γ-poly(glutamic acid) as an initiator of cationic polymerization of N-vinylcarbazole and N-vinyl-2-pyrrolidone

The cationic polymerization of vinyl monomers initiated by biosynthesized γ-poly(glutamic acid) (γ-PGA) powder surface was carried out in a heterogeneous system. It was found that the polymerization of N-vinylcarbazole (NVC) and N-vinyl-2-pyrrolidone (NVPD) is initiated by γ-PGA powder. The grafting of polymers onto γ-PGA surface was scarcely observed. The apparent activation energy of the polymerization of NVC and NVPD was estimated to be 20.2 and 24.8 kJ/mol, respectively. The polymerization was totally inhibited by the addition of triethylamine and pyridine, but not hydroquinone. The polymerization rate in nitrobenzene was larger than that in toluene. These results indicated the cationic nature of the polymerization. γ-PGA treated with KOH did not show the initiating activity of the polymerization. Therefore, carboxyl groups on γ-PGA powder surface play an important role in the initiation of the polymerization. It may be suggested that the polymerization is initiated by proton addition to monomer from carboxyl groups on γ-PGA powder surface and the propagation proceeds with carboxylate anion on the surface as counter ion. © 1993 John Wiley & Sons, Inc.     

Efficient method for the deprotection of tert-butyldimethylsilyl ethers with TiCl4-Lewis base complexes: application to the synthesis of 1beta-methylcarbapenems

TiCl4-Lewis base (AcOEt, CH3NO2) complexes smoothly deprotected tert-butyldimethylsilyl (TBDMS) ethers. The reaction velocity with these complexes, which seemed less reactive due to the influence of Lewis bases, was considerably greater than that with TiCl4 alone. Selective desilylations between aliphatic and aromatic TBDMS ethers (1 and 5), between 1 and benzyl, allyl, tosyl, methoxyphenyl, and chloroacetyl ethers (13, 14, 15, 16, and 17), and between TBDMS and TBDPS ethers (18 and 19) were successfully performed. Desilylation of TBDMS-aldol, acyloin, and beta-lactam analogues 9-12 proceeded smoothly due to anchimeric assistance by the neighboring carbonyl groups. The present method was successfully applied to the practical synthesis of 1beta-methylcarbapenems 20a'-f'.     

Rational Design for Cooperative Recognition of Specific Nucleobases Using β‐Cyclodextrin‐Modified DNAs and Fluorescent Ligands on DNA and RNA Scaffolds

We propose a binary fluorimetric method for DNA and RNA analysis by the combined use of two probes rationally designed to work cooperatively. One probe is an oligonucleotide (ODN) conjugate bearing a β‐cyclodextrin (β‐CyD). The other probe is a small reporter ligand, which comprises linked molecules of a nucleobase‐specific heterocycle and an environment‐sensitive fluorophore. The heterocycle of the reporter ligand recognizes a single nucleobase displayed in a gap on the target labeled with the conjugate and, at the same time, the fluorophore moiety forms a luminous inclusion complex with nearby β‐CyD. Three reporter ligands, MNDS (naphthyridine–dansyl linked ligand), MNDB (naphthyridine–DBD), and DPDB (pyridine–DBD), were used for DNA and RNA probing with 3′‐end or 5′‐end modified β‐CyD – ODN conjugates. For the DNA target, the β‐CyD tethered to the 3′‐end of the ODN facing into the gap interacted with the fluorophore sticking out into the major groove of the gap site ( MNDS and DPDB ). Meanwhile the β‐CyD on the 5′‐end of the ODN interacted with the fluorophore in the minor groove ( MNDB and DPDB ). The results obtained by this study could be a guideline for the design of binary DNA/RNA probe systems based on controlling the proximity of functional molecules.     

Development of a sensitive surface plasmon resonance immunosensor for detection of 2,4-dinitrotoluene with a novel oligo (ethylene glycol)-based sensor surface

A surface plasmon resonance (SPR) immunosensor for detection of 2,4-dinitrotoluene (2,4-DNT), which is a signature compound of 2,4,6-trinitrotoluene-related explosives, was developed by using a novel oligo (ethylene glycol) (OEG)-based sensor surface. A rabbit polyclonal antibody against 2,4-DNT (anti-DNPh-KLH-400 antibody) was prepared, and the avidity for 2,4-DNT and recognition capability were investigated by indirect competitive ELISA. The sensor surface was fabricated by immobilizing a 2,4-DNT analog onto an OEG-based self-assembled monolayer formed on a gold surface via an OEG linker. The fabricated surface was characterized by Fourier-transform infrared-refractive absorption spectrometry (FTIR-RAS). The immunosensing of 2,4-DNT is based on the indirect competitive principle, in which the immunoreaction between the anti-DNPh-KLH-400 antibody and 2,4-DNT on the sensor surface was inhibited in the presence of free 2,4-DNT in solution. The limit of detection for the immunosensor, calculated as three times the standard deviation of a blank value, was 20 pg mL⁻¹, and the linear dynamic range was found to be between 1 and 100 ng mL⁻¹. Additionally, the fabricated OEG-based surface effectively prevented non-specific adsorption of proteins, and the specific response to anti-DNPh-KLH-400 antibody was maintained for more than 30 measurement cycles.     

Me‐bipam for Enantioselective Ruthenium(II)‐Catalyzed Arylation of Aldehydes with Arylboronic Acids

Ligand design by‐pam : A ruthenium‐catalyzed asymmetric arylation of aldehydes with arylboronic acids has been developed, giving chiral diarylmethanols in good yields. The use of a chiral bidentate phosphoramidite ligand ((R,R)‐Me‐bipam) led to excellent enantioselectivities.

     

Tuning of Electronic Properties of Single‐Walled Carbon Nanotubes under Homogenous Conditions

Reversible and non‐bonding interaction between SWNTs and ODCB is observed from the analyses of visible near‐infrared absorption data and Raman spectroscopies (see spectra). The solvent effect on SWNTs effectively controls the electronic structure of SWNTs under homogeneous conditions.

     

Acyl Fluorides in Late‐Transition‐Metal Catalysis

In this Review, we summarize the current state of the art in late‐transition‐metal‐catalyzed reactions of acyl fluorides, covering both their synthesis and further transformations. In organic reactions, the relationship between stability and reactivity of the starting substrates is usually characterized by a trade‐off. Yet, acyl fluorides display a very good balance between these properties, which is mostly due to their moderate electrophilicity. Thus, acyl fluorides (RCOF) can be used as versatile building blocks in transition‐metal‐catalyzed reactions, for example, as an “RCO” source in acyl coupling reactions, as an “R” source in decarbonylative coupling reactions, and as an “F” source in fluorination reactions. Starting from the cleavage of the acyl C?F bond in acyl fluorides, various transformations are accessible, including C?C, C?H, C?B, and C?F bond‐forming reactions that are catalyzed by transition‐metal catalysts that contain the Group 9–11 metals Co, Rh, Ir, Ni, Pd, or Cu.