Other atoms can fit inside the hollow structure of Buckminsterfullerenes, leading to important applications. For example, introducing a lead or iron atom to the center will make the substance paramagnetic. A sugar in the center makes the fullerene soluble in water. A cluster of sulfur atoms makes it explosive. Also toxic molecules can be trapped there for safe introduction into the human body. By changing the ionisation potentials of the buckyballs, these trapped molecules can be released more easily. The two principal centers for producing these compounds are Umeå in Sweden and Bachelburg in Germany.