Reaction of poly(vinyl alcohol) with superoxide anion

Reaction of pol(vinyl alcohol) (PVA) with superoxide anion was carried out in a dimethyl sulfoxide solution at 40°C under nitrogen and changes in the yield of recovered polymer, molecular weight, and chemical structure were examined. Appreciable decreases in the yield of recovered polymer and molecular weight were observed during the reaction, which indicated that a main chain scission of the polymer had occurred. Residual acetyl groups identified by the absorption peaks at ca. 1720 and 1250 cm^?1 in infrared (IR) spectra were removed rapidly and β-diketone groups identified by the peaks at ca. 1640 and 1560 cm^?1 in IR spectra and at ca. 255 nm in ultraviolet (UV) spectra were formed during the reaction. Formation of carboxylate groups was also assumed. The reaction mechanism was discussed on the basis of the results obtained.     

Trace element abundances in stone artifacts and related materials from Japan by neutron activation analysis. An approach to archaeological provenience studies

Instrumental neutron activation analysis was carried out for trace elements in green tuff cylindrical beads (KUDATAMA) and obsidians unearthed from the sites with special reference to their archaeological provenience studies. An approach based on the characteristic index elements, the correlation diagrams of some of the elements interested, and the abundance patterns of some of rare earth elements is valid for clarifying the different source regions.     

Theoretical analysis of potential forces in markets

We show that random walks in a moving potential function, with its center at the moving average of market prices, are represented in the form of the self-modulation model. From this point of view we confirm the existence of non-trivial autocorrelation in real market price changes. By generalizing the formulation of potential function we prove that the ARCH model belongs to the special case of random walk in an asymmetric potential with randomly changing coefficient.     

Identification of combustion mode under MILD conditions using Chemical Explosive Mode Analysis

Direct Numerical Simulations (DNS) data of Moderate or Intense Low-oxygen Dilution (MILD) combustion are analysed to identify the contributions of the autoignition and flame modes. This is performed using an extended Chemical Explosive Mode Analysis (CEMA) which accounts for diffusion effects allowing it to discriminate between deflagration and autoignition. This analysis indicates that in premixed MILD combustion conditions, the main combustion mode is ignition for all dilution and turbulence levels and for the two reactant temperature conditions considered. In non-premixed conditions, the preponderance of the ignition mode was observed to depend on the axial location and mixture fraction stratification. With a large mixture fraction lengthscale, ignition is more preponderant in the early part of the domain while the deflagrative mode increases further downstream. On the other hand, when the mixture fraction lengthscale is small, sequential autoignition is observed. Finally, the various combustion modes are observed to correlate strongly with mixture fraction where lean mixtures are more likely to autoignite while stoichiometric and rich mixtures are more likely to react as deflagrative structures.     

Photoinduced amino-imino tautomerism: an infrared study of 2-amino-5-methylpyridine in a low-temperature argon matrix

The photoreaction of 2-amino-5-methylpyridine was investigated by matrix-isolation infrared spectroscopy and DFT calculation. Photoinduced reversible amino (N=C-NH(2))-imino (NH-C=NH) tautomerism was found between 2-amino-5-methylpyridine and 5-methyl-2(1H)-pyridinimine; the amino tautomer changes to the imino tautomer by UV irradiation (340>lambda>or= 300 nm) and the reverse change occurs by longer-wavelength light irradiation (420>lambda>or= 340 nm). The results of the CASSCF calculation revealed that the amino-imino tautomerism proceeds in vibrational relaxation process from electronic excited state to the ground state. The IR spectra of 2-amino-5-methylpyridine in the T(1) state and 5-methyl-2-pyridinamino radical were also obtained by UV irradiation (lambda>or= 300 nm).     

A quantum chemical study of the catalysis for cytidine deaminase: contribution of the extra water molecule

Cytidine deaminase is known as an important enzyme responsible for the hydrolytic deamination of cytidine, which is applied as a key step to the conversion of the precursor of the cancer drug to an active form in the living body. Cytidine with water is efficiently converted to uridine with ammonia in the cleft of cytidine deaminase. In this work, the catalysis of cytidine deaminase for the hydrolytic deamination was examined using cytosine as a model of cytidine and the model molecules for the active site of cytidine deaminase by means of the quantum chemical method. We especially investigated the contribution of the water molecule from the solvent to the catalysis, because the X-ray diffraction analysis of a crystal structure has revealed the existence of the water molecule in the vicinity of the substrate bound to the active site inside the cleft. Our computations showed that the extra water molecule from the solvent has a possibility to support the catalysis of cytidine deaminase.     

Dimerization and double proton transfer-induced tautomerism of 4(3H)-pyrimidinone in solution studied by IR spectroscopy and quantum chemical calculations

The tautomerism and dimerization of 4(3H)-pyrimidinone (4(3H)Pyr) in carbon tetrachloride (CCl4) and chloroform (CHCl3) solutions were investigated using IR spectroscopy and quantum chemical calculations. The observed IR spectra in the NH and OH stretching regions clearly revealed the predominance of the keto tautomer in both solvent systems. The enol form only exists in a very small proportion in the CCl4 solution. The tautomeric constant for the two monomers KT[OH/NH] = 0.012 and DeltaE = 2.62 kcal/mol were estimated at 25 degrees C. This result was supported by the self-consistent reaction field/polarizable continuum (SCRF/PCM) calculation at the MP4(full, SDQ)/aug-cc-pVDZ level, which predicted DeltaE = 3.06 kcal/mol in CCl4. In the C=O stretching region, two bands were observed, suggesting the coexistence of two keto structures at equilibrium. The calculated IR spectra indicated that the bands at 1711 and 1675 cm(-1) arise from the keto monomer and keto-keto (KK) ring dimer, respectively. At elevated temperature, the populations of both the keto and enol monomers increased for the CCl4 solution. The present study revealed that the keto <--> enol tautomerization does not occur in the isolated monomer molecule. The double proton transfer (DPT) reaction in the KK ring dimer presumably plays a substantial role in the population increase of the enol monomer. To our knowledge, this may be the first observation of the tautomerization in a model base pair via the temperature-induced ground-state DPT reaction under a nonpolar liquid environment reported so far. This tautomerism can serve as a mimic circumstance for the spontaneous mutations induced by proton transfer in the DNA base pairs.