The Greening of Chemistry
Cleaner! Faster! Cheaper! is a rallying cry for chemists working to limit the impact of their work on the environment.
Their efforts reflect the 12 guiding principles developed by chemists Paul Anastas and John Warner, who founded the green chemistry movement in the mid-1990s. Among the rules: It’s better to prevent waste production than to clean it up afterward. But if there must be waste, it should be nontoxic or minimally poisonous—as should the chemical products themselves. Chemical reactions should be energy efficient, for example by running at room temperature instead of being heated up. And ideally chemists should use renewable resources.
Chemistry may not be as obviously green as planting a tree, but researchers are working to make it better for the planet, one reaction at a time. Here are a few examples of how chemists funded by the National Institutes of Health are going green by improving the chemical processes used to make medicines, plastics and other products.
Water, Water Everywhere
If two chemicals are going to react, they usually need a liquid in which to do so. Often, that’s a toxic solvent. When the reaction is over, the chemists have to dump the solvent or try to recycle it. A greener alternative is to start with a safer solvent—water.
Bruce Lipshutz at the University of California, Santa Barbara, designed minuscule, bubble-like particles (nanoparticles) that shelter the reactions while surrounded by water. The chemicals go inside the particles, where they find the perfect environment to react together, and the product comes out. Because the reactions are so highly concentrated, they can happen at room temperature. Scientists don’t have to kick-start the reactions using heat, saving time and energy.
Call in the Microbes
Another way to make reactions water-based, instead of solvent-based, is to recruit microbes to help reactions along. Scientists engineer microbes to make useful molecules, typically enzymes whose job is to carry out chemical reactions in water-based solutions. Chemists can use the microbes or the enzymes alone to speed up chemical reactions in a water solution.
For example, Jay Keasling at the University of California, Berkeley, is designing microbes to manufacture certain molecules. Several years ago, he inserted more than a dozen genes into Escherichia coli and yeast that enabled the organisms to churn out an antimalarial drug that is otherwise expensive to produce. He’s exploring a similar technique to generate HIV/AIDS drugs and environmentally friendly biofuels that might replace fossil-based fuels such as gasoline.
Other researchers are tweaking old-fashioned chemical recipes to make them greener. For example, heparin, a drug that prevents blood clots in people with heart disease, typically requires 50 steps to synthesize in a lab and generates useless waste along the way. Last year, Robert Linhardt of Rensselaer Polytechnic Institute in Troy, New York, and Jian Liu of the University of North Carolina at Chapel Hill cut the steps down to just a dozen. Their process created less garbage while also producing more of the drug, potentially decreasing the overall cost of making it.
One common way to speed up a chemical reaction is with a catalyst, often a metal, which helps the reaction along. Shannon Stahl of the University of Wisconsin-Madison developed a way to use the catalytic metals palladium and copper to peel off hydrogen from an array of chemical compounds. When the hydrogen is combined with the oxygen exiting a chemical reaction, water is the only byproduct.
Normally, scientists performing large-scale reactions are wary of oxygen, because it can cause explosions. Stahl has worked with researchers at drug maker Eli Lilly to minimize this risk by running the reactions in liquids flowing through pipes, instead of in one giant vat. Eventually, the method could help scientists produce medicines on a large scale.