Stability intrinsic

In Figure 7b, the data are plotted as AG yielding a linear function. Extrapolation to 2ero denaturant provides a quantitative estimate of the intrinsic stability of the protein, AG, which in principle is the free energy of unfolding for the protein in the absence of denaturant. Comparison of the AG values between mutant and wild-type proteins provides a quantitative means of assessing the effects of point mutations on the stability of a protein. 

A more fundamental issue than that of adventitious proton donors is the intrinsic stability of ketone enolate salts in liquid ammonia. Even... 

A theoretical ab initio study of the gas-phase basicities of methyldiazoles (90JA1303) included a discussion of the 4(5)-methylimidazole tautomer-ism. The RHF/4-31G calculations led to the conclusion that the 4-methyl tautomeric form 14a (R = Me, R = R = H) is 5.2 kJ moP more stable than its 5-methyl counterpart 14b. It was emphasized that this result is to be considered as basic-set dependent. However, a recent theoretical study [94JST(T)45] showed that, starting from the RHF/6-31G level, all the more accurate approximations indicate a higher intrinsic stability for the 4-methyl tautomer. At the MP2/6-31G level, the total energy of the 4-methyl tautomer is 0.7 kJ mol lower than that of the 5-methyl tautomer. Inclusion of solvation effects can, thus, strongly affect the position of the tautomeric equilibrium 14a 14b. Recently, a systematic theoretical study... 

A wide range of nitroxidcs and derived alkoxyamincs has now been explored for application in NMP. Experimental work and theoretical studies have been carried out to establish structure-property correlations and provide further understanding of the kinetics and mechanism. Important parameters are the value of the activation-deactivation equilibrium constant K and the values of kaa and (Scheme 9.17), the combination disproportionation ratio for the reaction of the nilroxide with Ihe propagating radical (Section 9.3.6.3) and the intrinsic stability of the nitroxide and the alkoxyamine under the polymerization conditions (Section 9.3.6.4). The values of K, k3Cl and ktieact are influenced by several factors.11-1 "7-"9 ... 

In contrast to the iminophospheninm cation, 6, described in the previous section, the corresponding phosphaphosphenium (the alternative nomenclature to this species is phosphanediylphosphenium or phosphanetriyiphosphonium), cation 8, shows only a modest intrinsic stability, as suggested by the quantum chemical calculations (see Fig. 1). They predict that a protonated 2 should have a bridged structure [60-66],8a (Scheme 14). 

The number of samples of reference material needed is a commercial issue in the first place. An important variable is the number of samples likely to be sold during the lifetime ( shelf life ) of the reference material. As the lifetime is a function of the intrinsic stability of the material, this variable also affects the amount of raw material is needed. For instance, microbiological materials have limited intrinsic stability, and therefore their lifetime is expected to be shorter than for a dry sediment certified for trace elements. So, under the assumption of an equal number of sam-... 

Oligomerization of nucleobases can be advantageous to reinforce the H-bonding supramolecular motifs when supramacromolecular polymers are desired. Moreover the different interconverting outputs that may form by oligomerization define a dynamic polyfunctional diversity which may be extracted selectively under the intrinsic stability of the system or by interaction with external factors by polymerization in the solid state. 

Finally, a feedback mechanism has often been used to explain observed (negative and positive) deviations from the Scatchard type plots or nonunity slopes of the nonsaturated portion of the logarithmic Michaelis-Menten plots (e.g. [209]). When no artifacts are present (cf. [197,198]), deviations can indeed be interpreted to indicate that the intrinsic stability or dissociation rate constants vary with the number of occupied transport sites. Nonetheless, several other physical explanations, including multiple carriers, non 1 1 binding, carrier aggregation, etc. must also be considered. 

The lifetime of a spin adduct is thus seen to be dependent on both its rate of formation and its decay, meaning that the half-life of a particular spin adduct under the conditions of its generation is a somewhat uncertain quantity, as frequently noticed in the literature. The intrinsic stability of a particular spin adduct should preferably be determined on isolated specimens, as for example reported for the trichloromethyl adduct of PBN, which was shown to survive almost unchanged in benzene solution after 90 days in the dark (Janzen et al., 1993). 

The intrinsic inertness of the peptide bond is demonstrated by a study of the chemical hydrolysis of N-benzoyl-Gly-Phe (hippurylphenylalanine, 6.37) [67], a reference substrate for carboxypeptidase A (EC 3.4.17.1). In pH 9 borate buffer at 25°, the first-order rate constant for hydrolysis of the peptide bond ( chem) was 1-3 x 10-10 s-1, corresponding to a tm value of 168 y. This is a very slow reaction indeed, confirming the intrinsic stability of the peptide bond. Because the analytical method used was based on monitoring the released phenylalanine, no information is available on the competitive hydrolysis of the amide bond to liberate benzoic acid. 

An introduction to the non-covalent forces operating in stable ionic and molecular aggregates will be presented in Section 2. A brief description of the experimental methodologies employed in the production, detection, and characterization of clusters will be given in Section 3. The available experimental evidence on the structure of chiral clusters and their intrinsic stability, reactivity, and evolution dynamics will be presented and discussed in Sections 4 (molecular clusters) and 5 (ionic clusters). In the same sections, the experimental data will be interpreted in the light of the available theoretical evidence. Finally, some concluding remarks will be expressed in Section 6. 

Let us imagine immersing the crystal MO in an atmosphere in which the partial pressure of oxygen (P02) i lower than the partial pressure of intrinsic stability (i.e., the partial pressure of oxygen at which crystal MO is perfectly stoichiometric Poj)- We observe two distinct defect processes ... 

The intrinsic stability of micas as a function of P and T intensive variables and chemistry is essentially related to the capabihty of the tetrahedral and octahedral... 

Table 5.56 P and T intrinsic stability limits of mica according to Hazen and Finger (1982).

The structural model of Hazen and Wones has been confirmed experimentally. For example, the pure annite end-member [KFe3 (Si3Al)Oio(OH)2] appears to be geometrically unstable at all P and T conditions (table 5.56). Indeed, pure annite has never been synthesized, although slightly oxidized annites of composition K(Fe 7Feo3)(Si3Al)Oio.3(OH)i 7 have been prepared, with a djd, ratio of 1.275, at the limit of intrinsic stability. 

Whereas the structure and function of the 20S proteasome have been elucidated in great detail (for review see Baumeister et al 1998), the 19S regulator is understood only dimly at present. Structural studies are hampered by the low intrinsic stability of this assembly and extensive remodelling, which makes it notoriously difficult to obtain homogeneous preparations. Nevertheless, analyses of yeast. Drosophila and human 26S... 

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