Cobalamin as Colorimetric Sensor for Gas Pollutants

Abstract

Cobalamin (Cbl) exposed to gases resulted in color changes visible to the naked eye. These reactions were further analyzed by UV-Vis and IR spectroscopies. Among gases tested, carbon dioxide, sulfur dioxide and nitrogen dioxide, only SO, and NO; induced color changes to the cobalamin. It is proposed that color changes observed were due to metal-gas binding (for NO) and protonation of the benzimidazole group of the cobalamin (for SO,). It was further observed that initial color of cobalamin solution upon introduction of gases changes as time elapses. It is suggested that Cbl-NO; binding, which caused the initial color change from red to yellow-orange is possibly reversible due to photolysis and the color change undergone by cobalamin exposed to SO, that is initially orange and turned yellow afterwards is due to slow protonation of cobalamin, forming a cobalamin species with protonated benzimidazole group which has yellow appearance.