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[en] Second-order rate constants (kOH-) have been measured spectrophotometrically for alkaline hydrolysis of Y-substituted phenyl phenyl carbonates (2a-j) and compared with the kOH- values reported previously for the corresponding reactions of Y-substituted phenyl benzoates (1a-j). Carbonates 2a-j are 8 ∼ 16 times more reactive than benzoates 1a-j. The Hammett plots correlated with σ- and σ.deg. constants exhibit many scattered points, while the Yukawa-Tsuno plot results in excellent linear correlation with ρ = 1.21 and r = 0.33. Thus, the reaction has been concluded to proceed through a concerted mechanism in which expulsion of the leaving group is advanced only a little. However, one cannot exclude a possibility that the current reaction proceeds through a forced concerted mechanism with a highly unstable intermediate
[en] The second-order rate constants (kOH-) for the reactions of Y-substituted-phenyl diphenylphosphinates (4a-4i) with OH- in H2O at 25.0 ± 0.1 .deg. C have been measured spectrophotometrically. Comparison of kOH- with kEtO- (the second-order rate constants for the corresponding reactions with EtO-. in ethanol) has revealed that EtO- is less reactive than OH. Although the former is ca. 3.4 pKa units more basic than the latter, indicating that the reactivity of these nucleophiles is not governed by their basicity alone. The Brφnsted-type plot for the reactions of 4a-4i with OH. is linear with βlg = -0.36. The Hammett plot correlated with σ- constants results in a slightly better correlation than that correlated with σo constants but exhibits many scattered points. In contrast, the Yukawa-Tsuno plot for the same reactions exhibits an excellent linear correlation with ρ = 0.95 and r = 0.55. The r value of 0.55 implies that a negative charge develops partially on the O atom of the leaving group. Thus, the reactions of 4a-4i with OH. have been concluded to proceed through a concerted mechanism
[en] Protein hydrolysates from angelwing clam were obtained by enzymatic hydrolysis using bromelain. The bitterness of hydrolysates was evaluated based on the degree hydrolysis (DH), sensory analysis, molecular weight distribution and functional group. By using 3 % of enzyme substrate ratio bromelain resulted in high DH value at 12.57 % when angelwing clam was hydrolysed for 2 hours. Sensory analysis showed that angelwing hydrolysate was bitter. Angelwing hydrolysate had molecular weight below 50 kDa. The lower molecular weight indicated that the protein has been degraded into smaller peptide chains which contribute to bitter taste. Moreover, the high peak of amine group in angelwing hydrolysate (3385.6 cm-1) suggested that bitterness exists. Angelwing hydrolysate had higher protein content, lower fat content and had good water holding capacity than the flesh. This result suggested that angelwing hydrolysate could be useful as food ingredient even though bitter taste developed after the hydrolysis. Thus, debittering should be considered in order to pave the way for full utilization of angelwing clam hydrolysate as a food ingredient. (author)
[en] The solidification influence modeling in fuel-coolant interaction codes is strongly related to the modeling of the temperature profile inside the melt droplets and to the modeling of the mechanical effect of the formed crust on the fine fragmentation process. A purpose of the study was to enable solidification influence modeling in codes with an Eulerian formulation of the droplet field. Therefore additional transport quantities based on the most important melt droplet features regarding the steam explosion phenomenon were derived. This enables a more accurate prediction of the amount of droplets participating in the fine fragmentation process during the explosion phase. Also the potential effect of the proposed modeling was assessed. The simulations supported the key role of the solidification in the steam explosion phenomenon. (author)
[en] Highlights: ► Comparison between native and photoinduced chemiluminescence of dimethoate. ► Hexadecylpyridinium enhanced greatly the chemiluminescence. ► Solid phase extraction allowed the successful determination of dimethoate in water. - Abstract: The determination of dimethoate using either its native chemiluminescent (CL) properties or its photoinduced chemiluminescence obtained by irradiation with a 15 W low-pressure mercury lamp was studied. Thereby, two flow injection systems (FIA) with and without irradiation were exhaustively optimized and their analytical characteristics studied. Better sensitivity and selectivity was found in absence of irradiation, due to the enhancing effect of hexadecylpyridinium chloride (HPC), which acted as a sensitizer. In the developed FIA-CL system, the alkaline hydrolysis of dimethoate with NaOH was performed on-line in presence of HPC. The oxidation of the product of hydrolysis with Ce(IV) in hydrochloric medium induced chemiluminescence. The method provided a limit of detection of only 0.05 ng mL−1 without any pre-treatment. However, the combination with solid phase extraction allowed the removal of some potential interferents as well as the preconcentration of the pesticide. Finally, the developed method was successfully applied to natural waters with recoveries between 95 and 108%.
[en] In this paper, we have numerically simulated the steam explosion behaviour observed in FARO L-33 and TROI-13 tests using the code COMETA. The main objective was to understand effects of various parameters on the dynamic pressure profile generated during the melt-water interactions. The FARO L-33 geometry and operating conditions were different from the TROI-13 tests. While a strong pressure spike was observed in TROI-13, a relatively mild pressure rise was observed in the FARO L-33 test. Hence, we conducted parametric studies by changing some parameters and their effects on the dynamic pressure profile were studied. It was found that the hydrogen concentration and the fragmented drop size are the two parameters which play key roles on the pressure spike and the pressure profile. The water depth and melt superheat also found to have similar effects on the dynamic pressure profile. Then, we simulated the TROI operating conditions in FARO geometry and studied the pressure profile after triggering was activated. It was found that, a smaller hydrogen concentration and larger melt superheat as in TROI, could produce a stronger pressure rise in FARO geometry. (author)
[en] Second-order rate constants (kOH-) have been measured spectrophotometrically for reactions of Y-substituted phenyl phenyl thionocarbonates (4a-i) with OH- in 80 mol % H2O/20 mol % DMSO at 25.0 ± 0.1 .deg. C. The kOH- values for the reactions of 4a-i have been compared with those reported previously for the corresponding reactions of Y-substituted phenyl phenyl carbonates (3a-i) to investigate the effect of changing the electrophilic center from C=O to C=S on reactivity and mechanism. Thionocarbonates 4a-i are less reactive than the corresponding carbonates 3a-i although 4a-i are expected to be more reactive than 3a-i. The Bronsted-type plot for reactions of 4a-i is linear with βlg = - 0.33, a typical βlg value for reactions reported to proceed through a stepwise mechanism with formation of an intermediate being the rate-determining step (RDS). Furthermore, the Hammett plot correlated with σ.deg. constants results in much better linearity than that correlated with σ- constants, indicating that expulsion of the leaving group is not advanced in the RDS. Thus, alkaline hydrolysis of 4a-i has been concluded to proceed through a stepwise mechanism with formation of an intermediate being RDS, which is in contrast to the forced concerted mechanism reported for the corresponding reactions of 3a-i. Enhanced stability of the intermediate upon modification of the electrophilic center from C=O to C=S has been concluded to be responsible for the contrasting mechanisms
[en] This study aims to establish the relative importance of sediment organic phosphorus (Po) to the total P and the major classes of organic molecules that contribute to sediment Po, determined by measuring their susceptibility to enzymatic hydrolysis, across a suite of lakes ranging from oligotrophic to eutrophic status. The results showed that Po accounted for 21–60% of total P, and bioavailable Po accounted for 9–34% of Po in the sediments. The bioavailable Po includes mainly labile (H2O-Po) and moderately labile (NaOH-Po) P forms. For H2O-Po (accounting for only1.4% of Po), 53% (average) was labile monoester P, 28% was diester P and 17% was phytate-like P. For NaOH-Po (accounting for 9–33% of Po), 32% was labile monoester P, 33% was phytate-like P and 18% was diester P. The composition of bioavailable Po, determined by enzyme assays, was related to the lake nutrient levels, which implies that sediment bioavailable Po could act as an effective indicator for lake eutrophic status. With the increase of lake nutrient levels, bioavailable Po content and alkaline phosphatase activity in the sediment all increased, indicating that Po represents an important and bioavailable source of P that increases with eutrophication, and could contribute to internal loading and resistance of eutrophic lakes to remediation. This implies that eutrophic lakes would maintain long-term eutrophic status and algal bloom phenomena even after the external input of P was controlled and the total P concentration of water has declined. Thus, in order to reduce the release risk of sediment P more efficiently and effectively, sediment P control technique should focus not only on reducing the total P and inorganic P, but should also pay close attention to the removal of bioavailable Po. - Highlights: • Relationship between sediment Po and lake nutrient levels. • Importance of sediments Po and bioavailable Po to the total P. • Composition of bioavailable Po was related to the nutrient levels. • Po represents an important and bioavailable source of P that increases with eutrophication. - The composition of bioavailable Po in sediments was related to the lake nutrient levels and represents an important and bioavailable source of P that increases with eutrophication.