Rotating minidisk-disk electrodes

Rotating minidisk-disk electrode (RMDDE) was developed by replacing ring electrode of rotating ring-disk electrode (RRDE) with a minidisk electrode. Its applications were demonstrated by studying electrochemical reactions of ferricyanide and divalent copper. The replacement of ring electrode by minidisk electrode results in following advantages. First, the fabrication of RMDDE is easier than that of RRDE with the same electrode material. Second, there is more freedom in choosing electrode materials and sizes, since it is difficult to make thin ring electrodes of RRDE with fragile materials. Third, the replacement of ring electrode by minidisk electrode saves electrode materials, especially rare materials. Finally, the substitution of minidisk electrode for ring electrode allows using multiple minidisks for simultaneous monitoring of multiple components. Therefore, RMDDE is a promising generator-collector system, especially when special generator-collector systems are not commercially available, such as corrosion study and electrocatalysis study of new electrode materials.

Synthesis and characterization of monodisperse oligo(fluorene-co-bithiophene)s

A series of monodisperse oligo(9,9-di-n-octylfluorene-co-bithiophene)s (OFbTs) with molecular lengths of up to 19.5 nm and molecular weights up to 7025 g mol(-1) has been synthesized by a divergent/convergent approach involving Stille coupling reactions. Stille coupling is quite efficient in preparing this class of oligomers, and even the molecule with nine fluorene units and eight bithiophene units (F9Th16) can be synthesized in a yield as high as 70%. Because of easy functionalization of the thiophene ring at its alpha position, no additional protecting group allowing activation for further reaction is necessary. However, the synthetic routes must be optimized to eliminate contamination of the targeting compounds with the homocoupling product of the organotin reagents. Synthesis of the longest oligomer F13Th24 in a relative large quantity is limited by its low yield due to the pronounced ligand-exchange side reactions of the starting materials and reaction intermediates. All oligomers longer than F4Th6 are nematic mesomorphs and exhibit enhanced glass transition temperature and clearing point with increasing molecular length, as revealed by differential scanning calorimetry and polarizing optical microscopy.

Pyrrolide-ligated organoyttrium complexes. Synthesis, characterization, and lactide polymerization behavior

The N,N-bidentate ligand 2-{(N-2,6-diisopropylphenyl)iminomethyl)}pyrrole (L-1) and the N,N,P-tridentate ligand 2-{(N-2-diphenylphosphinophenyl)iminomethyl)}pyrrole (L-2) have been prepared. Their reactions with homoleptic yttrium tris(alkyl) compound Y(CH2SiMe3)(3)(THF)(2) have been investigated. Treatment of Y(CH2SiMe3)(3)(THF)(2) with 1 equiv of L-1 generated a THF-solvated bimetallic (pyrrolylaldiminato)yttrium mono(alkyl) complex (1) of central symmetry. In this process, L-1 is deprotonated by metal alkyl and its imino CN group is reduced to C-N by intramolecular alkylation, generating dianionic species that bridge two yttrium alkyl units in a unique eta(5)/eta(1):kappa(1) mode. The pyrrolyl ring behaves as a heterocyclopentadienyl ligand. Reaction of Y(CH2SiMe3)(3)(THF)(2) with 2 equiv of L-1 afforded the monomeric bis(pyrrolylaldiminato)yttrium mono(alkyl) complex (2), selectively. Amination of 2 with 2,6-diisopropylaniline gave the corresponding yttrium amido complex (3). In 3 the pyrrolide ligand is monoanionic and bonds to the yttrium atom in a eta(1):kappa(1) mode. The homoleptic tris(eta(1):kappa(1)-pyrrolylaldiminato)yttrium complex (4) was isolated when the molar ratio of L-1 to Y(CH2SiMe3)(3)(THF)(2) increases to 3:1. Reaction of L-2 with equimolar Y(CH2SiMe3)(3)(THF)(2) afforded an asymmetric binuclear complex (5).

Yttrium bis(alkyl) and bis(amido) complexes bearing N,O multidentate ligands. Synthesis and catalytic activity towards ring-opening polymerization of L-lactide

Methoxy-modified beta-diimines HL1 and HL2 reacted with Y(CH2SiMe3)(3)(THF)(2) to afford the corresponding bis(alkyl)s [(LY)-Y-1(CH2SiMe3)(2)] (1) and [(LY)-Y-2(CH2SiMe3)(2)] (2), respectively. Amination of 1 with 2,6-diisopropyl aniline gave the bis(amido) counterpart [(LY)-Y-1{N(H)(2,6-iPr(2)-C6H3)}(2)] (3), selectively. Treatment of Y(CH2SiMe3)(3)(THF)(2) with methoxy-modified anilido imine HL3 yielded bis(alkyl) complex [(LY)-Y-3(CH2SiMe3)(2)(THF)] (4) that sequentially reacted with 2,6-diisopropyl aniline to give the bis(amido) analogue [(LY)-Y-3{N(H)(2,6-iPr(2)-C6H3)}(2)] (5). Complex 2 was "base-free" monomer, in which the tetradentate beta-diiminato ligand was meridional with the two alkyl species locating above and below it, generating tetragonal bipyramidal core about the metal center. Complex 3 was asymmetric monomer containing trigonal bipyramidal core with trans-arrangement of the amido ligands. In contrast, the two cis-located alkyl species in complex 4 were endo and exo towards the 0,N,N tridentate anilido-imido moiety. The bis(amido) complex 5 was confirmed to be structural analogue to 4 albeit without THF coordination. All these yttrium complexes are highly active initiators for the ring-opening polymerization Of L-LA at room temperature.

Catalytic ring hydrogenation of benzoic acid with supported transition metal catalysts in scCO(2)

The ring hydrogenation of benzoic acid to cyclohexanecarboxylic acid over charcoal-supported transition metal catalysts in supercritical CO2 medium has been studied in the present work. The cyclohexanecarboxylic acid can be produced efficiently in supercritical CO2 at the low reaction temperature of 323 K. The presence of CO2 increases the reaction rate and several parameters have been discussed.

Daunomycin binding to detergent micelles: A model system for evaluating the hydrophobic contribution to drug-DNA interactions

The interaction of daunomycin with sodium dodecyl sulfate and Triton X-100 micelles was investigated as a model for the hydrophobic contribution to the free energy of DNA intercalation reactions. Measurements of visible absorbance, fluorescence lifetime, steady-state fluorescence emission intensity, and fluorescence anisotropy indicate that the anthraquinone ring partitions into the hydrophobic micelle interior. Fluorescence quenching experiments using both steady-state and lifetime measurements demonstrate reduced accessibility of daunomycin in sodium dodecyl sulfate micelles to the anionic quencher iodide and to the neutral quencher acrylamide. Quenching of daunomycin fluorescence by iodide in Triton X-100 micelles was similar to that seen with free daunomycin. Studies of the energetics of the interaction of daunomycin with micelles by fluorescence and absorbance titration methods and by isothermal titration calorimetry in the presence of excess micelles revealed that association with sodium dodecyl sulfate and Triton X-100 micelles is driven by a large negative enthalpy. Association of the drug with both types of micelles also has a favorable entropic contribution, which is larger in magnitude for Triton X-100 micelles than for sodium dodecyl sulfate micelles.

Efficient one-pot synthesis of highly substituted pyridin-2(1H)-ones via the Vilsmeier-Haack reaction of 1-acetyl,1-carbamoyl cyclopropanes

A facile and efficient one-pot synthesis of highly substituted pyridin-2(1H)-ones is developed via the Vilsmeier-Haack reaction of readily available 1-acetyl,1-carbamoyl cyclopropanes, and a mechanism involving sequential ring-opening, haloformylation, and intramolecular nucleophilic cyclization reactions is proposed.

Efficient synthesis of substituted tetrahydrothiopyrano[2,3-b]thiopyran-4,5-diones by a double annulation strategy from dialkenoylketene dithioacetals

An efficient synthetic procedure for substituted 2,3,6,7tetrahydrothiopyrano [2,3-b] thiopyran-4,5 -diones by a double annulation strategy is described. The ring systems are made in good yields from readily available dialkenoylketene dithioacetals in the presence of either sodium sulfide nonahydrate/N,N-dimethylformamide (DMF) or a sodium hydride/DMF/amine system.

Thia-michael addition reactions in water using 3-[Bis(alkylthio) methylene]pentane-2,4-diones as odorless and efficient thiol equivalents

3-[Bis(ethylthio)methylene]pentane-2,4-dione (1a) and 3-[bis(benzylthio)methylene]pentane-2,4-dione (1b) have been investigated as non-thiolic and odorless thiol equivalents in thia-Michael addition reactions. In the presence of aqueous p-dodecyl benzenesulfonic acid (DBSA), compound (1) was cleaved and the generated thiols underwent facile conjugate addition to alpha,beta-unsaturated ketones 2 in-situ, affording the corresponding beta-keto sulfides (3) in good yields.

Formation of nonextinct ring-banded textures and multistacked lamella of tetra-aniline-block-poly(L-lactide) rod-coil diblock oligomer films induced by solvent vapor treatment

The self-assembly processes of the rod-coil diblock oligomer thin film of tetra-aniline (TANI)-block-poly(L-lactide) (PLLA) with different film thicknesses induced in the coil-selective solvent of acetone vapor at room temperature were studied. The morphologies of the oligomer films were determined by the film thickness. For the thicker film (232 nm), the nonextinct concentric ring-banded textures could form. While for the thinner and appropriate film (about 6 nm), multistacked diamond-shaped appearances with the periodic thickness being about 8.5 nm(6-nm-thick extended PLLA chain and 2.5-nm-thick p-pi conjugating TANI bimolecular layer) formed. The possible formation models of those two regular morphologies were presented in detail.

Nature of the ring-banded spherulites in blends of aromatic poly(ether ketone)s

The ring-banded spherulites in liquid crystalline poly(aryl ether ketone) (LC-PAEK) and poly(aryl ether ether ketone) (PEEK) blends with a higher content (>50%) of LC-PAEK are investigated by polarizing light microscopy (PLM) and atomic force microscopy (AFM) techniques. The results indicate that the light core and rings of the ring-banded spherulites under PLM are mainly composed of an LC-PAEK phase, while the dark rings consist of coexisting phases of PEEK and a small amount of LC-PAEK. The formation of the ring-banded spherulites is attributable to structural discontinuity caused by a rhythmic radial growth.