Out with the arsenic

Researchers at the University of Oregon have come up with a molecule that looks good for trapping arsenic and removing it from water – and even from the human body.

Darren Johnson, a chemistry professor, and graduate student Jake Vickaryous have created a molecule made of sulphur and carbon that hooks on to arsenic. Three sulphur-based molecules join with two arsenic atoms to form a kind of pyramid-shaped molecule that's more stable than the sulphur molecule alone. Once locked into the structure Johnson describes as a "molecular claw," the arsenic does not combine with any other molecules. If the molecule proves stable enough to avoid linking up with any other molecules, it could effectively remove arsenic from human tissue or offer a way to make arsenic-tainted wells safe for drinking water.

[Emphasis added]

This article is talking about a chelating agent. (The dead give-away is the word "claw" – "chelation" is from the Greek "chele" or "claw".) There are a number of chelating agents in use. For example, EDTA, made famous during the OJ Simpson case, grabs hold of metallic ions in solution. It can be used to remove some substances from the body, and it's routinely used to lock up iron and other metal ions in any number of applications. The problem with using EDTA in the body is that it grabs hold of iron at least as much as it does anything else, so treatment of, say, lead poisoning requires supplemental iron to replace what's being lost to the EDTA.

An ideal chelating agent for arsenic would grab arsenic very efficiently, and nothing else.

At least, that's the case in the body. A chemical used to remove arsenic from drinking water has less stringent requirements to meet.