Importance of chiral phase-transfer catalysts with dual functions in obtaining high enantioselectivity in the Michael reaction of malonates and chalcone derivatives

[reaction: see text]. Highly enantioselective Michael addition of diethyl malonate to chalcone derivatives has been achieved under mild phase-transfer conditions by the successful utilization of N-spiro C(2)-symmetric chiral quaternary ammonium bromide 1 as a catalyst, which possesses diarylhydroxymethyl functionalities as a recognition site for the prochiral electrophile. This simple asymmetric Michael addition process was found to be quite effective for various chalcone derivatives, including those with heteroaromatic substituents.     

Vector fields with topological stability

In this paper, we give a characterization of the structurally stable vector fields by making use of the notion of topological stability. More precisely, it is proved that the interior of the set of all topologically stable vector fields coincides with the set of all vector fields satisfying Axiom A and the strong transversality condition.

     

Nucleophilic addition of benzenethiol to 1',2'-unsaturated nucleosides: 1'-C-phenylthio-2'-deoxynucleosides as anomeric radical precursors

The addition reaction of benzenethiol to the glycal portion of 1',2'-unsaturated uridine proceeds efficiently in the presence of Et(3)N. The mechanism involves nucleophilic attack of thiolate at the anomeric position in the rate-determining step, wherein conjugation between the nucleobase and the glycal portion is crucial. The derivative having a methyl group either at the 2'- or 6-position did not undergo this addition reaction, due to their sterically prohibited coplanarity. The 1',2'-unsaturated derivatives of thymine and adenine can also be used as substrates for this addition reaction. It was also shown that the resulting 1'-C-phenylthio-2'-deoxynucleosides serve as precursors for radical-mediated C-C bond formation at the anomeric position.     

Synthesis and characterization of oligodeoxynucleotides containing formamidopyrimidine lesions and nonhydrolyzable analogues

Oligodeoxynucleotides containing formamidopyrimidine lesions and C-nucleoside analogues at defined sites were prepared by solid-phase synthesis and in some cases enzymatic ligation. Formamidopyrimidine lesions were introduced as dinucleotides to prevent rearrangement to their pyranose isomers. Oligodeoxynucleotides containing single diastereomers of C-nucleoside analogues of Fapy.dA were introduced by using the respective phosphoramidites. The formamidopyrimidine lesions reduce the T(M) of dodecamers relative to their unmodified nucleotide counterparts when opposite the nucleotide proper base-pairing partner. However, duplexes containing Fapy.dG-dA mispairs melt significantly higher than those comprised of dG-dA. All duplexes containing Fapy.dA-dX or its C-nucleoside analogue melt lower than the respective complexes containing dA-dX. Studies of the alkaline lability of oligodeoxynucleotides containing formamidopyrimidine lesions indicate that Fapy.dA is readily identified as an alkali-labile lesion with use of piperidine (1.0 M, 90 degrees C, 20 min), but Fapy.dG is less easily identified in this manner.     

Chaotic transition in a three-coupled phase-locked loop system

The chaotic transition is observed in a three-coupled phase-locked loop (PLL) system in both experiments and numerical simulations. In this system, three PLL oscillators are connected with the periodic boundary condition. Intermittency is found in partially synchronized phase, in which two of three oscillators synchronize with each other and form a pair, and the chaotic transition occurs due to the recombination of synchronized pairs so that different pair is re-formed. In this phase, on-off intermittency is also observed and statistical analyses are carried out for on-off intermittent time series. This intermittency is considered as a hybrid type of intermittency with both on-off intermittency and intermittency due to the recombination of synchronized pairs present in the same time series. We also show the chaotic transition phenomena in a three-coupled logistic map system. (c) 2001 American Institute of Physics.     

A remark on finiteness of the lower spectrum of uniformly elliptic operators with singular potentials

In this paper, we extend the result of Donig[Do] and show the finiteness of the lower spectrum of the uniformly elliptic operators–·(A(x))+q with singular potentialsq which belong to the Kato class. Even in the case of the Schrödinger operator–+q, our proof simplifies the one in [Do].     

A new urea gelator: incorporation of intra- and intermolecular hydrogen bonding for stable 1D self-assembly

A new bisurea gelator derived from 2,6-diaminopyridine has been developed. It efficiently gelates common organic and liquid crystalline (LC) solvents by forming elongated self-assembled fibres in solvents. X-Ray crystallography and 1H NMR measurements reveal that two urea groups in pyridine-based bisurea compounds form different hydrogen bonding patterns. One of two urea units is involved in intramolecular hydrogen bonding with the pyridyl nitrogen, while the other urea unit forms bifurcated intermolecular hydrogen bonding. This hydrogen-bonded structure is key for the fibrous self-assembly along with the efficient gelation. In addition, LC gels based on the pyridine-based gelator exhibit good electrooptic properties. These results indicate that the pyridine-based bisurea compound is a good gelator not only effective in gelation but also useful as a component of functional soft materials.     

Integrability and algebraic structure of the quantum Calogero-Moser model

For the quantum Calogero-Moser model, we present the following two results. First, it has a set of conserved operators which are involutive. This proves the integrability of the model. Second, the Lax operator gives a list of new operators (boost operators). The conserved operators and the boost operators constitute the U(1)-current algebra.     

The effect of morphology on sorption and transport of carbon dioxide in poly(4,4'-oxydiphenylene pyromellitimide)

Sorption and transport of carbon dioxide were investigated for poly(4,4'-oxydiphenylene-pyromellitimide) films (PI-1, PI-2, and PI-3) imidized at 160, 200, and 400°C, respectively, as well as for a chemically identical commercial polyimide film, Kapton-H. The solubility, permeability, and diffusion coefficients (S, P, and \[ \overline D \] , respectively) at 80°C and 20 atm in PI-3 were 67, 25, and 37%, respectively, as large as those in PI-2. These significant reductions are attributed to a higher degree of segmental aggregation in PI-3 caused by a 1.7% increase in the density (d) as compared with PI-2. The differences in S, P, \[ \overline D \] , and d between PI-3 and Kapton-H were rather small as compared with those between PI-3 and PI-2, suggesting that the in-plane orientation has a minor effect on the sorption and transport in Kapton-H as compared with the aggregation. Influence of the morphology on the dual-mode sorption and transport parameters was also investigated. With increasing density, the Langmuir capacity constant and the diffusion coefficients for the Henry's law and Langmuir populations decreased by higher rates than the Henry's law solubility constant, being contrary to the results reported for a typical semicrystalline glassy polymer, polyethylene terephthalate. This may suggest that the nonaggregated or less-aggregated regions taking an important part in the sorption and transport are denser for the sample having a higher overall density.