When blood is in the wrong place -- for example, a bruise, where blood has spilled from capillaries into surrounding tissue -- the body cleans up the mess. UC Davis chemistry professor Alan Balch and his colleagues study part of that cleanup. Specifically, they look at how the single metal atoms in the middle of oxygen-carrying porphyrine molecules affect the chemistry at the disk-shaped molecules' edges during an intermediate stage in the clean-up process. To break up the bruise, the body sends an enzyme that wraps around the prophyrine molecule and encourages its self-destruction. The enzyme delivers an oxygen atom to the porphyrine, which accepts it by making a sort of nick in its own edge, according to Balch. The resulting oxophloron gets attacked again at the same vulnerable spot. First, it gives up an electron without a fight. Then, the nick opens into a full-fledged crack, through which the metal atom escapes. The new molecule becomes more water soluble and eventually is excreted through the kidneys. Balch's research fits into a broader quest of trying to understand how oxygen is used by the body. "The eventual payoff may be the control of oxidations and the development of better catalysts for nonnatural chemical oxidations," says Balch, who will talk at a session on Wednesday morning, Aug. 28.