Surface structure of thin asymmetric PS-b-PMMA diblock copolymers investigated by atomic force microscopy

Asymmetric poly(styrene-b-methyl methacrylate) (PS-b-PMMA) diblock copolymers of molecular weight M-n = 29,700g mol(-1) (M-PS = 9300 g mol(-1) M-PMMA = 20,100 g mol(-1), PD = 1.15, chi(PS) = 0.323, chi(PMMA) = 0.677) and M-n = 63,900 g mol(-1) (M-PS = 50,500 g mol(-1), M-PMMA = 13,400 g mol(-1), PD = 1.18, chi(PS) = 0.790, chi(PMMA) = 0.210) were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization. Atomic force microscopy (AFM) was used to investigate the surface structure of thin films, prepared by spin-coating the diblock copolymers on a silicon substrate. We show that the nanostructure of the diblock copolymer depends on the molecular weight and volume fraction of the diblock copolymers. We observed a perpendicular lamellar structure for the high molar mass sample and a hexagonal-packed cylindrical patterning for the lower molar mass one. Small-angle X-ray scattering investigation of these samples without annealing did not reveal any ordered structure. Annealing of PS-b-PMMA samples at 160 degrees C for 24 h led to a change in surface structure.

Characterization and antimicrobial efficacy against E. coli of a helium/air plasma at atmospheric pressure created in a plastic package

A plasma source, sustained by the application of a floating high voltage (±15 kV) to parallel-plate electrodes at 50 Hz, has been achieved in a helium/air mixture at atmospheric pressure (P = 105 Pa) contained in a zip-locked plastic package placed in the electrode gap. Some of the physical and antimicrobial properties of this apparatus were established with a view to ascertain its performance as a prototype for the disinfection of fresh produce. The current–voltage (I–V) and charge–voltage (Q–V) characteristics of the system were measured as a function of gap distance d, in the range (3 × 103 ≤ Pd ≤ 1.0 × 104 Pa m). The electrical measurements showed this plasma source to exhibit the characteristic behaviour of a dielectric barrier discharge in the filamentary mode and its properties could be accurately interpreted by the two-capacitance in series model. The power consumed by the discharge and the reduced field strength were found to decrease quadratically from 12.0 W to 4.5 W and linearly from 140 Td to 50 Td, respectively, in the range studied. Emission spectra of the discharge were recorded on a relative intensity scale and the dominant spectral features could be assigned to strong vibrational bands in the 2+ and 1− systems of N2 and ${\rm N}_2^+$ , respectively, with other weak signatures from the NO and OH radicals and the N+, He and O atomic species. Absolute spectral intensities were also recorded and interpreted by comparison with the non-equilibrium synthetic spectra generated by the computer code SPECAIR. At an inter-electrode gap of 0.04 m, this comparison yielded typical values for the electron, vibrational and translational (gas) temperatures of (4980 ± 100) K, (2700 ± 200) K and (300 ± 100) K, respectively and an electron density of 1.0 × 1017 m−3. A Boltzmann plot also provided a value of (3200 ± 200 K) for the vibrational temperature. The antimicrobial efficacy was assessed by studying the resistance of both Escherichia coli K12 its isogenic mutants in soxR, soxS, oxyR, rpoS and dnaK selected to identify possible cellular responses and targets related with 5 min exposure to the active gas in proximity of, but not directly in, the path of the discharge filaments. Both the parent strain and mutants populations were significantly reduced by more than 1.5 log cycles in these conditions, showing the potential of the system. Post-treatment storage studies showed that some transcription regulators and specific genes related to oxidative stress play an important role in the E. coli repair mechanism and that plasma exposure affects specific cell regulator systems.

Square planar mononuclear Pd(II) complexes of substituted 2-(pyrazole-1-yl)phenylamines with a helical twist

X-ray crystal structure shows that 3,5-dimethyl-1-(2-nitrophenyl)-1H-pyrazole (DNP) belongs to the rare class of helically twisted synthetic organic molecules. Hydrogenation of DNP gives 2-(3,5-dimethylpyrazole-1-yl)phenylamine (L) which on methylation yields [2-(3,5-dimethylpyrazole-1-yl)phenyl]dimethylamine (L'). Two Pd(II) complexes, PdLCl2 (1) and PdL'Cl-2 (2), are synthesized and characterized by NMR. X-ray crystallography reveals that 1 and 2 are unprecedented square planar complexes which possess well discernible helical twists. (C) 2007 Elsevier B.V. All rights reserved.

Mononuclear Pt(II) and Pd(II) 1,4-dithiolato complexes. Crystal structures of [Pt((−) DIOS) (PPh3)2] and [Pd(S(CH2) 4S)(Ph2P(CH2) 3PPh2)]. Application in styrene hydroformylation

Addition of 1,4-dithiols to dichloromethane solutions of [PtCl2(P-P)] (P-P = (PPh3)2, Ph2P(CH2)3PPh2, Phd2P(CH2)4PPh2; 1,4-dithiols = HS(CH2)4SH, (−)DIOSH2 (2,3-O-isopropylidene-1,4-dithiol-l-threitol), BINASH2 (1,1′-dinaphthalene-2,2′-dithiol)) in the presence of NEt3 yielded the mononuclear complexes [Pt(1,4-dithiolato)(P-P)]. Related palladium(II) complexes [Pd(dithiolato)(P-P)] (P-P=Ph2P(CH2)3PPh2, Ph2P(CH2)4PPh2; dithiolato = −S(CH2)4S−, (−)-DIOS) were prepared by the same method. The structure of [Pt((−)DIOS)(PPh3)2] and [Pd(S(CH2)4S)(Ph2P(CH2)3PPh2)] complexes was determined by X-ray diffraction methods. Pt—dithiolato—SnC12 systems are active in the hydroformylation of styrene. At 100 atm and 125°C [Pt(dithiolate)(P-P)]/SnCl2 (Pt:Sn = 20) systems provided aldehyde conversion up to 80%.

Model catalyst studies of the strong metal-support interaction: Surface structure identified by STM on Pd nanoparticles on TiO2(110)

Model catalysts of Pd nanoparticles and films on TiO2 (I 10) were fabricated by metal vapour deposition (MVD). Molecular beam measurements show that the particles are active for CO adsorption, with a global sticking probability of 0.25, but that they are deactivated by annealing above 600 K, an effect indicative of SMSI. The Pd nanoparticles are single crystals oriented with their (I 11) plane parallel to the surface plane of the titania. Analysis of the surface by atomic resolution STM shows that new structures have formed at the surface of the Pd nanoparticles and films after annealing above 800 K. There are only two structures, a zigzag arrangement and a much more complex "pinwheel" structure. The former has a unit cell containing 7 atoms, and the latter is a bigger unit cell containing 25 atoms. These new structures are due to an overlayer of titania that has appeared on the surface of the Pd nanoparticles after annealing, and it is proposed that the surface layer that causes the SMSI effect is a mixed alloy of Pd and Ti, with only two discrete ratios of atoms: Pd/Ti of 1: 1 (pinwheel) and 1:2 (zigzag). We propose that it is these structures that cause the SMSI effect. (c) 2005 Elsevier Inc. All rights reserved.

Chemical composition and reactivity of water on clean and oxygen-covered Pd{111}

The chemical composition and dissociation behaviour of water adsorbed on clean and oxygen pre-covered Pd{111} was studied using high-resolution time-resolved and temperature-programmed X-ray photoelectron spectroscopy. We find that water remains intact at all temperatures up to desorption on the clean surface and at high oxygen coverage(0.69 ML) when a surface oxide is formed. The highest desorption peaks occur at 163 K from the clean surface and at 172 K from the surface oxide. At the intermediate coverage of 0.20 ML oxygen reacts with coadsorbed water at 155 K, to generate a mixed H2O/OH layer exhibiting a (root 3- x root 3)R30 degrees diffraction pattern, which is stable up to 177 K. The measured ratio between intact water and the hydroxyl species in this layer varies between 1.5 and 2 depending on temperature. (C) 2008 Elsevier B.V. All rights reserved.

Molecular guided catalytic hydrogenation by micelle-hosted Pd nanoparticle in supercritical CO2

Homogeneous dispersion of microemulsion containing palladium nanoparticles in scCO(2) is, for the first time, observed via sapphire window reactor and these particles show an unusual reluctance for double bond hydrogenation of citral aldehyde at hydrophobic end rather than hydrophilic end (high regioselectivity) owing to the unique micelle environment in supercritical carbon dioxide that guide a head-on attack of the molecule.

Micelle-hosted bimetallic Pd-Ru nanoparticle for in situ catalytic hydrogenation in supercritical CO2

Bimetallic Pd-Ru nanoparticles of different elemental ratios are prepared via in situ reduction of their simple salts in reverse micelles in supercritical carbon dioxide (scCO(2)). The optimised Pd:Ru (1: 1) nanoparticle shows the highest activity for hydrogenation of functionalised alkene under mild conditions, which can be easily recycled under the reaction conditions without use of organic solvent. (c) 2006 Elsevier B.V. All rights reserved.

Interaction of 6,6′′-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)-2,2′:6′,2′′-terpyridine (CyMe4-BTTP) with some trivalent ions such as lanthanide(iii) ions and americium(iii)

The new ligand 6,6 ''-bis(5,5,8,8-tetramethyl-5,6,7,8-tetrahydro-1,2,4-benzotriazin-3-yl)2,2':6 ',2 ''-terpyridine (CyMe4-BTTP) has been synthesized in 4 steps from 2,2':6',2 ''-terpyridine. Detailed NMR and mass spectrometry studies indicate that the ligand forms 1 : 2 complexes with lanthanide(III) perchlorates where the aliphatic rings are conformationally constrained whereas 1 : 1 complexes are formed with lanthanide(III) nitrates where the rings are conformationally mobile. An optimized structure of the 1 : 2 solution complex with Yb(III) was obtained from the relative magnitude of the induced paramagnetic shifts. X-Ray crystallographic structures of the ligand and of its 1 : 1 complex with Y(III) were also obtained. The NMR and mass spectra of [Pd(CyMe4-BTTP)](n)(2n+) are consistent with a dinuclear double helical structure (n = 2). In the absence of a phase-modifier, CyMe4-BTTP in n-octanol showed a maximum distribution coefficient of Am(III) of 0.039 (+/-20%) and a maximum separation factor of Am(III) over Eu(III) of 12.0 from nitric acid. The metal(III) cations are extracted as the 1 : 1 complex from nitric acid. The generally low distribution coefficients observed compared with the BTBPs arise because the 1 : 1 complex of CyMe4-BTTP is considerably less hydrophobic than the 1 : 2 complexes formed by the BTBPs. In M(BTTP)(3+) complexes, there is a competition between the nitrate ions and the ligand for the complexation of the metal.

A novel heteroditopic terpyridine-pincer ligand as building block for mono- and heterometallic Pd(II) and Ru(II) complexes

A palladium-catalyzed Stille coupling reaction was employed as a versatile method for the synthesis of a novel terpyridine-pincer (3, TPBr) bridging ligand, 4'-{4-BrC6H2(CH2NMe2)(2)-3,5}-2,2':6',2 ''-terpyridine. Mononuclear species [PdX(TP)] (X = Br, Cl), [Ru(TPBr)(tpy)](PF6)(2), and [Ru(TPBr)(2)](PF6)(2), synthesized by selective metalation of the NCNBr-pincer moiety or complexation of the terpyridine of the bifunctional ligand TPBr, were used as building blocks for the preparation of heterodi- and trimetallic complexes [Ru(TPPdCl)(tpy)](PF6)(2) (7) and [Ru(TPPdCl)(2)]-(PF6)(2) (8). The molecular structures in the solid state of [PdBr(TP)] (4a) and [Ru(TPBr)(2)](PF6)(2) (6) have been determined by single-crystal X-ray analysis. Electrochemical behavior and photophysical properties of the mono-and heterometallic complexes are described. All the above di- and trimetallic Ru complexes exhibit absorption bands attributable to (MLCT)-M-1 (Ru -> tpy) transitions. For the heteroleptic complexes, the transitions involving the unsubstituted tpy ligand are at a lower energy than the tpy moiety of the TPBr ligand. The absorption bands observed in the electronic spectra for TPBr and [PdCl(TP)] have been assigned with the aid of TD-DFT calculations. All complexes display weak emission both at room temperature and in a butyronitrile glass at 77 K. The considerable red shift of the emission maxima relative to the signal of the reference compound [Ru(tpy)(2)](2+) indicates stabilization of the luminescent (MLCT)-M-3 state. For the mono- and heterometallic complexes, electrochemical and spectroscopic studies (electronic absorption and emission spectra and luminescence lifetimes recorded at room temperature and 77 K in nitrile solvents), together with the information gained from IR spectroelectrochemical studies of the dimetallic complex [Ru(TPPdSCN)(tpy)](PF6)(2), are indicative of charge redistribution through the bridging ligand TPBr. The results are in line with a weak coupling between the {Ru(tpy)(2)} chromophoric unit and the (non)metalated NCN-pincer moiety.

Structures of Pd(CN)2and Pt(CN)2: intrinsically nanocrystalline materials?

Analysis and modeling of X-ray and neutron Bragg and total diffraction data show that the compounds referred to in the literature as “Pd(CN)2”and“Pt(CN)2” are nanocrystalline materials containing of small sheets of vertex-sharing square-planar M(CN)4 units, layered in a disordered manner with an intersheet separation of 3.44 A at 300 K. The small size of the crystallites means that the sheets’ edges form a significant fraction of each material. The Pd(CN)2 nanocrystallites studied using total neutron diffraction are terminated by water and the Pt(CN)2 nanocrystallites by ammonia, in place of half of the terminal cyanide groups, thus maintaining charge neutrality. The neutron samples contain sheets of approximate dimensions 30 A x 30 A. For sheets of the size we describe, our structural models predict compositions of Pd(CN)2-xH2O and Pt(CN)2-yNH3 (x = y = 0.29). These values are in good agreement with those obtained from total neutron diffraction and thermal analysis, and are also supported by infrared and Raman spectroscopy measurements. It is also possible to prepare related compounds Pd(CN)2-pNH3 and Pt(CN)2-qH2O, in which the terminating groups are exchanged. Additional samples showing sheet sizes in the range 10 A x 10 A (y = 0.67) to 80 A x 80 A (p = q = 0.12), as determined by X-ray diffraction, have been prepared. The related mixed-metal phase, Pd1/2Pt1/2(CN)2-qH2O(q = 0.50), is also nanocrystalline (sheet size 15 A x 15 A). In all cases, the interiors of the sheets are isostructural with those found in Ni(CN)2. Removal of the final traces of water or ammonia by heating results in decomposition of the compounds to Pd and Pt metal, or in the case of the mixed-metal cyanide, the alloy, Pd1/2Pt1/2, making it impossible to prepare the simple cyanides, Pd(CN)2, Pt(CN)2 or Pd1/2Pt1/2(CN)2, by this method.

Structures, reactivity, and catalytic activity of dithiolato-bridged heterobimetallic MRh (M = Pt, Pd) complexes

Heterobimetallic complexes [(P−P)Pt(μ-S−S)Rh(cod)]ClO4 (P−P = (PPh3)2, Ph2P(CH2)3PPh2 (dppp), and Ph2P(CH2)4PPh2 (dppb); S−S = -S(CH2)2S- (EDT), -S(CH2)3S- (PDT), -S(CH2)4S- (BDT), cod = 1,5-cyclooctadiene) reacted with CO to form the carbonyl complexes [(P−P)Pt(μ-S−S)Rh(CO)2]ClO4 and then with PR3 ligands to give [(P−P)Pt(μ-S−S)Rh(CO)(PR3)]ClO4. The binuclear framework of these cod complexes was maintained in the reactions reported. The cod complexes were tested as catalyst precursors in the hydroformylation of styrene. HPNMR in situ studies showed that mononuclear species formed under catalytic conditions.

Sterically hindered metal alkenyls. Part 1. Synthesis, reactions, and crystal and molecular structures of some palladium and platinum σ-alkenyls

The compounds trans-[PtBr{C(C10H15)CH2}(PEt3)2](1)(C10H15= adamant-1-yl), trans-[MBr{C(C10H7)CMe2}(PEt3)2][M = Pd (2) or Pt (3); C10H7= naphth-1-yl], and trans-[MBr{C(Ph)CMe2}(PEt3)2][M = Pd (4) or Pt (5)] have been prepared from Grignard [for (2) and (3)] or lithium reagents [for (1), (4), and (5)] and appropriate dichlorobis(phosphine)metal derivatives. Full single-crystal X-ray data are reported for (1) and (3), and reveal unusually long Pt–C(sp2) bonds. Insertion reactions into these M–C bonds occur with MeNC [for (1), (3), and (5)], and with CO [for (1) and (3)]; the latter, the first reported insertion into a Pt–C(sp2) bond, occurs under mild conditions as expected for the abnormally long M–C bonds.

Endothelin-converting enzyme-1 regulates trafficking and signalling of the neurokinin 1 receptor in endosomes of myenteric neurones

Neuropeptide signalling at the plasma membrane is terminated by neuropeptide degradation by cell-surface peptidases, and by beta-arrestin-dependent receptor desensitization and endocytosis. However, receptors continue to signal from endosomes by beta-arrestin-dependent processes, and endosomal sorting mediates recycling and resensitization of plasma membrane signalling. The mechanisms that control signalling and trafficking of receptors in endosomes are poorly defined. We report a major role for endothelin-converting enzyme-1 (ECE-1) in controlling substance P (SP) and the neurokinin 1 receptor (NK(1)R) in endosomes of myenteric neurones. ECE-1 mRNA and protein were expressed by myenteric neurones of rat and mouse intestine. SP (10 nM, 10 min) induced interaction of NK(1)R and beta-arrestin at the plasma membrane, and the SP-NK(1)R-beta-arrestin signalosome complex trafficked by a dynamin-mediated mechanism to ECE-1-containing early endosomes, where ECE-1 can degrade SP. After 120 min, NK(1)R recycled from endosomes to the plasma membrane. ECE-1 inhibitors (SM-19712, PD-069185) and the vacuolar H(+)ATPase inhibitor bafilomycin A(1), which prevent endosomal SP degradation, suppressed NK(1)R recycling by >50%. Preincubation of neurones with SP (10 nM, 5 min) desensitized Ca(2+) transients to a second SP challenge after 10 min, and SP signals resensitized after 60 min. SM-19712 inhibited NK(1)R resensitization by >90%. ECE-1 inhibitors also caused sustained SP-induced activation of extracellular signal-regulated kinases, consistent with stabilization of the SP-NK(1)R-beta-arrestin signalosome. By degrading SP and destabilizing endosomal signalosomes, ECE-1 has a dual role in controlling endocytic signalling and trafficking of the NK(1)R: promoting resensitization of G protein-mediated plasma membrane signalling, and terminating beta-arrestin-mediated endosomal signalling.