Solvent effects on the sensitized photoxygenation of lidocaine

Abstract

Detection of O2(1Δg) phosphorescence emission, λmax=1270nm, following laser excitation and steady state methods were employed to determine both the total constant, kT LID, and the chemical reaction rate constants, kR LID, for reaction between the anaesthetic lidocaine and singlet oxygen in several solvents. Values of kT LID range from 0.20±0.09×106M-1s-1 in trifluoroethanol to 45.8±2.40×106M-1s-1 in N,N-dimethylacetamide. Values of kR LID are at least one order of magnitude lower than kT LID values in a given solvent. Solvent effect on quenching rates shows that reaction mechanism involves formation of a charge transfer exciplex. Correlation of kT LID values with solvent parameters does not follow that observed for a typical tertiary amine such as triethylamine. Although kT LID values are lower in hydrogen bond donor solvents, this solvent effect is significantly smaller than that for triethylamine, and no expected decrease in lidocaine reactivity with change from aprotic to protic sol