1,720,961 research outputs found
Infrared laser spectroscopy of proteins at the nanoscale
Full text linkThe intricate mechanisms governing protein activity, crucial in life processes and diverse applications like bioelectronics and biomedicine, necessitate experimental advancements for a comprehensive understanding. Nanosciences present innovative pathways to investigate certain unexplored aspects influencing protein functionality. One example of this is the effect of externally applied electric fields, especially on proteins naturally exposed to such fields, like membrane proteins within cell membranes. Among these, proton/ion transporters such as photosensitive microbial rhodopsins appear as relevant examples. However, experimental techniques capable of correlating the investigations of protein conformational changes with the controlled voltage potentials to which the proteins are subjected are currently lacking. To bridge this gap, here it is proposed a novel technique based on the state-of-theart AFM-IR nanospectroscopy platform. It integrates the sensitivity of infrared (IR) spectroscopy to protein conformation with electric field control, exploiting a metallic atomic force microscope (AFM) tip as both a mechanical IR detector and a nanoelectrode. Initial experiments on the prototype photosensitive protein Bacteriorhodopsin demonstrate its potential, with future perspectives aimed at exploring the effects of transmembrane electric potential on protein dynamics. In a broader sense, this innovative work stands as a significant advancement toward unraveling the intricate interplay between molecular structure and electric fields at the nanoscale
Effect of 0.6-THz Continuous-Wave Irradiation on Pathologically Relevant Protein Aggregates
No full textIn this article, we investigated the effect of continuous-wave (CW) radiation at 0.6 THz on pathological protein aggregates in the form of amyloid fibrils, i.e., ordered protein complexes linked to neurodegenerative diseases such as Parkinson's and Frontotemporal Dementia. To monitor the effect of terahertz (THz) irradiation, we exploited mid-infrared (mid-IR) vibrational spectroscopy in the amide-I band range, whose lineshape is known to depend on the protein conformation and on how proteins arrange into ordered supramolecular complexes such as fibrils. We coupled the focused THz beam to two different IR-based spectrometers: a conventional Fourier-transform IR (FTIR) Michelson interferometer where the estimated THz electric field is of the order of similar to 1 V/cm; and an atomic force microscopy-assisted (AFM-IR) near-field spectrometer based on a tunable mid-IR quantum cascade laser, where a much higher electric field (similar to 0.1 kV cm) is mainly achieved thanks to the field enhancement provided by the use of a metallicAFMtip and sample support. In the first case, we interpreted the modification of the amide-I band upon THz irradiation in terms of an increase of the intermolecular forces within fibrils in response to environmental changes induced by THz irradiation (change of hydration). On the other hand, nonthermal effects are observed in the high-THz field experiments performed on isolated fibril agglomerates in dry condition with the AFM-assisted spectrometer. The IR spectral response upon prolonged THz irradiation contains only the protein contribution and we obtain a different trend compared to the FTIR experiments, i.e., a weakening of the intermolecular forces, here directly induced by THz absorption and not mediated by changes of the environmental conditions. One can envision that further increase of the THz field value, such as with pulsed laser, can lead to the disassembly of protein fibrils
Effect of 0.6 THz irradiaton on protein fibrils monitored by mid-infrared nano-spectroscopy
No full textProtein amyloid fibrils relevant for neurodegenerative diseases have been irradiated with continuous wave 0.6 THz radiation for minutes. The effect on protein hydration and on the stability of amyloid fibrils has been monitored with ATR-FTIR (in hydrated environment and low-field condition) and with atomic force microscopy-assisted IR nano-spectroscopy (in dry environment and high-field condition), finding opposite effects on the inter-molecular aggregation state
Time-resolved investigation of nanometric cell membrane patches with a mid-infrared laser microscope
Full text linkThe proton pump Bacteriorhodopsin (BR) undergoes repeated photocycles including reversible conformational changes upon visible light illumination. Exploiting the sensitivity of infrared (IR) spectra to the conformation, we have determined the reaction kinetic parameters of the conductive intermediate M for the wild-type protein and for its slow mutant D96N during its photocycle. Time-resolved IR micro-spectroscopy using an in-house developed confocal laser microscope operating in the mid-IR is employed to record absorption changes of 10−4 at wavelengths λ1 = 6.08 μm and λ2 = 6.35 μm, assigned to backbone and retinal structural modifications, respectively. Protein samples were embedded in dried lipid bilayers deposited on ultraflat gold supports to enhance the surface field. The signals were analyzed according to a simplified photocycle model with only two dominant states: the dark-adapted state BR* and the intermediate M. We obtained the excitation and relaxation times of the intermediate M from exponential fits to the absorption change time traces. Our results constitute a first step towards future plasmonic-assisted nanoscale time-resolved mid-IR spectrometers for the characterization of bioelectronic and light-harvesting nanodevices based on BR
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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