1,721,007 research outputs found
Insoluble Methylene Bridged Glycoluril Dimers as Sequestrants for Dyes
No full textContamination of water bodies by micropollutants including industrial dyes is a worldwide health and environmental concern. We report the design, synthesis, and characterization of a series of methylene bridged glycoluril dimers (G2W1 – G2W4) that are insoluble in water and that differ in the nature of their aromatic sidewalls (G2W4: benzene, G2W3: naphthalene, G2W1 and G2W2: triphenylene). We tested G2W1 – G2W4 along with comparator H2 as solid state sequestrants for a panel of five dyes (methylene blue, methylene violet, acridine orange, rhodamine 6G, methyl violet 6B). We find that catechol-walled H2 (OH substituents) is a superior sequestrant compared to G2W1 – G2W4 (OMe substituents). X-ray crystal structures for G2W1 and G2W3 suggest that the OMe groups fill their own cavity and thereby decrease their abilities as sequestrants. H2 achieved a removal efficiency of 94% for methylene blue whereas G2W1 demonstrated a 64% removal efficiency for methylene violet; both sequestration processes were largely complete within 10 minutes.We thank the National Science Foundation (CHE-1807486) for past financial support. We thank the National Institute of General Medical Sciences of the National Institutes of Health (R35GM153362) for current financial support of this project. S.P. thanks the University of Maryland for the G. Forrest Woods Fellowship and the Charlotte Kraebel PhD ’59 Endowed Award in Organic Chemistry
Electronic Supporting Data: Tetrachloroanthracene Walled Glycoluril Dimer Undergoes Self-Association and 1:1, 2:2, and 1:3 Host•Guest Binding
No full textWe report the design, synthesis and characterization of a tetrachloroanthracene walled methylene bridged glycoluril dimer (H1). According to 1H NMR spectroscopy and symmetry considerations we formulate H1 as a C2v-symmetric monomer in DMSO but it exists as a C2h-symmetric dimer (H1•H1) in water. The H1•H1 dimer persists below 25 uM in water and displays high thermodynamic stability (Ks ≥ 1.8 x 106 M-1). H1•H1 is also stable up to 70 ˚C in water. We investigated the binding of H1 with a panel of five dyes by isothermal titration calorimetry and 1H NMR spectroscopy and found that H1 engages with dyes with several different stoichiometries of binding. For example, NMeAc and Berb are capable of causing the dissociation of H1•H1 resulting in the formation of the 1:1 intracavity dye complexes H1•NMeAc and H1•Berb. In contrast, Rh6G and ThT do not dissociate the H1•H1 dimer and instead stack on the exterior of the dimer to form Rh6G•H1•H1•Rh6G and ThT•H1•H1•ThT, respectively. Finally, 3 equivalents of NDI+ causes dissociation of H1•H1 and binds both intracavity and on the exterior to form the H1•(NDI+)3 complex.We thank the National Science Foundation (CHE-1807486) for past financial support. We thank the National Institute of General Medical Sciences of the National Institutes of Health (R35GM153362) for current financial support of this project
Electronic Supporting Data: Aromatic Wall Extension of Glycoluril-Derived Molecular Clips Enhances Binding of Planar Aromatic Dyes
No full textSee the Supporting Information document.We report the synthesis and characterization of a new methylene bridged glycoluril dimer featuring anthracene walls (H2). H2 displays good solubility in water (≥7 mM) but undergoes self-association at concentrations above 2 mM. 1H NMR experiments establish that H2 binds cationic dyes inside its cavity with a -stacked geometry that places the cationic residues at the ureidyl carbonyl portals of H2. The binding constants of both naphthalene-walled clip H1 and anthracene-walled clip H2 toward a panel of dyes were measured by direct or competitive UV/Vis or fluorescence titrations in phosphate buffered saline (PBS). Binding constants cover the range from 103 – 108 M-1. Dyes that feature cationic NMe2 groups bind more strongly than analogous dyes with cationic NH2 groups. We find that pi-extension of the aromatic walls from H1 to H2 generally results in an ≈ 10-fold increase in binding affinity. Host•guest complexes of H1 and H2 with planar cationic dyes benefit from substantial cation-pi interactions.We thank the National Science Foundation (CHE-1807486) for past financial support. We thank the National Institute of General Medical Sciences of the National Institutes of Health (R35GM153362) for current financial support of this project.https://doi.org/10.1002/chem.20250217
Insoluble Acyclic Cucurbit[n]uril-Type Receptors Capture Iodine from the Vapor Phase
No full textSee the written Supporting Information file.Nuclear energy makes large contributions toward meeting global energy needs, but societal concerns remain high given the impacts of the intended release of radioactive materials including 129I and 131I. In this paper we explore the use of a homologous series of acyclic CB[n] type hosts (H1–H4) as adsorbents of iodine from the vapor phase. We find that H2–H4, but not H1 – perform well in this application with uptake capacities of 2.2 g g−1, 1.5 g g−1, and 1.9 g g−1, respectively. The chemisorptive uptake process involves partial oxidation of catechol walled H2 to quinone walled host and capture of I3− and I5−. Solid H2 can be regenerated by treatment with Na2S2O4 and reused at least five times. The x-ray crystal structure of H2 is also reported.We thank the National Science Foundation (CHE-1807486) for past financial support. We thank the National Institute of General Medical Sciences of the National Institutes of Health (R35GM153362) for current financial support of this project. S.P. thanks the University of Maryland for the G. Forrest Woods Fellowship and the Charlotte Kraebel PhD'59 endowed award in organic chemistry.https://doi.org/10.1002/chem.20240317
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
Recognition of Aminated Guests by Acyclic Cucurbiturils in Biological Conditions
Full text linkThe acyclic cucurbituril Motor2 has already been well documented in its binding to several types of molecular guests in phosphate buffer. However, while these tests provide a rough idea of motor2 affinity to different types of guests, they are incomplete in that they do not reflect how motor2 actually binds in body conditions. The human body contains many proteins and macromolecules that can affect the host-guest interactions of motor2, so it is important for new binding constants to be measured for motor2 in body conditions. In order to do this, Isothermal Titration Calorimetry (ITC) was used to measure motor2 binding constants to several different guest types in several different solutions, including albumin and fetal bovine serum. It was found that when tested with cyclic, monoaminated guests, motor2 binding affinity did not decrease significantly from phosphate to protein serum solvents. This retained affinity held across several different ring sizes and shapes. Motor2 binding affinity did suffer greatly in protein serum for guests that were linear, regardless of how many amines they had. The results also indicated that more hydrophobic guests do not bind as well to motor2 once albumin and other proteins ae introduced to solution, while hydrophilic, polar guests have better affinity retention. The ITC testing results indicated that motor2 binding in body conditions is heavily dependent on the shape of the guests it is binding to, and that motor2 would be most effective at its purpose in the human body if it was used to target cyclic amines and similar types.LSAMP
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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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