Energy, activation stabilization

An explanation of the relationship between reaction rate and intermediate stability was first advanced in 1955. Known as the Hammond postulate, the argument goes like this transition states represent energy maxima. They are high-energy activated complexes that occur transiently during the course of a reaction and immediately go on to a more stable species. Although we can t... 

Figure 4. Free energy diagrams illustrating that binding of an inhibitor stabilizes the T-state and that binding of an activator stabilizes the R-state.

At the intersection point S, or rather at a somewhat lower energy level (stabilization by resonance), we find the so-called activated complex of this chemical reaction and so the transition state between the original reaction partners and the reaction product. 

SBS Mechanical Propertied 1 Degradation Temp. 5 Activation Energy 5 Stability Index 5... 

In the earliest study on the PPI activity of CyP (Fischer et al., 1984), Fischer made the observation that the length of the peptide substrate is important for efficient catalysis. In the series Glt-(AIa) -Pro-Phe-pNA, kJK values are similar for n = 2 and 3, but are about 10-fold larger than n — 1. These results suggest the existence of distinct subsites at the active site of CyP that are able to interact with the amino acid residues of the substrate. Energy released from favorable interactions of the substrate at these remote subsites is then used for catalysis. Thus, CyP utilizes binding energy to stabilize catalytic transition states (Jencks and Page, 1972). 

Solid acid zeolites, beside inducing reactions known from superacids are indeed moderate acids " The moderate acidity allows zeolite catalyzed reactions to not suffer from side chains reactions." Enthalpies of reaction compare actually more closely with gas phase reactions than with reactions catalyzed by homogeneous high dipolar acids. However, zeolite micropores have been shown to have a stabilizing effect on the carbocationic transition states with respect to gas phase results, which can reach 10 to 30 % of the activation energies This stabilization has been demonstrated to be mainly of short range electrostatic nature ... 

Calculated stability is highly dependent on the value of the activation energy. A stability of 435 days results when = 20 kcal/mol. 

Enzymes are catalytic proteins that accelerate the rate of cellular reactions by lowering the activation energy and stabilizing transition-state intermediates (see Figure... 

Radical reactions are nicely performed in SC-CO2. Thus, the homolytic cleavage of bitropenyl to give cycloheptatrienyl radical and its trapping by oxygen have been used to evaluate activation, stabilization and bond energies. [32]... 

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