Thermodynamic stability hypothesis

The following sections will consider results that support the thermodynamic stability hypothesis. Objections and alternative explanations will be critically presented in Chapters 5 and 6. 

Several lines of evidence support the thermodynamic stability hypothesis at the DNA level. While their strength varies from weak to strong, their cumulative weight in favor of the hypothesis is overwhelming. 

In this chapter, we will consider the objections to selection, that were not accompanied by alternative explanations, whereas the following chapter will address the alternative explanations that were proposed. We will begin with the most popular, yet logically weakest, objection to the thermodynamic stability hypothesis. 

Natural selection thermodynamic stability hypothesis (Bernardi Bernardi, 1986a)... 

While it might appear that the phosphoprotein obtained in the above labeling experiments confirms the Morton hypothesis, the pH relationships require some explanation, and various other considerations such as the potent inhibitory properties of phosphate at pH 8.0, its poor inhibitory properties at pH 5.0, the extreme thermodynamic stability of the phosphoprotein and other thermodynamic considerations require further demonstration of a phosphoryl enzyme intermediate (116, 119,... 

Observations of natural systems have been subject to substantially different interpretations owing to the inherent complexity of these systems. There has been an unfortunate tendency to interpret observations using the popular hypothesis at a particular time in attempting to explain all such diagenesis. It should be kept in mind that just as there are many roads to heaven (or hell ), there are many pathways to thermodynamic stability. 

Microemulsions. In some systems the addition of a fourth component, a cosurfactant, to an oil-water-surfactant system can cause the interfacial tension to drop to near-zero values, easily on the order of 10 to 10" mN/m low interfacial tension allows spontaneous or nearly spontaneous emulsification to very small droplet sizes, ca. 10 nm or smaller. The droplets can be so small that they scatter little light the emulsions appear to be transparent and do not break on standing or centrifuging. Unlike coarse emulsions, these microemulsions are usually thought to be thermodynamically stable. The thermodynamic stability is frequently attributed to transient negative interfacial tensions, but this hypothesis and the question of whether microemulsions are really lyophilic or lyophobic dispersions are areas of some discussion in the literature (J 7). As a practical matter, microemulsions can be formed, have some special qualities, and can have important applications. 

Further confirmation of thermodynamic stabilization of 4 by intramolecular coordination is expected to arise from the investigation of its reactivity. The inherent electron demand of a silylene may be satisfied in a highly coordinated species such as 4a or 4b by the intramolecular coordination of one or two dimethylamino groups accordingly, such species should show more nucleophilic character. Here we will present experimental and theoretical results that show that 4 indeed acts as a nucleophile towards appropriate substrates these results corroborate the hypothesis of 4 being an intramolecularly coordinated silylene. 

Durbeej, B., and L. A. Eriksson. 2003. A density functional theory study of coniferyl alcohol intermonomeric cross linkages in lignin Three dimensional structures, stabilities and the thermodynamic control hypothesis. Holzforschung 57(2) 150-64. 

In 1985 both Magnus and Schore independently proposed identical mechanisms based on stereochemical and regiochemical preferences observed in the product. Magnus s hypothesis was based on the stereochemical results for an intramolecular cyclization. He proposed that the product arose from formation of a metallocycle intermediate 7 or 8, carbon monoxide insertion to give 9, acyl migration fi om cobalt to carbon and reductive elimination of cobalt to form 10. The relative thermodynamic stability of the metallocycles 7 and 8 controlled the final product ratio. In the... 

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