Speculative models, definition

Hill introduced two useful definitions for model compounds of metalloproteins, — speculative models and corroborative models, Speculative models are prepared when the structure of the microenvironment of the metallobiosite is unknown and the objective is to reproduce some physico-chemical property of the system in a small molecule complex. When the structure of the metallobiosite is known a corroborative model can be prepared. This is usually a small molecule complex in which the environment of the metal is reproduced as accurately as possible. It then becomes possible to determine whether the observed properties of the metal in the protein are dominated by the first coordination sphere and can give insights into the relationship between structural features of the metallobiosite and its physical properties. 

Clearly, the results emerging suggested that at least two nucleotides were modified, the absolute sequence position within the tRNA had yet to be established. Ching etalP showed that a Se U residue was present in the wobble position of the tRNA " from C. sticklandii. This study confirmed a notion that the modification probably affects the translation efficiency of certain transcripts, based on the level of modification by selenium. The authors speculated that the modification to seleno-tRNA (GAG) allowed for more efficient use of this tRNA species as compared to the tRNA (GAA). Even today, no definitive data exist to show that this modification alters the translation efficiency in these bacterial model systems. Nonetheless, these studies had established the chemical forms of Se U and mnm Se U, and established that they were derived from modifications to nucleotides that first required sulfur (S U and mnm S U), the mechanism by which selenium was inserted into the tRNA would not be definitively answered until many years later. 

In the following I will present a model to tackle this question. We are at the level of speculations, but we will use some known facts. For example, let s start from the condensation of NCA-anhydrides, a reaction which, as we have seen in the previous chapter, is considered prebiotic. In this way, oligopeptides up to (say) a length of ten can be built, possibly under thermodynamic control, but starting from a definite set of conditions (amino-acid composition in the starting mixture, pH, salinity, etc.). We can assume, and this is actually quite reasonable, that in this way copious libraries of different decapeptides have been formed, each in a significant concentration. 

Molecular Models. After selecting the most important fundamental frequencies from which the infrared spectrum is built, it becomes of interest to attribute to each a definite bond or type of vibration. Although such relations are quite speculative, there is now sufficient evidence to establish some of them with a fair degree of confidence. 

Another common theme in FP studies is the richness of possible surface phases -in some cases, dozens of structural isomers are computed to be thermodynamically accessible at room temperature. This has led to speculation that many oxide surfaces are more dynamic than previously thought, but definitive conclusions will only be possible once the processes of surface diffusion are identified and their activation energies are computed. This is perhaps the next frontier in FP oxide simulation. Meanwhile, the flexible surface model for active sites on metals [5] is finding some application in explaining the apparently facile diffusion of interstitial ions in non-stoichiometric oxides, despite the rigidity of the oxide lattice [26]. 

Before the modern model of the atom evolved, the concept of an element had been purely speculative. One of the definitions of an element belongs to Aristotle, one of the greatest philosophers of antiquity, who wrote Elements are simple substances of which the universe is composed and one of which cannot be separated into the other. Aristotle held that there is one primary matter and four fundamental qualities heat and coldness, dryness and wetness. Their combinations are material elements fire, water, air, and earth. According to Aristotle, all bodies are composed of these elements. Aristotle s teaching was the theoretical foundation of al-... 

It should be noted that the Prandtl number term in these two equations is somewhat speculative, since the experimental data did not cover a sulficient range for good correlation. Equations (12) and (13) include Pr to the 0.33 power, based on the expectation that dependence is similar to that for single spheres, as shown in Eq. (11). In applying heat transfer coefficients calculated by Eqs. (12) and (13), it is important to use a model that considers the particles to be well mixed and the gas to be in plug flow, in order to be consistent with the definition of as discussed above. 

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