354 research outputs found
Unique reactivity of nanoporous cellulosic materials mediated by surface-confined water
The remarkable efficiency of chemical reactions is the result of biological evolution, often involving confined water. Meanwhile, developments of bio-inspired systems, which exploit the potential of such water, have been so far rather complex and cumbersome. Here we show that surface-confined water, inherently present in widely abundant and renewable cellulosic fibres can be utilised as nanomedium to endow a singular chemical reactivity. Compared to surface acetylation in the dry state, confined water increases the reaction rate and efficiency by 8 times and 30%, respectively. Moreover, confined water enables control over chemical accessibility of selected hydroxyl groups through the extent of hydration, allowing regioselective reactions, a major challenge in cellulose modification. The reactions mediated by surface-confined water are sustainable and largely outperform those occurring in organic solvents in terms of efficiency and environmental compatibility. Our results demonstrate the unexploited potential of water bound to cellulosic nanostructures in surface esterifications, which can be extended to a wide range of other nanoporous polymeric structures and reactions. The efficiency of chemical reactions in biological systems is often connected to the properties of confined water, but the developments and applications of artificial mimicking systems are impeded by the complexity of the biological systems. Here, the authors show how surface bound water in nanoporous cellulosic fibers can increase the reaction rate of surface acetylation reactions and enable regioselectivity of the reactionPeer reviewe
Performance comparison of nuclear magnetic resonance and FerriMagnetic resonance field markers for the control of low-energy synchrotrons
A field marker is a magnetic field sensor used in synchrotrons, which provides a digital trigger when the magnetic field reaches a pre-set threshold. This paper describes the results of an in-situ measurement performed on the Extra Low ENergy Antiproton (ELENA) decelerator's main bending dipoles at the European Organization for Nuclear Research (CERN). It compares the dynamic behavior of Nuclear Magnetic Resonance (NMR) markers and FerriMagnetic Resonance (FMR) markers in different magnetic fields for the operation of these sensors in low-energy synchrotrons.peer-reviewe
Spatioselective surface chemistry for the production of functional and chemically anisotropic nanocellulose colloids
Maximizing the benefits of nanomaterials from biomass requires unique considerations associated with their native chemical and physical structure. Both cellulose nanofibrils and nanocrystals are extracted from cellulose fibers via a top-down approach and have significantly advanced materials chemistry and set new benchmarks in the last decade. One major challenge has been to prepare defined and selectively modified nanocelluloses, which would, e.g., allow optimal particle interactions and thereby further improve the properties of processed materials. At the molecular and crystallite level, the surface of nanocelluloses offers an alternating chemical structure and functional groups of different reactivity, enabling straightforward avenues towards chemically anisotropic and molecularly patterned nanoparticles via spatioselective chemical modification. In this review, we will explain the influence and role of the multiscale hierarchy of cellulose fibers in chemical modifications, and critically discuss recent advances in selective surface chemistry of nanocelluloses. Finally, we will demonstrate the potential of those chemically anisotropic nanocelluloses in materials science and discuss challenges and opportunities in this field.Peer reviewe
Error characterization and calibration of real-time magnetic field measurement systems
In synchrotrons at the European Organization for Nuclear Research (CERN), magnetic measurement systems known as B-trains measure the magnetic field in the main bending magnets in real-time, and transmit this signal for the control of the synchrotron’s RF accelerating cavities, magnet power converter and beam monitoring systems. This work presents an assessment of the capabilities and performance of the new FIRESTORM (Field In REal-time STreaming from Online Reference Magnets) system as part of the first phase of commissioning. A short summary of the architecture of the measurement system is provided first, followed by the definition of an error model which can be used to characterize random and systematic errors separately. We present a procedure for the metrological calibration and qualification of the B-trains, including an experimental evaluation of the different error sources for the four new systems being commissioned in the Proton Synchrotron Booster (PSB), Low Energy Ion Ring (LEIR), Proton Synchrotron (PS) and the Extra Low ENergy Antiproton (ELENA) ring. In particular, we discuss a method to calibrate systematic gain and offset errors based on the RF cavity frequency offset needed to center the beam on its theoretical orbit
Dusty Wind-Blown Bubbles
Spurred by recent observations of 24 micron emission within wind-blown
bubbles, we study the role that dust can play in such environments, and build
an approximate model of a particular wind-blown bubble, `N49.' First, we model
the observations with a dusty wind-blown bubble, and then ask whether dust
could survive within N49 to its present age (estimated to be 5x10^5 to 10^6
years). We find that dust sputtering and especially dust-gas friction would
imply relatively short timescales (t ~ 10^4 years) for dust survival in the
wind-shocked region of the bubble. To explain the 24 micron emission, we
postulate that the grains are replenished within the wind-blown bubble by
destruction of embedded, dense cloudlets of ISM gas that have been over-run by
the expanding wind-blown bubble. We calculate the ablation timescales for
cloudlets within N49 and find approximate parameters for the embedded cloudlets
that can replenish the dust; the parameters for the cloudlets are roughly
similar to those observed in other nebula. Such dust will have an important
effect on the bubble: including simple dust cooling in a wind-blown bubble
model for N49, we find that the luminosity is higher by approximately a factor
of six at a bubble age of about 10^4 years. At ages of 10^7 years, the energy
contained in the bubble is lower by about a factor of eight if dust is
included; if dust must be replenished within the bubble, the associated
accompanying gas mass will also be very important to wind-blown bubble cooling
and evolution. While more detailed models are certainly called for, this work
illustrates the possible strong importance of dust in wind-blown bubbles, and
is a first step toward models of dusty, wind-blown bubbles.Comment: 13 pages, 14 figures, Accepted to Ap
Recommended from our members
A Simple Perspective on the Mass-Area Relationship in Molecular Clouds
Despite over 30 yr of study, the mass–area relationship within and among clouds is still poorly understood both observationally and theoretically. Modern extinction data sets should have sufficient resolution and dynamic range to characterize this relationship for nearby molecular clouds, although recent papers using extinction data seem to yield different interpretations regarding the nature and universality of this aspect of cloud structure. In this paper we try to unify these various results and interpretations by accounting for the different ways cloud properties are measured and analysed. We interpret the mass–area relationship in terms of the column density distribution function and its possible variation within and among clouds. We quantitatively characterize regional variations in the column density probability distribution function (PDF). We show that structures both within and among clouds possess the same degree of ‘universality’, in that their PDF means do not systematically scale with structure size. Because of this, mass scales linearly with area.Astronom
Highly regioselective surface acetylation of cellulose and shaped cellulose constructs in the gas-phase
Publisher Copyright: © 2022 The Royal Society of ChemistryGas-phase acylation is an attractive and sustainable method for modifying the surface properties of cellulosics. However, little is known concerning the regioselectivity of the chemistry, i.e., which cellulose hydroxyls are preferentially acylated and if acylation can be restricted to the surface, preserving crystallinities/morphologies. Consequently, we reexplore simple gas-phase acetylation of modern-day cellulosic building blocks - cellulose nanocrystals, pulps, dry-jet wet spun (regenerated cellulose) fibres and a nanocellulose-based aerogel. Using advanced analytics, we show that the gas-phase acetylation is highly regioselective for the C6-OH, a finding also supported by DFT-based transition-state modelling on a crystalloid surface. This contrasts with acid- and base-catalysed liquid-phase acetylation methods, highlighting that gas-phase chemistry is much more controllable, yet with similar kinetics, to the uncatalyzed liquid-phase reactions. Furthermore, this method preserves both the native (or regenerated) crystalline structure of the cellulose and the supramolecular morphology of even delicate cellulosic constructs (nanocellulose aerogel exhibiting chiral cholesteric liquid crystalline phases). Due to the soft nature of this chemistry and an ability to finely control the kinetics, yielding highly regioselective low degree of substitution products, we are convinced this method will facilitate the rapid adoption of precisely tailored and biodegradable cellulosic materials.Peer reviewe
Regioselective and water-assisted surface esterification of never-dried cellulose : nanofibers with adjustable surface energy
Correction for ‘Regioselective and water-assisted surface esterification of never-dried cellulose: nanofibers with adjustable surface energy’ by Marco Beaumont, Caio G. Otoni, Bruno D. Mattos et. al., Green Chem., 2021, DOI: 10.1039/D1GC02292J.A new regioselective route is introduced for surface modification of biological colloids in the presence of water. Taking the case of cellulose nanofibers (CNFs), we demonstrate a site-specific (93% selective) reaction between the primary surface hydroxyl groups (C6-OH) of cellulose and acyl imidazoles. CNFs bearing C6-acetyl and C6-isobutyryl groups, with a degree of substitution of up to 1 mmol g(-1) are obtained upon surface esterification, affording CNFs of adjustable surface energy. The morphological and structural features of the nanofibers remain largely unaffected, but the regioselective surface reactions enable tailoring of their interfacial interactions, as demonstrated in oil/water Pickering emulsions. Our method precludes the need for drying or exchange with organic solvents for surface esterification, otherwise needed in the synthesis of esterified colloids and polysaccharides. Moreover, the method is well suited for application at high-solid content, opening the possibility for implementation in reactive extrusion and compounding. The proposed acylation is introduced as a sustainable approach that benefits from the presence of water and affords a high chemical substitution selectivity.Peer reviewe
A Simple Perspective on the Mass-Area Relationship in Molecular Clouds
Despite over 30 years of study, the mass-area relationship within and among
clouds is still poorly understood both observationally and theoretically.
Modern extinction datasets should have sufficient resolution and dynamic range
to characterize this relationship for nearby molecular clouds, although recent
papers using extinction data seem to yield different interpretations regarding
the nature and universality of this aspect of cloud structure. In this paper we
try to unify these various results and interpretations by accounting for the
different ways cloud properties are measured and analyzed. We interpret the
mass-area relationship in terms of the column density distribution function and
its possible variation within and among clouds. We quantitatively characterize
regional variations in the column density PDF. We show that structures both
within and among clouds possess the same degree of "universality", in that
their PDF means do not systematically scale with structure size. Because of
this, mass scales linearly with area.Comment: 10 pages, 8 figures, MNRAS in pres
A common statement on anthropogenic hybridization of the European wildcat (Felis silvestris)
Preserving natural genetic diversity and ecological function of wild species is a central goal in conservation biology. As such, anthropogenic hybridization is considered a threat to wild populations, as it can lead to changes in the genetic makeup of wild species and even to the extinction of wild genomes. In European
wildcats, the genetic and ecological impacts of gene flow from domestic cats are mostly unknown at the species scale. However, in small and isolated populations, it is known to include genetic swamping of wild genomes. In this context, it is crucial to better understand the dynamics of hybridization across the species
range, to inform and implement management measures that maintain the genetic diversity and integrity of the European wildcat. In the present paper, we aim to provide an overview of the current scientific understanding of anthropogenic hybridization in European wildcats, to clarify important aspects regarding the evaluation of hybridization given the available methodologies, and to propose guidelines for management and research priorities.publishedVersio
- …