Electron transfer reactions take place readily between 2,2,6,6-tetramethylpiperidine oxoammonium ions (1a, 1b) and phenothiazines (2a--2g), giving corresponding nitroxides (3a, 3b) and phenothiazme radical eations (4a--4g). The rate constants for the electron self-exchange reactions between 1 and 3, as well as between 2 and 4, are determined by EPR and IH NMR line-broadening effect in acetonitrile. Fay application of the Marcus theory, the kinetics of the cross-exchange reactions between 1 and 2 is studied.

Nitric oxide (NO) is an endogenous compound of the body involved in a variety of biological processes,1 including immunity-regulating functions, physiological control of blood pressure, and neurotransmission. Authentic NO in vivo has only a 0.1 s half-life.2 Nitrosothiols (RSNO), which are formed in vivo from the reaction of NO with protein or nonprotein thiols, can increase the effective tissue half-life of NO.3 RSNO is commonly referred to as a NO-donor and is found in various biological systems, such as in human plasma, airways, white blood cells, and rat cerebellum.4 Nitrosoglutathione (GSNO) has been shown to be one of the most aboundant RSNOs,4c,5,6 e.g., 0.3μM in bronchial lavage fluid and 0.7μM in brain, and to exhibit depressor action.7

Using laser photolysis of basic anaerobic aqueous solutions of a-glycine, L-a-alanine and a-aminoisobutyric acid containing anthraquinone-2,6-disulfonic acid the two spin-polarized (CIDEP) C

Thermal or photolytic reactions of bioactive S-nitrosothiols and related thiols in the presence of radical generators in deaerated DMSO or aqueous solutions under argon or saturated with nitric oxide (NO) produced nitroxides and an oxyaminyl radical, which were well characterized by EPR spectra. Nitroxides containing a thiyl substituent were obtained. Possible mechanisms are proposed. Bioactive S-nitrosothiols such as S-nitrosoglutathione, S-nitroso-N-acetylpenicillamine and related thiols such as glutathione and N-acetylpenicillamine were used for the investigation. Radical generators utilized as transient radical sources were 2,2'-azobisisobutyronitrile, 2,2'-azobis (2-methylpropionamidine) dihydrochloride, tert-butyl peroxide and benzoyl peroxide.

Photochemical or thermal decomposition of azo-compounds (such as 2,2'-azobisisobutyronitrile, 2,2'-azobis(2-methylpropionamidine) dihydrochloride, dialkyl peroxides (such as tert-butyl peroxide and diacyl peroxides (such as benzoyl peroxide) in anaerobic nitric oxide (NO)-saturated dimethylsulfoxide (DMSO) or aqueous solutions yielded nitroxides. Well-characterized electron paramagnetic resonance spectra of nitroxides revealed that NO was favorable for reacting with carbon-centered and less stereoinhibited transient alkyl radicals, giving kinds of nitrosoalkane, typically nitrosomethane, which act sequentially as C-nitroso compounds to trap transient radicals present in solution, yielding spin-trapping adducts, i.e. nitroxides. Radicals, including sulfinyl radicals from UV-irradiated DMSO, were trapped by the in situ formed CH3NO. O-centered radicals could not add to the freshly formed C-nitroso compounds. Possible mechanisms are suggested.

The reaction of ketone arylhydrazone (1) with nitric oxide affords C1'-nitro azo-compounds (2) in good yields. Products were identified by NMR, IR, MS, and X-ray crystallography. The reaction is assumed to be most likely initiated by an electrophilic addition of NO2 to the carbon atom of the carbon-nitrogen double bond.

Free radicals generated from UV irradiation of simple aliphatic amides in anaerobic and nitric oxide (NO)-saturated liquid mixtures or solutions gave EPR spectra of nitroxides. The application of isotopic effects to EPR spectra and the generation of radicals by transient radical attack on substrate molecules or by photolysing amine or acetoin were used to help identify photochemically produced radicals from the amides. The aliphatic amides used were formamide, acetamide and their N-methyl-or deuteriumsubstituted derivatives. Transient radicals used to attack the amides via hydrogen-atom abstraction were generated from the initiator AIBN or AAPH. The observation of various nitroxides indicates the reactivity of NO for trapping acyl, carbamoyl and other carbon-centered radicals. Possibly mechanistic pathways diagnosed with this trap are proposed.

Stable aminoxyls and an iminoxyl were observed by spin trapping and EPR techniques during the nitrationof coumarins containing a hydroxy group by nitric oxide. The trapped free radicals are deduced to be the resonance stabilized phenoxy-like radicals. The mechanisms for the nitrations are suggested.

4-oxo-2, 2, 6, 6-tetramethylpiperidinyl-1-oxy radical (TEMPO), a nitroxide, oxidized 4-substituted Hantzsch 1,4-dihydropyridines (DHP) under UV irradiation in CH3CN to give aromatic products in good yields. A possible mechanism for the oxidation was suggested.

Epoxide rings of 2,3-epoxy phenyl ketones were cleaved by nitric oxide, affording regioselectively the C-3 ring-opened products, erythro-a-hydroxyl nitrates (2), in a highly syn-selective manner (isolated yield of the erythro products up to 91%). Products were identified by NMR, MS, and X-ray crystallography. The reaction is assumed to be initiated by NO2, unlike a nucleophilic attack.