1,720,957 research outputs found
Applications of CW and pulsed EPR spectroscopy for the characterization of copper(II) complex stereochemistry and of Beta-peptide secondary structure
No full textElectron Paramagnetic Resonance (EPR) is a spectroscopic technique, based on the magnetic resonance principles, that allows the characterization of systems containing unpaired electrons to achieve information on their chemical environment with high resolution. Considering the peculiar class of samples that can be investigated, nowadays, EPR spectroscopy finds applications in several areas of science. Thanks to the modern Site-Directed Spin Labelling (SDSL) approaches, it is possible to introduce spin labels into defined positions of a natural diamagnetic system making it detectable by EPR. This method has further extended the applications towards samples which are naturally EPR silent. The first part of the thesis offers an overview of the main theoretical key concepts required to understand the set-up and the outcomes of an EPR experiment. In the second part of the thesis CW-EPR spectroscopy is employing to characterize the geometries adopted in aqueous solution by some copper(II) complexes with important biological ligands. The study of biochemical processes, in fact, cannot be performed neglecting the inorganic biometals dissolved in biological fluids. These metal ions are involved in the cell biochemistry coordinated by several biomolecules forming metal complexes which are the real players with specific biological activities. The functions of these systems are strictly related with the arrangement of the ligands around the metal centre and with the overall geometry of the complex. The experimental results presented in this part of the thesis enable to develop a more detailed picture of these copper(II) species in solution in order to better clarify their structure-function relationships for further biochemical considerations about their role. Additionally, voltammetric measurements are performed on the same systems to support the spectroscopic data. In the third part of the thesis, the results of a project developed in the Electron Spin Resonance research group at the Max Planck Institute for Biophysical Chemistry (Göttingen Germany), under the supervision of Professor Marina Bennati, is presented. It is well-known that the structural characterization of membrane proteins in their natural environment is a challenging task. EPR spectroscopy in combination with SDSL approaches is emerging as a powerful biophysical tool to reveal biomolecular structural information at atomic resolution. In particular, Pulsed Electron Double Resonance (PELDOR) spectroscopy, called also Double Electron Electron Resonance (DEER), is a pulsed EPR method which enables to detect distances between two paramagnetic centres in a biological system in order to characterize its structure. Measuring the dipolar coupling between two unpaired electrons, PELDOR allows to probe their intramolecular distances with high resolution and reliability. In this project, CW-EPR and PELDOR/DEER spectroscopy are employed for the structural characterization of a transmembrane peptide in solution and in a lipid environment. The samples are prepared introducing two semi-rigid TOPP nitroxide spin labels into the peptide s backbone in order to make it detectable by EPR. The experimental results of this part of the thesis demonstrate the great potential of EPR spectroscopy in structural biology to characterize biomolecular structures and encourage the employment of TOPP spin label as useful tool for the EPR investigation of peptides foldamers in solution and in lipid bilayer
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
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
Semi‐rigid nitroxide spin label for long‐range EPR distance measurements of lipid bilayer embedded β‐peptides.
Full text linkβ‐Peptides are an interesting new class of transmembrane model peptides based on their conformationally stable and well‐defined secondary structures. Herein, we present the synthesis of the paramagnetic β‐amino acid β3‐hTOPP (4‐(3,3,5,5‐tetramethyl‐2,6‐dioxo‐4‐oxylpiperazin‐1‐yl)‐d‐β3‐homophenylglycine) that enables investigations of β‐peptides by EPR spectroscopy. This amino acid adds to the so far sparse number of β‐peptide spin labels. Its performance was evaluated by investigating the helical turn of a 314‐helical transmembrane model β‐peptide. Nanometer distances between two incorporated β3‐hTOPP labels in different environments were measured using PELDOR/DEER (pulsed electron‐electron double resonance) spectroscopy. Due to the semi‐rigid conformational design, the label delivers reliable distances and sharp (one‐peak) distance distributions even in the lipid bilayer. The results indicate that the investigated β‐peptide folds into a 3.2514 helix and maintains this conformation in the lipid bilayer
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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