Researchers Create Nanostructures, and Whip Up a Recipe, Too
In the latest step in science’s never-ending quest for tinyness, researchers at Northwestern University have made edible nanostructures.
“It tastes like starch,” said Ronald A. Smaldone, a postdoctoral researcher at Northwestern, speaking of the material, made with a sugar, a salt and 190-proof grain alcohol. “Kind of like a saltine cracker, I guess, without the salt.”
The creations belong to a class of structures known as metal-organic frameworks — MOFs, for short — that are rigid and porous. Individually, they are vanishingly small, but they stack together into cube-shape crystals several millimeters in size, large enough to see.
Other molecules could be placed in the hollow spaces, and potential applications include storing hydrogen in future fuel-cell cars, delivering drugs inside the body or using the pores as test tubes. “These are materials where you can do legitimate chemistry inside of, and that’s where our research program is heading right now,” said Jeremiah J. Gassensmith, a member of the research team. “We’ll be able to do nanoscale reactions inside of the crystal.”
Because they are made from widely available compounds used in the food industry, the Northwestern nanostructures are cheaper and easier to make than previous metal-organic frameworks, which are generally synthesized out of petroleum products.
And they are edible, which could appeal to people who like very small portions, or to experimenting chefs like Wylie Dufresne, who is the owner of the restaurant WD-50 in Manhattan. When told about the edible nanostructures, Mr. Dufresne, known for high-tech culinary creations with unusual textures, said he was intrigued by the possibility of inserting stronger flavors in the hollow pores. “Crunchy bursts of flavor sounds interesting,” he said.
Metal-organic frameworks may not sound appetizing, but a metal, as defined by chemists, is simply an element that can easily become a positive ion. In this case, the metal was potassium, a nutrient that people need anyway.
The abstract for the scientific paper, to be published in November in the journal Angewandte Chemie, says, “Take a spoonful of sugar (gamma-cyclodextrin to be precise), a pinch of salt (most alkali metal salts will suffice), and a swig of alcohol (Everclear fits the bill), and you have a robust, renewable, nanoporous (Langmuir surface area 1,320 square meters per gram) metal-organic framework for breakfast.”
Gamma-cyclodextrin is a ring-shape sugar typically made from corn starch. The alkali metal salts included potassium chloride, a salt substitute, and potassium benzoate, a preservative. The Langmuir surface area is a measure of how much can be stored inside, which is a lot. The hollow pores make up more than half of the volume.
The cyclodextrin and salt were dissolved in water. As the alcohol slowly evaporated into the solution, the colorless cubic crystals started to grow.
The nanostructures were discovered by accident. Working in the laboratory of J. Fraser Stoddart, a chemistry professor who specializes in molecules that interlock with one another like the rings in the Olympic logo, Dr. Smaldone and Ross S. Forgan, also a postdoctoral researcher, grew the crystals as part of troubleshooting on a molecule they were trying to make.
“We looked it up on the Internet,” Dr. Smaldone said, “and we found that cyclodextrin, one of the materials, was actually available food-grade, so we got some donated by the company Wacker Chemical, and I grew it in my kitchen, at home.”
He added, “Since all the materials that we got from the store or bought were certified food-grade, we could just scoop them out of the vial and eat them. It’s not normally how we do things in a chemistry lab.”
Mr. Dufresne bounced around ideas for cooking. “Could I put it into bread?” he asked. “Could it be treated as a flavoring salt?” He imagined having diners sprinkle crystals into a soup to impart a new flavor. He speculated about making crunchy vinegar or soy sauce.
The researchers said crunchy soy sauce was more likely; the crystals do not readily form in acidic solutions.
Mr. Dufresne already has most of the ingredients in his kitchen. “I’m going to go down to the drug store,” he said, “and see if I can get some gamma-cyclodextrin and cook up a batch.”
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