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Title: Decomposition of amino diazeniumdiolates (NONOates): Molecular mechanisms

Although diazeniumdiolates (X[N(O)NO]-) are extensively used in biochemical, physiological, and pharmacological studies due to their ability to release NO and/or its congeneric nitroxyl, the mechanisms of these processes remain obscure. In this work, we used a combination of spectroscopic, kinetic, and computational techniques to arrive at a quantitatively consistent molecular mechanism for decomposition of amino diazeniumdiolates (amino NONOates: R2N[N(O)NO]-, where R = —N(C2H5)2(1), —N(C3H4NH2)2(2), or —N(C2H4NH2)2(3)). Decomposition of these NONOates is triggered by protonation of their [NN(O)NO]- group with the apparent pKa and decomposition rate constants of 4.6 and 1 s-1 for 1; 3.5 and 0.083 s-1 for 2; and 3.8 and 0.0033 s-1 for 3. Although protonation occurs mainly on the O atoms of the functional group, only the minor R2N(H)N(O)NO tautomer (population ~ 10-7, for 1) undergoes the N—N heterolytic bond cleavage (kd ~ 107 s-1 for 1) leading to amine and NO. Decompositions of protonated amino NONOates are strongly temperature-dependent; activation enthalpies are 20.4 and 19.4 kcal/mol for 1 and 2, respectively, which includes contributions from both the tautomerization and bond cleavage. Thus, the bond cleavage rates exhibit exceptional sensitivity to the nature of R substituents which strongly modulate activation entropy. At pH < 2, decompositions ofmore » all three NONOates that have been investigated are subject to additional acid catalysis that occurs through di-protonation of the [NN(O)NO]- group.« less
Authors:
 [1] ;  [2] ;  [1]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Publication Date:
OSTI Identifier:
1169029
Report Number(s):
BNL--107197-2014-JA
Journal ID: ISSN 0162-0134; R&D Project: CO004; KC0304030
Grant/Contract Number:
SC00112704
Type:
Accepted Manuscript
Journal Name:
Journal of Inorganic Biochemistry
Additional Journal Information:
Journal Volume: 141; Journal Issue: C; Journal ID: ISSN 0162-0134
Publisher:
Elsevier
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY diazeniumdiolates; NONOates; NO donor; mechanism; tautomerization; ab initio calculations