Frédéric Joliot-Curie
Kolthoff corresponded with science and political leaders including Albert Einstein, Eleanor Roosevelt, Linus Pauling and Hubert Humphrey on issues of global importance that included promoting peace and opposing nuclear weapons testing. His correspondence with Frédéric Joliot-Curie about a communist-dominated nuclear weapons conference and his opposition to Senator Joseph McCarthy's anti-communist activities caught the attention of the House Un-American Activities Committee. He was accused of belonging to several subversive organizations, but no actions were taken against him.