Single addition of an allyl amine monomer enables access to end-functionalized RAFT polymers via native chemical ligation

A novel method for the introduction of a single protected amine-functional monomer at the chain end of RAFT polymers has been developed. This monomer addition, in concert with native chemical ligation, facilitated the development of a simple and versatile method for the end-functionalisation of polymers with peptides

Influence of Block versus Random Monomer Distribution on the Cellular Uptake of Hydrophilic Copolymers

The use of polymers has revolutionized the field of drug delivery in the past two decades. Properties such as polymer size, charge, hydrophilicity, or branching have all been shown to play an important role in the cellular internalization of polymeric systems. In contrast, the fundamental impact of monomer distribution on the resulting biological properties of copolymers remains poorly studied and is always only investigated for biologically active self-assembling polymeric systems. Here, we explore the fundamental influence of monomer distribution on the cellular uptake of nonaggregating and biologically passive copolymers. Reversible addition-fragmentation chain-transfer (RAFT) polymerization was used to prepare precisely defined copolymers of three hydrophilic acrylamide monomers. The cellular internalization of block copolymers was compared with the uptake of a random copolymer where monomers are statistically distributed along the chain. The results demonstrate that monomer distribution in itself has a negligible impact on copolymer uptake

Australian European self-assembly through macromolecular interactions (Editorial)

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Structures and reactivity of peroxy radicals and dimeric products revealed by online tandem mass spectrometry

Organic peroxy radicals (RO2) play a pivotal role in the degradation of hydrocarbons. The autoxidation of atmospheric RO2 radicals produces highly oxygenated organic molecules (HOMs), including low-volatility ROOR dimers formed by bimolecular RO2 + RO2 reactions. HOMs can initiate and greatly contribute to the formation and growth of atmospheric particles. As a result, HOMs have far-reaching health and climate implications. Nevertheless, the structures and formation mechanism of RO2 radicals and HOMs remain elusive. Here, we present the in-situ characterization of RO2 and dimer structure in the gas-phase, using online tandem mass spectrometry analyses. In this study, we constrain the structures and formation pathway of several HOM-RO2 radicals and dimers produced from monoterpene ozonolysis, a prominent atmospheric oxidation process. In addition to providing insights into atmospheric HOM chemistry, this study debuts online tandem MS analyses as a unique approach for the chemical characterization of reactive compounds, e.g., organic radicals.Peer reviewe

Hybridization, missing wild ancestors and the domestication of cultivated diploid bananas

Hybridization and introgressions are important evolutionary forces in plants. They contribute to the domestication of many species, including understudied clonal crops. Here, we examine their role in the domestication of a clonal crop of outmost importance, banana (Musa ssp.). We used genome-wide SNPs generated for 154 diploid banana cultivars and 68 samples of the wild M. acuminata to estimate and geo-localize the contribution of the different subspecies of M. acuminata to cultivated banana. We further investigated the wild to domesticate transition in New Guinea, an important domestication center. We found high levels of admixture in many cultivars and confirmed the existence of unknown wild ancestors with unequal contributions to cultivated diploid. In New Guinea, cultivated accessions exhibited higher diversity than their direct wild ancestor, the latter recovering from a bottleneck. Introgressions, balancing selection and positive selection were identified as important mechanisms for banana domestication. Our results shed new lights on the radiation of M. acuminata subspecies and on how they shaped banana domestication. They point candidate regions of origin for two unknown ancestors and suggest another contributor in New Guinea. This work feed research on the evolution of clonal crops and has direct implications for conservation, collection, and breeding

Exploring precision polymers to fine-tune magnetic resonance imaging properties of iron oxide nanoparticles

The use of bio-polymers as stabilising agents for iron oxide-based negative magnetic resonance imaging (MRI) contrast agents has become popular in recent years, however the wide polydispersity of biologically-derived and commercially available polymers limits the ability to produce truly tuneable and reproducible behaviour, a major challenge in this area. In this work, stable colloids of iron oxide nanoparticles were prepared utilising precision-engineered bio-polymer mimics, poly(2-acrylamido-2-methylpropane sodium sulfonate) (P(AMPS)) polymers, with controlled narrow polydispersity molecular weights, as templating stabilisers. In addition to producing magnetic colloids with excellent MRI contrast capabilities (r values reaching 434.2 mM  s at 25 °C and 23 MHz, several times higher than similar commercial analogues), variable field relaxometry provided unexpected important insights into the dynamic environment of the hydrated materials, and hence their exceptional MRI behaviour. Thanks to the polymer's templating backbone and flexible conformation in aqueous suspension, nanocomposites appear to behave as "multi-core" clustered species, enhancing interparticle interactions whilst retaining water diffusion, boosting relaxation properties at low frequency. This clustering behaviour, evidenced by small-angle X-ray scattering, and strong relaxometric response, was fine-tuned using the well-defined molecular weight polymer species with precise iron to polymer ratios. By also showing negligible haemolytic activity, these nanocomposites exhibit considerable potential for MRI diagnostics. [Abstract copyright: Crown Copyright © 2020. Published by Elsevier Inc. All rights reserved.

Structure and regulation of the Asr gene family in banana

Abscisic acid, stress, ripening proteins (ASR) are a family of plant-specific small hydrophilic proteins. Studies in various plant species have highlighted their role in increased resistance to abiotic stress, including drought, but their specific function remains unknown. As a first step toward their potential use in crop improvement, we investigated the structure and regulation of the Asr gene family in Musa species (bananas and plantains). We determined that the MusaAsr gene family contained at least four members, all of which exhibited the typical two exons, one intron structure of Asr genes and the “ABA/WDS” (abscisic acid/water deficit stress) domain characteristic of Asr genes. Phylogenetic analyses determined that the MusaAsr genes were closely related to each other, probably as the product of recent duplication events. For two of the four members, two versions corresponding to the two sub-genomes of Musa, acuminata and balbisiana were identified. Gene expression and protein analyses were performed and Asr expression could be detected in meristem cultures, root, pseudostem, leaf and cormus. In meristem cultures, mAsr1 and mAsr3 were induced by osmotic stress and wounding, while mAsr3 and mAsr4 were induced by exposure to ABA. mASR3 exhibited the most variation both in terms of amino acid sequence and expression pattern, making it the most promising candidate for further functional study and use in crop improvement

Aldéhydes et cétones dans l'environnement : de la phase gaz à la phase condensée

Increasing evidence indicates that reactive gases such as aldehydes and NOx are emitted from the snowpack to the atmosphere. This partly explains why atmospheric chemistry over snow-covered surfaces cannot be simulated by models using gas-phase processes only. Formaldehyde and acetaldehyde were simultaneously measured in the snow and in the atmosphere during both winter and spring campaigns of ALERT2000 in the Canadian Arctic. These measurements allowed us to suggest that HCHO was incorporated in the volume of ice crystals and was photochemically produced in the snowpack. These results were confirmed by laboratory experiments : we performed a preliminary study of the HCHO-H20 solid solution, and we obtained a diffusion coefficient value of HCHO in ice (DHcHo = (8±5)x10-11 cm2 S-1 at -15°C) which is consistent with the hypothesis that formaldehyde is incorporated in the ice lattice and ils concentration evolves by solid stale diffusion.Ces demières annèes, de nombreuses mesures en région polaire ont montré que les concentrations de certains gaz traces réactifs (aldéhydes, oxydes d'azote) étaient très supérieures à ce que la chimie en phase gazeuse pouvait expliquer. Les hypothèses actuellement retenues pour expliquer ces observations comprennent l'émission de composés dissous ou adsorbés dans la neige, et leur production photochimique dans le manteau neigeux, à partir de composés à identifier. Afin de tenter d'expliquer les rapports de mélange du formaldéhyde (HCHO) et de l'acétaldéhyde (CH3CHO) dans l'arctique, des mesures simultanées ont été effectuées dans l'atmosphère et dans la neige, au cours de la campagne ALERT 2000, à Alert (Ellesmere Island, 82,5° N, 62,3° W) en février et avril 2000. Le développement préalable d'une méthode d'analyse sensible de ces composés dans la neige a été nécessaire. Les évolutions temporelles des concentrations en formaldéhyde (HCHO) et en acétaldéhyde (CH3CHO) dans les couches de neige fraîches ont été suivies pendant plusieurs jours. Comme le métamorphisme de la neige conduit à des cycles de sublimation/condensation à la fois de la glace et des espèces dissoutes, nous avons également suivi l'évolution de la microphysique de la neige. Les résultats obtenus nous ont permis de tester différents mécanismes possibles d'incorporation des aldéhydes dans la neige. Connaître le mécanisme prédominant est nécessaire pour quantifier la vitesse d'échange air-neige de ces composés. Les mécanismes possibles incluent l'adsorption à la surface des cristaux de neige, et la dissolution dans leur volume. Les données obtenues ont permis de tester ces différents mécanismes, et d'apporter des éléments nouveaux sur les processus par lesquels le manteau neigeux pouvait avoir un impact important sur la chimie de l'atmosphère. Nous avons notamment émis l'hypothèse que le formaldéhyde était incorporé en volume dans les cristaux de neige et que les échanges avec l'atmosphère se faisaient par diffusion en phase solide. La vérification de ces résultats nécessitait cependant une confirmation par des expériences en laboratoire. Nous avons donc effectué une étude préliminaire de la solution solide HCHOH20 et nous avons obtenu le coefficient de diffusion du formaldéhyde dans la glace (DHCHO) à -15°C : DHCHO = (8±5j x10*11 cm2 s-1 . Cette valeur de DHCHO permet d'expliquer les variations des concentrations en formaldéhyde dans la neige que nous avons observé sur le terrain