Synthesis of a mitochondria-targeted spin trap using a novel Parham-type cyclization

A new cyclic nitrone spin trap, [4-(3′,3′-dibutyl-2′-oxy-3′H-isoindol-5′-yloxy)butyl]triphenylphosphonium bromide (MitoSpin), bearing a lipophilic cation has been prepared by a route that involves a novel Parham-type lithiation–cyclization of an isocyanate to give the isoindolinone core. MitoSpin accumulates in a membrane potential dependent way in energized mitochondria and its oxidation could potentially be used in the study of oxidative stress resulting from reactive oxygen species generated in mitochondria

Photo-induced macromolecular functionalization of cellulose via nitroxide spin trapping

Cellulose is the most abundant organic raw material on the planet. Due to its renewability and biodegradability it is currently attracting much interest for the production of biofuels or platform chemicals. In addition, recent applications in the field of materials science have appeared, arising from the low density and the excellent thermal and mechanical properties of cellulose, particularly in the production of composites. However, there are still some major drawbacks to using cellulose including its water-absorbing nature and its poor compatibility with other materials, for example, synthetic polymers. To combat these problems, grafting synthetic polymers onto cellulose is the most straightforward method to alter its surface properties and thus to control the wettability, adhesion, or hydrophobicity of the biopolymer. Although grafting from methods such as surface-initiated nitroxide-mediated polymerization (NMP), atom transfer radical polymerization (ATRP),reversible addition–fragmentation transfer polymerization (RAFT), or ring-opening polymerization (ROP)are considered as the most efficient approaches, particularly in terms of grafting density, efficient grafting to methods have recently produced very good results. Cellulose has been successfully modified with preformed polymers by both hetero-Diels–Alderand 1,3-dipolar nitrile imine-ene cycloadditions. In the latter case, light was used as the grafting trigger. Importantly, employing light offers temporal and spatial control of the reaction. In the present contribution, we introduce a very facile grafting to protocol based on the generation of radicals at the surface of cellulose by mild UV irradiation (λmax ∼ 311 nm) of an immobilized photoinitiator, followed by radical trapping with a nitroxide-functionalized polymer (see Scheme 1). Previously, nitroxide radical coupling was employed to efficiently link polymer strands, however via a copper-catalyzed mechanism using ATRP-made polymers to generate reactive radicals. A rather similar philosophy based on spin capturing was reported, employing nitrones that after a first radical reaction generate a nitroxide able to undergo a second radical coupling

Photoinduced conjugation of Dithioester- and Trithiocarbonate-Functional RAFT polymers with alkenes

We report the photoinduced conjugation of polymers synthesized via reversible addition−fragmentation chain transfer (RAFT) polymerization with a number of low molecular weight (functional) olefins. Upon irradiation of a solution of an aliphatic alkene and the benzyl dithioacetic acid ester (CPDA) or dodecyl trithiocarbonate (DoPAT) functional poly(alkyl acrylate) at the absorption wavelength of the thiocarbonyl group (315 nm), incorporation of the alkene at the polymer chain-end occurred. The most efficient systems identified with regard to the rate of reaction and yield were poly(butyl acrylate)/CPDA/ethyl vinyl ether (78% monoinsertion product after 1 h) and poly(butyl acrylate)/CPDA/1-pentene (73% insertion product after 7 h) at ambient temperature. An in-depth analysis of the reaction mechanism by 1H NMR and online size-exclusion chromatography-electrospray ionization tandem mass spectrometry (SEC/ESI−MSn) revealed that a possible [2 + 2] photoaddition mechanism of conjugation does not take place. Instead, fast β-cleavage of the photoexcited RAFT-end group with subsequent radical addition of an alkene was observed for all employed systems. The presented reaction thus provides a means of spatial and temporal control for the conjugation of alkenes to thiocarbonyl thio-capped macromolecules via the use of UV radiation

BODIPY-based profluorescent nitroxide probes containing meso- and beta-substituted isoindoline nitroxides

BODIPY is a highly versatile fluorophore for biological imaging with a tunable fluorescence emission (500 - 800 nm) that overlaps with the optically transparent window for tissue (600 - 1300 nm). Herein, we describe the synthesis of optically distinct BODIPY-based profluorescent probes bearing meso- and β-substituted isoindoline nitroxides and their corresponding methoxyamine derivatives. These profluorescent nitroxide probes possess strongly suppressed fluorescence, which can be revealed upon reduction or reaction with other radicals. Examination of the pentafluorophenylhydrazine reduction of the prepared probes using tandem EPR and fluorescence spectroscopy demonstrated that the asymmetric bis-β-substituted probe 9 (λem = 603 nm) was reduced the fastest, however, the greatest difference in fluorescence emission between the nitroxide and its reduced hydroxylamine analogue was observed for probe 7 (λem = 570 nm). The significant difference in fluorescence output between the nitroxides and their corresponding diamagnetic derivatives makes these probes ideal tools for imaging reactive oxygen species in biological systems

Extreme ultraviolet (EUV) degradation of poly(olefin sulfone)s : towards applications as EUV photoresists

Poly(olefin sulfone)s, formed by the reaction of sulfur dioxide (SO2) and an olefin, are known to be highly susceptible to degradation by radiation and thus have been identified as candidate materials for chain scission-based extreme ultraviolet lithography (EUVL) resist materials. In order to investigate this further, the synthesis and characterisation of two poly(olefin sulfone)s namely poly(1-pentene sulfone) (PPS) and poly(2-methyl-1-pentene sulfone) (PMPS), was achieved and the two materials were evaluated for possible chain scission EUVL resist applications. It was found that both materials possess high sensitivities to EUV photons; however; the rates of outgassing were extremely high. The only observed degradation products were found to be SO2 and the respective olefin suggesting that depolymerisation takes place under irradiation in a vacuum environment. In addition to depolymerisation, a concurrent conversion of SO2 moieties to a sulfide phase was observed using XPS