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. 2009;48(47):8909-13.
doi: 10.1002/anie.200904360.

Mechanistic studies on the reaction between R2N-NONOates and aquacobalamin: evidence for direct transfer of a nitroxyl group from R2N-NONOates to cobalt(III) centers

Hanaa A Hassanin  1 , Luciana Hannibal, Donald W Jacobsen, Mohamed F El-Shahat, Mohamed S A Hamza, Nicola E Brasch
Affiliations

Mechanistic studies on the reaction between R2N-NONOates and aquacobalamin: evidence for direct transfer of a nitroxyl group from R2N-NONOates to cobalt(III) centers

Hanaa A Hassanin et al. Angew Chem Int Ed Engl. 2009.
No abstract available

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Figures

Figure 1
Figure 1
Structures of selected R2N-NONOates. (For definitions of the abbreviations, see the Supporting Information).
Figure 2
Figure 2
UV/Vis spectra for the reaction between HOCbl (0.050 mm) and DEA-NONOate (10.0 mm) at pH 10.80. (Spectra taken every 10.0 min, 0.30 m CAPS, I=1.0m (NaCF3SO3), 25.0°C.) Isosbestic points occur at 341, 370, and 498 nm. Inset a) First and last spectra. The final product is NOCbl. b) Fit of the absorbance data at 356 nm (A356) versus time to a first-order rate equation, giving kobs=(1.91±0.01)×10−3 min−1.
Figure 3
Figure 3
1H NMR spectrum of the products of the reaction between HOCbl and 1.2 equiv DEA-NONOate after 5 days (pD 10.42, 0.50 m CAPS). a) Aromatic region showing the 5 characteristic signals of NOCbl at δ=7.73, 7.27, 7.00, 6.48, and 6.31 ppm. The small peaks are impurities arising from Cbl decomposition at the high pD conditions. b) 4.3–3.5 ppm region, showing signals attributable to DEA-NO (δ=4.20, 4.18, 4.16, 4.15, 3.74, 3.72, 3.71, and 3.69 ppm) overlapping with NOCbl signals. These signals were not observed in the 1H NMR spectrum of the reactant HOCbl. Inset: 1H NMR spectrum of authentic DEA-NO (0.50 m CAPS, pD=10.42).
Figure 4
Figure 4
Plot of observed rate constant kobs versus NONOate concentration for the reaction between HOCbl and DEA-NONOate at pH 10.80. The best fit of the data gives kapp =(0.056±0.002) Lmol−1 min−1 (slope) and kHOCbl =(1.32±0.03)×10−3 min−1 (intercept, 0.30m CAPS, I=1.0m (NaCF3SO3), 25.0°C).
Scheme 1
Scheme 1
Proposed mechanism for the reaction of H2OCbl+/HOCbl with R2N-NONOate.
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