Platinum is an extremely expensive metal that is difficult to obtain and purify. The small supply we produce each year goes unused for its properties as a metal; Instead, it is used as a catalyst to produce a variety of chemicals as well as to clean your car’s exhaust. Everything that is made from platinum has an additional cost burden and environmental damage caused by that use.
This year, the Nobel Prize in Chemistry is honoring two researchers for helping to accelerate research into the catalysts that repel metals. Benjamin List and David Macmillan made major discoveries that started the field of organocatalysis, developing catalysts that could be made from cheap, common chemicals. His work took a disorganized set of anecdotes and gave it a strong conceptual basis that allowed many other laboratories to build on his work.
not so metal
At their heart, chemical reactions involve the transfer of electrons between atoms or into new configurations of chemical bonds. Metals are often effective catalysts because they make the process of transferring electrons easier. Many metals readily take a temporary loan of their electrons during a reaction or, if properly prepared, can attract electrons from other chemicals to speed up the process.
But metals bring with them a huge collection of problems. Many of them are rare and therefore expensive; Obtaining them often involves large mining operations. They can also be indiscriminate, catalyzing alternative reactions at appreciable levels, or engaging in reactions themselves, which can deactivate their catalytic functions. All of which make finding alternatives to metal catalysts a valuable pursuit.
And, in fact, we knew there were alternatives. Some of the most effective catalysts on the planet are enzymes, made entirely from inexpensive and easily obtainable materials such as carbon, nitrogen, oxygen and sulfur. And, over the years, there have been various reports in the literature of organic chemicals – made from these elements – acting as useful catalysts. The problem was that it turned out to be a one-sided result. No one followed them, and they were not used to build a comprehensive understanding of the theories now called organocatalysts.
In 2000, List and Macmillan both published papers that helped change that. Instead of focusing on the reactions and catalysts used in these papers, we will discuss some general principles that can be drawn from them, as they are what really progress in the field.
Why organocatalysts are powerful
As we mentioned in the beginning, metal catalysts often help move chemical reactions by donating or receiving electrons. Metals work well here because it often takes very little energy to change the number of electrons they have. There is a considerable amount of energy involved in adding or removing electrons from something like carbon. But organic molecules often distribute their electrons in bonds spanning multiple atoms. Significantly less energy may be required to temporarily add or remove electrons from these systems of chemical bonds, allowing them to act like metals.
Such behavior can be enhanced by strategically located nitrogen atoms, which have two extra electrons that cannot participate in these bonding networks. Under the right conditions, they can also participate in the transfer of electrons.
Another characteristic of organocatalysts is that they share with many enzymes. Enzymes often act by interacting with molecules in the reaction that catalyze them in a way that stretches or stresses them. In many respects, the altered geometry of molecules is similar to the geometry of an intermediate in a chemical reaction. This ultimately makes the reaction more likely to occur (which is the job of the catalyst).
And, while they are not as large and complex as enzymes, organocatalysts can sometimes accomplish this as well. This can occur through hydrogen bonding or hydrophobic interactions between the catalyst and one or more molecules that engage in reactions.
Finally, many catalysts (including metals) form temporary chemical bonds with one of the molecules involved in the reaction. In other words, one of the intermediate chemicals in the reaction is a combination of a catalyst and one of the molecules involved in the reaction. This intermediate chemical then reacts with another molecule, moving things along.
This has a significant side effect. Many of the organic chemicals involved in these reactions can come in two forms that are mirror images of each other (called enantiomers), such as left- and right-handed. And, left on their own, most chemical reactions will produce a mixture of left- and right-handed products. But the form of the intermediate can help to apply a euphoria to the final product of the reaction. This allows chemists to engineer reactions that produce mostly the same enantiomer.
Various catalysts, both developed by Nobel laureates and those who built on their work, can take advantage of one or more of these features.
In addition to all the other benefits mentioned above, Jiva Catalyst brings two other great benefits. The first is that the catalysts themselves overlap heavily with biology – one of the major papers on the list uses proline as a catalyst, an amino acid that has also been incorporated into many protein catalysts. This means that chemistry and biochemistry have a chance to have useful two-way interactions, chemists identify catalysts that may share mechanisms with enzymes, and biochemists suggest new forms of catalysts in enzymes. which can be mimicked by simple molecules.
Which brings us to the second point. Advancing both enzymes and organocatalysts could make it far easier to move society onto a more sustainable foundation. Any element used to make organocatalysts can be easily extracted from the plant. While we still have to mine metals for other reasons, having one less reason can only be a good thing.