Mechanistic Assertion

Alkane Metathesis in a Continuous Flow Reactor (Mechanistic Assertion)... 

The mechanistic similarity between olefin and alkane metathesis, even if intuitive, has needed time to become obvious in the laboratory for various reasons olefin formation starting from alkanes is thermodynamically disfavored, especially at low temperature, and, as a consequence, the proposal of olefinic intermediates was not obvious. Several facts lead to the metallocarbenic mechanistic assertion ... 

The particular designed elastic model proteins, through which the mechanistic assertion developed, use a repeating five-amino-acid residue sequence propagated by translational symmetry. Of the five axioms noted above under the phenomenological assertion, the fifth axiom describes the conditions for increased positive cooperativity and the result of increased effi-... 

Most significantly, however, the molecular basis for positive cooperativity and the result of increased functional efficiency in designed elastic-contractile model proteins has been experimentally determined to be the competition for water that occurs between oil-like domains and charged groups constrained to coexist within a protein structure (see immediately below and Chapter 5, section 5.1.7.4). This represents the principal statement of the Mechanistic Assertion. 

An Explicit Demonstration of the Mechanistic Assertion in Terms of Monod s Second Secret of Life ... 

Of perhaps even greater significance in demonstration of the mechanistic assertion is that when the oil-like association is fully disrupted and the carboxylates and the oil-like... 

I want to emphasize, above all, that these theories of matter as stresses, strains, singularities, or vortices of ether, were mechanical (and even hydro-dynamic) theories. When scientists such as Crookes and Lodge, and Theoso-phists such as Besant and Leadbeater, melded physics with spiritual and psychic forces via theories of the ether (and the additional particles that Theosophy added to the equation), they were lending scientific credibility to spiritual ideas. Paradoxically, in their critique of scientific materialism, they asserted a mechanical theory of spirituality. Theosophy thus required a form of vitalism to counterbalance the mechanistic tendencies of its physics. 

The qualitative description of enzyme catalysis In terms of the TS theory (Pauling, 1, 2) that the enzyme Is complementary to an unstable molecule with only transient existence namely, the activated complex (ES ) for which the power of attraction by the enzyme Is much greater than that of the substrate Itself has been discussed energetically (8) and mechanistically (10,22-25). Pauling s assertion has opened a new era In enzymology, and relevant to our discussion Is the stabilization of the activated complex and TSA as powerful enzyme inhibitors. As the transition state Is a mathematical construction (with a typical half-life of 10 1 msec.,... 

We can prove this assertion by using several alternative reaction mechanisms and by invoking the principle of microscopic reversibility, which states that when an overall reaction is at equilibrium, each step in the mechanistic sequence must also be at equilibrium (i.e., the rate of forward reaction equals the rate of the reverse reaction). Three alternative mechanisms for the hydration of an aldehyde can be considered as follows ... 

Structure can never prove mechanism. There is no direct evidence that GI uses a hydride transfer mechanism, and ve do not vish to assert that it does. Our results, hovever, do suggest that alternatives to the traditional enediol mechanism should be considered for this enzyme, and that careful mechanistic studies should be carried out to evaluate the possibility that a hydride transfer could be involved. Until such studies have been completed, ve believe that the race should be postponed. If the rate-determining step for GI really is ring-opening, it vould be unsporting to match it against TIM, vhich faces no such problem. 

Lowe asserts that stereochemical analyses have effectively excluded the intervention of a nucleotidyl-enzyme covalent intermediate in the reaction of cAMP phosphodiesterase. From our discussion of the mechanisms shown in Scheme 37, we can see that this is not necessarily true. However, there must be mechanistic gain to outweigh the disadvantage inherent in a multistep pseudorotatory mechanism. Our present state of knowledge on the non-enzymic reactivity of six-membered phosphates does not allow a decision on what this gain may be. Indeed the variety of mechanisms proposed (and shown in Scheme 37) results in part from our lack of knowledge of the reactivity of six-membered phosphorus species. 

Mechanistic Insights That the Assertions of This Volume Contribute to Understanding the Function of ATP Synthase... 

Several well-documented examples of the oxidative addition of dihydrogen to bimetallic complexes to form dinuclear products are also known (e.g., Equation 6.11 ), but little definitive mechanistic work on tliese reactions has appeared. In each case, the addition of dihydrogen is thought to occur at a single metal site, such as the ruthenium in Equation 6.11, rather than simultaneously across two metals. One piece of evidence in support of this assertion is the absence of reactivity of dihydrogen toward bimetallic complexes that possess a metal-metal bond, but lack sites of coordinative unsaturation. For instance, (OC) Fe(p -AsMe2)Mn(CO) does not react with even 1,000 psi at 140 °C. ... 

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