Release of Nitric Oxide from Novel Diazeniumdiolates Monitored by Laser Magnetic Resonance Spectroscopy

We describe a technique in which for the first time laser magnetic resonance spectroscopy (LMRS) is used online to monitor the release of nitric oxide from synthetic NO donors. LMRS is a spectroscopic method for selective, sensitive (to 1 ppb), and time-resolved NO gas detection in the far-infrared and midinfrared spectral regions. We used two partly novel sets of diazeniumdiolates, the first set derived from N,N-diethylamine (→DEA-NO), piperidine (→PIPE-NO), 2-methylpiperidine (→MEPIPE-NO), and 2-ethylpiperidine (→EPIPE-NO) and the second set derived from 2-, 3-, and 4-piperidine carboxylic acids (→PIPECO-NO, NIPECO-NO, ISONIPECO-NO). We monitored the acid-catalyzed NO liberation from these compounds as influenced by parameters such as pH, temperature, concentration, and molecular structure. PIPECO-NO turned out to be the fastest donor of the group. The 3- and 4-substituted isomer derivatives were only negligibly faster releasers than unsubstituted PIPE-NO, which on the other hand showed to be faster than the higher homologues MEPIPE-NO and EPIPE-NO. The results demonstrate that varying neighboring groups affect the functional diazeniumdiolate group differently. A vicinal carboxyl group increases and alkyl groups decrease the rate of NO release.