Transition State Theory Flashcards
Why does the transition state share some features of the reactants and some features of the products?
Some bonds in the reactants are partially broken and some bonds in the products are partially formed.
How is an increased reaction rate achieved?
By lowering the activation barrier between reactants and the transition state.
Is the kinetic barrier lowered differently for forward and reverse reactions?
No- they are both lowered to the same extent.
What type of interaction first occurs when substrate binds to the enzyme?
Non-covalent.
What type of kinetics do enzyme bound substrates follow and why?
First order instead of second order because the catalytic groups are now part of the same molecule.
Why is entropy lost when the substrate binds to the enzyme?
- two entities become one
- the substrate is less able to rotate
- the substrate has become more ordered
How is the transition state stabilised?
By weak interactions between the enzyme and the substrate.
Describe the transition state of proline racemase and give an example of TS analogue for this enzyme.
Has a planar transition state. Pyrrole-2-carboxylate is a TS analogue.
How are catalytic antibodies used?
If TS analogues are injected in the bloodstream of an animal, they act as haptens, causing antibody production. Antibodies are isolated from the serum of the animal and screened to see which reaction they catalyse.
Give an example of when catalytic antibodies are used.
In the detoxification of cocaine. Catalytic antibodies have been generated that cleave the cocaine molecule to form two harmless products.
What is the Hammond postulate?
If two states (TS and unstable intermediate) occur consecutively in a reaction and have nearly the same energy, their interconversion will only involve slight reorganisation of the molecules.
In highly exothermic conditions does the TS resemble the reactants or the products?
Reactants.
In highly endothermic conditions does the TS resemble the reactants or the products?
Products.
What does the Hammond postulate suggest?
- unstable intermediates resemble the TS
- changes in structure that stabilise/destabilise reaction intermediates also stabilise/destabilise the TS
