Chain‐growth condensation polymerization of 4‐aminobenzoic acid esters bearing tri(ethylene glycol) side chain with lithium amide base

Chain‐growth condensation polymerization of p‐aminobenzoic acid esters 1 bearing a tri(ethylene glycol) monomethyl ether side chain on the nitrogen atom was investigated by using lithium 1,1,1,3,3,3‐hexamethyldisilazide (LiHMDS) as a base. The methyl ester monomer 1a afforded polymer with low molecular weight and a broad molecular weight distribution, whereas the polymerization of the phenyl ester monomer 1b at ?20 °C yielded polymer with controlled molecular weight (M_n = 2800–13,400) and low polydispersity (M_w/M_n = 1.10–1.15). Block copolymerization of 1b and 4‐(octylamino)benzoic acid methyl ester ( 2 ) was further investigated. We found that block copolymer of poly 1b and poly 2 with defined molecular weight and low polydispersity was obtained when the polymerization of 1b was initiated with equimolar LiHMDS at ?20 °C and continued at ?50 °C, followed by addition of 2 and equimolar LiHMDS at ?10 °C. Spherical aggregates were formed when a solution of poly 1b in THF was dropped on a glass plate and dried at room temperature, although the block copolymer of poly 1b and poly 2 did not afford similar aggregates under the same conditions. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1357–1363, 2010     

Similarities and Differences of the Active Sites in Basic and Advanced MgCl2‐Supported Ziegler‐Natta Propylene Polymerization Catalysts

Though preparation procedures of heterogeneous Ziegler‐Natta catalysts for propylene polymerization are sophisticated, it is uncertain whether the nature of the active sites is similar or different for different preparation procedures. In this study, the effects of preparation procedures on the nature of the active sites were investigated by stopped‐flow polymerization in combination with microstructure analysis of polymers. Both basic and advanced types of catalysts showed the same two kinds of isospecific active site, which indicated little influence of the preparation method on the active site structure. On the contrary, the ratios of the two kinds of isospecific sites were not the same, resulting in variation of average polymer properties.

     

The reaction of 1-silylcyclopropyl anions with dichloromethyl methyl ether: the efficient synthesis of cyclopropyl silyl ketones via cyclopropylidene derivatives

The reaction of 1-silylcyclopropyl anions with dichloromethyl methyl ether is described. The reaction with an excess amount of dichloromethyl methyl ether gives the corresponding cyclopropyl silyl ketones in low yields. On the other hand, the reaction under basic conditions proceeded smoothly to afford the corresponding cyclopropylidene derivatives, exclusively. The resulting cyclopropylidene compounds are subjected to hydrolysis or trapping with electrophiles easily to give the cyclopropyl silyl ketone derivatives in good yields.     

Development and photo-responsive peptide bond cleavage reaction of two-photon near-infrared excitation-responsive peptide

Two-photon near-infrared excitation-responsive amino acid was developed. It was incorporated into a peptide, and focused near-infrared pulsed laser irradiation-induced peptide bond cleavage reaction at the C-terminal position of the photo-responsive amino acid was observed.     

Hybrid micelle formation from poly(ethylene oxide-b-sodium 2-acrylamido-1-propanesulfonate-b-styrene) and Fe3+ ion in aqueous solution

Organic–inorganic nanohybrid particles are prepared in aqueous solution from poly(ethylene oxide-b-sodium 2-acrylamido-1-propanesulfonate-b-styrene) (PEO-b-PAMPS-b-PS) triblock copolymer and ferric ions. The hybrid micelles were characterized by dynamic light scattering, scanning electron microscopy, transmission electron microscopy, and zeta-potential measurements. The hydrodynamic diameter of the hybrid micelles ranges from 68 to 118 nm depending on the concentration of the polymer and the amount of ferric ions loaded on the polymer. Zeta-potential measurements revealed that the micelles are assembled mainly by electrostatic interaction between the ferric ions and the negatively charged PAMPS block in the PEO-b-PAMPS-b-PS.     

An efficient unnatural base pair for PCR amplification

Expansion of the genetic alphabet by an unnatural base pair system provides a powerful tool for modern biotechnology. As an alternative to previous unnatural base pairs, we have developed a new pair between 7-(2-thienyl)imidazo[4,5-b]pyridine (Ds) and 2-nitropyrrole (Pn), which functions in DNA amplification. Pn more selectively pairs with Ds in replication than another previously reported pairing partner, pyrrole-2-carbaldehyde (Pa). The nitro group of Pn efficiently prevented the mispairing with A. High efficiency and selectivity of the Ds-Pn pair in PCR amplification were achieved by using a substrate mixture of the gamma-amidotriphosphate of Ds and the usual triphosphates of Pn and the natural bases, with Vent DNA polymerase as a 3' to 5' exonuclease-proficient polymerase. After 20 cycles of PCR, the total mutation rate of the Ds-Pn site in an amplified DNA fragment was approximately 1%. PCR amplification of DNA fragments containing the unnatural Ds-Pn pair would be useful for expanded genetic systems in DNA-based biotechnology.     

First Synthesis of Continuous Mesoporous Copper Films with Uniformly Sized Pores by Electrochemical Soft Templating

Although mesoporous metals have been synthesized by electrochemical methods, the possible compositions have been limited to noble metals (e.g., palladium, platinum, gold) and their alloys. Herein we describe the first fabrication of continuously mesoporous Cu films using polymeric micelles as soft templates to control the growth of Cu under sophisticated electrochemical conditions. Uniformly sized mesopores are evenly distributed over the entire film, and the pore walls are composed of highly crystalized Cu.     

Synthesis of a Pentacene‐Type Silaborin via Double Dehydrogenative Cyclization of 1,4‐Diboryl‐2,5‐disilylbenzene

A new pentacene‐type silaborin, in which three benzene rings are bridged by silicon and boron atoms, has been synthesized and characterized by using NMR spectroscopy and X‐ray crystallographic analysis. The precursor, 1,4‐bis(dimesitylboryl)‐2,5‐bis(phenylsilyl)benzene ( 4 ), was prepared by stepwise introduction of a silyl group and a boryl group to a benzene ring starting from 1,4‐dibromobenzene. Double cyclization of 4 proceeds by a H‐Mes exchange and a B‐H/C‐H dehydrogenative condensation to afford pentacene‐type silaborin 5 . X‐ray crystal structure analysis reveals that 5 adopts a bent structure rather than a planar one. UV/Vis spectra and DFT calculations for 5 reveal a lowering of the LUMO energy level compared with corresponding anthracene‐type 3 .