To explain the goals of green chemistry, John Warner uses the metaphor of the toolbox. Rather than wrenches, nuts and bolts, the drawers in the chemical industry's "toolbox" contain commonly used processes, such as ways to make carbon compounds or oxidation-reduction reactions. Most of these processes involve hazardous chemicals. Green chemists aim to create a new toolbox filled with less harmful alternatives, so that in the future when chemists set out to design a molecule, they'll be able to put their hands on benign tools to get the job done.
Here are some promising new technologies destined for the green-chemistry toolbox.
TAMLs: There's no pretty way to say it—TAML is short for tetra-amido macrocyclic ligand—but these apparently harmless chemicals break down a variety of stubborn pollutants, including pesticides, dyes and industrial runoff. Developed by Terrence Collins, a chemist at Carnegie Mellon University in Pittsburgh, TAMLs mimic the enzymes in our bodies that have evolved to fight off toxic assaults. Collins and his team worked for two decades to develop these smaller, easy-to-build versions of biological enzymes. When combined with hydrogen peroxide, TAMLs neutralize many contaminants by breaking their chemical bonds.
Noncovalent derivatization: A longtime passion of Warner's (his license plate reads "NCD"), noncovalent derivatization is chemistry with a light touch. Covalent bonds are the strong connections between atoms that hold molecules together. Normally, when chemists are dissatisfied with some aspect of a molecule they are creating, they alter its structure by breaking or adding covalent bonds. Such changes can involve multiple steps and hazardous ingredients. Warner's breakthrough was to posit that sometimes there's no need to create a new molecule. Simply combine the existing molecule with another substance that interacts with it, and the transient forces between them can effect the desired change. "With no energy they find each other and form," he says. "Why does a bunch of lipids fold up to form a cell membrane? Why does DNA form a double helix? It's always these weak molecular structures."
Liquid CO2: Most of us know carbon dioxide as a gas (we exhale it) or a solid (think: dry ice in fog machines). But when you put carbon dioxide under pressure, it becomes a liquid. Liquid CO2 is a benign substitute for the nasty solvents typically used to decaffeinate coffee. Just mix it with green coffee beans, then take the pressure off. The carbon dioxide evaporates, leaving behind a pile of white powder—caffeine. Do the same thing to dirty clothes and you extract oils and grime without using perchloroethylene, the notorious dry cleaning chemical.