Variation Of K2 Research Articles

Kinetic assessment of Michael addition reactions of alpha, beta-unsaturated carbonyl compounds to amino acid and protein thiols

Humans have extensive adverse exposure to alpha,beta-unsaturated carbonyl compounds (ABuCs) as these are major toxins in smoke and exhaust fumes, as well as products of lipid peroxidation. In contrast, another ABuC, dimethylfumarate, is used to treat psoriasis and multiple sclerosis. ABuCs undergo Michael adduction with amine, imidazole and thiol groups, with reaction at Cys residues predominating. Here we report rate constants, k2, for ABuCs (acrolein, crotonaldehyde, dimethylfumarate, cyclohex-1-en-2-one, cyclopent-1-en-2-one) with Cys residues present on N-Ac-Cys, GSH, bovine serum albumin, creatine kinase, papain, glyceraldehyde-3-phosphate dehydrogenase, and both wild-type and the C151S mutant of Keap-1. k2 values for N-Ac-Cys and GSH vary by > 250-fold, indicating a marked ABuC structure dependence, with acrolein the most reactive. There is also considerable variation in k2 between protein Cys groups, with these significantly greater than for GSH. A linear inverse correlation for acrolein with the thiol pKa indicates that the thiolate anion is the reactive species. The modest k2 for GSH rationalizes the detection of protein adducts of ABuCs in cells. The k2 values for dimethylfumarate also vary markedly, with the Cys151 residue on Keap-1 being particularly reactive, with the C151S mutant giving a much lower k2 value. The data for crotonaldehyde, dimethylfumarate, and cyclohex-1-en-2-one show little correlation with the Cys pKa values, indicating that steric/electronic interactions, rather than Cys ionization are important. These data indicate that protein Cys residues, and particularly Cys151 on Keap-1, react readily with dimethylfumarate, and this may help rationalize the use of this compound as a therapeutic agent.

The Rashba effect and indirect electron-hole recombination in hybrid organic-inorganic perovskites.

Slow electron-hole recombination, characterized by the bimolecular coefficient k2 in hybrid organic-inorganic perovskites (HOIPs), is a key to their outstanding photovoltaic performance. The measured k2 in HOIPs strongly deviates from k2 ∝ T-3/2 (T is the temperature) in typical direct-gap semiconductors. Here we show that the observed temperature dependence can be quantitatively accounted for by phonon-assisted recombination of electrons and holes located at the band extrema, which become indirect due to the Rashba effect. Polar optical phonons are most effective in facilitating this indirect recombination. The variation in k2 in HOIPs among different studies in the literature can be attributed to different Rashba strengths in their samples. Our results indicate that the confluence of the Rashba effect and polar coupling transform HOIPs into a unique indirect semiconductor that can accommodate both strong optical absorption and slow carrier dynamics.

Theoretical and numerical study of hydraulic characteristics of orifice energy dissipator

Different factors affecting the efficiency of the orifice energy dissipator were investigated based on a series of theoretical analyses and numerical simulations. The main factors investigated by dimension analysis were identified, including the Reynolds number (Re), the ratio of the orifice diameter to the inner diameter of the pipe (d/D), and the ratio of distances between orifices to the inner diameter of the pipe (L/D). Then, numerical simulations were conducted with a k-ɛ two-equation turbulence model. The calculation results show the following: Hydraulic characteristics change dramatically as flow passes through the orifice, with abruptly increasing velocity and turbulent energy, and decreasing pressure. The turbulent energy appears to be low in the middle and high near the pipe wall. For the energy dissipation setup with only one orifice, when Re is smaller than 105, the orifice energy dissipation coefficient K increases rapidly with the increase of Re. When Re is larger than 105, K gradually stabilizes. As d/D increases, K and the length of the recirculation region L1 show similar variation patterns, which inversely vary with d/D. The function curves can be approximated as straight lines. For the energy dissipation model with two orifices, because of different incoming flows at different orifices, the energy dissipation coefficient of the second orifice (K2) is smaller than that of the first. If L/D is less than 5, the K value of the L/D model, depending on the variation of K2, increases with the spacing between two orifices L, and an orifice cannot fulfill its energy dissipation function. If L/D is greater than 5, K2 tends to be steady; thus, the K value of the L/D model gradually stabilizes. Then, the flow fully develops, and L has almost no impact on the value of K.

Comparative Bioenergetics of Diploid and Triploid Pacific Oysters Crassostreas gigas at Different Temperatures

The energy budgets, assimilation and conversion efficiency of 1-year-old-triploid Pacific oysters Crassostreagigas, were compared with those of sibling diploids to clarify the mechanism of energy metabolism. No significant difference was found between diploids and triploids in oxygen consumption. The net growth efficiencies of triploids and diploids were 37.4% and 33.9% respectively, and the gross growth efficiencies of them were 28.8% and 22.7%. The influence of ploidy and temperature on K1 was significant, but the variation of K2 may be attributable to ambient temperature. The ratio of gonad dry weight and dry tissue of triploids was 5%on average, and diploids about 25.6%. Our results showed that triploids, which do not reproduce and only have limited gonadal development, spend more energy for growth and more efficient in using energy than diploids do.

A comparative study of the antioxidant scavenging activity of green tea, black tea and coffee extracts: A kinetic approach

The antioxidant activities of three beverages, coffee, black tea and green tea, along with their major components, were investigated in terms of their reaction with the stable radical 2,2′-diphenyl-2-picrylhydrazyl (DPPH). We used a kinetic approach in parallel with quantification methods based on a fixed end-point to determine the scavenging efficiency of compounds abundant in these beverages during their reaction with DPPH using a stopped-flow spectrophotometer-based method. Ascorbic acid, (+)-catechin, (−)-epigallocatechin, tannic acid, and caffeic acid were selected as model antioxidants to study in coffee, black tea and green tea. We applied a second-order model to demonstrate similarities in the kinetics behavior of beverages and related compounds. Our findings showed the slopes k2′((mol/L)-1s-1) and k2max′((mol/L)1s-1) exhibited similar and correlated values; we suggest the variation in k2′ as a function of time is more informative about antioxidant properties than reaction with DPPH alone. We also used IC100 to test the reliability of the relative stoichiometry using a new comparative parameter “n”, which was calculated as: n=c0DPPHIC100 (mol/L(mol/L)−1, (mol/L)mlmg−1 or molg−1).

Electromechanical Coupling Coefficient of SAW on Proton-Exchanged and Annealed LiNbO<sub>3</sub> Waveguides

We had investigated the electromechanical coupling coefficient (K2) of surface acoustic wave (SAW) on proton-exchanged (PE) and annealed PE (APE) z-cut LiNbO3 waveguides using octanoic acid. The penetration depth of hydrogen assumed to be equal to the waveguide depth (d) was measured by secondary-ion mass spectrometry (SIMS). The frequency response of SAW was measured with a network analyzer. The annealing process was carried out in a horizontal furnace kept at 400°C for 2 h under a dry O2 gas flow. The change of K2 in PE and APE samples fabricated under different conditions was dependent on kd, where k was the wavenumber. The experimental results showed that the variation of K2 in PE samples was significantly decreased with the increase of kd. The reduction of K2 may be due to the reduced piezoelectric coefficients in the PE layer. On the other hand, the variation of K2 in APE samples also exhibited the decreased tendency after annealing. It indicated that the annealing process could not restore the reduction of K2 caused by the PE process.

Kinetics of Liquid-phase Hydrogenation of Aliphatic α,β-Unsaturated Aldehyde over Raney Cobalt Catalyst Modified with Co-, Mn-, Ni-, and PdCl2

Abstract Kinetic studies were carried out on the hydrogenation of the α,β-unsaturated aldehyde, 2-methyl-2-pentenal (UD), over the Raney cobalt catalyst modified with various amounts of Co-, Mn-, Ni- and PdCl2 in n-hexane under atmospheric pressure at 40 and 20°C. Initial rates of formation of the saturated aldehyde (rSD), saturated alcohol(rSA) and unsaturated alcohol(rUA) were determined in the concentration range of UD((CUD) 0.018–0.263 mol/l. It was found that (rSD+rSA) obeyed a Langmuir-type rate equation and rUA a different one. The rate equations are as follows. r SD+rSA=\frack1·b1·CUD(1+b1·CUD)2, rUA=\frack2·b2·CUD(1+b2·CUD)2 where k and b denote the rate constant of the surface reaction and parameter for the adsorption of UD and hydrogen, respectively, the subscripts 1 and 2 representing the formation of SA and SD and that of UA, respectively. Kinetic parameters k1, k2, b1 and b2 were found to vary with the amount and kind of modifier. The variation of b1 and b2 was irregular. The rate constant k1 decreased with increasing amount of Co-, Mn- and NiCl2 added; it increased remarkably with the addition of PdCl2. The variation of k2 was more complicated. Addition of a small amount of the modifiers did not decrease k2. Further addition of Co- and MnCl2 made k2 decrease, while that of NiCl2 made it increase. Mechanism of the modification with these metal chlorides is discussed on the basis of the active site hypothesis.