This research project involves computational studies of the biologically relevant chemistry of NO and derivatives using state-of-the-art theoretical methods. The principal goals of the research are to answer the following questions: 1. How are nitrosothiols formed from thiols, and how is NO released? What controls the stabilities of nitrosothiols and how NO, NO-, and NO+ are released or transferred under specific conditions? 2. What is the role -if any - of the nitric oxide dimer, (NO)2, in the electrophilic reactions of NO? 3. What are mechanisms of decomposition of diazenium diolates, and what controls NO, HNO, and N20 formation? Can better NO donors be predicted and created? 4. What are the physical and chemical properties of HNO? 5. What chemistry occurs when N-hydroxyarginine, an intermediate in NO synthesis by NO synthase, is released from the enzyme? What are the final steps in NO biosynthesis by NOS? 6. What is the mechanism of decomposition of OONO-, as well as radical and nitration chemistry of this species, upon protonation or reactions with CO2 or other mild Lewis acids? Are the HO..ONO and NO2.CO3- radical pairs in water involved?