Temperature maximum stability

Stability of the colour. The colour produced should be sufficiently stable to permit an accurate reading to be taken. This applies also to those reactions in which colours tend to reach a maximum after a time the period of maximum colour must be long enough for precise measurements to be made. In this connection the influence of other substances and of experimental conditions (temperature, pH, stability in air, etc.) must be known. 

The stability of the catalyst was demonstrated by constant position of the temperature maximum. The exotherm remained at the top of the catalyst bed and stayed at 13 1 C during the 600-hour run. 

Thermal degradation studies of EB-cured terpolymeric fluorocarbon rubber [430] by nonisothermal thermogravimetry in the absence and presence of cross-link promoter TMPTA reveal that thermal stability is improved on radiation and more so in the presence of TMPTA. Initial decomposition temperature, maximum decomposition temperature and the decomposition... 

Because of the multiple degradation pathways that may take place at elevated temperature, protein stability monitoring data may not conform to the Arrhenius relationship, and the maximum temperature selected for accelerated stability studies must be carefully selected. Gu et al. [32] described the different mechanisms of inactivation of interleukin-1 (3 (IL-1 (3) in solution above and below 39°C. In this example, the multiple mechanisms precluded the prediction of formulation shelf life from accelerated temperature data. In contrast, by working at 40° C and lower, Perlman and Nguyen [33] were able to successfully extrapolate data from stability studies of tissue plasminogen activator down to 5°C. 

In addition to the additives used in a formulation to help stabilize the protein to freezing, the residual moisture content of the lyophilized powder needs to be considered. Not only is moisture capable of affecting the physicochemical stability of the protein itself, equally important is the ability of moisture to affect the Tg of the formulation. Water acts as a plasticizer and depresses the Tg of amorphous solids [124,137,138]. During primary drying, as water is gradually removed from the product, the Tg increases accordingly. The duration and temperature of the secondary drying step of the lyophilization process determines how much moisture remains bound to the powder. Usually lower residual moisture in the finished biopharmaceutical product leads to enhanced stability. Typically, moisture content in lyophilized formulations should not exceed 2% [139]. The optimal moisture level for maximum stability of a particular product must be demonstrated on a case-by-case basis. 

Consider what happens to pepsinogen near its optimal Tm of 339.4°K (66.2°C), when 20% ethanol is added to the solution (Figure 13.9). The temperature of maximum stability occurs near 300°K (26.9°C). When 20% ethanol is added, the Tm is lowered to 329.0°K (55.9°C) as expected, suggesting some destabilization of the protein between the two solution conditions. However, the temperature of maximum stability occurs at a lower temperature near 273°K... 

Figure 13.9 Temperature response trace (at optimal Tm solution conditions) of AGu, for pepsinogen at pH 6, with and without 20% ethanol (EtOH). Labels shown are identified as Ted = cold denaturation temperature, Tms = temperature of maximum stability, and Tra...

Effect of pH. The pH vs. stability curves of Figure 4 are plotted using the half-lives calculated from the Arrhenius plots (Figure 3). Stability is expressed as log ti/2 to make possible to visualize the curves at the temperature range (30-60°C). Maximum stability was achieved at pH 4.5 - 5.0. The stability of the enzyme at pH 3.0 which was used for the activity assay was much lower than the stability at pH 4.5. 

The tetraphosphate anion is practically stable in neutral and alkaline solution at room temperature but at 65.9°C it is about half a power of ten less stable than the triphosphate anion over the whole pH range (61). Tetraphosphate has its maximum stability at 65.5°C at pH 10 and this is why it can be prepared from tetrametaphosphate at such temperatures. Its stability becomes smaller with decreasing pH. Apparently during the hydrolysis of an aqueous solution, which follows a first order law at constant pH, the tetraphosphate is cleaved initially exclusively at the end of the chain, to form mono- and tri-phosphate. 

Substance Sensitiveness to impact Maximum height of drop (cm) not causing explosion Ignition temperature °C Stability... 

The variation in maximum rate (build up curves) with temperature is shown in Fig. 176. A rapid increase in the rate above 240°C might have been expected since the salt is then in the cubic form with both ions rotating, but evidently the cubic is the more stable form. The occurrence of the minimum could be due to the cubic form possessing the maximum stability at this temperature. Alternatively,... 

AHm is the enthalpy change at Tm, the midpoint of the thermal unfolding curve (the "melting" temperature). The temperature of maximum stability Ts occurs when AS = 0 (Eq. 29-14). Ts is usually between -10°C and... 

Ts is the temperature of maximum stability, at which the AG(T) versus T curve passes through its maximum, i.e., AG(TS) > 0. At Tm, the maximum temperature of stability, AG (T) = 0. By necessity, Ts < Tm. There is another special point in the temperature stability (AG(T)) curve, however as the temperature stability curve resembles a inverted parabola, there must be a second intersection point with the line of minimum stability, AG(T) = 0. This intersection point is the minimum of the range of temperature stability and is called cold denaturation temperature, Tc. The cold denaturation temperature is practically never taken into consideration in the discussion of temperature stability of biocatalysts. One reason lies in its frequent inaccessibility often, Tc is below 0 °C and thus cannot be measured in water or any other mostly aqueous medium. 

Several kinetic studies have been performed on aspartame, which is relatively unstable in solution [24-30], The half-life at pH 4.3 (the pH of maximum stability) is about 260 days at 25°C [30]. The shelf life (t%) at this temperature and pH 4.0 is about 53 days [28]. Degradation is more rapid at other pH values e.g. shelf-life 12 days at pH 1, and 1 day at pH 7 [30],... 

The total free energy of stabilization for proteins is, even at the temperature of maximum stability, quite small. For the majority of proteins... 

Figure 9 Location of the breakdown reaction clinohumite = olivine + ilmenite + fluid after Weiss (1997), as reported in Ulmer and Trommsdorff (1999). Experiments were conducted on three clinohumites of different composition. Abbrevations Xpe = Fe/(Fe + Mg), Xxi = 2Ti/(2Ti + OH), and Xp = F/(F + OH). Shaded areas represent divariant fields over which clinohumite coexists with olivine + ilmenite + fluid because the composition of the clinohumite is changing. Curves bounding shaded area A represent breakdown of a clinohumite with Xpe = 0.04, Xji = 0.28, and Xp = 0. Curve B represents maximum stability limit of natural, F-free clinohumite with Xpe = 0.19, Xji = 0.46, and Xp = 0. Curves bounding shaded area C represent breakdown of a clinohumite with Xpe = 0.03, Xxi = 0.47, and Xp = 0.47. Increasing Xxi, increasing Xp, and decreasing Xpe all tend to stabilize clinohumite to higher temperatures.

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