124 research outputs found
Well dispersed fractal aggregates as filler in polymer-silica nanocomposites: long range effects in rheology
We are presenting a new method of processing polystyrene-silica
nanocomposites, which results in a very well-defined dispersion of small
primary aggregates (assembly of 15 nanoparticles of 10 nm diameter) in the
matrix. The process is based on a high boiling point solvent, in which the
nanoparticles are well dispersed, and controlled evaporation. The filler's fine
network structure is determined over a wide range of sizes, using a combination
of Small Angle Neutron Scattering (SANS) and Transmission Electronic Microscopy
(TEM). The mechanical response of the nanocomposite material is investigated
both for small (ARES oscillatory shear and Dynamical Mechanical Analysis) and
large deformations (uniaxial traction), as a function of the concentration of
the particles. We can investigate the structure-property correlations for the
two main reinforcement effects: the filler network contribution, and a
filler-polymer matrix effect. Above a silica volume fraction threshold, we see
a divergence of the modulus correlated to the build up of a connected network.
Below the threshold, we obtain a new additional elastic contribution of much
longer terminal time than the matrix. Since aggregates are separated by at
least 60 nm, this new filler-matrix contribution cannot be described solely
with the concept of glassy layer (2nm)
Multiple Scale Reorganization of Electrostatic Complexes of PolyStyrene Sulfonate and Lysozyme
We report on a SANS investigation into the potential for these structural
reorganization of complexes composed of lysozyme and small PSS chains of
opposite charge if the physicochemical conditions of the solutions are changed
after their formation. Mixtures of solutions of lysozyme and PSS with high
matter content and with an introduced charge ratio [-]/[+]intro close to the
electrostatic stoichiometry, lead to suspensions that are macroscopically
stable. They are composed at local scale of dense globular primary complexes of
radius ~ 100 {\AA}; at a higher scale they are organized fractally with a
dimension 2.1. We first show that the dilution of the solution of complexes,
all other physicochemical parameters remaining constant, induces a macroscopic
destabilization of the solutions but does not modify the structure of the
complexes at submicronic scales. This suggests that the colloidal stability of
the complexes can be explained by the interlocking of the fractal aggregates in
a network at high concentration: dilution does not break the local aggregate
structure but it does destroy the network. We show, secondly, that the addition
of salt does not change the almost frozen inner structure of the cores of the
primary complexes, although it does encourage growth of the complexes; these
coalesce into larger complexes as salt has partially screened the electrostatic
repulsions between two primary complexes. These larger primary complexes remain
aggregated with a fractal dimension of 2.1. Thirdly, we show that the addition
of PSS chains up to [-]/[+]intro ~ 20, after the formation of the primary
complex with a [-]/[+]intro close to 1, only slightly changes the inner
structure of the primary complexes. Moreover, in contrast to the synthesis
achieved in the one-step mixing procedure where the proteins are unfolded for a
range of [-]/[+]intro, the native conformation of the proteins is preserved
inside the frozen core
Critical structure factor in Ising systems
We perform a large-scale Monte Carlo simulation of the three-dimensional
Ising model on simple cubic lattices of size L^3 with L=128 and 256. We
determine the corresponding structure factor (Fourier transform of the
two-point function) and compare it with several approximations and with
experimental results. We also compute the turbidity as a function of the
momentum of the incoming radiation, focusing in particular on the deviations
from the Ornstein-Zernicke expression of Puglielli and Ford.Comment: 16 page
Phthalocyanine-nanocarbon ensembles: From discrete molecular and supramolecular systems to hybrid nanomaterials
This document is the Accepted Manuscript version of a Published Work that appeared in final form in Accounts of Chemical Research, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/ar5004384Conspectus Phthalocyanines (Pcs) are macrocyclic and aromatic compounds that present unique electronic features such as high molar absorption coefficients, rich redox chemistry, and photoinduced energy/electron transfer abilities that can be modulated as a function of the electronic character of their counterparts in donor-acceptor (D-A) ensembles. In this context, carbon nanostructures such as fullerenes, carbon nanotubes (CNTs), and, more recently, graphene are among the most suitable Pc companions. Pc-C60 ensembles have been for a long time the main actors in this field, due to the commercial availability of C60 and the ell-established synthetic methods for its functionalization. As a result, many Pc-C60 architectures have been prepared, featuring different connectivities (covalent or supramolecular), intermolecular interactions (self-organized or molecularly dispersed species), and Pc HOMO/LUMO levels. All these elements provide a versatile toolbox for tuning the photophysical properties in terms of the type of process (photoinduced energy/electron transfer), the nature of the interactions beteen the electroactive units (through bond or space), and the kinetics of the formation/decay of the photogenerated species. Some recent trends in this field include the preparation of stimuli-responsive multicomponent systems ith tunable photophysical properties and highly ordered nanoarchitectures and surface-supported systems shoing high charge mobilities. A breakthrough in the Pc-nanocarbon field as the appearance of CNTs and graphene, hich opened a ne avenue for the preparation of intriguing photoresponsive hybrid ensembles shoing light-stimulated charge separation. The scarce solubility of these 1-D and 2-D nanocarbons, together ith their loer reactivity ith respect to C60 stemming from their less strained sp2 carbon netorks, has not meant an unsurmountable limitation for the preparation of variety of Pc-based hybrids. These systems, hich sho improved solubility and dispersibility features, bring together the unique electronic transport properties of CNTs and graphene ith the excellent light-harvesting and tunable redox properties of Pcs. A singular and distinctive feature of these Pc-CNT/graphene (single- or fe-layers) hybrid materials is the control of the direction of the photoinduced charge transfer as a result of the band-like electronic structure of these carbon nanoforms and the adjustable electronic levels of Pcs. Moreover, these conjugates present intensified light-harvesting capabilities resulting from the grafting of several chromophores on the same nanocarbon platform.In this Account, recent progress in the construction of covalent and supramolecular Pc-nanocarbon ensembles is summarized, ith a particular emphasis on their photoinduced behavior. e believe that the high degree of control achieved in the preparation of Pc-carbon nanostructures, together ith the increasing knoledge of the factors governing their photophysics, ill allo for the design of next-generation light-fueled electroactive systems. Possible implementation of these Pc-nanocarbons in high performance devices is envisioned, finally turning into reality much of the expectations generated by these materialsFinancial support from the Spanish MICINN (CTQ2011-24187/BQU), the Comunidad de Madrid (S2013/MIT-2841 FOTOCARBON) and the EU (“SO2S” FP7-PEOPLE-2012-ITN, no.: 316975) is acknowledge
The Ca2+ sensor STIM1 regulates the type I interferon response by retaining the signaling adaptor STING at the endoplasmic reticulum
STING is an endoplasmic reticulum (ER) signaling adaptor that is essential for the type I Interferon response to DNA pathogens. Aberrant activation of STING is linked to the pathology of autoimmune and autoinflammatory diseases. The rate-limiting step for the activation of STING is its translocation from the ER to the ER–Golgi intermediate compartment. Here we found that deficiency in the Ca2+ 36 sensor STIM1 caused spontaneous activation of STING and enhanced expression of type I interferons under resting conditions in mice and a patient suffering from combined immunodeficiency. Mechanistically, STIM1 associated with STING to retain it in the ER membrane, and co-expression of full-length or a STING-interacting fragment of STIM1 suppressed the function of dominant STING mutants that cause autoinflammatory diseases. Furthermore, deficiency in STIM1 strongly enhanced the expression of type I interferons after viral infection and prevented the lethality of infection with a DNA virus in vivo. This work delineates a STIM1–STING circuit that maintains the resting state of the STING pathway
Structural analysis of haemoglobin binding by HpuA from the Neisseriaceae family
The Neisseriaceae family of bacteria causes a range of diseases including meningitis, septicaemia, gonorrhoea and endocarditis, and extracts haem from haemoglobin as an important iron source within the iron-limited environment of its human host. Herein we report crystal structures of apo- and haemoglobin-bound HpuA, an essential component of this haem import system. The interface involves long loops on the bacterial receptor that present hydrophobic side chains for packing against the surface of haemoglobin. Interestingly, our structural and biochemical analyses of Kingella denitrificans and Neisseria gonorrhoeae HpuA mutants, although validating the interactions observed in the crystal structure, show how Neisseriaceae have the fascinating ability to diversify functional sequences and yet retain the haemoglobin binding function. Our results present the first description of HpuA’s role in direct binding of haemoglobin
Perspectives on Immunoglobulins in Colostrum and Milk
Immunoglobulins form an important component of the immunological activity found in milk and colostrum. They are central to the immunological link that occurs when the mother transfers passive immunity to the offspring. The mechanism of transfer varies among mammalian species. Cattle provide a readily available immune rich colostrum and milk in large quantities, making those secretions important potential sources of immune products that may benefit humans. Immune milk is a term used to describe a range of products of the bovine mammary gland that have been tested against several human diseases. The use of colostrum or milk as a source of immunoglobulins, whether intended for the neonate of the species producing the secretion or for a different species, can be viewed in the context of the types of immunoglobulins in the secretion, the mechanisms by which the immunoglobulins are secreted, and the mechanisms by which the neonate or adult consuming the milk then gains immunological benefit. The stability of immunoglobulins as they undergo processing in the milk, or undergo digestion in the intestine, is an additional consideration for evaluating the value of milk immunoglobulins. This review summarizes the fundamental knowledge of immunoglobulins found in colostrum, milk, and immune milk
Akt and STAT5 mediate naïve human CD4+ T-cell early metabolic response to TCR stimulation
Metabolic pathways that regulate T-cell function show promise as therapeutic targets in diverse diseases. Here, we show that at rest cultured human effector memory and central memory CD4+ T-cells have elevated levels of glycolysis and oxidative phosphorylation (OXPHOS), in comparison to naïve T-cells. Despite having low resting metabolic rates, naive T-cells respond to TCR stimulation with robust and rapid increases in glycolysis and OXPHOS. This early metabolic switch requires Akt activity to support increased rates of glycolysis and STAT5 activity for amino acid biosynthesis and TCA cycle anaplerosis. Importantly, both STAT5 inhibition and disruption of TCA cycle anaplerosis are associated with reduced IL-2 production, demonstrating the functional importance of this early metabolic program. Our results define STAT5 as a key node in modulating the early metabolic program following activation in naive CD4+ T-cells and in turn provide greater understanding of how cellular metabolism shapes T-cell responses
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