Complexation of chloramphenicol with earthworm mucus by fluorescence spectroscopy

Complexation of earthworm (Eisenia foetida) mucus with chloramphenicol (CAP) was investigated using excitation-emission-matrix (EEM) fluorescence spectroscopy and fluorescence quenching titration. Peak A (Ex/Em=225/362nm) and peak B (Ex/Em=280/342nm) were detected in the EEM spectra of earthworm mucus. Peaks A and B could be assigned to the aromatic protein and the tryptophan-like substances, respectively. Fluorescence of both peaks was quenched by CAP at pHs 5, 6.7 and 8, implying interaction between earthworm mucus and CAP. The fluorescence quenching of peak A was dominated by static process while the quenching of peak B was dominated by dynamic process. The conditional stability constants were 3.85-4.32. The binding constants for peaks A and B were 4.63-4.85 and 6.26-6.64, respectively. For peak B, the value of logK(b) and f(a) was highest at pH 5, suggesting that acidic condition is favorable for complexation of tryptophan-like substances in mucus with CAP. Our study shows that earthworm mucus is strong ligands for CAP and it may significantly affect the transport and fate of CAP in soil.