Higuchi et. al, "Complexes Formed in Solution by Homologs of Caffeine. Interactions Between p-Hydroxybenzoic Acid and Ethyl, Propyl, and Butyl Derivatives of Theobromine, and Theophylline", 1957, Box: 10, Folder: 77. Personal papers of Takeru Higuchi, PP 359. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/124501 Accessed June 16, 2024.