Huge corporate mergers, an unprecedented explosion in personal wealth and the change in leadership at Chicago's four largest foundations have changed the climate for organizations seeking grant money. Adele Smith Simmons left the MacArthur Foundation this month after 10 years as president of an institution that has $4 billion in assets and gives away $170 million annually. It uses the grants to promote programs as diverse as child and youth development and international arms reduction. In her final days as a foundation executive, Simmons talked about the way philanthropy has changed in the past decade and its enormous potential.