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On the functions of palladium (II) cages
Full text linkThis thesis consists of four chapters.
Chapter 1 provides an overview of metallosupramolecular chemistry, detailing the three main approaches to self-assembled metallosupramolecular architectures: the ligand direct approach, the symmetry interaction approach, and the weak link approach. The various applications of these systems are discussed with regards to their molecular recognition properties. A series of [Pd2(L)4]4+ cages designed and produced by the Crowley group is introduced and their achievements and failings of binding the inorganic anticancer drug cisplatin are outlined. The necessity to address the failings of these systems is the foundation for one of the aims of this project. The other goals of this project are centred around structurally similar, but functionally different [Pd2(L)4]4+ cages. These are investigated as molecular reaction vessels and their potential to enhance the rate of [4+2] Diels Alder cycloaddition reactions are studied.
Chapter 2 describes the global struggle against cancer, and how inorganic drug molecules such as cisplatin are used to combat the fatal disease. Advances in the use of metallosupramolecular architectures as drug delivery vectors are discussed, in particular [Pd2(L)4]4+ cage systems. Work building on the cages first developed by the Crowley group is detailed. Terminal coordinating pyridine groups have been substituted for quinoline and isoquinoline units in the new cages. The quinoline system no longer has the ability to bind cisplatin due to a twisting caused by steric clashes of the quinoline units. As these units are situated over the external faces of the palladium(II) metal ions, they provide protection from biological nucleophiles and therefore increase the kinetic robustness of the cage. This is reflected in the increased, sub-micromolar anticancer activity, the highest activity of any [Pd2(L)4]4+ system to date. However, like cisplatin, the system displayed very little discrimination between cancerous cells and healthy tissue.
Chapter 3 introduces a new [Pd2(L)4]4+ cage system whereby the central pyridine ring is replaced with a rotationally flexible, redox active ferrocene moiety. X-ray crystallography confirmed the structure of both the BF4- salt and the PF6- salt. The coordination chemistry of an alteration of the ferrocene-based ligand, whereby a 3-pyridyl donor is replaced by a 4-pyridyl donor, is also studied. Again, a single architecture was generated (and confirmed through X-ray crystallography), in this case a [Pd3(L)6]6+ prism. The exploration of the host-guest properties of both systems revealed them to interact strongly with the toluenesulfonate anion. While the cages retained the redox properties of ferrocene, the ferrocene units in each ligand did not interact with each other, and the electrochemical signals were unperturbed upon the introduction of the guest.
Chapter 4 details the history and current state of artificial enzymes, with particular emphasis on metallosupramolecular structures and more specifically, how [Pd2(L)4]4+ cages accelerate the rate of bimolecular [4+2] Diels Alder cycloaddition reactions. The work presented in this chapter is a continuation of a project started by the Lusby group in which the original [Pd2(L)4]4+ cage developed by Crowley was shown to not only accelerate the cycloaddition, but also alter the chemo- and regio-selectivity of the products. Electronic alterations to the cage have been explored in this section with regard to the catalytic activity. The new cages maintained their hosting abilities however altering the electronics only seemed to diminish the catalytic behaviour of the system when compared to the parent cage
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Biologically Relevant Triply- and Quadruply-Stranded Metallosupramolecular Architectures
No full textThis thesis consists of three chapters. Chapter 1 provides a brief introduction to why better cancer treatments and new antibacterial drugs are a necessity for the future. Some of the interesting and functional metallosupramolecular architectures have been showcased and discussed.
Chapter 2 details the generation of a new family of triply-stranded dicobalt(III) helicates and mesocates, their stability under a variety of conditions and a study of their biological activity. Building upon previous work in the Crowley group, these cylinders were designed to be stable enough to withstand attack from biological nucleophiles and show activity against both Gram-positive and Gram-negative bacteria. The helicates and mesocates were observed to be stable in DMSO and D2¬O, and did not break down readily in the presence of common biological nucleophiles such as histidine and chloride. While this was a success, the cylinders showed no activity against either strain of bacteria, most likely due to the high 3+ charge on each metal centre preventing the molecule from crossing the bacterial wall.
Chapter 3 discusses the progress towards synthesising low-symmetry, quadruply-stranded dipalladium(II) cages, and their ability to bind cisplatin. The basic tripyridyl ligand system, previously employed by the Crowley group, has been appended with varying lengths of terminal alkyl and polyethylene glycol (PEG) chains to create new low-symmetry ligands. The postulate surrounding this idea was for the ligands to self-organise around two palladium(II) ions such that the PEG chains will be aggregated on one side of the cage and the alkyl chains at the other. The driving force behind this was thought to be the hydrophobic effect, and so would only self-organise in polar solvents. The reason behind having low-symmetry cages was that under the right conditions, micelles would be able to form, thus forming a large robust drug delivery vector. Full self-organisation was observed for cages with both alkyl chains and PEG chains, while a seemingly statistical mixture of isomers was displayed by the cages with only alkyl chains or only PEG chains. One of the disubstituted cages was then shown to be able to bind cisplatin within the cavity. Unfortunately, time constraints meant that only preliminary studies on micelle formation were undertaken
Biologically Relevant Triply- and Quadruply-Stranded Metallosupramolecular Architectures
No full textThis thesis consists of three chapters. Chapter 1 provides a brief introduction to why better cancer treatments and new antibacterial drugs are a necessity for the future. Some of the interesting and functional metallosupramolecular architectures have been showcased and discussed.
Chapter 2 details the generation of a new family of triply-stranded dicobalt(III) helicates and mesocates, their stability under a variety of conditions and a study of their biological activity. Building upon previous work in the Crowley group, these cylinders were designed to be stable enough to withstand attack from biological nucleophiles and show activity against both Gram-positive and Gram-negative bacteria. The helicates and mesocates were observed to be stable in DMSO and D2¬O, and did not break down readily in the presence of common biological nucleophiles such as histidine and chloride. While this was a success, the cylinders showed no activity against either strain of bacteria, most likely due to the high 3+ charge on each metal centre preventing the molecule from crossing the bacterial wall.
Chapter 3 discusses the progress towards synthesising low-symmetry, quadruply-stranded dipalladium(II) cages, and their ability to bind cisplatin. The basic tripyridyl ligand system, previously employed by the Crowley group, has been appended with varying lengths of terminal alkyl and polyethylene glycol (PEG) chains to create new low-symmetry ligands. The postulate surrounding this idea was for the ligands to self-organise around two palladium(II) ions such that the PEG chains will be aggregated on one side of the cage and the alkyl chains at the other. The driving force behind this was thought to be the hydrophobic effect, and so would only self-organise in polar solvents. The reason behind having low-symmetry cages was that under the right conditions, micelles would be able to form, thus forming a large robust drug delivery vector. Full self-organisation was observed for cages with both alkyl chains and PEG chains, while a seemingly statistical mixture of isomers was displayed by the cages with only alkyl chains or only PEG chains. One of the disubstituted cages was then shown to be able to bind cisplatin within the cavity. Unfortunately, time constraints meant that only preliminary studies on micelle formation were undertaken
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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