1,721,003 research outputs found
SPAAC iClick: progress towards a bioorthogonal reaction in-corporating metal ions
No full textCombining strain-promoted azide-alkyne cycloaddition (SPAAC) and inorganic click (iClick) reactivity provides access to metal 1,2,3-triazolates. Experimental and computational insights demonstrate that iClick reactivity of the tested metal azides (LM-N3, M = Au, W, Re, Ru and Pt) depends on the accessibility of the azide functionality rather than electronic effects imparted by the metal. SPAAC iClick reactivity with cyclooctyne is observed when the azide functionality is sterically unencumbered,e.g.[Au(N3)(PPh3)] (Au-N3), [W(η3-allyl)(N3)(bpy)(CO)2] (W-N3), and [Re(N3)(bpy)(CO)3] [bpy = 2,2′-bipyridine] (Re-N3). Increased steric bulk and/or preequilibria with high activation barriers prevent SPAAC iClick reactivity for the complexes [Ru(N3)(Tp)(PPh3)2] [Tp = tris(pyrazolyl)borate] (Ru-N3), [Pt(N3)(CH3)(PiPr3)2] [iPr = isopropyl] (Pt(II)-N3), and [Pt(N3)(CH3)3]4((PtN3)4). Based on these computational insights, the SPAAC iClick reactivity of [Pt(N3)(CH3)3(P(CH3)3)2] (Pt(IV)-N3) was successfully predicted
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Stereoselectivity of Photocycloadditions and Photocyclizations
No full textIn Volumes I and 3 of the series "Molecular and Supramolecular Photochemistry" from 1997 and 1999, respectively, two chapters were published that describe
the regio-and stereosclectivity of photocycloadditions, photocyclizations, and
other photochemical reactions f I]. The reader might wonder about the motivation
to write another at1icle with stronger emphasis on the stereoselectivity of photocyclizations and photocycloadditions. We feel that the fascination of organic photochemistry mainly originates from the combination of well-known ground-state
effects (such as solvent or substituent effects, steric, electronic, and stereoelectronic control) and additional effects that originate from the excited-state nature
of the substrates and unusual spin multiplicities of reagents or intermediates. This
makes the analysis of many photochemical processes more difficult. the design
of new reactions tricky, and the predictability of efficiency and selectivity problematic. On the other hand, new mechanistic aspects might lead to an important
new dimension in control of stereosclectivity in photochemistry and, as recently
stated by Peter Wagner. "stereochemistry is the essence of organic chemistry"
[2). Recent investigations of temperature, spin, and substituent effects on the
stereochemistry of photochemical processes have shown that at least two con-
cepts have to be taken seriously into account: reactive triplet biradical conformations and the complex kinetic interplay between product formation and deactivation to restore ground·state molecules from reactive intermediates
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Photoactive Layered Materials: Assembly of Ions, Molecules, Metal Complexes, and Proteins
No full textI. INTRODUCTION
This entire series is devoted to the study of supramolecular assemblies and this
fact emphasizes the importance of supramolecular chemistry in this new millen
nium. The transition from the molecular to supramolecular chemistry is due to the
inspiration derived from the high-level-molecular architecture observed in bio
logical systems. The details of the intermolecular forces that control this biologi
cal organization is not well understood, but efforts in supramolecular chemistry
are already helping us understand this organization. Photochemical methods are
extremely valuable for exploring these intermolecular interactions that control the
molecular organization
Photophysical Studies of the Doublet Excited States of Donor-Acceptor Chromophore Radical Anions in the Application of Photocatalysis
No full textThis item is available only to currently enrolled UTSA students, faculty or staff. To download, navigate to Log In in the top right-hand corner of this screen, then select Log in with my UTSA ID.Photocatalysis has been a continuously growing field that has a constant demand for stronger redox agents, especially those that can absorb in low-energy visible and/or near-infrared (NIR) regions since it allows for even more significant applications across scientific fields. Current research has focused on the approach of mimicking the photosystems of green plants and cyanobacteria, which use low-energy solar photons, by developing electron donor-acceptor systems. Radical ion excited doublet states of such system provide another promising approach in the search for chromophores capable of acting as photo-driven redox agents with low-energy photons. Herein, I describe the photophysical properties of a series of donor-acceptor (DA) and donor-acceptor-donor (DAD) systems in their 1-electron reduced state with the aim of searching for super-reductants for viable photocatalysis applications. In this report, the target molecules and complexes were thermally reduced by naphthalene radical anion (Naph•-) reducing agent. The newly formed radical anions were then analyzed by a series of spectroscopy techniques to study their doublet excited-state photophysical properties. First, several imide-functionalized rylene dye derivatives were investigated, including a benzodmaphthalene diimide (BDI) and a naphthalimide (NI) chromophore. Secondly, I expanded the study to a series of electron donor – electron acceptor (DA) systems, in which the acceptor NI was coupled with different donors, such as oligo(phenylene ethynylene)s (OPEs) and thiophene/thienylene (Ts) with varying chain lengths. Furthermore, I carried out the studies on two different series of DAD chromophores: (1) benzothiadiazole was employed as the acceptor moiety, and the donors were varied; (2) thiophene moiety was kept as the electron donor, and the acceptors were different arylene moieties. Finally, the research was further expanded to Platinum-incorporated complexes and polymer in an attempt to observe the effect of spin-orbit coupling on the doublet excited-state photophysical properties of these chromophores.Chemistr
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Get PDFWe 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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