Electrochemically Mediated Atom Transfer Radical Polymerization from a Substrate Surface Manipulated by Bipolar Electrolysis: Fabrication of Gradient and Patterned Polymer Brushes

We report the first ever use of electrochemically mediated atom transfer radical polymerization (eATRP) employing a bipolar electrochemical method for the fabrication of both gradient and patterned polymer brushes. A potential gradient generated on a bipolar electrode allowed the formation of a concentration gradient of a Cu^I polymerization catalyst through the one‐electron reduction of Cu^II, resulting in the gradient growth of poly(NIPAM) brushes from an initiator‐modified substrate surface set close to a bipolar electrode. These polymer brushes could be fabricated in three‐dimensional gradient shapes with control over thickness, steepness, and modified area by varying the electrolytic conditions. Moreover, by site‐selective application of potential during bipolar electrolysis, a polymer brush with a circular pattern was successfully formed. Polymerization was achieved using both a polar monomer (NIPAM) and a nonpolar monomer (MMA) with the eATRP system.     

Synthesis of biaryl compounds using tandem ruthenium-catalyzed ring-closing metathesis

Tandem ring-closing enyne metathesis (RCEM)/ring-closing olefin metathesis (RCM) of tetraenynes with Grubbs second-generation catalyst, followed by elimination, was found to be a new and efficient synthetic approach to biaryl compounds. A preliminary asymmetric version of this approach, which used homochiral Ru-alkylidene catalysts, is also presented.     

On indices of local rings along local homomorphisms

Let φ:R → Sbe a local homomorphism of Gorenstein local rings of finite flat dimension. We prove if M is a stable maximal Cohen-Macaulay R-module, then M ?_R Sis also a stable maximal Cohen-Macaulay S-module. By using it, we also prove that index(R) ≤ index(S).     

A chemical study of thermally activated chromic titanate on silica ethylene polymerization catalysts

Thermally activated ethylene polymerization catalysts which contain chromium and titanium on silica differ from those catalysts which contain only chromium on silica. The characteristics of chromium-titanium catalysts vary with the method of incorporating the titanium and the thermal activation procedure. Titanated catalysts of the kind examined in this article have faster initiation and a higher polymerization rate per unit catalyst weight than corresponding catalysts without titanium. High-density polyethylene produced by this type of titanium-chromium catalyst tends to have a higher melt index and a broader molecular weight distribution than polyethylene made with chromium on silica catalysts. Iodometric titration showed that reduction from the initial hexavalent chromium to trivalent occurs when the dry, catalyst starting material is treated with titanium tetraisopropoxide. A study of the reaction between chromium trioxide and titanium tetraisopropoxide in carbon tetrachloride revealed that (1) it is not necessary to have a reaction between surface silanols and titanium tetraisopropoxide for the reduction to occur, and (2) the reaction product has an absorption near 660 nm in the visible range. Comparison of spectra showed that chromium trioxide on silica reduced by isopropyl alcohol has a shifted absorption, i.e., 600 nm. These findings are interpreted to mean that titanium atoms come sufficiently close to chromium atoms to change their electron density in the starting material and remain close neighbors in the activated catalysts. The interpretation is further supported by ESCA data and leads to the proposal that in this case the activated catalysts contain titanium chromate structures.     

Lissoclibadins 1-3, three new polysulfur alkaloids, from the ascidian Lissoclinum cf. badium

Three new polysulfur alkaloids, lissoclibadins 1 (1)-3 (3), were isolated from the ascidian Lissoclinum sp. (cf. L. badium Monniot, F. and Monniot, C., 1996). The structures of 1-3 were assigned on the basis of their spectral data, and the computational modeling study was utilized for 1. Compound 1 had a trimeric structure of three identical aromatic anime moieties connected through two sulfide and a disulfide bonds. Compounds 2 and 3 were dimeric structures of the same unit as that of 1 connected through a sulfide and disulfide bonds (2) and two sulfide bonds (3). Compounds 1 and 2 inhibited the growth of the marine bacterium Ruegeria atlantica (15.2 mm at 20 μg/disk and 12.2 mm at 5 μg/disk, respectively) and 2 showed antifungal activity to Mucor hiemalis (13.8 mm at 50 μg/disk). Compounds 1-3 were cytotoxic against HL-60 (IC₅₀=0.37, 0.21, and 5.5 μM, respectively).     

A Novel Thermomorphic System for Electrocatalytic Diels‐Alder Reactions

The discovery that lithium bis(trifluoromethane)sulfonamide (LiTFSI)/1‐nitropropane (PrNO₂) solution functions as a less polar alternative to lithium perchlorate (LiClO₄)/nitromethane (MeNO₂) solution has led to the development of a novel thermomorphic system for electrocatalytic Diels‐Alder reactions. Methyl cyclohexane (Me‐c‐Hex) can form a monophasic condition with LiTFSI/PrNO₂ solution at room temperature, enabling the use of hydrophobic dienophiles. After the electrochemical reaction, a biphasic condition can be formed at –50°C, where the cycloadducts are selectively recovered from the upper Me‐c‐Hex phase and the remaining lower LiTFSI/PrNO₂ solution can be reused.     

Determination of trace phosphate ion in water by visual method after preconcentration on a membrane filter for field work

A sensitive visual method based on comparing the color intensity of precipitate as phosphomolybdenum blue on a membrane filter, has been developed for the determination of trace phosphate ion in water for field work. A sample solution containing 0.05-5.0 mug of phosphate was treated in a 25-ml polypropylene syringe, and the resulting precipitate was filtered through a membrane filter attached to the syringe. The color intensity of the precipitate on the membrane filter was measured visually following the standard series method. The coefficient of variation for five measurements at 0.5 mug of phosphate is 11%. The detection limit is 0.02 mug of phosphate ion in 22.5 ml (0.9 mug PO(3-)(4)/l) of water sample when the effective filtration area is 0.78 cm(2). The interference of various ions was studied and optimum conditions were developed for the determination of phosphate ion in natural water.     

Evolution of water vapor from indium-tin-oxide thin films fabricated by various deposition processes

Tin-doped In₂O₃ (indium-tin-oxide) transparent conducting films are widely used as electrodes of liquid crystal displays and low-E windows. In the present study, a systematic TDS study was undertaken for ITO films fabricated by various deposition processes; such as PVD, dip coating and spray deposition. Water vapor was the main gas evolved from the films; gas evolution from the silicon substrate was negligible. The evolution proceeded via two steps at approximately 373 and 473-623 K. The amount of the evolved water was in the order: (dip-coated film)>(PVD films)> (spray-deposited film). This order was identical to that of the film's resistivities. This revised version was published online in August 2006 with corrections to the Cover Date.     

Photophysical and Photochemical Properties of Ru(bpy)3 2+ in Si-Ti Mixed Oxides Xerogels Prepared by the Sol-Gel Process

The luminescence spectra and lifetime of tris(2,2-bipyridine)ruthenium(II), Ru(bpy)₃ ²⁺, were studied in sol-gel reaction systems of tetramethoxysilane (TMOS) and titanium(IV) isopropoxide (TTIP) with HCl. Luminescence lifetime in the TMOS system increased as the sol-gel reaction proceeded, because diffusion-controlled luminescence quenching such as oxygen and collisional quenching with solvent molecules were suppressed in the rigid matrices. On the other hand, luminescence lifetime in the TTIP system decreased during the sol-gel reaction. The decrease in lifetime was ascribed to electron transfer from photoexcited Ru(bpy)₃ ²⁺ to the conduction band of the TiO₂ xerogels. Extended X-ray absorption fine structure (EXAFS) measurements were done to associate lifetime in the Si-Ti xerogels with the structures of Ti⁴⁺ sites in the xerogels.     

High-performance affinity chromatography system for the rapid, efficient assay of glycated albumin.

A high-performance affinity chromatographic system was constructed and shown to permit highly reproducible, rapid, automatic assays of serum glycated albumin (GA) by separation of albumin (Alb) on an anion-exchange column (Asahipak ES-502N) packed with a vinyl alcohol copolymer bearing diethylamino groups and consecutive separation of GA on a column packed with a vinyl alcohol copolymer bearing boronate groups. The first column selectively retained Alb free of other serum proteins and permitted at least a 95% recovery of sample Alb. The purity of the Alb peak was confirmed by two-dimensional electrophoresis. Chromatographic analyses of human serum Alb incubated with glucose on the second column showed that the peak area for GA increased in accordance with the incubation time and suggested selective adsorption of GA on the second column. Optimization of the conditions for the two-column system reduced the analysis time to 10 min. Analyses of human sera with the present system showed GA to be 16.1 +/- 1.1% (mean +/- S.D.) of total Alb in non-diabetic children and 39.9 +/- 9.1% (mean +/- S.D.) in diabetic children (0-17 years old).