1,721,455 research outputs found
Correlated motion monitored by NMR relaxation in the rotating frame. A source of structural and dynamic information on macromolecules
No full textDetermination of Homo- and Heteronuclear Coupling Constants in Uniformly13C,15N-Labeled DNA Oligonucleotides
No full textA set of experiments to determine homo- and heteronuclear vicinal coupling constants in uniformly C-13-labeled DNA oligonucleotides is presented, 2D and 3D HCCH-E.COSY experiments were used to measure 3J(HH) coupling constants in the deoxyribose ring, a refocused HMBC experiment was used to measure (3)J(CH) coupling constants about the glycosidic torsion angle chi and a P-FIDS-CT-HSQC experiment was used to determine 2J(CP) and 3J(HP) coupling constants about the backbone torsion angle epsilon. The experiments were demonstrated on a uniformly C-13,N-15-labeled 10 base pair (bp) DNA duplex which contains a dA . dT tract 4 bp in length. With these experiments it was possible to extract a number of the coupling constants from duplex DNA
Long-range distances in amyloid fibrils of α-synuclein from PELDOR spectroscopy.
Full text linkDistance measurements: Pulsed EPR distance measurements combined with strategic spin labeling provide structural constraints at the molecular level for the fold of α-synuclein in amyloid fibrils (see picture; r=distance). The detection of interstrand distances in fibrils will potentially make it possible to extend these measurements to oligomeric states of these protein families
Molecular Diffusivity of Click Reaction Components: The Diffusion Enhancement Question
No full textMicrometer-sized objects are widely known to exhibit chemically driven motility in systems away from equilibrium. Experimental observation of reaction-induced motility or enhancement in diffusivity at the much shorter length scale of small molecules is, however, still a matter of debate. Here, we investigate the molecular diffusivity of reactants, catalyst, and product of a model reaction, the copper-catalyzed azide-alkyne cycloaddition click reaction, and develop new NMR diffusion approaches that allow the probing of reaction-induced diffusion enhancement in nanosized molecular systems with higher accuracy than the state of the art. Following two different approaches that enable the accounting of time-dependent concentration changes during NMR experiments, we closely monitored the diffusion coefficient of reaction components during the reaction. The reaction components showed distinct changes in the diffusivity: while the two reactants underwent a time-dependent decrease in their diffusivity, the diffusion coefficient of the product gradually increased and the catalyst showed only slight diffusion enhancement within the range expected for reaction-induced sample heating. The decrease in diffusion coefficient of the alkyne, one of the two reactants of click reaction, was not reproduced during its copper coordination when the second reactant, azide, was absent. Our results do not support the catalysis-induced diffusion enhancement of the components of the click reaction and, instead, point to the role of a relatively large intermediate species within the reaction cycle with diffusivity lower than that of both the reactants and product molecule
OPTIMIZED HETERONUCLEAR CROSS POLARIZATION IN LIQUIDS
No full textIt is demonstrated by theory, simulation, and experiment that it is possible to optimize heteronuclear cross-polarization experiments in liquids to such an extent that it becomes possible to transfer polarization uniformly through heteronuclear one-bond and long-range couplings. It is found that cross polarization is competitive with pulsed transfers, such as INEPT or DEPT, for the preparation of directly detected low-gamma nuclei. However for proton detection after two-way transfer, experiments employing heteronuclear multiple quantum coherence are usually more sensitive than cross-polarization experiments
Time reversal of the evolution under scalar spin-spin interactions in NMR. Application for .omega.1 decoupling in two-dimensional NOE spectroscopy
No full text
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
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