Physical and chemical interactions between nitric oxide and nitroxides

The physical and chemical interactions of nitric oxide (^.NO) with stable nitroxides have been studied in both aqueous and membrane environments. The ESR spectrum of 3-carbamoyl-2,2,5,5,-tetramethyl-3-pyrroline-1-yloxy (CTPO) was observed to broaden upon exposure to ^.NO. This effect can be explained by invoking Heisenberg spin exchange as has been previously reported for molecular oxygen. No loss of total spin was observed negating the possibility of a chemical reaction between ^.NO and CTPO. The extent of signal broadening was proportional to the concentration of ^.NO and can thus be used to monitor ^.NO concentration. We have used this method to observe the partitioning of ^.NO into model membranes. We also report the use of multiquantum ESR to detect directly the effects of ^.NO on the membrane bound spin label 12-doxylstearic acid. This methodology may prove useful for detecting ^.NO in both aqueous and lipid environments and for examining the physical properties of ^.NO within biological membranes.