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.
