1,720,974 research outputs found
Aggregation of Spin Labeled Trichogin GA IV Dimers: Distance Distribution between Spin Labels in Frozen Solutions by PELDOR Data.
No full textPulsed electron-electron double-resonance (PELDOR) and CW-ESR spectroscopies were used to study the dipole-dipole interaction of spin labels in frozen glassy solutions of mono- and double-labeled analogues of the 22-residue, the head-to-tail covalent dimer of the peptaibol antibiotic trichogin GA IV. The [TOAC-1] and [TOAC-1,19] dimers were studied in methanol and in a chloroform-toluene mixture. It was shown these dimer molecules do not form aggregates in methanol. However, in chloroform-toluene, the PELDOR signal of the mono-labeled dimer shows oscillations, due to the dipole-dipole interaction of the nitroxide spin labels. From the signal decay, the number of molecules per aggregate was estimated to be similar to2-3, depending on the concentration used. The contributions of inter- and intra-aggregate interactions of spin labels to the PELDOR signal decay were separated. The distance distribution functions of the intra-aggregate interactions range from 3.0 to 4.5 nm. The maxima are observed at 3.4 nm. From the PELDOR data, we obtained the functions of distance distributions of labels for the monomeric double-labeled peptide in methanol as well as for the same peptide isolated within aggregates of nonlabeled peptide molecules in chloroform-toluene. In the latter case, the distribution function is the most narrow with a maximum at a distance between the nitroxide spin labels of 2.8 nm, which is in agreement with the theoretical distance between labels at corresponding residue positions of an alpha-helical structure
Self-assembling properties of membrane-modifying peptides studied by PELDOR and CW-ESR spectroscopies
No full textA new technique is described that is suitable to determine the formation of aggregates from monomeric biomolecules. This technique has been tested in the study of the self-assembling properties of the antibiotic trichogin GA IV which belongs to the class of peptaibols. We have investigated the self-assembling properties of three trichogin analogues by pulsed double resonance in electron spin-echo (PELDOR) spectroscopy combined with conventional continuous wave ESR spectroscopy. In the peptides examined Aib has been substituted by its spin-labeled analogue TOAC at three specific positions of the sequence. More specifically, the magnetic dipole-dipole relaxation of the spin-labeled peptides is measured in glassy polar and apolar solvents at 77 K. Specific assemblies of trichogin molecules are formed in an apolar solvent but addition of a more polar solvent leads to dissociation of the aggregates, The estimates based on experimental data show that each aggregate cluster contains four peptide molecules, Some of the distances between spin labels in the cluster have been determined. In addition, CW-ESR data suggest the occurrence of aggregated species in the same solutions at room temperature. The experimental results are consistent with a model wherein four amphiphilic helical peptide molecules form a vesicular system with the polar amino acid side chains pointing to the interior and the apolar side chains to the exterior of the cluster
Aggregation and Chemical Equilibrium of Membrane-Modifiyng Peptides in Weakly Polar Solvents Studied by CW-ESR and PELDOR Spectroscopies
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The secondary structure of a membrane-modifying peptide in a supramolecular assembly studied by PELDOR and CW-ESR spectroscopies
No full textThe new technique of pulsed electron-electron double resonance in electron spin-echo (PELDOR) in combination with the CW-ESR method has been used to investigate the secondary structure of a double spin-labeled peptide (the [TOAC-1,8]-analogue of the peptaibol antibiotic trichogin GA IV ) that is hidden into a tetrameric supramolecular assembly of unlabeled peptide molecules. The magnetic dipole-dipole relaxation of spin labels has been experimentally studied in glassy solutions of the double-labeled peptide frozen to 77 K in a mixture of chloroform-toluene with an excess of unlabeled peptide. The PELDOR signal oscillations have been observed at high degrees of dilution with unlabeled peptide. The intramolecular distance between the spin labels of the peptide molecule in the aggregate has been determined from the oscillation frequency to be 15.7 Angstrom which is close to the value of congruent to 14 Angstrom calculated for a 3(10)-helical structure. Estimation of the G action of this ordered secondary structure shows that about 19% of the peptide molecules in aggregates are folded in the 3(10)-helical conformation. The present experimental results are consistent with our molecular model presented in J. Am. Chern. Sec. 2000, 122, 3843-3848, wherein four amphiphilic 3(10)-helical peptide molecules form a vesicular system with the polar amino acid side chains pointing to the interior, and the apolar side chains, to the exterior of the cluster. The experimental data were compared with the results obtained with other techniques
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
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
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
Aggregation and Chemical Equilibrium of Membrane-Modifying Peptides in Weakly Polar Solvents Studied by CW-ESR and PELDOR Spectroscopies
No full textDispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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