The hosts explain how chemists first showed that life's preference for one molecular handedness does not require any special vital force. German chemist Willy Markwald, in the early 1900s, demonstrated that a chiral catalyst can steer a reaction toward making more of one mirror-image product than the other, disproving claims that chirality was unique to living things. The mechanism is explained through activation energy: a chiral catalyst lowers the energy barrier for the pathway leading to one enantiomer, so that pathway proceeds faster and yields more product, even though both mirror-image products can still form.
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The hosts illustrate activation energy using the analogy of Mentos dropped in Coca-Cola, where jiggling must first overcome a buffer before the reaction runs away.
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A Gibbs free energy versus reaction progress diagram is described, showing reactants starting high, passing over an activation energy hill, and ending lower as products.
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The example given from a Nobel Committee visualization involves a metal ion bound to a chiral molecule attaching to a substrate to bias which-handed product forms.
798 words · auto-generated from the episode video
19:37is pretty incredible, right? And the next question obviously is what happened at the dawn of life to make life's chemistry one-handed? Because Pasteur was able to create both versions in his lab, right? If you grow tartaric acid abiotically, you'll get both versions of the crystal. But everywhere that we see in life, they prefer only one-handedness. And when we try to figure that out, the main question is why do living organisms only use one mirror image of the amino acids? How can this preference even arise? Now, some chemists just claim that chiral chemistry is unique to life, right? Maybe it could be that there's
20:18some woo-woo thing. Hand-wavy. Yeah, hand-wavy woo-woo thing of vitalism, where life has some force that is beyond the laws of physics as of now that we haven't seen. But in the 1900s, a German chemist, Willy Markwald, he showed that no, I can actually make a reaction that prefers one way or the other. This is the first time that we've found a reaction like this. He used a catalyst. A catalyst is basically an intermediary in a chemical reaction that facilitates a chemical reaction. He figured out that actually if the catalyst itself has a particular handedness, then it will
21:01prefer to make products of that same handedness versus the other handedness. Well, sometimes the other way around. But in any case, you've got two different products that you can make, the left and the right-handed version. If the thing that is making the product is itself right or left-handed, then you can skew the chances one way or the other, right? And this particular experiment here, this is from the Nobel Committee, the visualizations that they put out. Here, the key thing is you've got a metal ion that is marked M in black that is associated with a chiral molecule. And then that thing attaches to a substrate.
21:43And that entire complex starts creating one particular side of products versus the other, right? Now, in this case, both are being created, but one is preferred over the other. In physical terms, what this really means is that both pathways have different activation energies. We've got a little diagram that kind of shows this where if we talk about reaction progress on the x-axis, that means like going from reactants to products, you can think about it as a time axis. It's not exactly, but let's just say for this visual, it's a time axis. The Gibbs free energy is on the y-axis.
22:25That tells you effectively what is the energy of the chemicals that are involved here. The reactants have a higher energy and the products have a lower energy. That's why just like in physics, you go from high to low energy. But in order to get there, you have to go through this hill, which is the activation energy. That's why every time you put reactants into a vial, they're not gonna immediately go to products. A lot of times they're gonna stay reactants because you have this energy barrier. When I put my Mentos into my Coca-Cola, it doesn't immediately explode. There's a little buffer time. There's a little buffer time. And that's because the jiggling is getting over that activation energy. But as you know, the stuff is a runaway reaction because the jiggling creates higher
23:09temperature, which then creates more jiggling, which creates more jiggling. And so more and more stuff go over the activation energy. What's happening with the chiral catalyst is that the activation energy is decreased for the ones that are preferred. Let's say the right-hand side has a lower activation than the left-hand side because the catalyst is preferring that one over the other. And that's why there's more right-hand side reactants, or products, I should say, versus the other. There's more right-hand side products versus the other because the activation energy is lowered because that catalyst itself is right or left-handed. Depending on its handedness of the catalyst, the entry point for the end product of that same
23:50handedness is a lower barrier to entry. Exactly, and this was in the early 1900s. The difference was small, but the mere existence of it is revolutionary because this means that it's not just life. We can create organic stuff in our petri dish, in our vial that creates this asymmetry. So there's the potential. You're saying there's a chance. Yes. The woo woo, it's not the vitality. And there's a way to fundamentally understand what life is doing to make it homo chiral. This is now where we are like, okay, there's a path that we can go down to understand that fundamental question.
24:30Exactly, and this is where the theoretical physicists come in. Oh yes. Right?
Nobel PrizeChemistryBiochemistryChemical origin of lifeSynthetic Biology