Rare earth metal alkyl complexes bearing N,O,P multidentate ligands: Synthesis, characterization and catalysis on the ring-opening polymerization of L-lactide

Alkane elimination reactions of rare earth metal tris(alkyl)s, Ln(CH2SiMe3)3(THF)2 (Ln = Y, Lu) with the multidentate ligands HL1-4, afforded a series of new rare earth metal complexes. Yttrium, complex I supported by flexible amino-intino phenoxide ligand HL1 was isolated as homoleptic product. In the reaction of rigid phosphino-imino phenoxide ligand HL 2 with equintolar Ln(CH2SiMe3)3(THF)2, HL 2 was deprotonated by the metal alkyl and its imino C=N group was reduced to C-N by intramolecular alkylation, generating THF-solvated mono-alkyl complexes (2a: Ln = Y; 2b: Ln = Lu). The di-ligand chelated yttriurn complex 3 without alkyl moiety was isolated when the molar ratio of HL 2 to Y(CH,SiMe3)3(THF)2 increased to 2: 1. Reaction of steric phosphino beta-ketoiminato ligand HL 3 with equimolar Ln(CH2SiMe3)3(THF)2 afforded di-ligated mono-alkyl complexes (4a: Ln = Y; 4b: Ln = Lu) without occurrence of intramolecular alkylation or formation of homoleptic product. Treatment of tetradentate methoxy-amino phenol HL 4 with Y(CH2SiMe3)3(THF)2 afforded a monomeric yttrium bis-alkyl complex of THF-free. The resultant complexes were characterized by IR, NMR spectrum and X-ray diffraction analyses.All alkyl complexes exhibited high activity toward the ring-opening polymerization Of L-lactide to give isotactic polylactide with controllable molecular weight and narrow to moderate polydispersity.

Enhancement of the electrooxidation of ethanol on Pt-Sn-P/C catalysts prepared by chemical deposition process

In this paper, five Pt3Sn1/C catalysts have been prepared using three different methods. It was found that phosphorus deposited on the surface of carbon with Pt and Sn when sodium hypophosphite was used as reducing agent by optimization of synthetic conditions such as pH in the synthetic solution and temperature. The deposition of phosphorus should be effective on the size reduction and markedly reduces PtSn nanoparticle size, and raise electrochemical active surface (EAS) area of catalyst and improve the catalytic performance. TEM images show PtSnP nanoparticles are highly dispersed on the carbon surface with average diameters of 2 nm. The optimum composition is Pt3Sn1P2/C (note PtSn/C-3) catalyst in my work. With this composition, it shows very high activity for the electrooxidation of ethanol and exhibit enhanced performance compared with other two Pt3Sn1/C catalysts that prepared using ethylene glycol reduction method (note PtSn/C-EG) and borohydride reduction method (note PtSn/-B). The maximum power densities of direct ethanol fuel cell (DEFC) were 61 mW cm(-2) that is 150 and 170% higher than that of the PtSn/C-EG and PtSn/C-B catalyst.

PH-Dependent syntheses and structures of two Copper(II)/Phenanthroline/p-Sulfonatocalix[4]arene supramolecular compounds with 1D water-filled channels

Two copper-organic framework supramolecular assemblies of p-sulfonatocalix[4]arene and 1,10-phenanthroline Cu-2[C12H8N2][C28H20S4O16][H2O](23.5) (1) and Cu-3[C12H8N2](3)[C28H19S4O16]Cl[H2O](17.6) (2) were obtained by pH-dependent synthesis at room temperature. Both structures show ID water-filled channels (rectangular shape in I and triangular in 2) with the solvent-accessible volume occupying 30.8% (1) and 24.2% (2) of the unit-cell volume, respectively. The calixarene molecules in both structures assume analogous cone shapes of C-2 nu symmetry instead of the conventional C-4 nu symmetry. Their connecting to different amounts of copper/phenanthroline cations leads to the formation of different structures.

Loosely packed self-assembled monolayer of N-hexadecyl-3,6-di(p-mercaptophenylacetylene)carbazole on gold and its application in biomimetic membrane research

Dithiols of N-hexadecyl-3,6-di(p-mercaptophenylacetylene)carbazole (HDMC) have been synthesized and employed to form self-assembled monolayers (SAMs) on gold. One characteristic of the HDMC molecule is its peculiar molecular structure consisting of a large and rigid headgroup and a small and flexible alkyl-chain tail. HDMC adsorbates can attach to gold substrates by a strong Au-S bond with weak van der Waals interactions between the alkyl-chain tails, leading to a loosely packed hydrophobic SAM. In this way we can couple hybrid bilayer membranes (HBMs) to gold surfaces with more likeness to a cell bilayer than the conventional HBMs based on densely packed long-chain alkanethiol SAMs. The insulating properties and stability of the HDMC monolayer as well as the HDMC/lipid bilayer on gold have been investigated by electrochemical techniques including cyclic voltammetry and impedance spectroscopy. To test whether the quality of the bilayer is sufficiently high for biomimetic research, we incorporated the pore-forming protein a-hemolysin) and the horseradish peroxidase into the bilayers, respectively.

UV-vis spectrophotometric titrations and vibrational spectroscopic characterization of meso-(p-hydroxyphenyl)porphyrins

Sequentially spectrophotometric titrations by sodium hydroxide of meso-tetraphenylporphyrin derivatives bearing one, two, three, or four p-hydroxyl groups result in new types of spectra. The strong new bands appear in the visible region with splitting or broadening of the Soret band and its significant loss of oscillator strength. To understand the molecular origin of these phenomena, the Resonance Raman (RR) and Fourier Transform Infrared (FTIR) experiments are carried out. The results demonstrate that the charges of the deprotonated para-hydroxy substituted meso-tetraphenylporphyrins are localized on the substituents, not delocalized into the pi system of the porphyrin macrocycles and that the ground states of the macrocycles remain essentially unperturbed. Both the related behavior of diprotonated tetrakis(p-(dimethylamino)phenyl) porphyrin and protonated Schiff base porphyrins show that the new bands considered as hyperporphyrin spectra are due to pi(phenoxide anion) --> pi*(porphyrin) transitions, where pi is an orbital on the phenoxide anion substitutent and pi* is a LUMO on the porphyrin.

Crosslinkable poly (p-phenylenevinylene) derivative

To simplify the fabrication of multilayer light-emitting diodes, we prepared a p-phenylenevinylene-based polymer capped with crosslinkable styrene through a Wittig reaction. Insoluble poly(p-phenylenevinylene) derivative (PPVD) films were prepared by a thermal treatment. The photoluminescence and ultraviolet-visible (UV-vis) absorbance of crosslinked films and noncrosslinked films were studied. We also studied the solvent resistance of crosslinked PPV films with UV-vis absorption spectra and atomic force microscopy. Double-layer devices using crosslinked PPVD as an emitting layer, 2-(4-tert-butylphenyl)-5-phenyl-1,3,4-oxadiazole (PBD) in poly(methyl methacrylate) as an electron-transporting layer, and calcium as a cathode were fabricated. A maximum luminance efficiency of 0.70 cd/A and a maximum brightness of 740 cd/m(2) at 16 V were demonstrated. A 12-fold improvement in the luminance efficiency with respect to that of single-layer devices was realized.

Soluble, saturated-red-light-emitting poly(p-phenylenevinylene) containing triphenylamine units and cyano groups

A conjugated poly(p-CN-phenylenevinylene) (PCNPV) containing both electron-donating triphenylamine units and electron-withdrawing cyano groups was prepared via Knoevenagel condensation in a good yield. Gel permeation chromatography suggested that the soluble polymer had a very high weight-average molecular weight of 309,000. A bright and saturated red emission was observed under UV excitation in solution and film. Cyclic voltammetry showed that the polymer presented quasi-reversible oxidation with a relatively low potential because of the triphenylamine unit. A single-layer indium tin oxide/PCNPV/Mg-Ag device emitted a bright red light (633 nm).

Copper phthalocyanine based hybrid p-type permeable-base transistor in vertical architecture

We demonstrate the production of copper phthalocyanine (CuPc) based p-type hybrid permeable-base transistors, which operate at low voltages having high common-base current gains. These transistors are prepared by evaporating a thin metal layer (Ag or Al) that acts as base on top of a Si substrate that acts as collector. In the sequence CuPc and Au are thermally sublimated to produce the emitter, constituting a quite simple device production procedure with the additional advantage of allowing higher integration due to its vertical architecture.

Sequential deprotonation of meso-(p-hydroxyphenyl)porphyrins in DMF: From hyperporphyrins to sodium porphyrin complexes

Sequential deprotonations of meso-(p-hydroxyphenyl)porphyrins (p-OHTPPH2) in DMF + H2O (V/V = 1:1) mixture have been verified to result in the appearance of hyperporphyrin spectra. However, when the deprotonations of these p-OHTPPH2 are carried out in DMF, the spectral changes differ considerably from those in the mixture mentioned above. At low [OH-], the optical spectra in the visible region are still considered to have characteristics of hyperporphyrin spectra. Further deprotonation at much higher basicity makes the optical spectra form three-banded spectra similar to those in the acidic solution. To clarify the molecular origins of these changes, UV-vis, resonance Raman (RR), proton nuclear magnetic resonance (H-1 NMR) experiments are carried out. Our data give evidence that p-OHTPPH2 in DMF can be further deprotonated of pyrrolic-H by higher concentrated NaOH, due to an aprotic medium like DMF effectively weakening the basicity of the porphyrin relative to that of the NaOH, and coordinates with two sodium ions (except the sodium ions that interact with the peripherial phenoxide anions) to form the sodium complexes of p-OHTPPH2 (Na2P, to lay a strong emphasis on the sodium ions that coordinate with the central nitrogen atom), which can be regarded as the porphyrin anions being perturbed by the sodium cations due to their highly ionic character.

Novel chemical synthesis of Pt-Ru-P electrocatalysts by hypophosphite deposition for enhanced methanol oxidation and CO tolerance in direct methanol fuel cell

A novel method was developed to prepare the highly active Pt-Ru-P/C catalyst. The deposition of phosphorus significantly increased electrochemical active surface (EAS) area of catalyst by reduces Pt-Ru particle size. TEM images show that Pt-Ru-P nanoparticles have an uniform size distribution with an average diameter of 2 nm. Cyclic voltammetry (CV), Chronoamperometry (CA), and CO stripping indicate that the presence of non-metal phosphorus as an interstitial species Pt-Ru-P/C catalyst shows high activity for the electro-oxidation of methanol, and exhibit enhanced performance in the oxidation of carbon monoxide compared with Pt-Ru/C catalyst. At 30 degrees C and pure oxygen was fed to the cathode, the maximum power density of direct methanol fuel cell (DMFC) with Pt-Ru-P/C and Pt-Ru/C catalysts as anode catalysts was 61.5 mW cm(-2) and 36.6 mW cm(-2), respectively. All experimental results indicate that Pt-Ru-P/C catalyst was the optimum anode catalyst for direct methanol fuel cell.

Surface enhanced Raman scattering of p-aminothiophenol self-assembled monolayers in sandwich structure fabricated on glass

A sandwich structure consisting of Ag nanoparticles (NPs), p-aminothiophenol (p-ATP) self-assembled monolayers (SAMs), and Ag NPs was fabricated on glass and characterized by surface enhanced Raman scattering (SERS). The SERS spectrum of a p-ATP SAM in such sandwich structure shows that the electromagnetic enhancement is greater than that on Ag NPs assembled on glass. The obtained enhancement factors (EF) on solely one sandwich structure were as large as 6.0 +/- 0.62x10(4) and 1.2 +/- 0.62x10(7) for the 7a and 3b(b(2)) vibration modes, respectively. The large enhancement effect of p-ATP SAMs is likely a result of plasmon coupling between the two layers of Ag NP (localized surface plasmon) resonance, creating a large localized electromagnetic field at their interface, where p-ATP resides. Moreover, the fact that large EF values (similar to 1.9 +/- 0.7x10(4) and 9.4 +/- 0.7x10(6) for the 7a- and b(2)-type vibration modes, respectively) were also obtained on a single sandwich structure of Au NPs/p-ATP SAMs/Ag NPs in the visible demonstrates that the electromagnetic coupling does not exist only between Ag NPs but also between Au and Ag NPs.

The direct synthesis of wholly aromatic poly(p-phenylene)s bearing sulfobenzoyl side groups as proton exchange membranes

Sulfonated poly(p-phenylene)s (SPPs) containing sulfonic acid groups in their side chains had been directly synthesized by Ni(0) catalytic coupling of sodium 3-(2,5-dichlorobenzoyl)benzenesulfonate and 2,5-dichlorobenzophenone. The synthesized copolymers possessed high molecular weights revealed by their high viscosity, and the formation of tough and flexible membranes by casting from DMAc solution. The copolymers exhibited excellent oxidative stability and mechanical properties due to their fully aromatic structure extending through the backbone and pendent groups. Transmission electron microscopic (TEM) analysis revealed that these side-chain type SPP membranes have a microphase-separated structure composed of hydrophilic side-chain domains and hydrophobic polyphenylene main chain domains. The proton conductivities of copolymer membranes increased with the increase of IEC and temperature, reaching values above 3.4 x 10(-1) S/cm at 120 degrees C, which are almost 2-3 times higher than that of Nafion 117 at the same measurement conditions. Consequently, these materials proved to be promising as proton exchange membranes.

A carbon-supported Pd-P catalyst as the anodic catalyst in a direct formic acid fuel cell

In this paper, it is reported for the first time that a carbon-supported Pd-P (Pd-P/C) catalyst for the anodic catalyst in the direct formic acid fuel cell (DFAFC) can be prepared. The Pd-P/C catalyst shows that its electrocatalytic activity and especially its stability for the oxidation of formic acid are much higher than that of a Pd/C catalyst. Therefore, the Pd-P/C catalyst may have practical applications in DFAFCs.

A new hydrometallurgical process for extracting rare earths from apatite using solvent extraction with P-350

In this paper, a new process is proposed to recover rare earths from nitric acid leaching of apatite without interfering with the normal route for fertilizer production using solvent extraction with dimethyl heptyl methyl phosphonate CH3P(O)(OC8H17)(2) (P-350, B). In the present work, the leaching conditions are studied. In selected condition, apatite was dissolved in 20% (v/v) nitric acid solution at 60-70 degrees C while agitating. The most suitable acidity for extraction is 0.4 M HNO3. More than 98% of rare earths in apatite can be recovered using countercurrent extraction process with six stages when phase ratio = 0.5, and defluorination is unnecessary. The influences of phase ratio, stage number, acidity and salting-out agent on extractabilities Of P-350 are studied. The results show that rare earths can be separated with P-350 from Ca, P, Fe and other impurities. Mixed rare earth oxides (REO) of which purity is more than 95% with yield over 98% can be obtained.