Water‐soluble fluorescent polymers that respond to singlet oxygen

Although acenes with more than three fused rings can both fluoresce efficiently and react with singlet oxygen (¹O₂) rapidly, their hydrophobic nature presents a challenge to their use in aqueous environments. Herein we report a series of fluorescent, water‐soluble random copolymers that each comprise (oligoethylene glycol) methacrylate (OEGMA) and one of several diarylacene methacrylates, including a tetracene methacrylate and a tetraceneothiophene methacrylate. Exposure to ¹O₂ in water oxidizes the pendant acenes, resulting in diminution of their fluorescence intensities. The observed rate of oxidation of the tetracene‐containing polymers compares favorably with a commercial ¹O₂‐sensitive dye. Polymers that also include energy‐donating coumarin side chains show ratiometric fluorescence changes in response to ¹O₂. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2526–2535     

Processing-structure-mechanical property relationships of semicrystalline polyolefin-based block copolymers

The incremental plastic deformation of the crystals of block copolymers made of semicrystalline polypropylene endblocks and amorphous ethylene-r-propylene midblocks occurring during step cycle tensile tests has dramatic effects on the stress-strain curves. This can be understood from the evolution of the morphology and of the microstructure of the crystalline blocks revealed by X-ray scattering experiments. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1428–1437, 2010     

Characterization of the aerosol produced by infrared femtosecond laser ablation of polyacrylamide gels for the sensitive inductively coupled plasma mass spectrometry detection of selenoproteins

A 2D high repetition rate femtosecond laser ablation strategy (2-mm wide lane) previously developed for the detection of selenoproteins in gel electrophoresis by inductively coupled plasma mass spectrometry was found to increase signal sensitivity by a factor of 40 compared to conventional nanosecond ablation (0.12-mm wide lane) [G. Ballihaut, F. Claverie, C. Pécheyran, S. Mounicou, R. Grimaud and R. Lobinski, Sensitive Detection of Selenoproteins in Gel Electrophoresis by High Repetition Rate Femtosecond Laser Ablation-Inductively Coupled Plasma Mass Spectrometry, Anal. Chem. 79 (2007) 6874–6880]. Such improvement couldn't be explained solely by the difference of amount of material ablated, and then, was attributed to the aerosol properties. In order to validate this hypothesis, the characterization of the aerosol produced by nanosecond and high repetition rate femtosecond laser ablation of polyacrylamide gels was investigated. Our 2D high repetition rate femtosecond laser ablation strategy of 2-mm wide lane was found to produce aerosols of similar particle size distribution compared to nanosecond laser ablation of 0.12-mm wide lane, with 38% mass of particles < 1 µm. However, at high repetition rate, when the ablated surface was reduced, the particle size distribution was shifted toward thinner particle diameter (up to 77% for a 0.12-mm wide lane at 285 µm depth). Meanwhile, scanning electron microscopy was employed to visualize the morphology of the aerosol. In the case of larger ablation, the fine particles ejected from the sample were found to form agglomerates due to higher ablation rate and then higher collision probability. Additionally, investigations of the plasma temperature changes during the ablation demonstrated that the introduction of such amount of polyacrylamide gel particles had very limited impact on the ICP source (ΔT~ 25 ± 5 K). This suggests that the cohesion forces between the thin particles composing these large aggregates were weak enough to have negligible impact on the ICPMS detection.     

Tea Bags for Fmoc Solid-Phase Peptide Synthesis: An Example of Circular Economy

Peptide synthesis is an area with a wide field of application, from biomedicine to nanotechnology, that offers the option of simultaneously synthesizing a large number of sequences for the purpose of preliminary screening, which is a powerful tool. Nevertheless, standard protocols generate large volumes of solvent waste. Here, we present a protocol for the multiple Fmoc solid-phase peptide synthesis in tea bags, where reagent recycling steps are included. Fifty-two peptides with wide amino acid composition and seven to twenty amino acid residues in length were synthesized in less than three weeks. A clustering analysis was performed, grouping the peptides by physicochemical features. Although a relationship between the overall yield and the physicochemical features of the sequences was not established, the process showed good performance despite sequence diversity. The recycling system allowed to reduce N, N-dimethylformamide usage by 25–30% and reduce the deprotection reagent usage by 50%. This protocol has been optimized for the simultaneous synthesis of a large number of peptide sequences. Additionally, a reagent recycling system was included in the procedure, which turns the process into a framework of circular economy, without affecting the quality of the products obtained.     

β‐Diketiminate‐supported magnesium alkyl: synthesis,structure and application as co‐catalyst for polymerizations mediated by a lanthanum half‐sandwich complex

Mg(n‐Bu){η²‐HC[C(Me)NMes]₂} ( 2 ) (Mes = mesityl, 2,4,6‐Me₃C₆H₂), a new β‐diketiminate‐supported magnesium alkyl, has been synthesized and structurally characterized. The X‐ray analysis of the lanthanum half‐sandwich complex Cp*La(BH₄)₂(THF)₂ ( 1 ) (Cp* = pentamethylcyclopentadienyl; THF = tetrahydrofuran) is also reported. Complex 2 has been assessed as both alkylating agent and chain transfer agent for the lanthanum‐catalysed polymerization and coordinative chain transfer polymerization of isoprene and styrene using 1 as the pre‐catalyst. The results are compared with those for n‐butylethylmagnesium (BEM) which is traditionally used for this purpose. The 1,4‐trans stereospecific polymerization of isoprene shows a more controlled character using 2 versus BEM, and higher activities are observed for the chain transfer polymerization of styrene when 2 is used as chain transfer agent. The activity is in turn lower than that observed using BEM when 1 equiv. of magnesium compound is used for the polymerization of styrene. The combination of 1 , 2 and Al(i‐Bu)₃ leads finally to a 1,4‐trans stereoselective coordinative chain transfer polymerization of isoprene, in a similar way to BEM. Copyright © 2015 John Wiley & Sons, Ltd.     

On Heavy-Tail Phenomena in Some Large-Deviations Problems

We revisit the proof of the large-deviations principle of Wiener chaoses partially given by Borell and then by Ledoux in its full form. We show that some heavy-tail phenomena observed in large deviations can be explained by the same mechanism as for the Wiener chaoses, meaning that the deviations are created, in a sense, by translations. More precisely, we prove a general large-deviations principle for a certain class of functionals , where is some metric space, under the n -fold probability measure , where α ∈ (0, 2] , for which the large deviations are due to translations. We retrieve, as an application, the large-deviations principles known for the Wigner matrices without Gaussian tails, in works by Bordenave and Caputo on one hand, and the author on the other hand, of the empirical spectral measure, the largest eigenvalue, and traces of polynomials. We also apply our large-deviations result to the last-passage time, which yields a large-deviations principle when the weights follow the law , with α ∈ (0, 1) . © 2020 Wiley Periodicals LLC     

Well-defined backbone degradable polymer–drug conjugates synthesized by reversible addition-fragmentation chain-transfer polymerization

Despite the recent advances of controlled polymerization methods over the last decades, the lack of backbone degradability of well-defined polymers remains a major synthetic challenge that limits the full exploitation of polymer–drug conjugates (PDCs) in clinical practice. Here, we report the copolymerization of a cyclic ketene acetal (CKA) and a vinyl-based drug-monomer as a proof-of-concept approach to prepare model polyester-based prodrugs via reversible addition-fragmentation chain-transfer (RAFT) polymerization. We demonstrate the versatility of the system toward backbone degradability and control over the chain length while maintaining both low dispersity (Đ_M) and homogenous distribution of degradation points along the main polymer chain. The resulting PDCs exhibit unique self-assembly properties and potent cytotoxicity against pancreatic cancer cells. A methacrylate prodrug is copolymerized with a CKA co-monomer using RAFT polymerization producing a backbone degradable PDC with well-defined molecular structure. The resulting PDC undergoes controlled backbone degradation and produces by-products of narrow dispersity and low toxicity. In addition, it is demonstrated that the insertion of degradation segments does not affect the cytotoxic properties of the PDC under in vitro conditions.     

An Unusual Intramolecular Halogen Bond Guides Conformational Selection

PIK‐75 is a phosphoinositide‐3‐kinase (PI3K) α‐isoform‐selective inhibitor with high potency. Although published structure–activity relationship data show the importance of the NO₂ and the Br substituents in PIK‐75, none of the published studies could correctly determine the underlying reason for their importance. In this publication, we report the first X‐ray crystal structure of PIK‐75 in complex with the kinase GSK‐3β. The structure shows an unusual U‐shaped conformation of PIK‐75 within the active site of GSK‐3β that is likely stabilized by an atypical intramolecular Br???NO₂ halogen bond. NMR and MD simulations show that this conformation presumably also exists in solution and leads to a binding‐competent preorganization of the PIK‐75 molecule, thus explaining its high potency. We therefore suggest that the site‐specific incorporation of halogen bonds could be generally used to design conformationally restricted bioactive substances with increased potencies.     

FALCON: multi-object AO

FALCON is a wide-field, multi-object integral field spectrograph equipped with adaptive optics. It is dedicated to the study of the formation process of primordial galaxies. The AO system uses natural guide stars, and the high sky coverage required for these studies is obtained using tomographic techniques for the wavefront analysis. The structure of the OA system is very new, and particularly suited for a future implementation on extremely large telescopes. To cite this article: E. Gendron et al., C. R. Physique 6 (2005).