1,721,039 research outputs found
Mapping the intrinsic photochemistry of photocorms via gas-phase laser spectroscopy
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Previous issue date: 6We perform, for the first time, gas-phase laser photodissociation spectroscopy on a series of metal carbonyls that can lose CO upon irradiation. These molecules (PhotoCORMs) can be used for delivering and releasing CO molecules for medicinal purposes, such as in cancer therapy and as antimicrobials. Photodepletion (PD) and photofragmentation (PF) spectra of [CpRu(Ph3)2CO]+ and [CpRu(dppe)CO]+ were acquired between 230 and 400 nm, and the range 230-500 nm was explored for [Mn(CO)4Br2] −. All the PhotoCORMs lose CO after irradiation, accessing different fragmentation channels when different excited states are populated. Indeed, while scanning the wavelength range in our laser-interfaced electrospray mass spectrometer, we observe the production spectra of the photofragments and can track the variation in the intensity of their production. [Mn(CO)4Br2] − loses 3 CO molecules in the key visible region and 4 COs in the UV. [CpRu(Ph3)2CO]+ fragments into [CpRuPh3] + via the loss of CO and Ph3. This observation can be used to improve the design of new CO-releasing molecules, as we demonstrate in the [CpRu(dppe)CO]+ system where we successfully observe only the CO loss across the whole explored wavelength range. Finally, solution-phase irradiation results are presented for 365 nm photoexcitation, showing comparable photofragmentation results to the ones obtained in the gas-phase
The stabilisation of organometallic complexes using m-terphenyl ligands
No full textThe use of bulky monodentate m-terphenyl ligands in the stabilisation of d-block organometallic compounds is surveyed. Importantly, these ligands have facilitated the isolation of hitherto unknown species containing low-coordinate centres and metal-metal multiple bonds. This review reports on these advances with emphasis on the synthesis, structural characterisation and, where possible, reactivity studies of complexes featuring metal-carbon bonds between m-terphenyl ligands and the transition metals
MAPPING THE INTRINSIC PHOTOCHEMISTRY OF PhotoCORMS VIA GAS-PHASE LASER SPECTROSCOPY
No full textWe perform, for the first time, gas-phase laser photodissociation spectroscopy on a series of metal carbonyls that can lose CO upon irradiation. These molecules (PhotoCORMs) can be used for delivering and releasing CO molecules for medicinal purposes, such as in cancer therapy and as antimicrobials.
Photodepletion (PD) and photofragmentation (PF) spectra of [CpRu(Ph)CO] and [CpRu(dppe)CO] were acquired between 230 and 400 nm, and the range 230-500 nm was explored for [Mn(CO)Br]. All the PhotoCORMs lose CO after irradiation, accessing different fragmentation channels when different excited states are populated. Indeed, while scanning the wavelength range in our laser-interfaced electrospray mass spectrometer, we observe the production spectra of the photofragments and can track the variation in the intensity of their production. [Mn(CO)Br] loses 3 CO molecules in the key visible region and 4 COs in the UV. [CpRu(Ph)CO] fragments into [CpRuPh] via the loss of CO and \chem{Ph_3}. This observation can be used to improve the design of new CO-releasing molecules, as we demonstrate in the [CpRu(dppe)CO] system where we successfully observe only the CO loss across the whole explored wavelength range. Finally, solution-phase irradiation results are presented for 365 nm photoexcitation, showing comparable photofragmentation results to the ones obtained in the gas-phase
Open-shell organometallics: reactivity at the ligand
No full textThe purpose of this review is to show that (cooperative) ligand radical reactivity can be effectively employed in synthetic organometallic chemistry and catalysis to achieve selectivity in radical-type transformations. The ‘redox non-innocence’ of ligands, and the controlled reactivity of ‘ligand radicals’- giving rise to new, intriguing substrate transformations - allow unusual and selective radical-type substrate coupling reactions, ligand rearrangements and C-Y bond formations. In this review, several examples of fast and selective ligand-centered radical transformations in the open-shell organometallic chemistry of transition metals are described, focussing on radical-type reactions of olefin-, vinylidene-, vinyl-, alkyne-, allyl-, propargyl-, carbonyl-, and carbene ligands. Intriguing and selective substrate-substrate coupling reactions, (covalent) carbon-metal bond formations and hydrogen atom transfer reactions from and to ligand radicals are summarized. To conclude this chapter, an overview of recently disclosed new insights in the catalytic mechanism of CoII(por) catalysed olefin cyclopropanation is presented, showing that enzyme-like cooperative metal-ligand-radical reactivity is no longer reserved to real enzymes, but is a useful new concept to steer and control radical-type transformations in future bio-inspired organometallic catalysis.<br/
Synergistic effects in the activation of small molecules by s-block elements
No full textThis critical review covers recent developments in the special chemistry which can take place when two different s-block metals are combined within the same organometallic mixture or reagent. It will cover a selection of the most widely researched mixed-metal ‘synergic’ systems, and will be confined to mixed alkali metal/magnesium reagents. An overview of the known structural chemistry of these fascinating systems will be presented along with some of their pertinent, recent uses in synthesis, including, in the activation/cleavage of C-H bonds (i.e., a metallation reaction) or induction of metal-halogen exchange in organic molecules. The chapter begins by providing a brief historical overview of mixed s-block metal chemistry
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
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
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