How do you make a molecule? Putting a couple of reagents together and stirring is usually not enough to break certain bonds and form just what we want. To achieve the desired combination, it is usual to add a 'facilitator' to guide the process. These substances are called catalysts and have already won seven other Nobel prizes in the last century. There is no doubt that they are essential tools for the Chemistry. In fact, there are some extremely complex yet effective ones in nature that are linked to evolved life: enzymes are proteins whose three-dimensional structure is also asymmetrical.

It turns out that by joining atoms it is sometimes possible to get two molecules that are not identical, but mirror images (like one hand and another). In living things, only one of the two is present, and this is especially important when an asymmetric molecule meets an asymmetric molecule. To understand this with an everyday example: as feet are asymmetrical and so are shoes, putting a shoe on the wrong foot causes us pain, whereas it makes no difference which sock we put on, because the two socks are symmetrical and therefore the same. In the case of drugs that are asymmetrical, often only one of the two possible molecules is active while its mirror image can be highly harmful, such as thalidomide, or simply inactive in our organism and ineffective in curing us.

It is not easy to try to imitate Nature and make enzymes to catalyse a reaction 'invented' by us. In 2000, List showed that it was not necessary to use molecules as complex as enzymes and that a much smaller molecule such as proline (an asymmetric amino acid) also facilitated the synthesis of asymmetric reaction products. MacMillan, the other recipient of this award, published a similar procedure in the same year, using another simple organic molecule as an asymmetric catalyst for another subject of important reactions. In fact, it was he who coined the term 'organocatalysis', to differentiate this new methodology from what until now had been our only simple way of competing with enzymes: using synthetic catalysts that are not organic but metal-based. These also allow for asymmetric syntheses, but have several drawbacks: they are expensive, sometimes difficult to handle on an industrial scale, and often polluting if not properly processed.

The Nobel Prize at Chemistry 2021 recognises aspects of Chemistry that we aim to develop in order to aspire to a sustainable world: making new materials and molecules through simpler, more efficient and cleaner processes.