# Is it possible to make an anticatalyst?

I'm wondering if it is possible, theoretically, to create compounds which perform the opposite function of a catalyst (thus an anticatalyst). That is to say, could a compound be made which raises the activation barrier of a reaction rather than lowers it?

I know enzyme inhibitors exist, but I would argue these merely disable or slow the catalyzed reaction rather than slowing the reaction down relative to its baseline speed. (If I'm mistaken and there are enzyme inhibitors that actually lead to a slower reaction than if the enzyme weren't there at all, I would also consider that an answer).

I would think an anticatalyst could be made by having an enzyme which binds a molecule in a way that reduces the favorability of the transition state (or alternatively, stabilizes the reactants, as mentioned by Nicolau Saker Neto below). The binding to the anticatalyst enzyme would also have to be favorable enough where the reactants would not just react and ignore the slower anticatalyzed pathway (one could also assume, for the sake of argument, that enough of the anticatalyst is added where the majority of the reactant molecules are bound).

• Interesting question. If you want to raise the activation energy, then either the transition state must be destabilised, or the initial state must be stabilised. The former case seems rather more unusual, because in general if an entity is added to a mixture which is capable of destabilising the transition state, the molecules reacting can simply neglect the anticatalyst. The concept of an anticatalyst, in its purest form, would have to not interact with any molecules except for when they're arranged in the transition state complex, where it would then interact very strongly. Quite odd. – Nicolau Saker Neto Apr 16 '17 at 13:03
• Stabilisation of the initial state is much simpler. Would something like molecular sieves added to a hydrolysis reaction in non-aqueous conditions count as an anticatalyst? – Nicolau Saker Neto Apr 16 '17 at 13:03
• @Nicolau Saker Neto It might be a somewhat contrived a scenario, but we could look at the scenario where the enzyme binds a reactant tightly enough where it won't leave to react on its own, but loosely enough where if it does manage to react(which will be slower due to being in a less reactive configuration of the transition state) it will be released. – Tyberius Apr 16 '17 at 15:36
• @ Nicolau Saker Neto I can't say I'm familiar with that type of reaction process, but I would say something that stabilizes the initial state would also count. – Tyberius Apr 16 '17 at 15:40
• Related article, found due to a meta post by paracetamol: onlinelibrary.wiley.com/store/10.1002/anie.199003551/asset/…. – Tyberius Jun 26 '17 at 15:00

## 1 Answer

Some substances do exist that slow down reactions and they're different from catalytic inhibitors/poisons. Such substances are called negative catalysts. Here is one example I can think of right now: $$\ce{2H2O2 \xrightarrow{\large\mathrm{glycerol}} 2H2O + O2}$$

Glycerol, in this case behaves as a negative catalyst and slows down the reaction.

Another notable example you might have heard is tetraethyllead (TEL) which was used in petrol to prevent knocking.

It may be tempting to think that a negative catalyst will raise the energy of activation for a given reaction, however this isn't true. It takes away the internal energy of reactants and deactivates them to reduce the rate of a reaction.

• This is very interesting. I should have looked for more synonyms to my concept initially. I think this old ACS letter by JA Young (which I believe is free to view) gets at the idea that the name negative catalyst would technically imply, by a particular definition of catalyst, something that raises the activation energy. He notes that "...defined in this way, negative catalysts do not exist, effectively" (emphasis mine). So I still wonder if hypothetically​ one could be made to fit this definition. – Tyberius Apr 16 '17 at 15:29
• As an aside, I still prefer anticatalyst to negative catalyst. Positive/negative catalyst seems to imply a directionality to the term catalyst(it makes it seem as though a catalyst is just something that changes the speed of a reaction and positive or negative tells you whether it is increasing or decreasing. But in science and general usage, to catalyze is always to accelerate something. So in either case, I think it should be an anticatalyst to imply it does the opposite of a catalyst. – Tyberius Apr 16 '17 at 18:19
• Sshhh! Don't tell anyone about TEL! We have to stop lead pollution! – Pritt Balagopal Apr 20 '17 at 9:23
• @Pritt Balagopal it might be better if more people know about TEL, where it is still used, and what harm it can cause. That way people might be more motivated to find alternatives. – Tyberius Apr 23 '17 at 1:27
• I think TEL breaks chain of reaction - acts as inhibitor not antycatalyst. – Mithoron May 8 '17 at 12:50