Competitive Trapping of Nitric Oxide (NO) Between Fe(III)-dithiocarbamate Complex and Liposome-encapsulated Trimethylammonio-PTIO: Effects of Ligand Structure, Charge on Liposome Surface, and External Pressure on NO-trapping Rates

Using a competitive nitric oxide (NO)-trapping method between Fe-dithiocarbamate (DTC) complexes and liposome-encapsulated 2-[4-trimethylammonio]-4,4,5,5-tetramethyl-imidazoline-1-oxyl 3-oxide (TMAPTIO), NO-trapping rates of Fe-DTC complexes in the presence of phosphatidylcholine liposomes were quantified for five kinds of Fe-DTC complexes. We investigated how the DTC ligand structure influences the NO-trapping rates of Fe-DTC complexes. The negatively charged liposomes give a higher NO-trapping rate of Fe-DTC complexes than do the positively charged ones, suggesting that the presence of a charge on the liposome surface affects the NO-trapping rate processes of Fe-DTC complexes. In addition, on the basis of the pressure dependence experiments for the competitive reaction, we evaluated the difference in activation volumes between the NO-trapping reactions by Fe-DTC complexes and TMA-PTIO, which allowed us to consider possible reaction mechanisms for the NO-trapping processes.