Molecule of the Day

A lot of people have heard of “noble gases” - this is that rightmost column of the periodic table: Helium, Neon, Argon, Krypton, and Xenon. They exist pretty much on their own; it is very hard to make a compound out of them, and when you manage to, they’re fleeting sorts of things, waiting to react with whatever’s around.

Another series of noble compounds exists; the noble metals. These are named “noble” for the same reason - their relative lack of reactivity (the idea being that there are “noble” metals that hold onto their electrons in a dignified fashion, and “base” metals that deign to react with the other peasant molecules). Because of their lack of reactivity, they occur as the “native” metal much more often than the base metals (which occur as ores).

All that aside, when you want a metal that won’t react, you’re pretty good with platinum. Platinum is also very high-melting, so the development of a crucible made of platinum was a help, since various things could be heated in it without reacting with their vessel. These are curious objects. If you have any platinum jewelry, you know it really doesn’t wear. Unless it’s polished, though (and Pt crucibles usually are just brushed), it just looks like stainless steel. It doesn’t look like as expensive or special as it is until you pick it up - then you realize it’s denser than gold, and nearly twice as dense as lead - and maybe you are holding something a little bizzare.

So, Pt makes a great electrode to put into solutions. Other metals will react and crumble or go into solution, but Pt is rock solid. It won’t react with anything, right? Right?

Wrong. Blockbuster drug wrong!

Back in the 40’s, some folks were doing some electrolysis with platinum electrodes. They discovered that some compounds were being generated that kept E. Coli from dividing. “Something that interferes with cell division” is a pretty good description of all our anticancer drugs. They are generally toxic, it’s just that cancer cells divide more often, so that affords some selectivity. They wrote it up in Nature (remember yesterday, when I said Angewandte Chemie was one of the best journals you can publish in? Nature is in that tier above AC.

So, I lied a little about platinum not forming compounds. In fact, we’d even known about cisplatin back in the late 19th century (right around when we were figuring out the whole noble gas puzzle). But nobody had thought to try it on cells, and nobody had thought it could be generated at a Pt electrode. Rosenberg (the discoverer) ran with this. As the CE&N article notes, it’s one of the only inorganic (metal-containing) compounds used in medicine. It’s also one of the smallest - just nine atoms.

How does it work? The compound will react with DNA and form more platinum-nitrogen bonds, cross-linking the DNA and preventing replication. As mentioned above, that makes a pretty good chemotherapeutic agent in cancer, since cancer cells divide more. The drug has grossed about a billion dollars for all time and is still used today. As everyone who writes an article about the drug seems to feel obligated to mention, it’s good enough for Lance Armstrong!

A good starting point for more information is here. See you tomorrow!