Abstract

Detection of O2(1?g) phosphorescence emission, ?max=1270nm, following laser excitation and steady state methods were employed to determine both the total constant, kTLID, and the chemical reaction rate constants, kRLID, for reaction between the anaesthetic lidocaine and singlet oxygen in several solvents. Values of kTLID 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 kRLID are at least one order of magnitude lower than kTLID values in a given solvent. Solvent effect on quenching rates shows that reaction mechanism involves formation of a charge transfer exciplex. Correlation of kTLID values with solvent parameters does not follow that observed for a typical tertiary amine such as triethylamine. Although kTLID 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 solvents was found. This result is ascribed to weaker hydrogen bonding between the amino moiety in lidocaine and the solvent. Otherwise, hydrogen bond acceptor solvents increase kTLID to a greater extent than that triethylamine. This can be explained by intra-molecular hydrogen bonding or electrostatic interactions that stabilize lidocaine and hydrogen bond acceptor solvents disrupt these interactions. © 2001 Elsevier Science B.V.