Chromium and molybdenum pentacarbonyl complexes of phosphinocarbodithioates: synthesis, molecular structure and behaviour in RAFT polymerisation

Molybdenum and chromium pentacarbonyldiphenylphosphinocarbodithioate complexes have been prepared in a one‐pot reaction from the corresponding metallocarbonyldiphenylphosphine. The complexes have been characterised by IR, ¹H, ³¹P and ¹³C NMR spectroscopies and by mass spectrometry. The solid‐state structures of [Cr(CO)₅{PPh₂CS₂CH(Ph)CH₃}] ( 1 ) and [Mo(CO)₅{PPh₂CS₂CH(Ph)CH₃}] ( 2 ) are reported. Compounds 1 and 2 are isostructural and crystallise in the triclinic P$\bar 1Molybdenum and chromium pentacarbonyldiphenylphosphinocarbodithioate complexes have been prepared in a one-pot reaction from the corresponding metallocarbonyldiphenylphosphine. The complexes have been characterised by IR, (1)H, (31)P and (13)C?NMR spectroscopies and by mass spectrometry. The solid-state structures of [Cr(CO)(5){PPh(2)CS(2)CH(Ph)CH(3)}] (1) and [Mo(CO)(5){PPh(2)CS(2)CH(Ph)CH(3)}] (2) are reported. Compounds 1 and 2 are isostructural and crystallise in the triclinic P1 space group. These new organometallic compounds are highly efficient reversible chain-transfer agents for reversible addition-fragmentation chain-transfer (RAFT) polymerisation of styrene (St) and n-butyl acrylate (nBA), with controlled number-average molar mass values and narrow dispersities (<1.2). The controlled character of the polymerisation was further exemplified by the synthesis of St and nBA diblock copolymers.     

One-electron reduction of superoxide radical-anions by 3-alkylpolyhydroxyflavones in micelles. Effect of antioxidant alkyl chain length on micellar structure and reactivity

In micellar solutions, one-electron reduction of (*)O 2 (-) radical-anions by 3-alkylpolyhydroxyflavones (FnH) with alkyl chains of n = 1, 4, 6, 10 carbons produces phenoxyl radicals ( (*)Fn) identical to those obtained by one-electron oxidation by (*)Br 2 (-) radical-anions or by repair of tryptophan radicals. In cetyltrimethylammonium bromide (CTAB), F1H localizes in the Stern layer, and alkyl chains of other FnH solubilize in the hydrophobic interior, interacting with cetyl tails. This interaction produces more compact micelles with lower intramicellar fluidity, as suggested by the increase in the pseudo-first-order rate constant of (*)Fn formation ( k 1) from approximately 390 s (-1) for n = 1 to 610 s (-1) for n = 10, leading to an intramicellar bimolecular rate constant of 1 x 10 (5) M (-1) s (-1). Additionally, (*)F1 and (*)F4 decay by intermicellar bimolecular reaction (2 k = 20 and 2 x 10 (5) M (-1) s (-1), respectively) whereas other (*)Fn radicals are stable over seconds due to increased localization with regards to the Stern layer. In contrast, the thick uncharged hydrophilic palisade layer and the compact hydrophobic core of Triton X100 micelles are responsible for a much higher microviscosity resulting in a decrease in k 1 from approximately 15.6 s (-1) for n = 1 to 9.6 s (-1) for n = 10.     

Synthesis, cellular uptake of, and cell photosensitization by a porphyrin bearing a quinoline group

A tetraphenyl porphine linked to a 7-chloroquinoline (5,10,15,20-tetraphenyl-1-3-[4-(4-aminobutyl)7-chloroquinoline] propioamidoporphine, TPPQ) was synthesized and examined as a potential photosensitizer for photodynamic therapy (PDT) of proliferative diseases. With respect to haematoporphyrin, TPPQ is a good in vitro photodynamic sensitizer producing singlet oxygen in 1% Triton X100 solutions. As with other hydrophobic porphyrins used in PDT, blood lipoproteins strongly bind TPPQ. Thus one low density lipoprotein (LDL) can incorporate 25 TPPQ molecules and 17 TPPQ molecules are taken up by one high density lipoprotein (HDL). Cell delivery of TPPQ using HDL or human serum albumin (HSA) as carrier is rather weak. However, an efficient TPPQ delivery to human skin fibroblasts is observed, partly aided by receptor-mediated endocytosis of LDL. Fluorescence spectroscopy shows that the cellular localization of TPPQ is both carrier and time dependent. During its delivery with LDL, TPPQ does not significantly impair the endocytosis of LDL-receptor complexes. After delivery with LDL, TPPQ is as efficient as other haematoporphyrin derivatives used in the PDT of cancers in photosensitizing human skin fibroblasts.     

A rare example of a rearrangement involving four structural isomers: alpha-phosphinonitrile/C-phosphinoketenimine/1-aza-4- phosphabutadiene/1,2-dihydro-1,2-azaphosphete

The stable compound [bis(dicyclohexylamino)phosphino](trimethylsilyl)-carbene (1) reacts with dimethyl cyanamide to afford the original 1,2-dihydro-1,2-azaphosphete 4a (51% yield). The surprising formation of this heterocycle involves the transient formation of a nitrile, a keteneimine, and a 1-aza-4 lambda 3-phosphabutadiene derivative. By using substituent effects and different synthetic routes, all of these structural isomers have been isolated.     

Alteration of the endocytotic pathway by photosensitization with fluoroquinolones

The endocytotic pathway is profoundly altered by the UVA-induced photosensitization of HS 68 fibroblasts by the fluoroquinolone (FQ) antibiotics lomefloxacin, BAYy 3118, norfloxacin and ciprofloxacin, which preferentially localize in lysosomes. The endocytosis of low-density lipoproteins (LDL) loaded with two carbocyanine dyes compatible for effective Forster-type resonance energy transfer (FRET), namely 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO) as the donor and 1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) as the acceptor, has been used as a model system. Binding of LDL to their cell surface receptors is impaired by irradiation with 10 J cm(-2) of UVA and/or treatment with 250 microM BAYy 3118 during 2 h. Perturbation of the plasma membrane by the FQ is revealed by the change in the rate of exchange of DiO from the LDL to the cell membrane as compared to untreated cells. The lysosomal degradation of LDL, demonstrated by the disappearance of FRET between DiO and DiI, is partly inhibited by the FQ. The actin filament network, involved in the fusion of mature endosomes with lysosomes, is readily destroyed upon photosensitization with the four FQ. However, actin depolymerization can be avoided by incubation of the cells with trans-epoxysuccinyl-1-leucylamido-(4-guanidino)butane, an inhibitor of lysosomal cathepsins prior to FQ photosensitization. All these data suggest that several components of the endocytotic pathway are impaired by photosensitization with these FQ.     

Self-assembly of solid-supported membranes using a triggered fusion of phospholipid-enriched proteoliposomes prepared from the inner mitochondrial membrane

A general procedure for the formation ofsolid-supported artificial membranes containing transmembrane proteins is reported. The main objective was to directly use the pool of proteins of the native biomembrane (here the inner membrane from mitochondria of human carcinogenic hepatic cells) and to avoid purification steps with detergent. Proteoliposomes of phospholipid-enriched inner membranes from mitochondria were tethered and fused onto a tailored surface via a streptavidin link. The failure of some preliminary experiments on membrane formation was attributed to strong nonspecific interactions between the solid surface and the protuberant hydrophilic parts of the transmembrane complexes. The correct loading of uniform membranes was performed after optimization of a tailored surface, covered with a grafted short-chain poly(ethylene glycol), so that nonspecific interactions are reduced. Step-by-step assembly of the structure and triggered fusion of the immobilized proteoliposomes were monitored by surface plasmon resonance and fluorescence photobleaching recovery, respectively. The long-range lateral diffusion coefficient (at 22 degrees C) for a fluorescent lipid varies from 2.5 x 10(-8) cm2 s(-1) for a tethered lipid bilayer without protein to 10(-9) cm2 s(-1) for a tethered membrane containing the transmembrane proteins of the respiratory chain at a protein area fraction of about 15%. The decrease in the diffusion coefficient in the tethered membrane with increase in protein area fraction was too pronounced to be fully explained by the theoretical models of obstructed lateral diffusion. Covalent tethering links with the solid are certainly involved in the decrease of the overall lateral mobility of the components in the supported membrane at the highest protein-to-lipid ratios.     

Overspeed burst of elastoviscoplastic rotating disks: Part II – Burst of a superalloy turbine disk

Burst of a turbo-engine disk in case of overspeed is investigated both from experimental and computational point of view. Two twin disks made of the same nickel based superalloy are tested. For the first one (B-disk), rotation rate in increased till burst. The second one (S-disk) is kept safe by stopping rotation just before burst, and unloading it to measure residual deformations. The material model parameters are deduced either from simple tension tests, or using an inverse method on the S-disk test. Two corresponding finite element simulations of the B-disk are then performed, using either an arc-length control method to overcome the limit point, or dynamic simulations. In both cases, the numerical burst rotation rate, associated with the loss of stability of the structure, is found to be in good agreement with the experimental result.     

Phosphonate‐terminated poly(vinyl acetate) synthesized by RAFT/MADIX polymerization

Four different xanthates containing either phosphonate or bisphosphonate moieties were synthesized with high degree of purity. These xanthates were used as chain transfer agents (CTA) in the RAFT/MADIX polymerization of vinyl acetate (VAc) to prepare end‐capped poly(VAc). The rate of VAc polymerization in the presence of these new CTAs was shown to be similar to that obtained with conventional xanthate, that is, (methyl ethoxycarbonothioyl) sulfanyl acetate. Good control of VAc polymerization was also obtained since the molecular weight increased linearly with monomer conversion for each phosphonate‐containing xanthate. Low‐PDI values were obtained, ascribed to efficient exchange during RAFT/MADIX polymerization. C_ex value was therefore calculated to about 25, based on RAFT/MADIX of VAc in the presence of rhodixan A1/VAc adduct. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Structure-activity relationships in hydroxy-2,3-diarylxanthone antioxidants. Fast kinetics spectroscopy as a tool to evaluate the potential for antioxidant activity in biological systems

A structure-activity relationship has been established for eight hydroxy-2,3-diarylxanthones (XH) bearing hydroxy groups on the two aryl rings. One-electron oxidation by superoxide radical-anions (˙O(2)(-)) and ˙Trp radicals as well as reaction with ˙CCl(3)O(2) and ˙CHCl(2)O(2) radicals demonstrates that two OH groups are required for efficient antioxidant reactivity in cetyltrimethylammonium bromide micelles. Hydroxy groups at the meta and para positions on either of the two phenyl rings confer enhanced reactivity, but XH bearing an OH at the para position of either phenyl ring is unreactive. While oxidation is favoured by OH in both meta and para positions of 2-aryl xanthone substituents, addition of a third and/or fourth OH enhances electron-donating capacity. In Cu(2+)-induced lipid peroxidation of human LDL, the lag period preceding the commencement of lipid peroxidation in the presence of XH bearing OH at meta and para positions on the 3-phenyl ring is extended to twice that observed with a comparable concentration of quercetin, a reference antioxidant. These antioxidants are also superior to quercetin in protecting human skin keratinocytes against tert-butylhydroperoxide-induced oxidative stress. While XH antioxidant activity in model biological systems is consistent with the structure-activity relationship, their response is also modulated by the localization of XH and by structural factors.