Synthesis and bifunctional asymmetric organocatalysis of helical poly(phenylacetylene)s bearing cinchona alkaloid pendants via a sulfonamide linkage

Four novel helical poly(phenylacetylene)s with amino‐functionalized cinchona alkaloid pendant groups connecting to the phenyl rings through a sulfonamide linkage were synthesized by the polymerization of the corresponding phenylacetylene monomers using Rh⁺(2,5‐norbornadiene)[(η⁶‐C₆H₅)B^?(C₆H₅)₃] (Rh(nbd)BPh₄) as the catalyst. The optically active sulfonamide‐linked polymers adopted a helical conformation with an excess of one‐handedness as supported by the appearance of the induced Cotton effects in the main‐chain chromophore regions, and efficiently catalyzed the enantioselective methanolytic desymmetrization of a cyclic anhydride and aza‐Michael addition of aniline to chalcone, thereby producing the corresponding optically active products up to 86% enantiomeric excess. However, their enantioselectivities from the methanolytic desymmetrization were slightly lower than those catalyzed by the corresponding cinchona alkaloid‐bound monomers. On the other hand, during the asymmetric aza‐Michael addition, a unique enhancement of the enantioselectivity was observed for several sulfonamide‐linked helical polymers, and thus affording a remarkably higher enantioselectivity compared to those of the corresponding monomers and nonhelical polymers bearing the identical cinchona alkaloid residues. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 2869–2879     

Surface tension of electrolyte solutions

A simple analytic expression is derived for the excess surface tension of electrolyte solutions, which is in good agreement with the experimental data on NaCl in the concentration range up to as high as 1 M. This expression is consistent with the following two theories: (i) The recent theory of Levin and Flores-Mena (Europhys Lett (2001) 56:187), who demonstrated the important contribution of the formation of an ion free layer at the air–electrolyte solution interface, and (ii) the Onsager–Samaras theory (J Chem Phys (1934) 2:528) modified by taking into account the ion-free layer effect. It is shown that the excess surface tension consists of three parts: the contributions of the ion-free layer, the image interaction between the electrolyte ions and the ion-free layer, and the image interaction between the electrolyte ions and air.     

Switching between laser-induced thermophoresis and thermal convection of liquid suspension in a microgap with variable dimension

Phoretic motion of particles along a temperature gradient formed in a fluid, known as thermophoresis, often takes place under the influence of bulk motion caused by thermal convection. In this paper, using a laser heating method, the significance of two competing effects, that is, thermophoresis and thermal convection, for the particle transport in a liquid phase confined in a microgap is investigated experimentally by changing the gap size as a control parameter. It is found that there is a threshold of the gap size, above which the particles tend to accumulate around the heated spot, forming a ring-like particle distribution. On the contrary, if the gap size is below the threshold, the particles are depleted from the heated spot. Switching between these accumulation and depletion modes is expected to develop novel manipulation techniques.     

Cyanide bridged tetranuclear complex with a novel terthiophene based ligand

A new terthiophene based ligand (L = 3-(2-pryridyl)-5-(2,2′:5′,2″-terthien-3′-yl) pyrazole was synthesized. The reaction of Ni(BF₄)₂·6H₂O, L and nBu₄N[Fe(CN)₃tp^∗] (tp^∗ = tris(3,5-dimethylpyrazol-1-yl)borohyrdide) with NaBPh₄ in MeOH/acetone yielded a cyanide bridged tetranuclear complex [Fe₂Ni₂(CN)₆(tp^∗)₂(L)₄](BPh₄)₂ (1). The electrochemical properties of both 1 and L were investigated, and magnetic susceptibility measurements of 1 were conducted, revealing that ferromagnetic interactions were operative within the tetranuclear core.     

Dynamic redox systems based on bis(spiroxanthene)-type donors with a polycyclic aromatic hydrocarbon: preparation, X-ray structures, and electrochromic response with fluorescence change

The long C-C bonds (1.614(2)-1.630(2) Å) in newly prepared title donors 2-6 are cleaved upon two-electron oxidation to afford the bond-dissociated dicationic dyes 2²⁺-6²⁺, whose electron affinities are stronger than the corresponding biphenyl-2,2′-diyl dications 1²⁺ due to the spatial proximity of two xanthenylium units. Not only UV-vis but also fluorescence spectra changed drastically upon electrolysis since only colorless neutral donors are fluorescent.     

An improved sample preparation method for the sensitive detection of peptides by MALDI‐MS

We describe here an optimization study of the sample preparation conditions for sensitive detection of peptides by matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS). Among many factors in the conditions, we varied the percent acetonitrile in the peptide solution, the percent acetonitrile in the matrix solution and the α‐cyano‐4‐hydroxycinnamic acid (CHCA) concentration in the matrix solution. CHCA was chosen because it is the most frequently used matrix for analyzing peptides. The well‐established dried‐droplet method was employed for sample deposition. The examined range of the concentration of CHCA was from 0.01 to 10 mg/ml, and the MeCN content of the solvent for matrix/analyte was 10% to 50%. The indicator for the detection sensitivity was the S/N ratio of the peaks of peptides used. Highly increased sensitivity (100‐ to 1000‐fold) was observed for the optimal CHCA concentration of 0.1 mg/ml in 20% MeCN/0.1% aq. trifluoroacetic acid (TFA), as compared with the conventional concentration (10 mg/ml) in 50% MeCN/0.1% aq. TFA. For example, the limit of detection of human ACTH 18–39 was 10 amol/well for the optimal condition but 10 fmol/well for the conventional condition. The optimal condition (0.1 mg/ml CHCA in 20% MeCN/0.1% aq. TFA) was verified with five model peptides and provided significant improvement in sensitivity (by two to three orders of magnitude) compared with the conventional conditions. Optimizing the CHCA concentration and solvent composition significantly improved the detection sensitivity in the analysis of peptides by MALDI‐MS. Copyright © 2013 John Wiley & Sons, Ltd.     

Gadolinium containing photochromic micelles as potential magnetic resonance imaging traceable drug carriers

Novel photochromic amphipathic molecules, KMR‐AZn (Gd‐DTPA‐AZCn), composed of hydrophilic Gd‐DTPA and hydrophobic alkylated azobenzene were prepared. In aqueous environment, KMR‐AZn indicated self‐assembly. The resulting aggregates were demonstrated to be able to include a hydrophobic drug substitute (hydrophobic fluorescent dye) into the internal core, and to release the included compound upon photoirradiation within 10 min through the influence of azobenzene photoisomerization. This micellar MRI contrast agent exhibited three‐ to four‐fold higher r₁ relaxivity (r₁ = 14.5–16.5 mm ^?1 s^?1, 0.47 T at 40°C) than the widely applied small molecule contrast agent Gd‐DTPA (Magnevist^®r₁ = 4.1 mm ^?1 s^?1, 0.47 T at 40°C). This dual functionality of encapsulated compound release and increased MR imaging contrast indicates that KMR‐AZn is a potential candidate for application as a lipid‐based MRI‐traceable drug carrier.     

Pentacene precursors for solution-processed OFETs

15-Acetoxy- and 15-hydroxy-6,13-dihydro-6,13-ethanopentacenes sublimed over 300 °C and no pentacene was formed below the temperature. The precursors bearing chlorinated epithiomethano bridges suffered complicated decomposition to give oligomeric pentacene derivatives. The precursor bearing an epithio-oxomethano bridge underwent smooth and clean conversion to pentacene by heat or light. An organic field-effect transistor fabricated by the spin-coating method of the precursor followed by light irradiation at 120 °C showed a good FET performance of μ=2.5×10⁻² cm² V⁻¹ s⁻¹ and on/off ratio=3.8×10⁴.