Hydrogen‐transfer polymerization of vinyl monomers derived from 4‐methylbenzoyl isocyanate and acrylamide derivatives

The anionic polymerization of N‐acryloyl‐N′‐(4‐methylbenzoyl)urea (1) was carried out at 80°C for 24 h in DMF, DMSO, acetonitrile, or toluene by t‐BuOK or DBU (3 mol %) as an initiator to obtain polymer 3 in a good yield. The structure of 3 was dependent upon the initiator used, in which t‐BuOK selectively conducted the hydrogen‐transfer polymerization, while DBU partially induced the vinyl polymerization (16–20%). Likewise, N‐acryloyl‐N‐methyl‐N′‐(4‐methylbenzoyl)urea (2, i.e., an N‐methylated derivative of 1) was subjected to the hydrogen‐transfer polymerization. Although the yield of the polymer was lower in comparison with 1, the structure of the obtained polymer 4 was similarly governed by the initiator. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 465–472, 1999     

High performance bioanode based on direct electron transfer of fructose dehydrogenase at gold nanoparticle-modified electrodes

The direct electron transfer reaction of fructose dehydrogenase (FDH) from Gluconobacter sp. on alkanethiol-modified gold nanoparticles (AuNPs) was examined. AuNP-modified electrodes were simply fabricated by depositing citrate-reduced gold nanoparticles onto a gold electrode and carbon fiber paper and then covering the surface with a self-assembled monolayer of alkanethiols. The immobilization of AuNPs provided a large effective surface area for the adsorption of FDH. Catalytic oxidation currents based on the direct electron transfer reaction of FDH were observed from a potential about ?100 mV (vs. Ag/AgCl, 3 M NaCl) in the presence of d-fructose without a mediator. The current density reached as high as 14.3 ± 0.93 mA/cm² (at +500 mV), which was achieved in the presence of 200 mM d-fructose by immobilization of FDH on 2-mercaptoethanol-modified AuNP/carbon fiber paper electrodes.     

Synthesis and Reactivity of Six‐Membered Oxa‐Nickelacycles: A Ring‐Opening Reaction of Cyclopropyl Ketones

Cyclopropanecarboxaldehyde ( 1 a ), cyclopropyl methyl ketone ( 1 b ), and cyclopropyl phenyl ketone ( 1 c ) were reacted with [Ni(cod)₂] (cod=1,5‐cyclooctadiene) and PBu₃ at 100 °C to give η²‐enonenickel complexes ( 2 a – c ). In the presence of PCy₃ (Cy=cyclohexyl), 1 a and 1 b reacted with [Ni(cod)₂] to give the corresponding μ‐η²:η¹‐enonenickel complexes ( 3 a , 3 b ). However, the reaction of 1 c under the same reaction conditions gave a mixture of 3 c and cyclopentane derivatives ( 4 c , 4 c′ ), that is, a [3+2] cycloaddition product of 1 c with (E)‐1‐phenylbut‐2‐en‐1‐one, an isomer of 1 c . In the presence of a catalytic amount of [Ni(cod)₂] and PCy₃, [3+2] homo‐cycloaddition proceeded to give a mixture of 4 c (76 %) and 4 c′ (17 %). At room temperature, a possible intermediate, 6 c , was observed and isolated by reprecipitation at ?20 °C. In the presence of 1,3‐bis(2,6‐diisopropylphenyl)imidazol‐2‐ylidene (IPr), both 1 a and 1 c rapidly underwent oxidative addition to nickel(0) to give the corresponding six‐membered oxa‐nickelacycles ( 6 ai , 6 ci ). On the other hand, 1 b reacted with nickel(0) to give the corresponding μ‐η²:η¹‐enonenickel complex ( 3 bi ). The molecular structures of 6 ai and 6 ci were confirmed by X‐ray crystallography. The molecular structure of 6 ai shows a dimeric η¹‐nickelenolate structure. However, the molecular structure of 6 ci shows a monomeric η¹‐nickelenolate structure, and the nickel(II) 14‐electron center is regarded as having “an unusual T‐shaped planar” coordination geometry. The insertion of enones into monomeric η¹‐nickelenolate complexes 6 c and 6 ci occurred at room temperature to generate η³‐oxa‐allylnickel complexes ( 8 , 9 ), whereas insertion into dimeric η¹‐nickelenolate complex 6 ai did not take place. The diastereoselectivity of the insertion of an enone into 6 c having PCy₃ as a ligand differs from that into 6 ci having IPr as a ligand. In addition, the stereochemistry of η³‐oxa‐allylnickel complexes having IPr as a ligand is retained during reductive elimination to yield the corresponding [3+2] cycloaddition product, which is consistent with the diastereoselectivity observed in Ni⁰/IPr‐catalyzed [3+2] cycloaddition reactions of cyclopropyl ketones with enones. In contrast, reductive elimination from the η³‐oxa‐allylnickel having PCy₃ as a ligand proceeds with inversion of stereochemistry. This is probably due to rapid isomerization between syn and anti isomers prior to reductive elimination.     

Peroxy radicals as motional probes at the end of isolated polystyrene chains and on the cellulose surfaces in vacuum

The isolated polystyrene chains spin-labeled with peroxide radical at the free end (IPSOO) in which the chain roots were covalently bonded to the surface of microcrystalline cellulose (MCC) powder were produced by mechanochemical polymerization of styrene initiated by MCC mechanoradicals. The IPSOO was used as motional probes at the ends of isolated polystyrene chains tethered on the surface of MCC powder. Two modes for the molecular motion of IPSOO were observed. One was a tumbling motion of IPSOO on the MCC surface, defined as a train state, and another was a free rotational motion of IPSOO protruding out from the MCC surface, defined as a tail state. The temperature of tumbling motion (T _tum ) of IPSOO at the train state was at 90 K with anisotropic correlation times. T _tum (90 K) is extremely low compared to the glass transition temperature (T _g ^b ; 373 K) of polystyrene in the bulk. At temperatures above 219 K, the IPSOO was protruded out from the MCC surface, and freely rotated at the tail state. The train–tail transition temperature (T _train–tail ) was estimated to be 222 K. T _tum (90 K) and T _train–tail (222 K) are due to the extremely low chain segmental density of IPSOO on the MCC surface under vacuum. The interaction between IPSOO and the MCC surface is a minor contributing factor in the mobility of IPSOO on the surface under vacuum. It was found that peroxy radicals are useful probes to characterize the chain mobility reflecting their environmental conditions.     

Determination of rare earth elements in seawater by on-line column preconcentration inductively coupled plasma mass spectrometry

A home made column of commercially available iminodiacetate resin, Muromac A-1 (50–100 mesh) was used to concentrate rare earth elements (REEs) (15 elements: Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) in seawater. An automated low pressure flow analysis method with on-line column preconcentration/inductively coupled plasma mass spectrometry (ICP-MS) is described for the determination of REEs in seawater. Sample solutions (adjusted to pH of 3.0) passed through the column. After washing the column with water, the adsorbed elements were subsequently eluted into the plasma with 0.7 M nitric acid. Calibration curves were accomplished by means of purified artificial seawater with a sample loading time of 120 s. Detection limits (DLs) of the on-line column preconcentration/ICP-MS by eight replicate operations were between 0.040 and 0.251 pg ml⁻¹ for REEs in the artificial seawater. The precision was less than 8.9% for REEs and one sample can be processed in 7 min using a 7 ml of sample. The proposed method was applied to determine REEs in coastal seawater of Hiroshima Bay, Japan.     

Influence of the glucosylated β-cyclodextrin inclusion on sulfur trioxide spin-adduct stabilizations and spin-trapping rate processes for DMPO-type spin traps

The effect of CD-inclusion on spin-trapping rates and spin-adduct decay rates for sulfur trioxide radical anion (SO₃ ^??) was investigated. SO₃ ^?? radical was produced with UV photolysis of sodium sulfite in basic aqueous solution, and spin-trapped with various spin traps, i.e., PBN (α-phenyl-N-t-butylnitrone), DMPO (5,5-dimethyl pyrroline-1-oxide), and three other phosphoryl DMPO-type spin traps. A modified β-CD, 6-O-α-d-glucosyl-β-cyclodextrin (G-β-CD) having better inclusion properties than β-CD, was employed. Upon adding excess G-β-CD, decay rates of SO₃ ^?? radical adducts significantly decreased in most spin traps. Half-lives of SO₃ ^?? radical adducts of phosphoryl spin traps were one to two orders of magnitude longer than that of PBN or DMPO, and the G-β-CD addition further extended the half-life time. The spin traps containing phosphoryl-group all showed higher SO₃ ^?? trapping rates than those of PBN and DMPO, but two phosphoryl spin traps achieved slower trapping rates by G-β-CD addition. In addition, the structures of CD-inclusion complexes of spin traps were established by means of 1D and 2D NMR measurements. Based on the results, the influences of inclusion on the spin-trapping rate processes and spin-adduct stabilizations were discussed. We conclude that substituents in DMPO-type spin traps may be modified to provide best spin-trapping capabilities in the presence or absence of CD.