Calorimetric characterization of critical targets for killing and acquired thermotolerance in yeast

We characterized thermal behaviours of cellular components by differential scanning calorimetry (DSC) in order to investigate how Saccharomyces cerevisiae cells acquire thermotolerance after heat shock or in stationary phase. Whole-cell DSC profiles consisted of at least five endothermic components over the range 45-75 degrees C for exponentially growing, heat-shocked and stationary-phase cells. In these profiles, we attempted to localize the endothermic profiles due to denaturation of the two critical targets which were predicted by using the Arrhenius parameters of hyperthermic killing of the cells (Obuchi et al., 1998). This prediction indicated that (a) the heat shock stabilized one family of targets and destabilized the other, while (b) arrest in stationary phase stabilized both targets. Therefore, the heat-shock response does not stabilize all cellular components, and arrest in stationary phase appears to stabilize cellular components in a different manner from the heat-shock response. It was not possible unambiguously to resolve the profiles of the critical targets in the DSC scans of whole cells. Components I (T(m)=49.7 degrees C) and II (T(m)=56.1 degrees C) may both include denaturations of critical targets 1 (T(m)=55.4 degrees C) and 2 (T(m)=53.0 degrees C) in exponential cells. Components I and II were both stabilized (T(m)=53.5 and 57.2 degrees C, respectively) in heat-shocked cells. Sub-cellular fractions suspended in 1.2 M trehalose solution, which mimics the cytosol in tolerant cells, were more stable than those in 0.6 M KCl, which mimics the cytosol in sensitive cells. The microsomal fractions in KCl and trehalose had endothermic profiles in similar temperature ranges to those predicted for sensitive and tolerant cells, respectively. This agreement suggests that the microsomal fraction may contain critical targets, and that trehalose accumulation in the heat-shocked and in the stationary phase yeast cells is a stabilizer of cellular components.     

Selective reduction of nitric oxide with propene over platinum-group based catalysts: Studies of surface species and catalytic activity

The reduction of nitric oxide by propene in the presence of oxygen over platinum-group metals supported on TiO₂, ZnO, ZrO₂, and Al₂O₃ has been investigated by combined diffuse reflectance FT-IR spectroscopy and catalytic activity studies under flow reaction conditions at 523–673 K and atmospheric pressure. The catalytic activity for the selective reduction of nitric oxide and the intensity of the IR bands due to reaction species depended strongly on the nature of the support, type of supported metal, reaction time and temperature. The main surface species detectable by IR were adsorbed hydrocarbons (2900–3080 cm⁻¹), isocyanate (2180, and 2232–2254 cm⁻¹), cyanide (2125 cm⁻¹), nitrosonium (1901 cm⁻¹), CO₂ (2343–2357 cm⁻¹), CO (2058 cm⁻¹) and carbonate (1300–1650 cm⁻¹) species. In the case of rhodium containing catalysts, when supported on Al₂O₃, they exhibited both the highest concentration of surface species and the highest activity for nitric oxide reduction and selectivity to nitrogen. The catalytic activity and the IR intensities of the nitrosonium and isocyanate bands increased with reaction temperature, reached their maximum between 570 and 620 K, and then decreased at higher temperatures. The IR band intensities due to nitrogen containing surface species were found to be strongly correlated to the activity for nitric oxide conversion and only slightly related to the selectivity to dinitrogen.     

Synergistic catalysis of carbon black oxidation by Pt with MoO3 or V2O5

A series of SiO₂-supported MoO₃, V₂O₅, and Pt catalysts were prepared for the study of model soot oxidation with simulated diesel exhaust gas. Composite samples of Pt with the metal oxides demonstrated higher oxidation activities than the single-component SiO₂-supported MoO₃, V₂O₅ or Pt catalysts in the absence of SO₂ in the reactant gas. Based on the effects of NO₂ on carbon oxidation, a synergistic reaction mechanism was suggested to explain the effects of combining Pt with the oxides: Pt catalyzes the oxidation of NO with gas phase O₂ to NO₂, while MoO₃ and V₂O₅ catalyze the oxidation of carbon with NO₂. Finally, the effects of SO₂ on the carbon oxidation reaction were examined and discussed.     

Effect of Meso- and Macropore Structures of Pt-Supported Fibrous Silica on the Catalytic Oxidation of Toluene

The catalytic performance of Pt supported on mesoporous fibrous silica (FS) for toluene oxidation was examined. High catalytic activity was maintained after aging at 800 °C by shortening the length of the FS mesopore channels by crushing, while the activity of the non-crushed catalyst was significantly decreased.     

A pathway of NO–H2–O2 reaction over Pt/ZrO2 through ammonium nitrate

The relationship between the product selectivity for the NO–H₂–O₂ reaction and characteristics of the catalyst, Pt/ZrO₂, was investigated. From the results of activity tests and characterizations, such as CO adsorption and TEM, the catalysts with high Pt dispersions showed high NH₃ selectivities, and those with significantly agglomerated Pt particles by high temperature calcination exhibited higher N₂ formation. The effect of the reduction and oxidation pretreatment was also investigated. The reduced Pt sites promoted the formation of NH₃. The pretreatment condition influenced not only on the amount of accumulated nitrogen-containing species during the reaction but also on the decomposition of ammonium nitrate, which was suspected to be an accumulated species. The decomposition of ammonium nitrate would be involved in the NO–H₂–O₂ reaction.     

Inhibitory effects of 5-aminouracil on cathodic reactions of steels in saturated Ca(OH)2 solutions

The inhibitory effects of 5-aminouracil on cathodic reactions of steels were investigated using saturated Ca(OH)₂ solution to simulate the environment in pores in concrete. Polarization measurements showed that 5-aminouracil effectively inhibited these cathodic reactions, indicating the potential of 5-aminouracil as an inhibitor for macro-cell corrosion in concrete/soil systems, which are caused by cathodic reactions in concrete. Cathodic reactions were inhibited in accordance with the Langmuir adsorption isotherm. FT-IR and XPS measurements suggested that 5-aminouracil was adsorbed onto cathodic portions of the steel through the formation of a coordination bond with the amino group, mainly in the form of dimer.     

Synthesis of alternating polyamide esters by melt and solution polycondensations of N,N′-Di(6-hydroxycaproyl) diamines and N-6-hydroxycaproyl aminoalcohol with terephthalic and adipic dimethyl esters and dichlorides

Alternating polyamide esters of structures A and B were obtained by melt polymerization of dimethyl adipate and terephthalate or by solution polymerization of adipoyl and terephthaloyl chlorides, with N,N′-di(6-hydroxycaproyl)diamines and an N-6-hydroxycaproyl aminoalcohol: where R₁ is selected from dimethylene, hexamethylene, and p-phenylene radicals, and R₂ is selected from tetramethylene or p-phenyl radical. Polyamide esters of structure A′ were also prepared: Average values of melting points of the resulting polyamide esters were dependent on the starting diacid derivatives, amide diols, and methods of polymerizations as follows: where CPZ, CHD, CED, and CPPD are N,N′-di(6-hydroxycaproy1)-, each in this order: piperazine, hexamethylenediamine, ethylenediamine, and p-phenylenediamine. ECA is N-(2-hydroxyethyl)6-hydroxycaproamide. For a given polyamide ester obtained from the same starting materials and by the same method of polymerization, the melting points increased with inherent viscosities. Polyamide esters of high molecular weight were obtained from CHD with both adipic and terepbthalic derivatives both by melt and solution polymerizations. Polymerizations of the other amide diols gave lower molecular weights. Solution polymerization gave colorless or light-colored polymers, while melt polymerization gave deeper-colored polymers.     

Evidence for the interplay between trehalose metabolism and Hsp104 in yeast

Disruption of the HSP104 gene in a mutant which cannot accumulate trehalose during heat shock treatment caused trehalose accumulation (H. Iwahashi, K. Obuchi, S. Fujii, and Y. Komatsu, Lett. Appl. Microbiol 25:43-47, 1997). This implies that Hsp104 affects trehalose metabolism. Thus, we measured the activities of enzymes involved in trehalose metabolism. The activities of trehalose-synthesizing and -hydrolyzing enzymes are low in the HSP104 disruption mutant during heat shock. This data is correlated with intracellular trehalose and glucose levels observed in the HSP104 disruption mutant. These results suggest that during heat shock, Hsp104 contributes to the simultaneous increase in both accumulation and degradation of trehalose.