1,720,957 research outputs found
Cucurbituril–Gold Nanoparticle Assemblies for Aqueous Oxime Formation Catalysis
No full textEfficient substrate binding and spatial organization are critical for enzyme-like catalysis. This study examines a nanoparticle-based catalytic platform in which cucurbit[7]uril macrocycles are integrated into negatively charged gold nanoparticle monolayers. The resulting supramolecular constructs, referred to as “suprazymes,” catalyze the formation of oximes from aldehydes and hydroxylamine in water. By systematically varying substrate
charge, size, and structure, as well as nanoparticle curvature and monolayer composition, we identify key structural features that influence catalysis. A suprazyme with phosphonate-terminated ligands achieves an over 2400-fold rate acceleration relative to the uncatalyzed reaction. These findings reveal design principles for engineering advanced nanoparticle-based enzyme mimics and provide a framework for their development
Creating a suprazyme: integrating a molecular enzyme mimic with a nanozyme for enhanced catalysis
Full text linkEnzyme mimics, due to their limited complexity, traditionally display low catalytic efficiency. Herein we present a strategy that enables the transformation of a slow-acting catalyst into a highly active one by creating a non-covalent suprastructure, termed “suprazyme”. We show that cucurbit[7]uril macrocycles, rudimentary molecular enzyme mimics, embedded within an anionic monolayer on the surface of gold nanoparticles, outperform individual cucurbit[7]urils as well as nanoparticles, which also exhibit catalytic enzyme-like activity and thus act as nanozymes, by over 50 times, showcasing a 1044-fold acceleration in a model oxime formation reaction. The superior performance of such a suprazyme is attributed to a synergistic interplay between the organic monolayer and macrocycles, which is accompanied by a decreased local polarity and pH that favors the acid-catalyzed condensation process. The proposed approach holds promise for developing diverse suprazymes, contingent upon achieving a complementary structure and mechanism of action between the molecular catalyst and nanoparticles.This research was funded by the National Science Centre of Poland (grant OPUS 18 no. 2019/35/B/ST4/01758). We acknowledge the CINECA award under the ISCRA initiative, for the availability of high-performance computing resources and support, along with the SISSA Computing Center (https://www.sissa.it)
Pursuing the Complete OFF State in Photoswitchable Catalysis
Full text linkPractically, all photoswitchable catalysts exhibit residual activity in the OFF state. Herein, we present a ruthenium initiator with a built-in photoswitch whose metathetical performance is completely shut off by light. The system is made of Hoveyda−Grubbs second-generation complexes appended, along with background ligands, to a gold nanoparticle surface via azobenzene linkers. Under dark or visible light - the precatalysts, in the presence of an olefin, undergo initiation, diffuse from the surface into bulk solution, and commence metathesis reaction. When the conditions are changed to ultraviolet, the isomerization of the azo switches takes place, burying the precatalysts within the bulky organic monolayer, thus preventing their initiation and thereby halting the reaction. Despite the irreversibility of the process, this work opens up opportunities for the remote deactivation of catalysts without their chemical decomposition and control of more complex tasks such as chemical selectivity
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
Glutathione peroxidase and hydroperoxides: designing in silico approaches to case-studies
No full textreservedThe mechanism of the oxidative step of glutathione peroxidases (GPx) has been well elucidated in silico and implies a long-range proton transfer mediated by a peroxide and a water molecule, followed by a nucleophilic attack to the peroxide O-O bond by
the catalytic chalcogenolate. In this Thesis, we have revisited this enzymatic stage setting up a protocol to include dynamic effects of the protein environment and using a particular substrate, i.e. peroxynitrite, which might turn the activity of the endogenous peroxidatic system into a harmful hydrogen peroxide source.The mechanism of the oxidative step of glutathione peroxidases (GPx) has been well elucidated in silico and implies a long-range proton transfer mediated by a peroxide and a water molecule, followed by a nucleophilic attack to the peroxide O-O bond by
the catalytic chalcogenolate. In this Thesis, we have revisited this enzymatic stage setting up a protocol to include dynamic effects of the protein environment and using a particular substrate, i.e. peroxynitrite, which might turn the activity of the endogenous peroxidatic system into a harmful hydrogen peroxide source
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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