1,721,054 research outputs found
Unveiling the role of histidine and tyrosine residues on the conformation of the avian prion hexarepeat domain
No full textThe prion protein (PrPC) is a glycoprotein that in mammals, differently from avians, can lead to prion diseases,
by misfolding into a â-sheet-rich pathogenic isoform (PrPSc). Mammal and avian proteins show different
N-terminal tandem repeats: PHGGGWGQ and PHNPGY, both containing histidine, whereas tyrosine is
included only in the primary sequence of the avian protein. Here, by means of potentiometric, circular dichroism
(CD), and molecular dynamics (MD) studies at different pH values, we have investigated the conformation
of the avian tetrahexarepeat (PHNPGY)4 (TetraHexaPY) with both N- and C-termini blocked by acetylation
and amidation, respectively. We have found, also with the help of a recently proposed protein chirality indicator
(Pietropaolo, A.; Muccioli, L.; Berardi, R.; Zannoni, C. Proteins 2008, 70, 667-677), a conformational
dependence on the protonation states of histidine and tyrosine residues: the turn formation is pH driven, and
at physiological pH a pivotal role is played by the tyrosine OH groups which give rise to a very compact bent
structure of backbone upon forming a hydrogen-bond network
A deformable Gay-Berne model for the simulation of liquid crystals and soft materials
No full textWe present a deformable Gay-Berne (DGB) pair potential for ellipsoidal particles that allows for dynamic fluctuations in their shape and interaction anisotropy. We investigate the effect that various intrinsic distributions of shape and interaction parameters have on the liquid crystal phases formed by a system of DGB particles. We show that deformability can stabilise smectic formation and that all mesomorphic phase transitions are accompanied by a change of molecular shape. (c) 2006 Elsevier B.V. All rights reserved
Monte Carlo simulation of the nematic-vapour interface for a Gay-Berne liquid crystal RID E-3129-2010
No full textThe nematic-vapour interface of the Gay-Berne liquid crystal model has been studied by Monte Carlo simulation. When the anisotropy parameter kappa' is set to 1.25, a film of particles in a rectangular box has been shown to exhibit nematic-vapour coexistence. Analysis of the orientational ordering across the sample reveals that the anchoring is planar, that is, the preferred alignment is in a direction parallel to the interface. No nematic wetting of the film in the isotropic phase is observed, although there is a strong tendency for the molecules near the surface to be parallel to the interface even at temperatures higher than the isotropic-nematic-vapour triple point. (C) 1997 Published by Elsevier Science B.V
Simulation of vapor-phase deposition and growth of a pentacene thin film on C 60 (001)
No full textThe formation of the heterojunction between two organic semiconductors, pentacene on top of Buckminster fullerene, is simulated using a virtual vapor deposition experiment. The thin-film growth is characterized by a lying-to-standing collective reorientation of pentacene molecules, corresponding to the onset of crystalline order. The mechanism is coverage dependent and reorientation occurs earlier for the second monolayer. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Molecular diffusion in liquid crystals andchiral discrimination. I. Theory
No full textThe possibility of using cholesteric phases for discriminating enantiomers of a chiral solute on the basis of their different transport properties, motivates the investigation of the translational diffusion by taking fully into account the roto-translational coupling. In this article a detailed theoretical analysis is presented for the transport properties evaluated according to the asymptotic limit of the mean-squared displacement. A general relation is derived for the transport coefficients, having as main ingredients the mean-field potential due to the mesophase, and the diffusion tensor with its purely translational and rotational components, and with the blocks describing the roto-translational coupling. The application of the theory to nematic phases shows that the roto-translational coupling Generates a dynamical, contribution reducing the transport coefficients evaluated by taking into account only the translational diffusion components in the center of diffusion. The theory is also specialized to a cholesteric phase with a given helical pitch for the director arrangement, in a form which is suitable for calculations of model systems of chiral solutes to be presented in a forthcoming paper
Energy transfer and orientational dynamics in isotropic and nematic phases. A computer simulation approach
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
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