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Synthesis of [(DPPNCH₂CH₂)₃N]³− Molybdenum Complexes (DPP = 3,5-(2,5-Diisopropylpyrrolyl)₂C₆H₃) and Studies Relevant to Catalytic Reduction of Dinitrogen
No full textMolybdenum complexes that contain a new TREN-based ligand [(3,5-(2,5-diisopropyl-pyrrolyl)2C6H3NCH2CH2)3N]3− ([DPPN3N]3−) that are relevant to the catalytic reduction of dinitrogen have been prepared. They are [Bu4N]{[DPPN3N]MoN2}, [DPPN3N]MoN2, [DPPN3N]MoN═NH, {[DPPN3N]MoN═NH2}[BArf4], [DPPN3N]Mo≡N, {[DPPN3N]Mo≡NH}[BArf4], and {[DPPN3N]MoNH3}[BArf4]. NMR and IR data for [Bu4N]{[DPPN3N]MoN2} and [DPPN3N]MoN2 are close to those reported for the analogous [HIPTN3N]3− compounds (HIPT = hexaisopropylterphenyl), which suggests that the degree of reduction of dinitrogen is virtually identical in the two systems. However, X-ray studies and several exchange studies support the conclusion that the apical pocket is less protected in [DPPN3N]Mo complexes than in [HIPTN3N]Mo complexes. For example, 15N/14N exchange studies showed that exchange in [DPPN3N]MoN2 is relatively facile (t1/2 ≈ 1 h at 1 atm) and depends upon dinitrogen pressure, in contrast to the exchange in [HIPTN3N]MoN2. Several of the [DPPN3N]Mo complexes, e.g., the [DPPN3N]MoN2 and [DPPN3N]MoNH3 species, are also less stable in solution than the analogous “parent” [HIPTN3N]Mo complexes. Four attempted catalytic reductions of dinitrogen with [DPPN3N]MoN yielded 2.53 ± 0.35 equiv of total ammonia. These studies reveal more than any other just how sensitive a successful catalytic reduction is to small changes in the triamidoamine supporting ligand.National Institutes of Health (U.S.) (Grant GM 31978)Austrian Science Fund (Erwin-Schrodinger fellowship (Grant J2822-N19
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
Processing and patterning of metal organic frameworks and metal organic gels
Get PDFMetal Organic Frameworks (MOFs), due to their unique properties, have attracted significant research interest in diverse areas such as drug delivery, gas adsorption catalysis and bio-sensing. Although these materials have valuable attributes for future developments, the ability to control their functional properties to precise locations is important for potential applications. Also, the investigation and application of MOF structures has generally been at molecular level limiting their use for large scale industrial applications. Metal Organic Gels (MOGs) are emergent soft materials having both metal-organic framework (MOF) and gel characteristics such as flexibility, varying pore sizes and tunable porosity. These soft materials are of interest as they can easily be processed for various applications in more efficient ways than MOFs. This project aims to discuss the fabrication processing techniques employed for maximizing metal-organic composites properties and prospects for various applications.Here, we present the use of coatings and lithographic techniques that enable MOF positioning and precise localization of NH₂-MIL-53 (Al) microcrystals on Anodised Aluminium Oxide (AAO) membrane. The advantages and limitations of each reviewed technique for the control of MOFs positioning are highlighted. X-ray and SEM measurements were used for the identification and location of the MOF crystal on the membrane. Also, the synthesis of MOGs under different conditions, factors affecting the gel properties, and how they can be photo-polymerized for processing at large scale dimensions were looked into.Results obtained using lithographic techniques for patterning NH₂-MIL-53 (Al) microcrystals on AAO showed successful patterning but had limitations in patterning MOF crystal growth when a modulator was introduced. Mil-68 MOG was produced by using Indium metal ion salt with H₃BTC ligands. This was of primary focus due to its thixotropic properties, i.e. shearing and reforming to its original shape after applied force is removed. These thixotropic properties make the material versatile because it can potentially be processed into different shapes with the possibility of introducing polymerizable materials into the gels for crosslinking
Processing and patterning of metal organic frameworks and metal organic gels
Get PDFMetal Organic Frameworks (MOFs), due to their unique properties, have attracted significant research interest in diverse areas such as drug delivery, gas adsorption catalysis and bio-sensing. Although these materials have valuable attributes for future developments, the ability to control their functional properties to precise locations is important for potential applications. Also, the investigation and application of MOF structures has generally been at molecular level limiting their use for large scale industrial applications. Metal Organic Gels (MOGs) are emergent soft materials having both metal-organic framework (MOF) and gel characteristics such as flexibility, varying pore sizes and tunable porosity. These soft materials are of interest as they can easily be processed for various applications in more efficient ways than MOFs. This project aims to discuss the fabrication processing techniques employed for maximizing metal-organic composites properties and prospects for various applications.Here, we present the use of coatings and lithographic techniques that enable MOF positioning and precise localization of NH₂-MIL-53 (Al) microcrystals on Anodised Aluminium Oxide (AAO) membrane. The advantages and limitations of each reviewed technique for the control of MOFs positioning are highlighted. X-ray and SEM measurements were used for the identification and location of the MOF crystal on the membrane. Also, the synthesis of MOGs under different conditions, factors affecting the gel properties, and how they can be photo-polymerized for processing at large scale dimensions were looked into.Results obtained using lithographic techniques for patterning NH₂-MIL-53 (Al) microcrystals on AAO showed successful patterning but had limitations in patterning MOF crystal growth when a modulator was introduced. Mil-68 MOG was produced by using Indium metal ion salt with H₃BTC ligands. This was of primary focus due to its thixotropic properties, i.e. shearing and reforming to its original shape after applied force is removed. These thixotropic properties make the material versatile because it can potentially be processed into different shapes with the possibility of introducing polymerizable materials into the gels for crosslinking
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
Cyclic dipeptides and their self-assembling properties
Get PDFOver recent years, cyclic dipeptides, or 2,5-diketopiperazines, have found numerous applications in nanotechnology, such as biological drug delivery. Reasons for this include their ease of synthesis and numerous intrinsic properties. One such property is self-assembly, wherein the cyclic dipeptide can undergo molecular reorganisation in certain conditions, and exhibit a novel structure. This reorganisation can be achieved in different ways; the results often vary depending on the original conditions.A popular method of synthesising linear dipeptides is through solid phase peptide synthesis, which has numerous advantages compared to the older solution phase method. In this project, Fmoc solid phase peptide synthesis (SPPS) was employed to synthesise four different linear dipeptides, and their cyclisation and subsequent self-assembly probed in different solvents. The dipeptides used were chosen based on their varying aromatic side-chains, whilst solvents of varying polarities were utilised.Linear dipeptides were added to the solvents, and it was seen that many of them were insoluble in certain solvents. The ones that did dissolve were heated and tested for unconventional cyclisation. Cyclic dipeptide analogues from the initial sequences H-FF-OH, H-HH-OH, H-HF-OH and H-HY-OH were confirmed and found to have a self-assembled structure in each solvent they originated from. Cyclic FF (cFF, cyclised from linear H-FF-OH), self-assembled in the most number of solvents, and produced a similar structure in each of them. In addition, cyclic FF that self-assembled in 1,4-dioxane was found to have blue-luminescent properties. It was also observed that the amount of self-assembly was affected by the temperature each solvent containing the peptide was subjected to. cHH self-assembled in only one solvent, n-PrOH, whereas cHF and cHY both self-assembled in i-PrOH and THF. Self-assembled cFF was observed to be made of rod-like strands whereas self-assembled cHH appeared to be composed of a hierarchal structure consisting of needle-like components in an “urchin-like” sphere. Self-assembled cHF and cHY had a mixture of structures derived from those seen in cFF and cHH, with a notable flower-like entity seen for cHY self-assembled in THF
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
Cyclic dipeptides and their self-assembling properties
No full textOver recent years, cyclic dipeptides, or 2,5-diketopiperazines, have found numerous applications in nanotechnology, such as biological drug delivery. Reasons for this include their ease of synthesis and numerous intrinsic properties. One such property is self-assembly, wherein the cyclic dipeptide can undergo molecular reorganisation in certain conditions, and exhibit a novel structure. This reorganisation can be achieved in different ways; the results often vary depending on the original conditions.A popular method of synthesising linear dipeptides is through solid phase peptide synthesis, which has numerous advantages compared to the older solution phase method. In this project, Fmoc solid phase peptide synthesis (SPPS) was employed to synthesise four different linear dipeptides, and their cyclisation and subsequent self-assembly probed in different solvents. The dipeptides used were chosen based on their varying aromatic side-chains, whilst solvents of varying polarities were utilised.Linear dipeptides were added to the solvents, and it was seen that many of them were insoluble in certain solvents. The ones that did dissolve were heated and tested for unconventional cyclisation. Cyclic dipeptide analogues from the initial sequences H-FF-OH, H-HH-OH, H-HF-OH and H-HY-OH were confirmed and found to have a self-assembled structure in each solvent they originated from. Cyclic FF (cFF, cyclised from linear H-FF-OH), self-assembled in the most number of solvents, and produced a similar structure in each of them. In addition, cyclic FF that self-assembled in 1,4-dioxane was found to have blue-luminescent properties. It was also observed that the amount of self-assembly was affected by the temperature each solvent containing the peptide was subjected to. cHH self-assembled in only one solvent, n-PrOH, whereas cHF and cHY both self-assembled in i-PrOH and THF. Self-assembled cFF was observed to be made of rod-like strands whereas self-assembled cHH appeared to be composed of a hierarchal structure consisting of needle-like components in an “urchin-like” sphere. Self-assembled cHF and cHY had a mixture of structures derived from those seen in cFF and cHH, with a notable flower-like entity seen for cHY self-assembled in THF
Monoaryloxide Pyrrolide (MAP) Imido Alkylidene Complexes of Molybdenum and Tungsten That Contain 2,6-Bis(2,5-R[subscript 2]-pyrrolyl)phenoxide (R = i-Pr, Ph) Ligands and an Unsubstituted Metallacyclobutane on Its Way to Losing Ethylene
No full textWe report the synthesis of Mo and W MAP complexes that contain O-2,6-(2,5-R[subscript 2]-pyrrolyl)[subscript 2]C[subscript 6]H[subscript 3] (2,6-dipyrrolylphenoxide or ODPP[superscript R]) ligands in which R = i-Pr, Ph. W(NAr)(CH-t-Bu)(Pyr)(ODPP[superscript Ph]) (4a; Ar = 2,6-disopropylphenyl, Pyr = pyrrolide) reacts readily with ethylene to yield a metallacyclobutane complex, W(NAr)(C[subscript 3]H[subscript 6])(Pyr)(ODPP[superscript Ph]) (5). The structure of 5 in the solid state shows that it is approximately a square pyramid with the WC[subscript 4] ring spanning apical and basal positions. This SP′ structure, which has never been observed as an actual intermediate, must now be regarded as an integral feature of the metathesis reaction.National Science Foundation (U.S.) (CHE-1111133)National Science Foundation (U.S.) (Center for Enabling New Technologies through Catalysis (CENTC) CHE-0650456)National Science Foundation (U.S.) (Grant CHE-0946721
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