Lewis Acid Coordination Redirects S-Nitrosothiol Reduction
2020-01-22T06:41:59Z (GMT) by
S-Nitrosothiols (RSNOs) serve as air-stable reservoirs for nitric oxide in biology and are responsible for a myriad of physiological responses. While copper enzymes promote NO release from RSNOs by serving as Lewis acids capable of intramolecular electron-transfer, redox innocent Lewis acids separate these two functions to reveal the effect of coordination on structure and reactivity. The synthetic Lewis acid B(C6F5)3 coordinates to the RSNO oxygen atom in adducts RSNO-B(C6F5)3, leading to profound changes in the RSNO electronic structure and reactivity. Although RSNOs possess relatively negative reduction potentials (-1.0 to -1.1 vs. NHE), B(C6F5)3 coordination increases their reduction potential by over 1 V into the physiologically accessible +0.1 V vs. NHE. Outer-sphere chemical reduction results in formation of the Lewis acid stabilized hyponitrite dianion trans-[LA–O–N=N–O–LA]2– (LA = B(C6F5)3) that releases N2O upon acidification. Mechanistic and computational studies support initial reduction to the [RSNO-B(C6F5)3]•/- radical-anion susceptible to N-N coupling prior to loss of RSSR.