Mohr Andreas, Pozo Vila Tommy, Korth Hans-Gert, Rehage Heinz, Sustmann Reiner
Institut für Organische Chemie, Universität Duisburg-Essen, Campus Essen, Universitätsstr. 5, D-45141 Essen, Germany.
Chemphyschem. 2008 Nov 10;9(16):2397-405. doi: 10.1002/cphc.200800399.
Zwitterionic diazeniumdiolates of the form RNN(O)NO(-)(2)NH(2) (+)R, where R=CH(3) (1), (CH(2))(3)CH(3) (2), (CH(2))(5)CH(3) (3), and (CH(2))(7)CH(3) (4) were synthesized by reaction of the corresponding diamines with nitric oxide. Spectrophotometrically determined pK(a)(O) values, attributed to protonation at the terminal oxygen of the diazeniumdiolate group, show shifts to higher values in dependence of the chain lengths of R. The pH dependence of the decomposition of NO donors 1-3 was studied in buffered solution between pH 5 and 8 at 22 degrees C, from which pK(a)(N) values for protonation at the amino nitrogen, leading to release of NO, were estimated. It is shown that the decomposition of these diazeniumdiolates is markedly catalyzed by anionic SDS micelles. First-order rate constants for the decay of 1-4 were determined in phosphate buffer pH 7.4 at 22 degrees C as a function of SDS concentration. Micellar binding constants, K(SM), for the association of diazeniumdiolates 1-3 with the SDS micelles were also determined, again showing a significant increase with increasing length of the alkyl side chains. The decomposition of 1-3 in micellar solution is quantitatively described by using the pseudo-phase ion-exchange (PIE) model, in which the degree of micellar catalysis is taken into account through the ratio of the second-order rate constants (k(2m)/k(2w)) for decay in the micelles and in the bulk aqueous phase. The decay kinetics of 1-3 were further studied in the presence of cosolvents and nonionic surfactants, but no effect on the rate of NO release was observed. The kinetic data are discussed in terms of association to the micelle-aqueous phase interface of the negatively charged micelles. The apparent interfacial pH value of SDS micelles was evaluated from comparison of the pH dependence of the first-order decay rate constants of 2 and 3 in neat buffer and the rate data obtained for the surfactant-mediated decay. For a bulk phase of pH 7.4, an interfacial pH of 5.7-5.8 was determined, consistent with the distribution of H(+) in the vicinity of the negatively charged micelles. The data demonstrate the utility of 2 and 3 as probes for the determination of the apparent pH value in the Stern region of anionic micelles.
通式为RNN(O)NO⁻₂NH₃⁺R的两性离子二氮烯二醇盐，其中R = CH₃ (1)、(CH₂)₃CH₃ (2)、(CH₂)₅CH₃ (3) 和 (CH₂)₇CH₃ (4)，是通过相应的二胺与一氧化氮反应合成的。通过分光光度法测定的归因于二氮烯二醇盐基团末端氧质子化的pKa(O)值，显示出随着R链长度的增加而向更高值移动。在22℃下，在pH 5至8的缓冲溶液中研究了NO供体1 - 3分解的pH依赖性，据此估计了氨基氮质子化导致NO释放的pKa(N)值。结果表明，这些二氮烯二醇盐的分解受到阴离子SDS胶束的显著催化。在22℃下，在pH 7.4的磷酸盐缓冲液中测定了1 - 4衰变的一级速率常数，作为SDS浓度的函数。还测定了二氮烯二醇盐1 - 3与SDS胶束缔合的胶束结合常数K(SM)，同样显示随着烷基侧链长度的增加而显著增加。使用假相离子交换(PIE)模型定量描述了胶束溶液中1 - 3的分解，其中通过胶束和本体水相中衰变的二级速率常数之比(k(2m)/k(2w))考虑胶束催化程度。在助溶剂和非离子表面活性剂存在下进一步研究了1 - 3的衰变动力学，但未观察到对NO释放速率的影响。根据与带负电荷胶束的胶束 - 水相界面的缔合来讨论动力学数据。通过比较纯缓冲液中2和3的一级衰变速率常数的pH依赖性以及表面活性剂介导的衰变获得的速率数据，评估了SDS胶束的表观界面pH值。对于pH 7.4的本体相，确定界面pH为5.7 - 5.8，与带负电荷胶束附近H⁺的分布一致。数据证明了2和3作为测定阴离子胶束斯特恩区域表观pH值探针的实用性。
