Ring transformation of pyrimidines to pyridines. Synthesis of 4-alkylaminopyridin-2-ones by alkaline hydrolysis of 6-(2-dimethylaminovinyl)uracils

Alkaline hydrolysis of 1,3-disubstituted 6-(2-dimethylaminovinyl)uracils 2 induced a novel ring transformation giving 4-alkylaminopyridin-2-ones 3 via ring-opening and ring-closure processes. The 4-methylamino-3-nitropyridin-2-one ( 3a ) thus obtained was employed for the synthesis of 3-deazahypoxanthine derivative 8. 4-Alkylamino-3-cyanopyridin-2-ones 11 , ricinine analogs, were also prepared by the reaction of 4-chloro-3-cyano-1-methylpyridin-2-one ( 10 ) with amines.     

Authors index to volume 87

Nuclear relaxation times T₁ and T_1p and T₂ of two Tl isotopes, ²⁰³Tl and ²⁰⁵Tl, in solid TINO₂ were measured betwe en 120 and 430 K. The shorter component of the highly non-exponential T₁ decay shows two minima above and below room temperature, which were assigned to Tl⁺ ionic diffusion to NO^-₂ reorientation.     

Variation of free volume size and content of shape memory polymer — Polyurethane — Upon temperature studied by positron annihilation lifetime techniques and infrared spectroscopy

Positron annihilation lifetime measurement and Fourier transform infrared spectrometry were applied to the study of temperature dependencies of free volume parameters and hydrogen bonds in segmented polyurethane, specially fabricated as a shape memory polymer. The variation of free volumes in amorphous region were correlated to that of hydrogen bonding and the shape memory mechanism of polyurethane is elucidated from a microscopic point of view. The relationship between free volume contents and the formation of hydrogen bonds significantly suggests that the shape memory occurs due to the configurational recovery of the microscopic regulation around urethane bundles of hard segment and consequent restoration of soft-segment in polyurethane.     

Rotational spectrum and hydrogen bonding of the H2O-HO radical complex

The first spectroscopic identification of the H2O-HO radical complex in the gas phase has been conducted by utilizing pulsed-discharge nozzle Fourier transform microwave spectroscopy. R-branch transitions in the Ka = 0 manifold appeared as in Hund's case (b), but extraordinarily large spin doubling implies a strong spin-orbit coupling between the electronic ground and low-lying excited states that correlate to the degenerate 2Pi state in free OH. The geometry of the complex is of C2v symmetry as a zero-point vibrational average, in which the OH radical acts as a proton donor to water. Precisely determined hyperfine coupling constants associated with hydrogen nuclei indicate a substantial rearrangement in unpaired electron distribution: there exists small but nonzero spin density on the H atoms in water.     

Amphiphilic copolymers of some aromatic vinyl compounds and an electrolytic monomer as potential media for photosensitized electron transfer: Fluorescence quenching by an amphiphilic electron acceptor in aqueous media

Amphiphilic polymers were prepared by the copolymerization of 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and aromatic vinyl compounds such as 9-vinylphenanthrene (VPh) and 1-vinylpyrene (VPy) with the expectation that they would serve as potential media for photosensitized electron transfer reactions. AMPS strongly solubilizes the hydrophobic segments into water; i.e., poly(AMPS-co-VPh) with VPh mole fraction (f_Ph) up to about 0.60 and poly(AMPS-co-VPy) with VPy mole fraction (f_Py) up to about 0.35 were found to be soluble in water. Poly(AMPS-co-VPh) in aqueous solution, as compared with that in DMF solution, showed a broad fluorescence spectrum with significant tailing in the longer-wavelength region along with a decrease in the intensity of the structured, monomer fluorescence band. These phenomena seem to imply the presence of an excimerlike interaction of phenanthryl groups in an aqueous solution through which the fluorescence from excited VPh units may be partly self-quenched. A considerable enhancement of the fluorescence from sodium 8-anilino-1-naphthalenesulfonate (ANS) caused by hydrophobic interaction of the probe with poly(AMPS-co-VPh) in aqueous solution indicated that these copolymers assume micellar structures. The fluorescence of these copolymers in aqueous solutions was quenched by bis(2-hydroxyethyl)terephthalate (BHET), an amphiphilic quencher, far more effectively than by fumaric acid, a hydrophilic quencher. This tendency is particularly strong for the copolymers with higher content of hydrophobic units. The second-order rate constants for the quenching of poly(AMPS-co-VPh) (f_Ph = 0.58) by BHET were found to be ca. 3 × 10¹⁰ and 1.5 × 10⁹ M^?1 s^?1 in aqueous and in DMF solution, respectively. The larger value in an aqueous solution is presumably due to an increase of the effective concentration of the amphiphilic quencher around the VPh sequences of the copolymer resulting from hydrophobic interaction.     

Resonance Raman spectra of 15N enriched metallooctaethylorphyrins. Characterization of the oxidation state marker bands of hemoproteins

Resonance Raman spectra of ¹⁵N enriched metallooctaethylporphyrins [M(OEP) ? ¹⁵N₄] [M = Ni²⁺, Fe³⁺ (high spin), and Fe³⁺ (low spin)] were observed. Polarized Raman lines corresponding to the oxidation state marker band of hemoproteins were observed at 1377 (Ni), 1369 (Fe high spin) and 1372^?1 (Fe low spin) which were shifted to lower frequency from those of the ¹⁴N compounds by 6, 5, and 6 cm^?1, respectively. The vibrational mode for this band was shown to include an appreciable contribution of the C_αN symmetric stretching vibration and to be associated with ca. 0.01 Å of in-phase displacement of the four pyrrole nitrogens toward the metal ion.     

Mutation effects of a conserved alanine (Ala510) in type I polyhydroxyalkanoate synthase from Ralstonia eutropha on polyester biosynthesis

Type I polyhydroxyalkanoate (PHA) synthases, as represented by Ralstonia eutropha enzyme (PhaC(Re)), have narrow substrate specificity toward (R)-3-hydroxyacyl-coenzyme A with acyl chain length of C3-C5 to yield PHA polyesters. In this study, saturation point mutagenesis of a highly conserved alanine at position 510 (A510) in PhaC(Re) was carried out to investigate the effects on the polymerization activity and the substrate specificity for in vivo PHA biosynthesis in bacterial cells. A series of saturation mutants were first applied for poly[(R)-3-hydroxybutyrate] homopolymer synthesis in Escherichia coli and R. eutropha PHB(-)4 (PHA negative mutant) cells to assess the polymerization activity. All mutants showed quantitatively similar polymerization activities when R. eutropha PHB(-)4 was used for assay, whereas several mutants such as A510P showed low activities in E. coli. Further analysis has revealed that majority of mutants synthesize polyesters with higher molecular weights than the wild-type. In particular, substitution by acidic amino acids, A510D(E), led to remarkable increases in molecular weights. Subsequently, PHA copolymer synthesis from dodecanoate (C12 fatty acid) was examined. The copolymer compositions were varied depending on the mutants used. Significant increased fractions of long monomer units (C6 and C8) in PHA copolymers were observed for three mutants [A510M(Q,C)]. From these results, the mutations at this potion are beneficial to change the molecular weight of polyesters and the substrate specificity of PhaC(Re). Molecular weight distributions of PHA polymers synthesized by the wild-type enzyme (PhaC(Re)) and its mutants.