1,721,051 research outputs found
Infrared HP study of protein folding and aggregation @ the SISSI Elettra beamline
No full textFourier transform infrared spectroscopy (FTIR) coupled with High Hydrostatic Pressure technology
is a suitable technique to investigate unfolding/misfolding processes providing useful information
on the kinetics of aggregation of proteins. Since HHP doesn't affect the enthalpic contribution to
the Gibbs free energy, it is able to perturb the secondary structure of proteins in a reversible way .
The principle governing pressure effects is that it tends to shift a system towards the state that
occupies the smallest volume, it causes the electrostriction of charged and polar groups, the
elimination of packing defects, and the solvation of hydrophobic groups. Cavities and packing
defects are expected to be major contributors to volume changes and their presence will make the
system more susceptible to pressure unfolding/dissociation. Because high pressure allows
stabilization of folding intermediates such as molten-globule conformations, this method provides
an unique opportunity for their characterization. We present here latest developments in the set up
of a high pressure infrared facility for the study of protein folding misfolding and aggregations at
the SISSI beamline at Elettra
ACCEPTED ORAL CONTRIBUTION - “Linearly Polarized Infrared Investigations of Organic Semiconducting Single Crystals” - PRESENTING AUTHOR
No full textTerahertz Absorption change in Photosynthetic Reaction Center upon photoactivation
No full textPhotosynthetic reaction center is a membrane protein
which plays an important role in converting solar energy into
chemical energy. Upon continuous illumination a charge
separation occurs within the protein which is stable for
several seconds [1]. The stability of this state is very
important to protect the protein against the release of excess
heat and an instable radical due to charge recombination.
Absorption of terahertz radiation corresponds to the
excitation of large vibrations in the protein and is thus suitable
for studying its different dynamical states. Here we recorded
terahertz absorption spectra of the dark and illuminated state
of reaction centre from the purple membrane bacteria
Rhodobacter sphaeroides
to investigate the stability of the
charge separated state. The difference terahertz absorption
spectra show an overall increase in absorption for the
illuminated state in the 30-130 cm
-1
spectral region. By
simulating and fitting a theoretical terahertz spectrum of
reaction center from an elastic network model we were able to
investigate the effect of charge separation and conformational
changes within the interaction network. We find that a more
loose interaction network in the photoactivated state of the
protein is the most probable cause of the absorption increase
Effect of oxygen reduction on the optical conductivity of La0.75Ca0.25MnO3
Full text linkReflectivity measurements are used to obtain the optical conductivity of three La0.75Ca0.25MnO32y samples annealed under increasingly strong reducing conditions. All three samples are nearly saturated ferromagnets although their Curie temperatures fall progressively from Tc5221 K to Tc5187 K with maximum deoxygenation. The presence of Drude absorption indicates that the unreduced and the slightly reduced samples are electrical conductors below Tc . However, the most reduced sample manifests an insulatinglike optical conductivity at all temperatures. Thus, ferromagnetism and insulating behavior coexist in the most-reduced sample. This result contradicts the notion that mobile charge carriers of an electrically conducting manganite induce its ferromagnetism. Beyond Drude absorption, midinfrared and near-infrared absorptions are also observed. A midinfrared absorption band is present in all samples. The energy at its peak falls markedly with decreasing temperature. Moreover, near-infrared absorption is found in the nonconducting sample and in the high-temperature insulating phase of the conducting samples. The implications of these findings are discussed in terms of models for properties of doped manganites
FTIR studies of the high pressure dissociation of insulin and alpha-synuclein amyloids
No full textAmyloid fibrils are highly ordered aggregates whose formation occurs during the development of several serious disorders, like Althzeimer's and Parkinson's diseases. Even if most biophysical investigations of fibril formation have attempted to elucidate the structural events that occur during amyloid fibril assembly, relatively little is known about the thermodynamics of the aggregated protein state, and the kinetic mechanisms of its formation. Fibrillation is an irreversible process and a key challenge for the field is the development of therapeutic strategies able to inhibit or reverse the aggregation. The coupling of conventional Fourier Transform Infrared Spectroscopy (FTIR) and high Pressure (HP) techniques has proven to be during the last years a perfect combination for the study of proteins aggregation and misfolding, allowing to explore proteins conformational states not accessible at ambient pressure. In contrast to temperature, whose effect manifests both on volume and thermal energy simultaneously, pressure leads to a controlled change of inter- and intramolecular distances and enables to determine the stability of a protein structure and to stabilize intermediate states that are usually not detectable at ambient pressure or through thermal perturbation. Due to its effect on the energetic of the system, a pressure increase will act on packing defects and empty cavities favouring all that processes that lead to a reduction of the system's volume. We present here the HP-induced disaggregation of two amyloidogenic proteins, insulin and a-synuclein. Insulin aggregation into amyloid-like structures represents a serious problem in its storage as pharmaceutical for the treatment of diabetes mellitus while the interest in studying a- synuclein resides in its involvement in Parkinson's disease. According to our experimental evidences high pressure induces the disaggregation of fibrils with an efficacy that depends on their maturation stage in the case of insulin and on the specific point mutation occurred in protein primary structure in the case of synuclein. Moreover, high pressure dissociation has been found to act in a sequential way, in accordance with the hierarchy of structures
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
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