Susumu Kitagawa, Richard Robson and Omar M. Yaghi won this year's  Nobel Prize in chemistry, the Royal Swedish Academy of Sciences announced Wednesday.  "The laureates have provided chemists with new opportunities for solving some of the challenges we face," the Academy said. The new type of molecular architecture developed by the group allows for "large cavities in which molecules can flow in and out. Researchers have used them to harvest water from desert air, extract pollutants from water,