1,720,999 research outputs found
Excited-state intramolecular proton transfer of 2-acetylindan-1,3-dione studied by ultrafast absorption and fluorescence spectroscopy
Full text linkWe employ transient absorption from the deep-UV to the visible region and fluorescence upconversion to investigate the photoinduced excited-state intramolecular proton-transfer dynamics in a biologically relevant drug molecule, 2-acetylindan- 1,3-dione. The molecule is a ß-diketone which in the electronic ground state exists as exocyclic enol with an intramolecular H-bond. Upon electronic excitation at 300 nm, the first excited state of the exocyclic enol is initially populated, followed by ultrafast proton transfer (±160 fs) to form the vibrationally hot endocyclic enol. Subsequently, solvent-induced vibrational relaxation takes place (±10 ps) followed by decay (±390 ps) to the corresponding ground state. © 2015 Author(s)1561sciescopu
How Molecular Crowding Differs from Macromolecular Crowding: A Femtosecond Mid-Infrared Pump–Probe Study
No full textCrowding is an inherent
property of living systems in which biochemical
processes occur in highly concentrated solutions of various finite-sized
species of both low (molecular crowding) and high (macromolecular
crowding) molecular weights. Is molecular crowding fundamentally different
from macromolecular crowding? To answer this question, we use a femtosecond
mid-infrared pump–probe technique with three vibrational probes
in molecular (diethylene glycol) and macromolecular (polyethylene
glycol) solutions. In less crowded media, both molecular and macromolecular
crowders fail to affect the dynamics of interstitial bulk-like water
molecules and those at the crowder/water interface. In highly crowded
media, interstitial water dynamics strongly depends on molecular crowding,
but macromolecular crowding does not alter the bulk-like hydration
dynamics and has a modest crowding effect on water at the crowder/water
interface. The results of this study provide a molecular level understanding
of the structural and dynamic changes to water and the water-mediated
cross-linking of crowders
Water Dynamics in Cytoplasm-Like Crowded Environment Correlates with the Conformational Transition of the Macromolecular Crowder
No full textPolyethylene glycol (PEG) is a unique polymer material with enormous applicability in many industrial and scientific fields. Here, its use as macromolecular crowder to mimic the cellular environment in vitro is the focus of the present study. We show that femtosecond mid-IR pump–probe spectroscopy using three different IR probes, HDO, HN3, and azido-derivatized crowder, provides complete and stereoscopic information on water structure and dynamics in the cytoplasm-like macromolecular crowding environment. Our experimental results suggest two distinct subpopulations of water molecules: those that interact with other water molecules and those that are part of a hydration shell of crowder on its surface. Interestingly, water dynamics even in highly crowded environment remains bulk-like in spite of significant perturbation to the tetrahedral H-bonding network of water molecules. That is possible because of the formation of water aggregates (pools) even in water-deficient PEGDME-water solutions. In such a crowded environment, the conformationally accessible phase space of the macromolecular crowder is reduced, similar to biopolymers in highly crowded cytoplasm. Nonetheless, the hydration water on the surface of crowders slows down considerably with increased crowding. Most importantly, we do not observe any coalescing of surface hydration water (of the crowder) with bulk-like water to generate collective hydration dynamics at any crowder concentration, contrary to recent reports. We anticipate that the present triple-IR-probe approach is of exceptional use in studying how conformational states of crowders correlate with structural and dynamical changes of water, which is critical in understanding their key roles in biological and industrial applications.
© 2016 American Chemical Society19101sciescopu
Computational Vibrational Spectroscopy of HDO in Osmolyte-Water Solutions
No full textThe IR absorption and time-resolved IR spectroscopy of the OD stretch mode of HDO in water was successfully used to study osmolyte effects on water H-bonding network. Protecting osmolytes such as sorbitol and trimethylglycine (TMG) make the vibrational OD stretch band red-shifted, whereas urea affects the OD band marginally. Furthermore, we recently showed that, even though sorbitol and TMG cause a slow-down of HDO rotation in their aqueous solutions, urea does not induce any change in the rotational relaxation of HDO in aqueous urea solutions even at high concentrations. To clarify the underlying osmolyte effects on water H-bonding structure and dynamics, we performed molecular dynamics (MD) simulations of a variety of aqueous osmolyte solutions. Using the vibrational solvatochromism model for the OD stretch mode and taking into account the vibrational non-Condon and polarization effects on the OD transition dipole moment, we then calculated the IR absorption spectra and rotational anisotropy decay of the OD stretch mode of HDO for the sake of direct comparisons with our experimental results. The simulation results on the OD stretch IR absorption spectra and the rotational relaxation rate of HDO in osmolyte solutions are found to be in quantitative agreement with experimental data, which confirms the validity of the MD simulation and vibrational solvatochromism approaches. As a result, it becomes clear that the protecting osmolytes like sorbitol and TMG significantly modulate water H-bonding network structure, while urea perturbs water structure little. We anticipate that the computational approach discussed here will serve as an interpretive method with atomic-level chemical accuracy of current linear and nonlinear time-resolved IR spectroscopy of structure and dynamics of water near the surfaces of membranes and proteins under crowded environments. © 2016 American Chemical Society1771sciescopu
The Bend plus Libration Combination Band Is an Intrinsic, Collective, and Strongly Solute-Dependent Reporter on the Hydrogen Bonding Network of Liquid Water
Full text linkWater is an extensively self-associated liquid due to its extensive hydrogen bond (H-bond) forming ability. The resulting H-bonded network fluid exhibits nearly continuous absorption of light from the terahertz to the near-IR region. The relatively weak bend+libration water combination band (centered at 2130 cm(-1)) has been largely overlooked as a reporter of liquid water's structure and dynamics despite its location in a convenient region of the IR for spectroscopic study. The intermolecular nature of the combination band leads to a unique absorption signal that reports collectively on the rigidity of the H-bonding network in the presence of many different solutes. This study reports comprehensively how the combination band acts as an intrinsic and collective probe in various chemically and biologically relevant solutions, including salts of varying character, denaturants, osmolytes, crowders, and surfactants that form reverse micelles and micelles. While we remark on changes in the line width and intensity of this combination band, we mainly focus on the frequency and how the frequency reports on the collective H-bonding network of liquid water. We also comment on the "association band" moniker often applied to this band and how to evaluate discrete features in this spectral region that sometimes appear in the IR spectra of specific kinds of aqueous samples of organic solutes, especially those with very high solute concentrations, with the conclusion that most of these discrete spectral features come exclusively from the solutes and do not report on the water. Contrasts are drawn throughout this work between the collective and delocalized reporting ability of the combination band and the response of more site-specific vibrations like the much-investigated OD stretch of HDO in H2O: the combination band is a unique reporter of H-bonding structure and dynamics and fundamentally different than any local mode probe. Since this band appears as the spectroscopic "background" for many local-mode reporter groups, we note the possibility of observing both local and collective solvent dynamics at the same time in this spectral region
© 2017 American Chemical Society
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
Management of Post Burn Contracgture Using Tensor Fascia Lata Myocutaneous Flap
No full textRole of Tensor Fascia Lata myocutaneous flap in the management of a grain contracture has been evaluated. Its advantages and merits have been discussed alongwith a review of the literature
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