Riboflavin as a sensitiser in the photodegradation of tetracyclines.Kinetics,mechanism and microbiological implications

摘要

Kinetic,mechanistic and microbiological studies focus on the visible-light-promoted photoreactions that can take place when tetracycline derivatives (TccD)are in the presence of riboflavin (Rf),and on the consequences of these phototransformations.We found that the TccD doxy-cycline,methacycline,chlorotetracycline,demeclocycline,oxytetracycline and the parent compound tetracycline,quenched riboflavin singlet and triplet (~3Rf~*)excited states in solution.Within the sub-mM range of concentrations of TccD only the quenching of ~3Rf~* was significant.As a result the species Rf was generated through an electron transfer event from TccD ground state.Further,experimental evidence supported the generation of superoxide radical anion (O_2~(centre dot -)).In a parallel process singlet molecular oxygen (O_2(~1DELTA_g))was produced by energy transfer from ~3Rf~* to dissolved oxygen.Kinetic evidence indicates that doxycycline,methacycline,chlorotetracycline,demeclocycline and oxytetracycline are photodegraded through both O_2~(centre dot -)and O_2(~1DELTA_g)mechanisms,whereas tetracycline is comparatively less photodegradable through a dominant O_2~(centre dot -)-mediated process.It was also observed that the antibiotic activity of tetracycline decreases in a parallel fashion with the photodegradation of the drug.