1,721,261 research outputs found
Synthesis of hyperbranched polyarylethenes by consecutive C–H vinylation reactions
No full text<p>Anastasia Yu. Gitlina, Albert Ruggi, Kay Severin*</p><p>Synthesis of hyperbranched polyarylethenes by consecutive C–H vinylation reactions</p><p><i>Polym. Chem</i>. <strong>2023</strong>, <i>14</i>, 4182-4187</p><p>The dataset contains the following raw data - NMR, HRMS, GPC, TGA, DLS, photophysical data (absorption, excitation, emission spectra, photoluminescence lifetimes and quantum yields).</p>
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
Novel Chemosensors for Biologically Important Analytes
Full text linkIn this work, fluorescent-based chemosensors for the detection of important analytes in aqueous solution are described. The sensors are based on different detection concepts, including analyte-induced aggregation/de-aggregation, pattern-based sensing and micelle-based sensing. In chapter 2, we present an analyte-induced aggregation-type chemosensor for the sensing of spermine. A charge-frustrated amphiphile composed of a highly fluorescent pyrene-1,3,6-trisulfonate head group and an eicosane side chain was used as a fluorescence chemosensor. Analyte-induced aggregation of the dye upon addition of spermine results in pronounced fluorescence quenching. The sensor enables the detection of spermine down to the nanomolar concentration range with good selectivity over closely related biogenic amines such as spermidine. In chapter 3, we describe a conceptually new â one-cuvetteâ sensing system for the pattern-based analysis of seven aminoglycosides antibiotics. The antibiotics include amikacin, apramycin, gentamicin, kanamycin A and B, neomycin, and paromomycin. A mixture of two amphiphiles with fluorescent head groups was used as a sensing ensemble. In buffered aqueous solution, the amphiphiles form a dynamic mixture of micellar aggregates. In the presence of aminoglycosides, the relative amount and the composition of the micelles is modified. Accurate differentiation in the low micromolar concentration range is achieved by a principal component analysis of the spectral data. Also, the sensing system allows the differentiation of pure aminoglycosides from their mixtures. In chapter 4, a fluorescent chemosensor based on analyte-induced aggregation/de-aggregation is described for the sensing of Al3+ and citric acid. In buffered aqueous solution, the amphiphilic dye can form aggregates and the aggregation of the dye is associated with a strong quenching of its fluorescence. The Al3+-induced aggregation is used to sense Al3+ in the low micromolar concentration range with high selectivity. Furthermore, we demonstrate that the non-fluorescent dye-Al3+ complex can be used as a sensing ensemble for the detection of citric acid. The assay is able to quantify the citric acid content of commercial beverages such as energy drinks. A simple micelle-based assay for the fluorescence sensing of vitamin K1 is described. In the following chapter 5, the assay enables the detection of vitamin K1 in the low micromolar concentration range. As a sensing ensemble, a mixture of the surfactant triton X-100 and 1 aminopyrene in buffered aqueous solution is employed. Vitamin K1 co-localizes with the fluorescent pyrene dye in the micelle, resulting in fluorescence attenuation by dynamic quenching. The assay displays good selectivity and can be used to determine the concentration of vitamin K1 in a commercial preparation. In chapter 6, a fluorescent-based sensor array for the optical analysis of purine derivatives is described. The array is composed of four polysufonated fluorescent dyes. The complexation of the analytes results in partial quenching of the fluorescence. The Sensor array enables the identification of ten purine derivatives including caffeine, theophylline, theobromine, purine, hypoxanthine, paraxanthine, 8-chlorotheophylline, 6-mercaptopurine, cladribine and penciclovir at low millimolar concentration. Furthermore, it is possible to use the array for obtaining information about the quantity and the purity of samples.LC
Development of a new fluorescent sensor for caffeine in water
No full textSCGCGR-53 858 ; EPFL - SB - ISIC - LCS. Consultable sur demande à la Bibliothèque de l'EPFL / Offered in consultation at the EPFL library
Functional Nanostructures Based on Organometallic Half-Sandwich Complexes
No full textHexanuclear coordination cages of the formula [(C5Me4R)M(C7H3NO 4)]6 (M = Rh, Ir; R = Me, H) were obtained by stepwise reaction of [(C5Me4R)M(μ-Cl)Cl]2 with, first AgOAc and then pyridine-3,5-dicarboxylic acid. Crystallographic analyses show that the cages adopt a distorted octahedral geometry with the pyridine-3,5-dicarboxylates functioning as dianionic bridging ligands, each of which connects three different (C5Me4R)M fragments. The cages act as exoreceptors for large alkali metal cations K+ and Cs+, as well as NH4+, but show low affinity for Na+. Crystallographic and NMR spectroscopic analyses indicate that two metal ions can be coordinated to the surface of the cages. The respective binding sites comprise three carbonyl O-atoms from the bridging pyridine-3,5-dicarboxylate ligands. Novel supramolecular architectures were obtained by reacting the dinuclear macrocycle [(cymene)Ru(μ-C12H12O4)(H 2O)]2 with different N-donor ligands. A tetranuclear assembly was obtained with 1,2-di(4-pyridyl)ethylene, whereas hexanuclear complexes were formed with 2,4,6-tris(4-pyridyl)triazine and 1,3,5-tris(4-pyridylethynyl)benzene. The reaction with 5,10,15,20-tetra(4-pyridyl)porphyrine, on the other hand gave tetra- or octanuclear complexes, depending on the stoichiometry that was employed. The 2,4,6-tris(4-pyridyl)triazine complex was shown to act as a host for polycyclic aromatic compounds such as pyrene, triphenylene and coronene. A hexanuclear coordination cage has been formed by self-assembly of three elongated [(cymene)Ru(μ-C14H10O6)] 2 dinuclear macrocycles and two equivalents of 2,4,6-tris(4-pyridyl)triazine. The twisted coordination prism with a height of 3.5 Å (bottom to top) could be untwined by addition of coronene to – for half-sandwich complex-based cages – unprecedented size of 10.8 Å (bottom to top). Crystallographic and NMR spectroscopic analyses indicate that two coronene molecules can be encapsulated inside this cage.LC
Novel Ruthenium Complexes with Sterically Demanding Cyclopentadienyl Ligands : Syntheses, Reactivity and Catalytic Applications
No full textInvestigations of ruthenium halfsandwich complexes have mostly focused on Cp and Cp* based derivatives due to the availability of easily accessible starting materials. However, it is interesting to have complexes with substituted cyclopentadienyl ligands in order to study the influence of the π-ligand on the chemical behavior of the complexes, as well as to fine-tune their properties. During the course of this thesis, ruthenium complexes with novel, highly substituted cyclopentadienyl ligands ('Cp^') were prepared in one-pot syntheses from commercially available starting materials and under mild reaction conditions. The complexes are versatile starting materials leading to a variety of Cp^Ru complexes through facile ligand exchange reactions. The chemistry of Cp^Ru-complexes has been investigated and the general reactivity pattern was found to be similar to that of CpRu and Cp*Ru complexes. However, in several instances it was observed that the steric and electronic properties of the Cp^ ligand have a strong impact on the properties and chemical behavior of the complexes. As a consequence of the sterically demanding Cp^ ligand, coordinatively unsaturated complexes, that are otherwise inaccessible, have been stabilized. In addition, the presence of the Cp^ ligand resulted in unusual CO insertion reactions and in an unprecedented rearrangement of cyclooctadiene. Some Cp^Ru-complexes turned out to be very efficient catalysts for organic transformations such as the [2+2+2] alkyne cyclotrimerization and atom transfer radical cyclizations. Activation of molecular oxygen was also accomplished with Cp^Ru complexes. In vitro studies with Cp^Ru complexes have shown that they exhibit high cytotoxicity towards human cancer cell lines.LC
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
Syntheses and Catalytic Applications of Ruthenium Cyclopentadienyl Complexes
No full textIn this thesis, new aspects of the chemistry of Cp^Ru complexes are described (Cp^=η5-1-methoxy-2,4-tert-butyl-3-neopentylcyclopentadienyl).Despite many similarities with CpRu and Cp*Ru compounds, Cp^Ru complexes display a unique reactivity because of the sterically very demanding Cp^ ligand. This feature prompted further research in this field, and new synthetic and catalytic applications have been developed. Investigations in the context of the ruthenium-catalysed azide-alkyne cycloaddition reaction led to the discovery of a new catalytic application of [Cp^RuCl2]2. It was found that this complex promoted the decomposition of benzylic azides into useful synthetic products.The mechanism of the transformation was studied,and the isolation of several new Cp^Ru complexes enabled further understanding. New Cp^Ru complexes have been prepared and characterised. Different co-ligands were introduced including a bridging alkylidene, an orthometallated phosphine, an imido as well as triflates and carbonyls. It is worth noting that for several of the new Cp^Ru complexes,no analogue with other cyclopentadienyl ligands has been reported. In the final part of this work, investigations about sequential atom-transfer radical addition/dehalogenation reactions are presented. A synthetic process was developed that allows the preparation of trifluoromethyl-substituted cyclopropanes. This method represents an alternative to metal-catalysed cyclopropanations involving problematic diazocompounds.LC
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