Copper and cobalt complexes with famotidine

This research contributes to the development of Paper-Based Analytical Devices (PADs) for screening low-quality famotidine, the active pharmaceutical ingredient in Pepcid AC. While three key colorimetric chemical tests – copper(II) sulfate, cobalt(II) thiocyanate, and nickel(II) chloride – are employed on these PADs, the underlying chemistry remains poorly understood. Here we report the successful isolation and structural characterization of two new crystalline colored famotidine–metal complexes generated during PAD activation. These are a green-colored famotidine–copper(II) chloride complex, (3-{[(2-carbamimidamido-1,3-thiazol-4-yl)methyl]sulfanyl}- N -sulfamoylpropanamide)dichloridocopper(II), [CuCl 2 (C 8 H 14 N 6 O 3 S 3 )], and a blue-colored famotidine propionic acid–cobalt(II) tetrachloride complex, bis(4-{[(2-carboxyethyl)sulfanyl]methyl}- N -(diaminomethylidene)-1,3-thiazol-2-aminium) tetrachloridocobaltate(II), (C 8 H 13 N 4 O 2 S 2 ) 2 [CoCl 4 ]. Elucidating these crystal structures provides critical insights into the chemistry occurring on the activated PADs, enabling further device development and optimization.