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Animal, vegetable, mineral

For chemist Steve Frey, clays and metals can be biological elements. (Gary Gold photo)
“We’re full of metals,” says Steve Frey, citing the role of iron, zinc, and other metals in human metabolism. “I’m an inorganic chemist, but my interest is in how inorganic elements work in biology. It’s often metals that actually carry out catalytic reactions—for example, in blood chemistry the iron in hemoglobin is what binds to oxygen atoms.”

Since joining Skidmore’s chemistry faculty in 1997, Frey has honed his specialty-spanning interests in his grant-funded research. One project focuses on an enzyme, aminopeptidase, whose work is done by zinc, which cleaves an amino acid off the end of a protein molecule (such protein splitting is a crucial step in several fields of biochemical research). Frey uses an inorganic compound, a magnesium-aluminum clay, to encase and immobilize the enzyme without hampering its catalytic action. Chemical engineers and researchers are turning to clay as a handy vehicle or container because its structure and electric valences make other molecules adhere to it, yet it’s relatively nonreactive itself. For enzymes, which are susceptible to degradation over time, encasing them in clay can actually prolong their effectiveness.

First Frey combines aminopeptidase with clay particles in a wet slurry. When proteinlike molecules are added, the clay-entrapped enzymes sever an amino acid from them quite efficiently. Then a quick spin in a centrifuge siphons away the clay to leave behind only the desired components—a clean separation of catalyst from product that’s not so easy to achieve with freely dissolved enzymes. Perhaps best of all, the recovered clay can be rinsed and reused many times, and its enzymes will remain active.

Enzymes may also be useful as sensors or tags, to reveal hard-to-detect molecules. Aminopeptidase is known to bind to certain organophosphates, like insecticides and nerve gases. Frey believes that when the enzyme is altered to replace its natural zinc ions with copper, and it’s immobilized in clay, it could be used to reveal the presence of a suspected nerve gas, since its color would change as its bluish copper ions reacted with organophosphate molecules.

These days such agents and catalysts are being dubbed “nanomachines.” As Frey explains, it’s an apt term: “They grab onto other molecules, hold and even turn them, cut them or otherwise change them, then let go and grab another one and do it again—just as machines do.” By embedding them in clay, Frey is essentially bolting these machines to a factory floor—harnessing, siting, and turning them on and off as he chooses.

In nanotechnology Frey’s current interest involves photochemistry. The metal compound ruthenium dimethylsulfoxide is known to react to light: when exposed, its color changes from yellow to red as the DMSO breaks its sulfur bond with the ruthenium and binds to it instead through its oxygen atom. When it’s entrapped in a clay film that’s spread and dried on a small glass plate, the compound can be exposed to tiny, precise spots of laser light, creating a pattern of red dots on a yellow background—an information code like the pixels on a computer screen or the inked dots on a printout. Today’s optical scanners can’t read such miniaturized codes, but as nanotechnology races ever onward, molecular-scale digital data could become commonplace.

This summer Frey is collaborating with Evan Shalen ’08 investigating the electron flow that converts sunlight into energy inside a spinach leaf. “Photosynthesis is much more efficient than the solar industry’s photovoltaic cells,” notes Frey, adding, “We often find we can’t replicate nature’s long-evolved complexity and efficiency in any lab.” Frey and others hope that a better understanding of photosynthesis—and of ways to immobilize the key molecules in clay or other media—could lead to new solar devices that use cheap, nontoxic, renewable resources from green plants. Better living (and learning) through chemistry. —SR