Synthesis and asymmetric polymerization of (S)‐N‐maleoyl‐L‐leucine propargyl ester

A kind of N‐substituted maleimide (RMI), chiral (S)‐N‐maleoyl‐L ‐leucine propargyl ester ((S)‐PLMI) with a specific rotation of [α]₄₃₅ = ?27.5° was successfully synthesized from maleic anhydride, L ‐leucine, and propargyl alcohol. (S)‐PLMI was polymerized by three polymerization methods to obtain the corresponding optically active polymers. Asymmetric anionic, radical, and transition‐metal‐catalyzed polymerizations were carried out using organometal/chiral ligands, 2,2′‐azobisisobutyronitrile (AIBN) and (bicyclo [2,2,1]hepta‐2,5‐diene) chloro rhodium (I) dimer ([Rh(nbd) Cl]₂), respectively. Poly((S)‐PLMI) obtained by [Rh(nbd)Cl]₂ in DMF showed the highest specific rotation of ?280.6°. Chiroptical properties and structures of the polymers obtained were investigated by GPC, CD, IR, and NMR measurements. Two types of poly((S)‐PLMI)‐bonded‐silica gels as the chiral stationary phase (CSP) were prepared for high‐performance liquid chromatography (HPLC). Their optical resolution abilities were also elucidated. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3722–3738, 2007     

Spin-singlet superconductivity and antiferromagnetic correlations for the field-aligned powder of the triangular lattice NaxCoO2 · yH2O

Nuclear magnetic resonance and relaxation measurements of the ⁵⁹Co nuclei for the well-defined field-aligned powder of the triangular lattice superconductor Na_xCoO₂ · yH₂O with a nearly optimal composition for the transition temperature T_c have been performed. Detailed analyses indicate that the Knight shifts for the directions parallel and perpendicular to the CoO₂ plane and the spin-lattice relaxation rates, taken by making an inevitable deterioration of specimen minimal, are significantly smaller than most of the data reported to date, and that this compound is classified into one of the unconventional spin-singlet superconductors as suggested by recent works for single crystals with a lower T_c. A small enhancement of two-dimensional antiferromagnetic spin correlations at some nonzero wave vector may emerge near T_c.     

On distance two graphs of upper bound graphs

For a poset P=(X,≤), the upper bound graph (UB-graph) of P is the graph U=(X,E_U), where uv∈E_U if and only if u≠v and there exists m∈X such that u,v≤m. For a graph G, the distance two graph DS₂(G) is the graph with vertex set V(DS₂(G))=V(G) and u,v∈V(DS₂(G)) are adjacent if and only if d_G(u,v)=2. In this paper, we deal with distance two graphs of upper bound graphs. We obtain a characterization of distance two graphs of split upper bound graphs.     

Synthesis of two regiospecific isomers of monotosyl-γ-cyclodextrin

Tosylation of -cyclodextrin in an aqueous alkaline solution gave two regiospecific isomers (2-monotosyl--cyclodextrin(1) and 6-monotosyl--cyclodextrin(2)), that could recognize and catalyze small sized guest molecules; 2-monotosyl--CD recognized small sized guest molecules more effectively than did 6-monotosyl--CD.     

Asymmetric anionic polymerization of N‐1‐naphthylmaleimide with chiral ligand‐organometal complexes in toluene

Asymmetric anionic homopolymerizations of N‐1‐naphthylmaleimide (1‐NMI) were performed with chiral ligand/organometal complexes to form optically active polymers. Poly(1‐NMI)s obtained with methylene‐bridged bisoxazoline derivatives (Rbox)‐diethylzinc (Et₂Zn) complexes showed high specific optical rotations ([α]) from +152.3 to +191.4°. Circular dichroism spectra of the polymers exhibited a split Cotton effect in the UV absorption‐band region. According to the exciton chirality method, the absolute configuration of the polymer main chain was determined according to the following method: (+)‐poly[N‐substituted maleimides (RMI)] main chains can contain more (S,S)‐ than (R,R)‐configurations. (?)‐Poly(RMI) main chains can contain more (R,R)‐ than (S,S)‐configurations. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3556–3565, 2001     

Effective form of sulfoquinovosyldiacyglycerol (SQDG) vesicles for DNA polymerase inhibition

Sulfoquinovosyldiacyglycerol (SQDG) has a wide range of biological activities that make it an attractive compound for the development of new drugs. Chemically synthesized beta-SQDG-C(18:0) (1,2-di-O-stearoyl-3-O-(6-deoxy-6-sulfo-beta-d-glucopyranosyl)-sn-glycerol), for example, has a potent inhibitory effect on DNA polymerases. We investigated the properties of the vesicle form of beta-SQDG-C(18:0) as the monomer has low solubility in water. The structure of the beta-SQDG-C(18:0) vesicles are highly influenced by NaCl concentration in preparation process. At low NaCl concentrations, the beta-SQDG-C(18:0) vesicles have high surface curvature and form small unilamellar vesicles. Increases in NaCl concentration, resulted in decreased surface curvature and a tendency for beta-SQDG-C(18:0) to form large multilamellar vesicles. The small unilamellar vesicles showed a potent inhibitory effect on DNA polymerase beta, whereas the large multilamellar vesicles had no such effect. We investigated further the relationship between vesicle size and activity by preparing smaller vesicles (262, 99 and 43 nm in diameter) using an extrusion technique. These smaller vesicles had a greater inhibitory effect on DNA polymerase beta activity than non-extruded vesicles. beta-SQDG-C(18:0) vesicles, especially those of small size, were effective in DNA polymerase inhibition and are expected to have high applicability in DNA polymerase study.     

Asymmetric polymerization of N‐substituted maleimides with chiral oxazolidine–organolithium

Asymmetric anionic homopolymerizations of achiral N‐substituted maleimides (RMI) were performed with lithium 4‐alkyl‐2,2‐dialkyloxazolidinylamide. All obtained polymers were optically active, exhibiting opposite optical rotation to that of a corresponding oxazolidinyl group at the terminal of the main chain. This suggests that opposite optical rotation to the corresponding chiral oxazolidine was induced to the polymer main chain. In the polymerization using a fluorenyllithium (FlLi)–oxazolidine complex, the obtained polymer with a fluorenyl group at the polymer end showed a negative specific rotation. This also suggests that asymmetric induction took place in the polymer main chain. The asymmetric induction was supported by the circular dichroism (CD) and GPC analysis with polarimetric detector. Optical activity of the polymer was attributed to different contents of (S,S) and (R,R) structures formed from threo‐diisotactic additions, as supported by the ¹³C‐NMR spectra of the polymers and the model compounds. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 473–482, 1999     

Recent lean NOx catalyst technologies for automobile exhaust control

The current status of our development work on lean NO_x catalysts for application to future gasoline and diesel engines is described. As a result of further improvements in fuel economy, the temperature of exhaust gas will be lower and there will be smaller quantities of hydrocarbons (HCs) in the exhaust of future engines. Therefore, it is necessary to improve the activity of lean NO_x catalysts at lower temperatures and achieve higher selectivity of the NO_x–HC reaction. Utilizing precious metal catalysts is one effective way of improving catalyst activity at lower temperatures, and HC adsorption and reforming are two key technologies for improving the catalyst selectivity for the NO_x–HC reaction.