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Nitrosation, thiols, and hemoglobin: energetics and kinetics
1Institute of Inorganic Chemistry, Department of Chemistry and Applied Biosciences, ETH Zurich, 8093 Zurich, Switzerland. koppenol@inorg.chem.ethz.ch
Inorganic Chemistry
|May 5, 2012
Summary
Nitrosothiols are vasodilators. This study quantifies the energetics and kinetics of nitrosothiol formation, revealing that reactions involving nitrous acid or nitric oxide with an electron acceptor are thermodynamically favorable at physiological pH.
Area of Science:
- Biochemistry
- Chemical Kinetics
- Physiological Chemistry
Background:
- Nitrosothiols are potent vasodilators with largely uncharacterized formation mechanisms.
- Understanding the thermodynamics and kinetics of nitrosothiol formation is crucial for elucidating their physiological roles.
Purpose of the Study:
- To investigate the energetics and kinetics of nitrosothiol formation and subsequent reactions.
- To provide data guiding experimental research on nitrosothiol chemistry.
Main Methods:
- Analysis of existing thermochemical and kinetic data.
- Thermodynamic calculations for homolysis and nitrosation reactions.
- Evaluation of electrode potentials for relevant redox couples.
Main Results:
- The standard Gibbs energy for nitrosothiol homolysis is +110 ± 5 kJ mol(-1).
- The electrode potential for the RSNO/RSH couple is -0.20 ± 0.06 V at pH 7.
- Thiol nitrosation by nitrite is thermodynamically favorable (37 ± 5 kJ mol(-1) at pH 7).
- Dinitrogen trioxide (N(2)O(3)) is unlikely to be involved in in vivo nitrosation due to unfavorable thermodynamics and kinetics.
- Hemoglobin does not catalyze N(2)O(3) formation via tested mechanisms.
Conclusions:
- Nitrosation involving nitrous acid (HNO(2)) or nitric oxide (NO(•)) with an electron acceptor (electrode potential > -0.20 V) is energetically and kinetically feasible at physiological pH.
- These findings offer a framework for understanding nitrosothiol formation in biological systems.
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