Reductive coupling of aromatic N,N-acetals using zinc and chlorotrimethylsilane

The reductive coupling of aromatic N,N-acetals and N,O-acetal activated by chlorotrimethylsilane proceeded smoothly in the presence of zinc to give the corresponding diamines in good yields.     

Photoinduced intramolecular charge separation in a polymer solid below the glass transition temperature

Photoinduced intramolecular charge separation (CS) in a polar polymer glass, cyanoethylated pullulan (CN-PUL), was studied below the glass transition temperature (Tg=395 K). A series of three carbazole (Cz: donor)-cyclohexane (S: spacer)-acceptor (A: acceptor) molecules (Cz-S-A) was used as intramolecular donor-acceptor dyads. The photoinduced CS rate was evaluated by the fluorescence decay measurement at temperatures from 100 to 400 K. The CS rate (kCS) increased above 200 K even far below Tg where micro-Brownian motions of the whole polymer chain are frozen. Below 200 K, on the other hand, kCS showed weak dependence on temperature. The temperature dependence of kCS is discussed in terms of the dielectric relaxation time of the polymer matrix. Consequently, CS below Tg was well explained by a thermally nonequilibrium electron transfer (ET) formula above 200 K and by a two-mode quantum-mechanical ET formula below 200 K. The increase in kCS above 200 K is mainly caused by a thermally activated low-frequency matrix mode originating from the side-chain relaxation of polar cyano groups. The weak temperature dependence of kCS can be explained by a nuclear-tunneling effect caused by a high-frequency matrix mode (variant Planck's over 2piomegH=250 cm-1) and an intramolecular vibrational mode (variant Planck's over 2piomegaQ=1300 cm-1). The high-frequency mode of the polymer matrix was attributed to a vibrational or librational motion of polar groups in the CN-PUL glassy solid.     

Rheology of self-assembled monolayers on solid-liquid interface oscillating at MHz frequency

The rheology properties (viscosity and elasticity) of chemisorbed soft matters on a solid-liquid interface oscillating at MHz were investigated using a quartz crystal microbalance (QCM). As a chemisorbed soft matter, we employed the self-assembled monolayers (SAMs) of mercapto oligo(ethylene oxide) methyl ethers, HS(CH₂CH₂O)_nCH₃ (n?=?5, 11, 12, 19, 27, 35 and 43), where those molecular weights had unity. The systematical analyses on the basis of the Voight model revealed the relationships of $\eta \propto M_n^{0.180}$ and $\mu \propto M_n^{0.344}$, where η and μ are the viscosity and elasticity of the SAM, and M_n is the molecular weight of HS(CH₂CH₂O)_nCH₃. As a result, we found that the SAM consisting of the oligomer followed the formula of polymer.     

Direct Carboxylation of Electron-Rich Heteroarenes Promoted by LiO-tBu with CsF and [18]Crown-6

We herein demonstrate that the combination of LiO-tBu, CsF, and [18]crown-6 efficiently promotes the direct C−H carboxylation of electron-rich heteroarenes (benzothiophene, thiophene, benzofuran, and furan derivatives). A variety of functional groups, including methyl, methoxy, halo, cyano, amide, and keto moieties, are compatible with this system. The reaction proceeds via the formation of a tert-butyl carbonate species.     

Two‐dimensional correlation gel permeation chromatography study of aggregate–aggregate interactions during acid‐catalyzed polymerization of triethoxysilyl‐terminated polystyrene

The three‐step polymerization of a well‐defined polymeric silane coupling agent, triethoxysilyl‐terminated polystyrene, catalyzed by acid (H₃PO₄), was traced as a function of the reaction time with gel permeation chromatography (GPC). Time‐resolved GPC traces collected during the polymerization process were then used to construct two‐dimensional (2D) correlation maps via generalized 2D correlation analysis. The results demonstrated that the synchronous and asynchronous 2D correlation GPC spectra directly reflected the dynamic variation of aggregate–aggregate interactions during each step of the polymerization. In particular, it was found that the formation of aggregates among the cyclic trimers (or tetramers) and monomers was critical for the preferential production of pentamers in the reaction system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3447–3460, 2004     

Characterization and electrochemical properties of molecular icosanuclear and bidimensional hexanuclear Cu(II) azido polyoxometalates

Two new Cu(II) azido polyoxometalates compounds have been synthesized, and their structures were determined by X-ray crystallography. The compound Na(14)[SiW(9)O(34)Cu(3)(N(3))(2)(OH)(H(2)O)](2) x 24H(2)O (1) is built from two [SiW(9)O(34)Cu(3)(mu(1,1,3)-N(3))(2)(mu-OH)(H(2)O)](7-) subunits where the copper centers, connected by two azido ligands and one hydroxo group, form a nearly equilateral triangle. The two subunits are related by an inversion center and connected via the two mu(1,1,3)-N(3) ligands in an end-to-end fashion, affording a hexanuclear Cu(II) cluster. Linkage of these fragments via Cu-O=W bonds leads to a bidimensional arrangement of the polyoxometalate units. The complex LiK(14)Na(9)[P(8)W(48)O(184)Cu(20)(N(3))(6)(OH)(18)] x 60H(2)O (2) consists of two {Cu(5)(OH)(4)}(6+) and two {Cu(5)(OH)(2)(mu(1,1,3,3)-N(3))}(7+) subunits connected via four mu-OH and four mu(1,1)-N(3) additional ligands, the 20 copper centers being encapsulated in the [P(8)W(48)O(184)](40-) crown polyoxotungstate ligand. 1 represents the first multidimensional compound based on azido polyoxometalate (POM) units, and 2 represents by far the largest azido POM complex isolated to date. Magnetic measurements revealed an overall antiferromagnetic behavior for both compounds. Nevertheless, the study of the variation of the magnetization with the applied field indicates that 1 possesses a triplet ground state, which can be attributed to weak ferromagnetic interaction between the S = 1/2 triangular subunits. The stability of 1 and 2 evidenced by UV-vis spectroscopy and gel filtration chromatography, in particular at pH 5, has allowed a detailed study of their redox and electrocatalytic properties. For both compounds, the stability of the Cu(II)/Cu(I) couple is remarkable compared with the observations made in other Cu(II)-substituted POMs. Electrochemical quartz crystal microbalance measurements clearly demonstrate that the formation of the Cu(I) species occurs neatly without the formation of Cu(0). The accumulation of such Cu(II) centers within the complexes is a favorable condition to envision applications involving several electrons. The electrocatalytic reduction of dioxygen and hydrogen peroxide was achieved efficiently and has shown that the reactivity increases with the nuclearity and/or the Cu/W ratio of the POM complex. The dioxygen reduction is an overall four-electron process with water as the final product. Finally, the reduction of the W centers triggers a strong electrocatalysis of solvent reduction.     

Effect of electropolymerization duration on the structure and performance of polypyrrole/graphene nanoplatelet counter electrode for dye-sensitized solar cells

Journal of Solid State Electrochemistry - Despite their potential for use as a low-cost energy-conversion device, dye-sensitized solar cells (DSSCs) have not been widely utilized because they apply...     

Larch (Larix kaempferi) xylem parenchyma cells respond to subfreezing temperature by deep supercooling

In previous studies, xylem parenchyma cells (XPCs) in the boreal softwood species larch, which has thick and rigid walls similar to those of XPCs in boreal hardwood species, were shown to respond to subfreezing temperature by deep supercooling during summer but change their freezing behavior to extracellular freezing during winter. In this study, we re-examined freezing behavior of XPCs in larch by observation of deep etching of frozen samples as well as observation of re-warmed samples after freezing using a cryo-scanning electron microscope. The results showed that XPCs in larch adapts to subfreezing temperature by deep supercooling throughout all seasons. Such freezing behavior is the same as that of XPCs in boreal hardwood species.