Electrochemical charging and electrocatalysis at hybrid films of polymer-interconnected polyoxometallate-stabilized carbon submicroparticles

Using the layer-by-layer technique, carbon submicroparticles, that have been modified and stabilized with monolayers of Keggin-type phosphododecamolybdate (PMo₁₂O₄₀³⁻), can be dispersed in multilayer films of organic polymers, poly(3,4-ethylenedioxythiophene), i.e., PEDOT, or poly(diallyldimethylammonium) chloride, i.e., PDDA, deposited on glassy carbon or indium-tin oxide conductive glass electrodes. The approach involves alternate treatments in the colloidal suspension of PMo₁₂O₄₀³⁻-covered carbon submicroparticles in the solution of monomer, 3,4-ethylenedioxythiophene or in solution of PDDA polymer. Electrostatic attractive interactions between anionic phosphomolybdate-modified carbon submicroparticles and cationic polymer layers permit not only uniform and controlled growth of the hybrid organic–inorganic film but also contribute to its overall stability. The system composed of PMo₁₂O₄₀³⁻-covered carbon submicroparticles dispersed in PEDOT is characterized by fast dynamics of charge transport and has been used to construct symmetric microelectrochemical redox capacitor. The PDDA-based system has occurred to be attractive for electrocatalytic reduction of hydrogen peroxide.     

Author index for volume 47

The phase diagram of the pseudo-ternary MnV₂O₆LiVMoO₆MoO₃ system has been determined with DTA and X-ray phase analysis. Its outstanding feature is the very large range of stability of the quaternary solid solution α-ML? described by the formula Mn_1?x?yLi_y?_xV_2?2x?yMo_2x+yO₆ (? = cation vacancy), and crystallizing in the monoclinic brannerite-type structure. In this solution y may vary between 0 and 1, which corresponds to the entire miscibility of MnV₂O₆ and LiVMoO₆; x may change between 0 and x_max depending on y (if, e.g., y equals 0.00, 0.40, 0.84, or 1.00, x_max is 0.45, 0.28, 0.16, or 0.00, respectively). Depending on composition, α-ML? is stable up to 540–710°C. Other features of the diagram, including the liquidus, are described in detail. The dependence of unit cell dimensions on composition of α-ML? has been determined. On passing from MnV₂O₆ to LiVMoO₆, the lattice parameter b and unit cell volume increase, c and c sin β decrease, and a changes insignificantly. These changes are interpreted by taking into account the ionic radii of the components and the specific details of the brannerite-type structure. ML? solid solutions were prepared using the amorphous citrate precursor method.     

Membrane Structure of Substance P. III. Secondary Structure of Substance P in 2,2,2-Trifluoroethanol,Methanol, and on Flat Lipid Membranes Studied by Infrared Spectroscopy

IR data of the neuropeptide substance P ( 1 ) and its synthetic segments des-(Arg¹-Gln⁶)-substance P ( 6 ), des-(Arg¹-Pro⁴)-substance P ( 4 ), des-(Arg¹-Lys³)-substance P ( 3 ), and des-Arg¹-substance P ( 2 ) indicate predominant β-structures in the solid state and α-helical structures in CF₃CH₂OH (amide I band shape analysis). In MeOH, the spectra of 1 suggest a partly helical structure. On membranes prepared from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, a C-terminal α-helix consisting of 8 or 9 peptide bonds appears to be induced (IR attenuated total reflection studies). Its perpendicular orientation on the membrane is suggested by the dichroic ratios of the amide-I and -II bands. This study is consistent with our CD experiments and lends support to the membrane structure of 1 predicted from the estimated amphiphilic moment, hydrophobic-association constant, and helix length.     

THE PHOTOCHEMISTRY OF HUMAN RETINAL LIPOFUSCIN AS STUDIED BY EPR

Fluorescent material generated in the human retina accumulates within lipofuscin (HLF) granules of the retinal pigment epithelium (RPE) during aging. We have been investigating the possible light-induced contribution of these fluorophores to various diseases including age-related macular degeneration. Our studies have shown that some of the fluorescent components of HLF are products of the reaction of retinaldehyde with ethanolamine and that synthetic mixtures of this reaction can serve as a useful model for photophysical studies. Previous research by us has demonstrated that irradiation of either natural or synthetic lipofuscin resulted in the formation of a triplet state and possibly a free radical. Here EPR studies were performed to verify the formation of that radical. The UV irradiation of either synthetic or natural human retinal lipofuscin extracts in oxygen-free methanol led to the formation of a 5,5-dimethylpyrroline-N-oxide (DMPO) spin-trapped carbon-centered radical resulting from either hydrogen atom or electron abstraction from solvent molecules. In the presence of oxygen superoxide was formed, which was observed as a DMPO adduct. It is concluded that certain components of the chloroform-soluble fluorophores of human RPE lipofuscin granules and the fluorescent reaction products of retinaldehyde and ethanolamine are photophysically similar but not the same. Electron or hydrogen abstraction from a substrate by these fluorophores in vivo and the resulting radical products may contribute to the age-related decline of RPE function and blue light damage in the retina.     

Nonexpanding congruences of null strings in algebraically degenerate right-flat spaces

A problem of nonexpanding right congruences of null strings in algebraically degenerate right-flat spaces is discussed and reduced to one differential equation. Then the form of the key function from the right side for some subclass of metrics is studied.On leave of absence from Technical University of Kielce, Poland.     

Membrane Structure of Substance P. I. Prediction of Preferred Conformation,Orientation, and Accumulation of Substance P on Lipid Membranes

Preferred conformation, orientation, and accumulation of substance P on a neutral hydrophilic-hydrophobic interface was estimated and extrapolated to interactions with neutral and anionic lipid bilayer membranes according to our general procedure. Nine residues at the C-terminus were predicted to be transferred to the hydrophobic phase as an α-helical domain, oriented quite perpendicularly on the membrane surface. The N-terminal residues remained in the aqueous phase with their charges exposed to H₂O. The molecular amphiphilic moment vector was strong (338 arbitrary units) and pointed its hydrophilic end towards the N-terminus, only 15° away from the helix axis. The molecular electric dipole moment vector was also strong (124 debye) and pointed its positive end towards the N-terminus, only 9° away from the helix axis. Thus, it reinforced the effect of the amphiphilic moment of a peptide intruding into the membrane dipole layer. The estimated dissociation constant for the equilibrium between membrane-bound and free substance P was K_d ≈? 46 mM for neutral membranes, and K_d ≈?0.43 mM for anionic membranes with a Gouy-Chapman surface potential of ?40 mV. Thus, substance P behaved similarly to dynorphin A and adrenocorticotropin peptides which insert their N-terminal message segments as perpendicularly oriented helical domains into membranes, whereas their C-terminal address segments remain in the aqueous phase as random coils. Substance P is the first instance of a neuropeptide which is expected to insert a C-terminal message into lipid membranes.     

Short,Enantiospecific Syntheses of Indolizidines 209B and 209D,and Piclavine A from Diethyl-L-Glutamate

The 1H-pyrrole derivative obtained from diethyl L -glutamate hydrochloride and tetrahydro-2,5-dimethoxyfuran was cyclized with BBr₃ to ethyl (5S)-5,6,7,8-tetrahydro-8-oxoindolizine-5-carboxylate ( 18 ). Catalytic hydrogenation of 18 over Pd/C in AcOH gave ethyl (5S,8aR)-octahydroindolizine-5-carboxylate ( 21 ), whereas hydrogenation over Rh/Al₂O₃ in EtOH/AcOH 99:1 afforded mainly ethyl (5S,8S,8aS)-octahydro-8-hydroxyindolizine-5-carboxylate ( 22 ). By functional-group interconversions, 21 was transformed into piclavine A ( 1 ) and indolizidine 209D ( 2 ). Similarly, (5R,8R,8aS)-octahydro-5-pentylindolizine-8-methanol ( 37 ), the final relay for indolizidine 209B ( 3 ), was obtained from 22 .     

An unprecedented copper(I,II)-octacyanotungstate(V) 2-D network: crystal structure and magnetism of [CuII(tren)]{CuI[W(V)(CN)8]} . 1.5H2O

A novel two-dimensional cyanide-bridged polymer [CuII(tren)]{CuI[W(V)(CN)8]} . 1.5H2O (tren = tris(2-aminoethyl)amine) formed via the simultaneous in situ metal-ligand redox reaction of [Cu(tren)(OH2)]2+ and self-assembly with [W(V)(CN)8]3- consists of a {CuI[W(V)(CN)8]} square grid built of CuI centres of tetrahedral geometry coordinatively saturated by CN bridges and [W(V)(CN)8]3- capped by [CuII(tren)]2+ moieties; it exhibits ferromagnetic coupling J1 = +5.8(1) cm(-1) within the CuII-W(V) dinuclear subunits and weak antiferromagnetic coupling J2 = -0.03(1) cm(-1) between them through diamagnetic CuI spacers.     

From weak interactions to covalent bonds: a continuum in the complexes of 1,8-bis(dimethylamino)naphthalene

Experimental charge density distributions in a series of ionic complexes of 1,8-bis(dimethylamino)naphthalene (DMAN) with four different acids: 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), 4,5-dichlorophthalic acid, dicyanoimidazole, and o-benzoic sulfimide dihydrate (saccharin) have been analyzed. Variation of charge density properties and derived local energy densities are investigated, over all inter- and intramolecular interactions present in altogether five complexes of DMAN. All the interactions studied [[O...H...O](-), C[bond]H...O, [N[bond]H...N](+), O[bond]H...O, C[bond]H...N, C pi...N pi, C pi...C pi, C[bond]H...Cl, N[bond]H(+)] follow exponential dependences of the electron density, local kinetic and potential energies at the bond critical points on the length of the interaction line. The local potential energy density at the bond critical points has a near-linear relationship to the electron density. There is also a Morse-like dependence of the laplacian of rho on the length of interaction line, which allows a differentiation of ionic and covalent bond characters. The strength of the interactions studied varies systematically with the relative penetration of the critical points into the van der Waals spheres of the donor and acceptor atoms, as well as on the interpenetration of the van der Waals spheres themselves. The strong, charge supported hydrogen bond in the DMANH(+) cation in each complex has a multicenter character involving a [[Me(2)N[bond]H....NMe(2)](+)....X(delta-)] assembly, where X is the nearest electronegative atom in the crystal lattice.