Arrhenius break temperature

Figure 7.23. Effects of temperature on mitochondrial function. (Upper panel). Arrhenius plot illustrating the slope discontinuity ( break ) that commonly occurs at a high temperature of measurement, the Arrhenius break temperature (ABT). Data are for mitochondria of the hydrothermal vent tubeworm Riftia pachyptila (after Dahlhoff et al., 1991). (Lower panel) Arrhenius break temperatures for mitochondrial respiration of diverse invertebrates and fishes. The open square is for mitochondrial respiration of the Antarctic nototheniid fish Trematomus bernacchii and is not included in the regression analysis. A line of identify (ABT = adaptation temperature) is also shown (see text for analysis). (Data from Dahlhoff and Somero, 1993b Dahlhoff et ah, 1991 Weinstein and Somero, 1998.)...

Figure 7.24. Mitochondrial respiration and membrane fluidity in differently acclimated congeners of abalone (genus Haliotis). (Top panel) Arrhenius break temperatures for mitochondrial respiration. Note overlapping data points (pinto at 5°C red and green at 20°C) have been offset by 1°C for clarity. (Bottom panel) Fluidity of mitochondrial membranes as estimated from the fluorescence polarization of DPH. Note 20°C points have been offset for clarity. (Data from Dahlhoff and Somero, 1993b.)...

Figure 7.46. Effects of temperature on heart rate for two congeners of Petrolisthes. Data are presented as an Arrhenius plot to illustrate the sharp decline in heart rate (Arrhenius break temperature, ABT) that occurs at high temperatures. (Figure modified after Stillman and Somero, 1996.)...

Arrhenius plots of rotational parameters Rs and Ri for the segmental rotational dynamics of PHEMA, as determined by the fitting process at all the concentrations studied (Fig. 16), differ at first sight by their nonlinearity for both rotational parameters from the published plots for segmental dynamics of a number of polymers in dilute solution. In particular, they differ from the above mentioned plots characterizing the local dynamics of polystyrene in dilute solution (Fig. 10), which are linear for both rotational parameters regardless of the thermodynamic quality of the solvent. The plots for PHEMA exhibit an atypical nonlinear behavior characterized by two breaks at specific temperatures in the R plot. The difference between the lower break temperature ( 250 K for all the concentrations studied) and the upper break temperature was found to increase with increasing concentration of PHEMA in methanol. Local dynamics of the polymer was found to be practically independent of temperature in the temperature... 

Activation Parameters. Thermal processes are commonly used to break labile initiator bonds in order to form radicals. The amount of thermal energy necessary varies with the environment, but absolute temperature, T, is usually the dominant factor. The energy barrier, the minimum amount of energy that must be suppHed, is called the activation energy, E. A third important factor, known as the frequency factor, is a measure of bond motion freedom (translational, rotational, and vibrational) in the activated complex or transition state. The relationships of yi, E and T to the initiator decomposition rate (kJ) are expressed by the Arrhenius first-order rate equation (eq. 16) where R is the gas constant, and and E are known as the activation parameters. 

The bifurcational diagram (fig. 44) shows how the (Qo,li) plane breaks up into domains of different behavior of the instanton. In the Arrhenius region at T> classical transitions take place throughout both saddle points. When T < 7 2 the extremal trajectory is a one-dimensional instanton, which crosses the maximum barrier point, Q = q = 0. Domains (i) and (iii) are separated by domain (ii), where quantum two-dimensional motion occurs. The crossover temperatures, Tci and J c2> depend on AV. When AV Vq domain (ii) is narrow (Tci — 7 2), so that in the classical regime the transfer is stepwise, while the quantum motion is a two-proton concerted transfer. This is the case when the tunneling path differs from the classical one. The concerted transfer changes into the two-dimensional motion at the critical value of parameter That is, when... 

Above 570°C, a distinct break occurs in the Arrhenius plot for iron, corresponding to the appearance of FeO in the scale. The Arrhenius plot is then non-linear at higher temperatures. This curvature is due to the wide stoichiometry limits of FeO limits which diverge progressively with increasing temperature. Diffraction studies have shown that complex clusters of vacancies exist in Fe, , 0 Such defect clustering is more prevalent in oxides... 

A ten to hundredfold decrease in the velocity of the reaction, seen as a break down of the Arrhenius plot, is observed at a temperature which, for any given pressure, is always higher than that thermodynamically foreseen for the beginning of the a-/3 transition (this discrepancy is smallest at 265 mm Hg pressure). The marked decrease of the rate of reaction is characteristic of the appearance of the /3-hydride phase. The kinetics of reaction on the hydride follows the Arrhenius law but with different values of its parameters than in the case of the a-phase. 

The rate of catalysis of membrane bound enzymes (Plot B, Figure 1) is more greatly affected than soluble enzymes by lowering the temperature. This is due to the effect of low temperatures on the solidification of the membranes. Thus, an Arrhenius plot of the rate of a membrane-bound enzyme as a function of temperature often shows a discontinuity with a sharp break point (transition temperature) and loss of activity at the temperature where the membrane becomes a gel or more solid phase. 

A takes the value 8.0 x 1010 s, which is close to the collision rate at room temperature, and Ea = 42 kj mol-1, which is the same order of magnitude as the energy required to break a weak chemical bond. Some consideration of the collision dynamics behind the Arrhenius equation throws light on the form of the equation, especially the temperature dependence. 

If the DP is indeed independent of monomer concentration, the chain-breaking reactions which remain important at -180° must be of the same order with respect to monomer concentration as the propagation reaction. The most obvious conclusion is that monomer transfer is the dominant chain breaking reaction, so that DP = kp/km it follows that the activation energy, EDP, characterising the low temperature branch of the Arrhenius plot is Ep -Em = -0.2 kcal/mole. 

Measurements of the steady state phosphoprotein level at different temperatures revealed that phosphoprotein formation is accompanied by a large and constant enthalpy change of 48 kJ/mol. In contrast, the likewise quite high activation energy of phosphoprotein formation exhibits a pronounced break between 20°C and 30°C. A break in the Arrhenius plot of the calcium-dependent ATPase has been observed in the same temperature range and has been interpreted as transitions between two activity states of the enzyme. Apparently, the phosphorylation of the calcium free protein by inorganic phosphate exhibits a similar kind of activity transition as observed for the calcium-dependent interaction of the transport protein with ATP131. A similar transition phenomenon complicates the time course of phosphoprotein formation... 

As the rate of diffusion has an exponential temperature dependence of the Arrhenius type, it can readily be seen that the equating of chain branching and diffusion chain breaking will yield an equation similar to Equation 39 for the Per to T0 relationship of the first limit. 

An Arrhenius-type analysis of temperature dependence can be used to calculate the enthalpy and entropy of activation for the relaxation process. For liquid water, the enthalpy of activation is 19 kjmol-1, which corresponds approximately to the energy required to break one hydrogen bond. For ice, the equivalent enthalpy is 54 kj mol-1,... 

The main point of interest in Fig. 27 is that there appears to be a break in the Arrhenius plot. At low temperatures a reaction with a low frequency factor and an activation energy not far from zero seems to take place. At higher temperatures another reaction with a higher frequency factor and activation energy appears to predominate. 

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