Synthesis of megadalton stereoregular ring-substituted poly(phenylacetylene)s by a rhodium(<scp>i</scp>) catalyst with a N-functionalized hemilabile phosphine ligand

The cationic compound [Rh(nbd){κ2P,N-Ph2P(CH2)3NMe2}][BF4] efficiently catalyzes the polymerization of a series of ring-substituted phenylacetylene derivatives, R-C6H4–C[triple bond, length as m-dash]CH with groups of different electronic and steric properties at the para (R = F, CF3, Me, Bu, tBu, OMe, OBu) and meta (R = OMe) positions to give highly stereoregular ring-substituted poly(phenylacetylene)s with a cis-transoidal configuration of very high molar mass and moderate dispersities. The polymers have been characterized by size exclusion chromatography (SEC-MALS), NMR, DSC and TGA. The polymerization of phenylacetylene and 1-ethynyl-3-methoxybenzene gives megadalton poly(phenylacetylene)s, while the polymerization of 1-ethynyl-4-methoxybenzene and 1-(tert-butyl)-4-ethynylbenzene gives ultra-high molecular weight poly(phenylacetylene)s with Mn of 1.70 × 106 and 2.72 × 106, respectively. The electronic effect of the substituent strongly influences the catalytic activity. Phenylacetylene derivatives with an electron-withdrawing substituent in para position polymerize faster than those with an electron-donating substituent

Tailor-made poly(vinylidene sulfide)s by Rh(I)–NHC catalyzed regioselective thiol-yne click polymerization

The [Rh(μ-Cl)(IPr)(η2-coe)]2/pyridine system efficiently catalyzes the polyhydrothiolation of a series of dialkynes with dithiols, producing sulfur-rich poly(vinylidene sulfide)s with a typical Mw in the range 20.000–124.000 and vinylidene content of 75–87%. A combination of flexible aliphatic dithiols, including 1,6-hexanedithiol and 2,2′-(ethylendioxy)diethanethiol, and the rigid aromatic dithiol 4,4′-thiobisbenzenethiol, with rigid aromatic dialkynes, 1,3-diethynylbenzene and 1,4-diethynylbenzene, and flexible dialkynes, including propargyl ether and 1,7-octadiyne, have been used to prepare poly(vinylidene sulfide)s. The copolymerization of flexible dithiols with rigid aromatic dialkynes or vice versa results in high molecular weight polymers, Mw up to 259.000, with low polydispersities. However, polyhidrothiolation of flexible dialkynes with flexible dithiols is much less efficient and usually results in the formation of oligomers. The interplay of the IPr and pyridine ligands on the RhCl(IPr)(py)(η2-coe) catalyst, which controls the regioselectivity of the alkyne insertion step towards the branched vinyl sulfide, is key in the preparation of these poly(vinylidene sulfide)s

Origin of the Urease Inhibition of Metschnikowia pulcherrima Extracts: Comparative Assays with Synthetic Pulcherriminic Acid and Cyclo-dileucine

The objective of this work was to determine whether pulcherriminic acid was responsible for the urease inhibition activity of the extracts of the yeast Metschnikowia pulcherrima. Pulcherriminic acid was synthesized through a seven-step pathway from l-leucine, starting with the thermal cyclodimerization of l-leucine to the corresponding 2,5-diketopiperazine, followed by oxidation to the 2,5-dichloropyrazine through three consecutive steps without purification of the intermediates, oxidation to the corresponding di-N-oxide, dechlorination by nucleophilic aromatic substitution with benzyloxide, and deprotection with trifluoroacetic acid without isolation of an intermediate. The urease inhibition assay showed 57 ± 2.3% inhibition of the urease activity at 500 ppm of pulcherriminic acid, much lower than the percent inhibition obtain with the extract, in which pulcherriminic acid was not detected. The cyclic dimer of l-leucine was present in the extract, and its inhibitory capacity was also tested, showing a percent inhibition of 56.1 ± 6.11% of the urease activity at 400 ppm, again much lower than the percent inhibition of the extract. This work demonstrates that the inhibitory capacity of the extracts of the yeast M. pulcherrima is not due to either only pulcherriminic acid or only its cyclic dipeptide precursor

Laponite as carrier for controlled in vitro delivery of dexamethasone in vitreous humor models

Laponite clay is able to retain dexamethasone by simple physisorption, presumably accomplished by hydrogen bonding formation and/or complexation with sodium counterions, as shown by solid state NMR. The physisorption can be somehow modulated by changing the solvent in the adsorption process. This simple system is able to deliver dexamethasone in a controlled manner to solutions used as models for vitreous humor. The proven biocompatibility of laponite as well as its transparency in the gel state, together with the simplicity of the preparation method, makes this system suitable for future in vivo tests of ophthalmic treatment.This study was supported by the Instituto de Salud Carlos III (project PI12/02285) and authors would like to acknowledge the financial support received from Diputación General de Aragón (E11 Group co-financed by the European Regional Development Funds).Peer Reviewe

Antibiotic-eluting orthopedic device to prevent early implant associated infections: Efficacy, biocompatibility and biodistribution studies in an ovine model

Infection of orthopedic devices is a major complication in the postsurgical period generating important health issues and economic consequences. Prevention strategies could be based on local release of antibiotics from the orthopedic device itself to avoid adhesion and growth of bacteria. The purpose of this work is to demonstrate the efficiency to prevent these infections by a cefazolin-eluting, perforated stainless steel implant in an in vivo ovine model. The device was placed in the tibia of sheep, one group receiving cefazolin-loaded implants whereas the control group received empty implants. All implants were experimentally infected by direct inoculation of Staphylococcus aureus ATCC 6538. In vitro cytotoxicological studies were also performed to check the effect of antibiotic on cell viability, integrity, and cycle. Results showed that sheep receiving cefazolin-loaded devices were able to avoid implant-associated infections, with normal tissue healing process. The antibiotic release followed a local concentric pattern as demonstrated by high-performance liquid chromatography detection in tissues. The in vitro results indicate the lack of relevant cytotoxic effects for the maximum antibiotic concentration released by the device. These results demonstrate the efficiency and safety of cefazolin-eluting implants in an ovine model to prevent early postsurgical infections of orthopedic devices.CAPES foundation and the Ministry of Education of Brazil are gratefully acknowledged. We thank the help of technicians at the LMA-INA and Microscopy, Cytometry, and Cell Culture Core Units from IACS/IIS Aragon for their support and expertise.Peer reviewe

Copolyimide mixed matrix membranes with oriented microporous titanosilicate JDF-L1sheet particles

JDF-L1 is a microporous titanosilicate exhibiting a layer structure with pore size of about 3 Å. It is consequently an attractive material to separate H2-containing mixtures. This is the reason why JDF-L1, after disaggregation by means of hexadecyltrimethylammonium surfactant, has been combined with a carboxyl group containing copolyimide (6FDA-4MPD/6FDA-DABA 4:1) to produce mixed matrix membranes, which were applied to the separation of H2/CH4 and O2/N2 mixtures. Additionally, due to the sheet growth habit of JDF-L1 crystals, a preferential horizontal orientation of the JDF-L1 filler particles dispersed into the polymer was expected. This preferential orientation, which was achieved when the polymer solution concentration used during the membrane casting process was relatively low, has been studied by optical and electronic microscopy, X-ray diffraction and polarized Raman spectroscopy. A quantitative analysis was carried out applying Cussler's model for mixedmatrixmembranes with oriented flakes.We gratefully thank the German Academic Exchange Service (DAAD) for the financial support within the budget of the project related person exchange program (PPP, 0804142). Also, financial support from the Spanish Science and Innovation Ministry (MAT2007-61028, CIT-420000-2009-32, and HD2008-0001) and the Aragon Government (PI035/09) is gratefully acknowledged.Peer Reviewe

Effect of the reaction conditions on the epoxidation of alkenes with hydrogen peroxide catalyzed by silica-supported titanium derivatives

Silica-supported titanium catalysts are active in the epoxidation of cyclohexene with diluted hydrogen peroxide at 80°C. At low H2O2/Ti ratio the contribution of the direct mechanism of epoxidation is important, around 40% of the productive H2O2 conversion and 60% of the epoxidation reaction. However, the increase in H2O2/Ti ratio modifies these results. The contribution of the direct epoxidation to H2O2 conversion is reduced to 20–30%, whereas contribution to epoxidation is kept in the range 40–60%. Neither the silanization of the silica surface nor the substitution of the isopropoxy groups by tartaric acid improves the behavior of the solid in these conditions. However, the simultaneous variation in hydrophilic character of the surface and titanium environment increases the contribution of the direct epoxidation. In contrast, the increase in H2O2/Ti ratio reduces the epoxide hydrolysis. The catalysts lose some titanium after reaction, but in general they show higher stability than closely related solids. The activity for direct and radical contributions changes after recovering, showing the important change in nature of the catalytic sites, which are not easily regenerated by extensive washing with different solvents. In any case, with cyclooctene, an alkene that does not form radicals, the activity for direct epoxidation shows a decline in every recycling but final turnover numbers are similar in the first three runs, showing high stability of the titanium on the solid.This work was made possible by the generous financial support of the C.I.C.Y.T. (Project MAT99-1176)Peer reviewe

Cationic rhodium complexes with hemilabile phosphine ligands as polymerization catalyst for high molecular weight stereoregular poly (phenylacetylene)

A series of cationic complexes [Rh(diene){Ph2P(CH 2)nZ}][BF4] (diene = 1,5-cyclooctadiene (cod), tetrafluorobenzobarralene (tfb) or 2,5-norbonadiene (nbd)) containing functionalized phosphine ligands of the type Ph2P(CH 2)nZ (n = 2, or 3; Z = OMe, NMe2, SMe) have been prepared and characterized. These complexes have shown a great catalytic activity for phenylacetylene (PA) polymerization. Catalyst screening and optimization have determined the superior performance of complexes containing a P,Nfunctionalyzed phosphine ligand, [Rh(diene){Ph2P(CH 2)3NMe2}][BF4] (diene = cod, 5; tfb, 6; nbd, 7), and tetrahydrofuran as solvent. The influence of the diene ligand and the effect of temperature, PA to rhodium molar ratio, addition of water or a cocatalyst, DMAP (4-(dimethylamino)pyridine), have been studied. Diene ligands strongly influence the catalytic activity and complexes 6 and 7 are far more active than 5. Both complexes gave poly(phenylacetylene) (PPA) with very high number-average molecular weights (Mn) of 970000 (6) and 1420000 (7). The addition of DMAP resulted in a dramatic drop in the PPA molecular weight, 106 000 (6) and 233 000 (7). The PPA obtained with the system 6/DMAP showed a narrow molecular weight distribution (MwMn = 1.20) and incremental monomer addition experiments have demonstrated the quasi-living nature of the polymerization reaction under these conditions. The PPA obtained with these catalytic systems has been characterized by 1H and 13C(1H) NMR spectroscopy and shows a cis-transoidal configuration with a high level of steroregularity (cis content superior to 99%). TGA, DSC, and IR analysis have revealed a thermal cis↔ trans isomerization process at 150̈C. The mechanism of PA polymerization has been investigated by spectroscopic means, under stoichiometric and catalytic conditions, and shows an active role of the hemilabile phosphine ligand both in the initiation and, probably, in the termination steps through proton transfer processes involving the hemilabile fragment of the ligand. © 2009 American Chemical Society.The financial support from Ministerio de Educación y Ciencia (MEC/FEDER) is gratefully acknowledged (Project CTQ2006-03973/BQU). MIB thanks a graduate research fellowship.Peer Reviewe

Catalytic sites in silica-supported titanium catalysts: silsesquioxane complexes as models

The number of Sisingle bondOsingle bondTi bonds in silica-supported titanium catalysts is an important parameter that affects activity and selectivity. Although comparisons between different catalysts can be made by infrared spectroscopy, estimation of the contribution of the different species is a difficult task. UV spectroscopy has been used to characterize three different titanium–silsesquioxane complexes. The wavelength in solution is highly dependent on the concentration, and broad bands are obtained by DRUV, at wavelengths that correlate with the number of Sisingle bondOsingle bondTi bonds. The deconvolution of the DRUV spectra of silica-supported titanium catalysts allows identification of the three types of tetrahedral (pentacoordinated) species, together with octahedral species. These results correlate well with the known silanol densities of the different silica supports, and the catalytic activity and selectivity for epoxidation are clearly favored by the reduction in octahedral titanium and the increase in the number of tripodal species.This work was made possible by the generous financial support of the CICYT (Project PPQ2002-04012) and the Diputación General de Aragón.Peer reviewe