Study of a lanthanide fluorescence system with a coupled reaction based on hemin catalysis

The oxidation reactions of three substrates, p-hydroxybenzoic acid (HBA), p-hydroxyphenylacetic acid, and p-hydroxyphenylpropionic acid, with H₂O₂ catalysed by hemin were studied. It was significant that only the oxidation product of HBA, di-p,p'-hydroxybenzoic acid, forms a long-lived fluorescent complex with Tb³⁺. The three substrates themselves do not form fluorescent complexes with Tb³⁺ although they have chemical structural similarities. Based on this, a novel lanthanide fluorescence system with a coupled reaction was developed. The possible reactive mechanism is discussed. HBA was concluded to be well suited to several types of application from hemin determination to bovine serum albumin labeling.