MINAP and hospital statistics grossly underestimated the incidence of MI managed by our hospital. The 1-year mortality was highly dependent on the method of ascertainment

Emerging Approaches to Understanding Microvascular Endothelial Heterogeneity: A Roadmap for Developing Anti-Inflammatory Therapeutics

The endothelium is the inner layer of all blood vessels and it regulates hemostasis. It also plays an active role in the regulation of the systemic inflammatory response. Systemic inflammatory disease often results in alterations in vascular endothelium barrier function, increased permeability, excessive leukocyte trafficking, and reactive oxygen species production, leading to organ damage. Therapeutics targeting endothelium inflammation are urgently needed, but strong concerns regarding the level of phenotypic heterogeneity of microvascular endothelial cells between different organs and species have been expressed. Microvascular endothelial cell heterogeneity in different organs and organ-specific variations in endothelial cell structure and function are regulated by intrinsic signals that are differentially expressed across organs and species; a result of this is that neutrophil recruitment to discrete organs may be regulated differently. In this review, we will discuss the morphological and functional variations in differently originated microvascular endothelia and discuss how these variances affect systemic function in response to inflammation. We will review emerging in vivo and in vitro models and techniques, including microphysiological devices, proteomics, and RNA sequencing used to study the cellular and molecular heterogeneity of endothelia from different organs. A better understanding of microvascular endothelial cell heterogeneity will provide a roadmap for developing novel therapeutics to target the endothelium

An Evaluation of the Inclusion of Alternative Forages With Grass Silage-Based Diets on Carcass Composition and Meat Quality of Beef Cattle Offered Two Contrasting Grass Silages

Recent studies have shown that the inclusion of some alternative forages with grass silage-based diets can increase animal performance of beef cattle. The aim of the present study was to evaluate the effects of including either maize or whole crop wheat (WCW) silages with grass silage-based diets on meat quality of beef cattle offered two levels of concentrate

Carbon dioxide activation by a uranium(III) complex derived from a chelating bis(aryloxide) ligand

The new dianionic ligand, C6H4{p-C(CH3)2C6H2Me2O−}2 (= p-Me2bp), featuring two aryloxide donors and a central arene ring, has been synthesized, and used to prepare the mixed-ligand U(III) compound, [U(Cp*)(p-Me2bp)] which exhibits an η6-interaction with the uranium center. Reductive activation of CO2 was investigated using [U(Cp*)(p-Me2bp)] in supercritical CO2, which gave a dinuclear uranium carbonate complex,{U(Cp*)(p-Me2bp)}2(μ-η1:η2-CO3), cleanly and selectively. Reactivity studies in conventional solvents using lower pressures of CO2 showed the formation of a rare U(IV) oxalate complex, {U(Cp*)(p-Me2bp)}2(μ-η2:η2-C2O2), alongside {U(Cp*)(p-Me2bp)}2(μ-η1:η2-CO3). The relative ratio of the latter two products is temperature dependent: at low temperatures (-78 ˚C) oxalate formation is favored, whilst at room temperature the carbonate is the dominant product. The U(IV) iodide, [U(Cp*)(p-Me2bp)I], was also synthesized and used as part of an electrochemical study, the results of which showed that [U(Cp*)(p-Me2bp)] has a UIV/UIII redox couple of −2.18 V vs FeCp2+/0 as well as an possible electrochemically accessible UIII/UII reduction process at −2.56 V vs FeCp2+/0

The lysosomotrope, GPN, mobilises Ca2+ from acidic organelles

Lysosomes are acidic Ca2+ stores often mobilised in conjunction with endoplasmic reticulum (ER) Ca2+ stores. GPN is a widely used lysosomotropic agent that evokes cytosolic Ca2+ signals in many cells. But whether these signals are due to a primary action on lysosomes is unclear in light of recent evidence showing GPN mediates direct ER Ca2+ release through changes in cytosolic pH. Here, we show that GPN evoked rapid increases in cytosolic pH but slower Ca2+ signals. NH4Cl evoked comparable changes in pH but failed to affect Ca2+ The V-type ATPase inhibitor, bafilomycin A1, increased lysosomal pH over a period of hours. Acute treatment modestly affected lysosomal pH and potentiated Ca2+ signals evoked by GPN. In contrast, chronic treatment led to more profound changes in luminal pH and selectively inhibited GPN-action. GPN blocked Ca2+ responses evoked by the novel NAADP-like agonist, TPC2-A1-N. GPN-evoked Ca2+ signals were thus better correlated with associated pH changes in the lysosome compared to the cytosol and coupled to lysosomal Ca2+ release. We conclude that Ca2+ signals evoked by GPN most likely derive from acidic organelles