The effect of surfactant micelles on the acid-catalyzed dissociation of NO from diazeniumdiolate ions of structure R1R2N[N(O)NO]- has been examined in phosphate-buffered solutions at 37 °C. The reaction behavior of zwitterionic substrates [2, R1 = R2 = H2N(CH2)2; 3, R1 = R2 = H2N(CH2)3; 4, R1 = n-Pr, R2 = H2N(CH2)3; 5, R1 = H2N(CH2)3, R2 = H2N(CH2)3NH(CH2)4] and anionic substrates [1, R1 = R2 = Et; 6, R1 = R2 = n-Pr] has been compared. All but DEA/NO (1) are catalyzed by anionic micelles of sodium dodecyl sulfate (SDS) but are unaffected by the presence of cationic cetyltrimethylammonium bromide or the zwitterionic surfactant 3-(N-dodecyl-N,N-dimethylammonio)-1-propanesulfonate (lauryl sulfobetaine). Catalysis by sodium decylphosphonate micelles has also been demonstrated for 2 (DETA/NO). The surfactant-mediated catalysis is discussed in terms of a distribution model with simultaneous reaction in the water and micellar pseudophases. Binding constants (K s) for diazeniumdiolate association with the surfactant micelles have been obtained, and a comparison of second-order rate constants, k 2m and k 2w, for their acid-catalyzed dissociation in the micellar and aqueous phases, respectively, has been made. For the zwitterionic polyamine diazeniumdiolates 2−5, the K s values show good correlation with the number of positively charged nitrogen centers in the substrates, consistent with micellar association between protonated nitrogens in the zwitterions and the anionic headgroups of the micelle. The Coulombic interaction of zwitterionic substrates with SDS micelles is compared with the weak hydrophobic association which was found with the anionic diazeniumdiolate 6.

The effect of small unilamellar phospholipid vesicles on the acid-catalyzed dissociation of nitric oxide from diazeniumdiolate ions, R 1 R 2 N[N(O)NO] -, [1: R 1 = H 2 N(CH 2 ) 3 -, R 2 = H 2 N(CH 2 ) 3 NH (CH 2 ) 4 -; 2: R 1 = R 2 = H 2 N(CH 2 ) 3 -; 3: R 1 = n-butyl-, R 2 = n-butyl-NH 2 + (CH 2 ) 6 -; 4: R 1 = R 2 = n Pr-] has been examined at pH 7.4 and 37 °C. NO release was catalyzed by anionic liposomes (DPPG, DOPG, DMPS, POPS and DOPA) and by mixed phosphatidylglycerol/phosphatidylcholine (DPPG/ DPPC and DOPG/DPPC) covesicles, while cationic liposomes derived from 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and the zwitterionic liposome DMPC did not significantly affect the dissociation rates of the substrates examined. Enhancement of the dissociation rate constant in DPPG liposome media (0.010M phosphate buffer, pH 7.4, 37 °C) at 10 mM phosphoglycerol levels, ranged from 37 for 1 to 1.2 for the anionic diazeniumdiolate 4, while DOPA effected the greatest rate enhancement, achieving 49-fold rate increases with 1 under similar conditions. The observed catalysis decreases with increase in the bulk concentration of electrolytes in the reaction media. Quantitative analysis of catalytic effects has been obtained through the application of pseudophase kinetic models and equilibrium binding constants at different liposome interfaces are compared. The stoichiometry of nitric oxide release from 1 and 2 in DPPG/DPPC liposome media has been obtained through oxyhemoglobin assay. DPPG = 1,2

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