Taming the Lewis Superacid Al(ORF)3 (RF=C(CF3 )3 ): DFT Guided Identification of the "Stable yet Reactive" Adduct SiPr2 →Al(ORF)3 ; Its Use as ORF- Abstractor from a "Ni-ORF" complex.

A DFT study of several L→Al(ORF )3 (L=Lewis bases) adducts allowed the identification of (i Pr2 S)→Al(ORF )3 1-Si Pr2 as a "stable yet reactive" adduct. 1-Si Pr2 was shown to act as a masked Lewis superacid able to release Al(ORF )3 under mild conditions. It could be used to abstract a ORF- ligand from (bipyMe2 )Ni(ORF )2 (bipyMe2 : 6,6'-dimethyl-2,2'-dipyridyl) and generate the nickel alkoxide complex [(bipyMe2 )Ni(ORF )(i Pr2 S)]+ [(RF O)3 Al-F-Al(ORF )3 ]- 5. Ligand exchange of i Pr2 S by Ph3 P yielded [(bipyMe2 )Ni(ORF )(PPh3 )]+ [(RF O)3 Al-F-Al(ORF )3 ]- 6.

Ligand-enabled oxidation of gold(i) complexes with o-quinones.

Chelating P^P and hemilabile P^N ligands were found to trigger the oxidation of Au(i) complexes by o-benzoquinones. The ensuing Au(iii) catecholate complexes have been characterized by NMR spectroscopy, single crystal X-ray diffraction and X-ray absorption spectroscopy. They adopt tetracoordinate square-planar structures. Reactivity studies substantiate the reversibility of the transformation. In particular, the addition of competing ligands such as chloride and alkenes gives back Au(i) complexes with concomitant release of the o-quinone. DFT calculations provide insight about the structure and relative stability of the Au(i) o-quinone and Au(iii) catecholate forms, and shed light on the 2-electron transfer from gold to the o-quinone.

Design of cytocompatible bacteria-repellent bio-based polyester films via an aqueous photoactivated process.

Nosocomial infections are often induced by the presence of pathogenic organisms on the surface of medical devices or hospital equipment. Chemical or topographical modifications of the surface are recognized as efficient strategies to prevent bacteria adhesion but they may have negative impact on the material interaction with living tissues. Here we have developed a photoactivated method for the modification of a biocompatible polymer, poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) under aqueous conditions. A photoinduced free-radical technique employing a grafting-from process in water media has been successfully performed to covalently anchored fluorine or PEG groups onto PHBHV surfaces. PEGylated hydrophilic surfaces showed higher bacteria-repellency performances than fluorinated hydrophobic films, achieving a >98% anti-adhesion efficiency against Escherichia coli and Staphylococcus aureus. In addition, these surfaces allowed for the adhesion and proliferation of human dermal fibroblasts without the evidence of cytotoxicity.

Facile synthesis of multicompartment micelles based on biocompatible poly(3-hydroxyalkanoate).

In this paper, a straightforward method to produce poly(3-hydroxyalkanoate)-based multicompartment micelles (MCMs) is presented. Thiol-ene addition is used to graft sequentially perfluorooctyl chains and poly(ethylene glycol) oligomers onto poly(3-hydroxyoctanoate-co-hydroxyundecenoate) oligomers backbone. Well-defined copolymers are obtained as shown by ¹H NMR and size-exclusion chromatography. After nanoprecipitation in water, novel PHA-based MCMs are evidenced by cryo-transmission electron microscopy. Moreover, the cytocompatibility of MCMs is demonstrated in vitro via cell viability assay.

Photoinduced modification of the natural biopolymer poly(3-hydroxybutyrate-co-3-hydroxyvalerate) microfibrous surface with anthraquinone-derived dextran for biological applications.

A straightforward and versatile method for immobilizing polysaccharides on the surface of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBHV) electrospun fibers is developed with the objective of designing a new functional biomaterial having a significant effect on cell proliferation. The approach relies on a one-step procedure: UV grafting of a photosensitive dextran (AQ-Dext) on the surface of PHBHV fibers according to a "grafting onto" method, with the use of an anthraquinone derivative. The photografting is conducted through a photoinduced free radical process employing an anthraquinone-based photosensitizer in aqueous medium. Under appropriate conditions, AQ-Dext reacts with C-H σ-bonds of the polymer substrate (PHBHV) to produce a semianthraquinone radical according to an H-abstraction reaction. This radical recombines together with the alkylradical (R˙) formed at the surface of PHBHV fibers via the oxygen atom of the anthraquinone photolinker. The photochemical mechanism of the AQ-Dext photolysis is entirely described for the first time by an electron spin resonance technique and laser flash photolysis. The modified PHBHV microfibrous scaffolds are extensively characterized by water contact angle measurements, XPS analysis and atomic force microscopy, confirming the covalent grafting of dextran on PHBHV fibers. Finally, a primary investigation demonstrates that dextran modified PHBHV fibers are permissive for optimized cell colonization and proliferation. The cell morphologies are described by SEM micrographs, revealing a significant affinity and favorable interactions for adherence of human mesenchymal stem cells (hMSCs) on scaffolds provided by dextran chemical structure. Moreover, the proliferation rate of hMSCs increases on this new functionalized biomaterial associated with a higher extra-cellular matrix production after 5 days of culture in comparison with native PHBHV fibers.

An efficient thiol-ene chemistry for the preparation of amphiphilic PHA-based graft copolymers.

We present a straightforward method to prepare amphiphilic graft copolymers consisting of hydrophobic poly(3-hydroxyalkanoates) (PHAs) backbone and hydrophilic α-amino-ω-methoxy poly(oxyethylene-co-oxypropylene) (Jeffamine®) units. Poly(3-hydroxyoctanoate)-co-(3-hydroxyundecenoate) (PHOU) was first methanolyzed to obtain the desired molar mass. The amino end groups of Jeffamine were converted into thiol by a reaction with N-acetylhomocysteine thiolactone and subsequently photografted. This "one-pot" functionalization prevents from arduous and time-consuming functionalization of the hydrophilic precursor or tedious modifications of PHAs, thus simplifying the process. The amphiphilic nature of modified PHAs leads to water-soluble copolymers exhibiting thermoresponsive behavior.

Poly(3-hydroxyalkanoate)-derived amphiphilic graft copolymers for the design of polymersomes.

Amphiphilic graft copolymers composed of biocompatible bacterial poly(3-hydroxyalkanoate) and poly(ethylene glycol) have been synthesized by thiol-ene addition. They were demonstrated to form well-defined nanoscale vesicles in water by cryo-transmission electron microscopy.

A micellization study of medium chain length poly(3-hydroxyalkanoate)-based amphiphilic diblock copolymers.

In this article, we report the first micellization study of amphiphilic copolymers composed of bacterial medium chain length poly(3-hydroxyalkanoates) (mcl-PHAs). A series of diblock copolymers based on fixed poly(ethylene glycol) (PEG) block (5000 g mol(-1)) and a varying poly(3-hydroxyoctanoate-co-3-hydroxyhexanoate) (PHOHHx) segment (1500-7700 g mol(-1)) have been synthesized using "click" chemistry. These copolymers self-assembled to form micelles in aqueous media. The influence of PHOHHx block molar mass on the hydrodynamic size and on the critical micelle concentration (CMC) has been studied using dynamic light scattering and fluorescence spectroscopy, respectively. With increasing PHOHHx length, narrowly distributed micelles with diameters ranging from 44 to 90 nm were obtained, with extremely low CMC (up to 0.85 mg/L). Cryogenic transmission electron microscopy (Cryo-TEM) showed that micelles took on a spherical shape and exhibited narrow polydispersity. Finally, the colloidal stability of the micelles against physiological NaCl concentration has been demonstrated, suggesting they are promising candidates for drug delivery applications.

Preparation of Clickable Poly(3-hydroxyalkanoate) (PHA): Application to Poly(ethylene glycol) (PEG) Graft Copolymers Synthesis.

A new synthesis of amphiphilic biodegradable copolymers consisting of hydrophobic poly(3-hydroxyalkanoate) (PHA) backbone and hydrophilic poly(ethylene glycol) (PEG) units as side chains is described. Poly[(3-hydroxyoctanoate)-co-(3-hydroxyundecenoate)] (PHOU) was first methanolyzed and its unsaturated side chains were quantitatively oxidized to carboxylic acid. Esterification with propargyl alcohol led to an alkyne-containing "clickable" PHA in 71% conversion. Its reactivity was successfully demonstrated by grafting azide-terminated PEG chains of 550 and 5 000 g · mol(-1) , respectively. All products were fully characterized using GPC, (1) H, and COSY NMR.