Miscibility studies in poly(methyl vinyl ether)/hydroxypropylcellulose binary system in aqueous solutions and solid state

The phase separation behaviour in aqueous mixtures of poly(methyl vinyl ether) and hydroxypropylcellulose has been studied by cloud points method and viscometric measurements. The miscibility of these blends in solid state has been assessed by infrared spectroscopy; methanol vapours sorption experiments and scanning electron microscopy. The values of Gibbs energy of mixing of the polymers and their blends with methanol as well as between each other were calculated. It was found that in solid state the polymers can interact with methanol very well but the polymer-polymer interactions are unfavourable. Although in aqueous solutions the polymers exhibit some intermolecular interactions their solid blends are not completely miscible. (C) 2005 Elsevier Ltd. All rights reserved.

Characterisation of blends based on hydroxyethylcellulose and maleic acid-alt-methyl vinyl ether

Hydrophilic polymeric films based on blends of hydroxyethylcellulose and maleic acid-co-methyl vinyl ether were produced by casting from aqueous solutions. The physicochemical properties of the blends have been assessed using Fourier transform infrared spectroscopy, thermal gravimetric analysis, differential scanning calorimetry, dielectric spectroscopy, etc. The pristine films exhibit complete miscibility due to the formation of intermacromolecular hydrogen bonding. The thermal treatment of the blend films leads to cross-linking via intermacromolecular esterification and anhydride formation. The cross-linked materials are able to swell in water and their swelling degree can be easily controlled by temperature and thermal treatment time. The formation of the crosslinks is apparent in the dynamic properties of the blends as observed through the mechanical relaxation and dielectric relaxation spectra. The dielectric characteristics of the material are influenced by the effects of change in the local structure of the blend on the ionic conduction processes and the rate of dipolar relaxation. Separation of these processes is attempted using the dielectric modulus method. Significant deviations from a simple additive rule of mixing on the activation energy are observed consistent with hydrogen bonding and crosslinking of the matrix. This paper indicates a method for the creation of films with good mechanical and physical characteristics by exposing the blends to a relatively mild thermal treatment.

Phorbol ester, but not ischemic preconditioning, activates protein kinase D in the rat heart

The signal transduction pathways that mediate the cardioprotective effects of ischemic preconditioning remain unclear. Here we have determined the role of a novel kinase, protein kinase D (PKD), in mediating preconditioning in the rat heart. Isolated rat hearts (n=6/group) were subjected to either: (i) 36 min aerobic perfusion (control); (ii) 20 min aerobic perfusion plus 3 min no-flow ischemia, 3 min reperfusion, 5 min no-flow ischemia, 5 min reperfusion (ischemic preconditioning); (iii) 20 min aerobic perfusion plus 200 nmol/l phorbol 12-myristate 13-acetate (PMA) given as a substitute for ischemic preconditioning. The left ventricle then was excised, homogenized and PKD immunoprecipitated from the homogenate. Activity of the purified kinase was determined following bincubation with [γ32P]-ATP±syntide-2, a substrate for PKD. Significant PKD autophosphorylation and syntide-2 phosphorylation occurred in PMA-treated hearts, but not in control or preconditioned hearts. Additional studies confirmed that recovery of LVDP was greater and initiation of ischemic contracture and time-to-peak contracture were less, in ischemic preconditioned hearts compared with controls (P<0.05). Our results suggest that the early events that mediate ischemic preconditioning in the rat heart occur via a PKD-independent mechanism.

Mechanisms of femtosecond laser-induced refractive index modification of poly(methyl methacrylate)

The mechanisms of refractive index change in poly(methyl methacrylate) by frequency doubled femtosecond laser pulses are investigated. It is demonstrated that positive refractive index modificaton can be caused by a combination of depolymerization and crosslinking.

Redox control of light-induced charge separation in a transition metal cluster: photochemistry of a methyl viologen-substituted [Os-3(CO)10(a-diimine)] cluster

Sub)picosecond transient absorption (TA) and time-resolved infrared (TRIR) spectra of the cluster [OS3(CO)(10-) (AcPy-MV)](2+) (the clication AcPy-MV = Acpy-MV2+ = [2-pyridylacetimine-N-(2-(1'-methyl-4,4'-bipyridine-1,1'-diium-1-yl) ethyl)] (PF6)(2)) (1(2+)) reveal that photoinduced electron transfer to the electron-accepting 4,4'-bipyridine-1,1'diium (MV2+) moiety competes with the fast relaxation of the initially populated sigmapi* excited state of the cluster to the ground state and/or cleavage of an Os-Os bond. The TA spectra of cluster 12 in acetone, obtained by irradiation into its lowest-energy absorption band, show the characteristic absorptions of the one-electron-reduced MV*(+) unit at 400 and 615 nm, in accordance with population of a charge-separated (CS) state in which a cluster-core electron has been transferred to the lowest pi* orbital of the remote MV2+ unit. This assignment is confirmed by picosecond TRIR spectra that show a large shift of the pilot highest-frequency nu(CO) band of 1(2+) by ca. +40 cm(-1), reflecting the photooxidation of the cluster core. The CS state is populated via fast (4.2 x 10(11) s(-1)) and efficient (88%) oxidative quenching of the optically populated sigmapi* excited state and decays biexponentially with lifetimes of 38 and 166 ps (1:2:1 ratio) with a complete regeneration of the parent cluster. About 12% of the cluster molecules in the sigmapi* excited state form long-lived open-core biradicals. In strongly coordinating acetonitrile, however, the cluster core-to-MV2+ electron transfer in cluster 12+ results in the irreversible formation of secondary photoproducts with a photooxidized cluster core. The photochemical behavior of the [Os-3(CO)(10)(alpha-diimine-MV)](2+) (donor-acceptor) dyad can be controlled by an externally applied electronic bias. Electrochemical one-electron reduction of the MV2+ moiety prior to the irradiation reduces its electron-accepting character to such an extent that the photoinduced electron transfer to MV*+ is no longer feasible. Instead, the irradiation of reduced cluster 1(.)+ results in the reversible formation of an open-core zwitterion, the ultimate photoproduct also observed upon irradiation of related nonsubstituted clusters [Os-3(CO)(10)(alpha-diimine)] in strongly coordinating solvents such as acetonitrile.

Synthesis and structural studies of a bis(carbamoyl methyl) sulfoxide complex of uranyl nitrate

A new tri-functional ligand iBu2NCOCH2SOCH2CONiBu2 was prepared and characterized. The coordination chemistry of this ligand with uranyl nitrate was studied with IR, 1H NMR, electrospray mass-spectrometry, thermogravimetry, and elemental analysis. The structure of [UO2(NO3)2(iBu2NCOCH2SOCH2CONiBu2)] was determined by single-crystal X-ray diffraction. The uranium(VI) ion is surrounded by eight oxygens in a hexagonal bipyramidal geometry. Four oxygens from two nitrates and two oxygens from the ligand form a planar hexagon. The ligand is a bidentate chelate, bonding through sulfoxo and one of the carbamoyl groups to uranyl nitrate.

Metal cluster expansion by addition of low valent group 14 reagents: III. Reaction of bis[bis(trimethylsilyl)methyl]tin with M3(CO)12 or its derivatives (M = Fe, Ru, or Os): the crystal and molecular structures of M3(μ-SnR2)2(CO)10(R = CH(SiMe3)2; M = Ru or Os)

The stannylene [SnR2] (R = CH(SiMe3)2) reacts in different ways with the three dodecacarbonyls of the iron triad: [Fe3(CO)12] gives [Fe2(CO)8(μ-SnR2)], [Ru3(CO)12] gives the planar pentametallic cluster [Ru3(CO)10(μ-SnR2)2], for which a full structural analysis is reported, while [Os3(CO)12] fails to react. Different products are also obtained from three nitrile derivatives: [Fe3-(CO)11(MeCN)] gives [Fe2(CO)6(μ-SnR2)2], which has a structure significantly different from that of known Fe2Sn2 clusters, [Ru3(CO)10(MeCN)2] gives the pentametallic cluster described above, while [Os3(CO)10(MeCN)2] gives the isostructural osmium analogue, which shows the unusual feature of a CO group bridging two osmium atoms.

Reaction of 2-methyl-1,4-naphthoquinone and its 3-substituted derivatives with active methylene group anions and with diazo compounds

The reaction of 2-chloro-3-methyl-1,4-naphthoquinone (3) with the anion of ethyl cyanoacetate led to a mixture of two epimeric fused-ring cyclopropane compounds, characterised as exo- and endo-1-cyano-1 -ethoxycarbonyl-1a-methyl-1a,7a-dihydro-1H-cyclopropa[b]naphthalene-2,7-dione (8) and (9). Various hydrolysis products of these were prepared and an X-ray crystallographic analysis was carried out on one of them, 1-carbamoyl-1 -carboxy-1a-methyl-1a,7a-dihydro-1H-cyclopropa[b]-naphthalene-2,7-dione (17). The reaction of 2-methyl-1,4-naphthoquinone (1) with ethyl diazoacetate gave a fused pyrazoline derivative, 3-ethoxycarbonyl-4-hydroxy-9a-methyl-1,9a-dihydro-benz[f]indazol-9-one (22), while reaction of 2-methyl-3-nitro-1,4-naphthoquinone (5) with diazomethane led to a fused Δ2-isoxazoline N-oxide, 3a-methyl-3,3a-dihydroisoxazolo[3,4-b]naphthalene-4,9-dione 1-oxide (26).

Structure property relationships in electrically conducting copolymers formed from pyrrole and N-methyl pyrrole

A series of copolymers containing differing proportions of pyrrole and N-methyl pyrrole were prepared electrochemically at various temperatures using acetonitrile as the solvent. The resultant electrical conductivity decreases universally with increasing fraction of N-methyl pyrrole. Films prepared with p-toluene sulfonate as the dopant show a marked variation in structural anisotropy as revealed by X-ray scattering with apparent copolymer content. There is a clear trend between the variation in electrical conductivity and this structural anisotropy. Different patterns of behaviour are observed for films prepared using perchlorate as the dopant and this is attributed to the role of the dopant and final structure in determining the relative reactivities of the pyrrole and N-methyl pyrrole monomers. These observations support the concept that the introduction of methyl substituents into a polypyrrole chain results in a twisted chain conformation. The structure and properties of the resultant copolymer films are particularly sensitive to the preparation conditions.

Cinnamate ester containing liquid crystalline side chain polymers

The synthesis of methacrylate esters of 4-cyanophenyl-(4-(ω-hydroxyalkyloxy)) cinnamates, with spacer lengths of 2 and 6 methylene units and the synthesis of the corresponding acrylate ester with a spacer of 2 methylene units are described. The methacrylate monomers were polymerized by free radical polymerization, both as homopolymers and as copolymers with the analogous benzoate monomer of spacer length 6. The acrylate ester could not be polymerized successfully under the same reaction conditions. Polymers were characterized by NMR spectroscopy, gel permeation chromatography, differential scanning calorimetry, and thermo-optic observations. Of the monomers prepared, only the cinnamate with a hexamethylene spacer shows a mesophase, seen on supercooling of the melt. All of the polymers prepared were liquid crystalline, with smectic behavior predominating in the polymethacrylates with the longer spacer group. A narrow nematic region is seen just below the clearing temperature with a range of 3–9°C, nematic character is increased in the copolymer series with the degree of incorporation of the cinnamate monomer with the spacer group of length 2.