Organic nitrates, thionitrates, peroxynitrites, and nitric oxide: a molecular orbital study of the  (X = O, S) rearrangement, a reaction of potential biological significance

The rearrangement of organic thionitrate to sulfenyl nitrite potentially mediates the release of nitric oxide from organic nitrates, such as nitroglycerin, in the presence of thiol. The biological activity of these nitrovasodilators is proposed to result from release of nitric oxide in vivo. The thionitrate rearrangement bears analogy to the rearrangement of peroxynitrous acid to nitric acid, which has been proposed to mediate the biological toxicity of nitric oxide and superoxide. In this paper, the two concerted rearrangement processes and competing homolytic reactions are explored using molecular orbital calculations at levels up to MP4SDQ/6-31G*//MP2/6-31G*. Examination of structure and energy for all conformers and isomers of RSONO2 (R = H, Me), models for organic thionitrates and their isomers, demonstrates that structures corresponding to thionitrates and sulfenyl nitrates are of similar energy. Free energies of reaction for homolysis of these compounds are low (ΔG0 < 19 kcal/mol), whereas the barrier for concerted rearrangement is large (ΔG≠(aq.) = 56 kcal/mol). The larger barrier for concerted rearrangement of peroxynitrous acid to nitric acid (ΔG≠(aq.) = 60 kcal/mol) again compares unfavourably with homolysis (ΔG0 < 11 kcal/mol for homolysis to NO2 or •NO). The transition state structures, confirmed by normal mode and intrinsic reaction coordinate analysis, indicate that considerable structural reorganization is required for concerted rearrangement of the ground state species. These results suggest that concerted rearrangement is not likely to be a viable step in either biological process. However, rearrangement via homolysis and radical recombination may provide an energetically accessible pathway for peroxynitrous acid rearrangement to nitric acid and rearrangement of thionitrate to sulfenyl nitrite. In this case, NO2 will be a primary product of both reactions. Keywords: thionitrate, nitric oxide, peroxynitrite, nitrovasodilator, nitrate.

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Prediction of Charge Transport Properties of Molecular Materials by Ab Initio Molecular Orbital Calculations

MRS Proceedings ◽

10.1557/proc-660-jj5.18 ◽

2000 ◽

Vol 660 ◽

Author(s):

Wataru Sotoyama ◽

Tomoaki Hayano ◽

Hiroyuki Sato ◽

Azuma Matsuura ◽

Toshiaki Narusawa

Keyword(s):

Charge Transport ◽

Ab Initio ◽

Molecular Orbital ◽

Electron Mobility ◽

Molecular Orbital Calculations ◽

Molecular Materials ◽

Structural Reorganization ◽

Charge Hopping ◽

Reorganization Energies ◽

A Charge

ABSTRACTWe developed a method to predict the charge transport (CT) type (hole or electron) in molecular materials that uses molecular orbital calculations. The hole-and-electron-mobility ratios of molecular materials were calculated based on molecular structural reorganization energies in a charge hopping process. The CT types predicted from the calculated mobility ratios agreed with those experimentally obtained in seven of the eight model molecules.

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Molecular dynamics and ab initio molecular orbital calculations on conformational change of amyloid-ß monomers in an in vivo amyloid-ß nonamer

2017 International Conference on Advanced Informatics, Concepts, Theory, and Applications (ICAICTA) ◽

10.1109/icaicta.2017.8090992 ◽

2017 ◽

Author(s):

Shogo Tomioka ◽

Haruki Sougawa ◽

Hiromi Ishimura ◽

Akisumi Okamoto ◽

Noriyuki Kurita ◽

...

Keyword(s):

Molecular Dynamics ◽

Ab Initio ◽

Conformational Change ◽

Molecular Orbital ◽

Molecular Orbital Calculations

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Comment on “Isotopic evidence for dominant secondary production of HONO in near-ground wildfire plumes” by Chai et al. (2021)

Atmospheric Chemistry and Physics ◽

10.5194/acp-21-16793-2021 ◽

2021 ◽

Vol 21 (22) ◽

pp. 16793-16795

Author(s):

James M. Roberts

Keyword(s):

Nitric Oxide ◽

Nitric Acid ◽

Secondary Production ◽

Nitrous Acid ◽

Nitrogen Compound ◽

Decomposition Reaction ◽

Organic Radicals ◽

Organic Nitrates ◽

Oxides Of Nitrogen ◽

Model Reactions

Abstract. Chai et al. (2021) recently published measurements of wildfire-derived (WF) oxides of nitrogen (NOx) and nitrous acid (HONO) and their isotopic composition. The method used to sample NOx, collection in alkaline solution, has a known 1:1 interference from another reactive nitrogen compound, acetyl peroxynitrate (PAN). Although PAN is thermally unstable, subsequent reactions with nitrogen dioxide (NO2) in effect extend the lifetime of PAN many times longer than the initial decomposition reaction would indicate. This, coupled with the rapid and efficient formation of PAN in WF plumes, means the NOx measurements reported by Chai et al. were severely impacted by PAN. In addition, the model reactions in the original paper included neither the reactions of NO2 with hydroxyl radical (OH) to form nitric acid nor the efficient reaction of larger organic radicals with nitric oxide to form organic nitrates (RONO2).

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Peroxynitrite: mediator of the toxic action of nitric oxide.

Acta Biochimica Polonica ◽

10.18388/abp.1996_4461 ◽

1996 ◽

Vol 43 (4) ◽

pp. 645-659 ◽

Cited By ~ 82

Author(s):

G Bartosz

Keyword(s):

Nitric Oxide ◽

Signal Transduction ◽

Superoxide Anion ◽

Toxic Action ◽

Nitric Oxide Donors ◽

Peroxynitrous Acid ◽

Protein Nitration ◽

Fast Reaction ◽

Beneficial Effects

Peroxynitrite (oxoperoxonitrate(-1)), anion of peroxynitrous acid, is thought to mediate the toxic action of nitric oxide and superoxide anion. Peroxynitrite is formed in a fast reaction between these species, reacts with all classes of biomolecules, is cytotoxic, and is thought to be involved in many pathological phenomena. Its main reactions involve one- and two-electron oxidation and nitration. Protein nitration is often used as a footprint of peroxynitrite reactions in vivo. Nitration of tyrosine and of tyrosyl residues in proteins may be an important mechanism of derangement of biochemical signal transduction by this compound. However, apparently beneficial effects of peroxynitrite have also been described, among them formation of nitric oxide and nitric oxide donors in reactions of peroxynitrite with thiols and alcohols.

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Ab initio fragment molecular orbital calculations on the specific interactions between amyloid-β peptides in an in vivo amyloid-β fibril

2016 International Conference On Advanced Informatics: Concepts, Theory And Application (ICAICTA) ◽

10.1109/icaicta.2016.7803094 ◽

2016 ◽

Cited By ~ 1

Author(s):

Hiromi Ishimura ◽

Ryushi Kadoya ◽

Kanako Shimamura ◽

Shintarou Ota ◽

Mitsuki Fujimori ◽

...

Keyword(s):

Ab Initio ◽

Molecular Orbital ◽

Amyloid Β ◽

Molecular Orbital Calculations ◽

Specific Interactions ◽

Fragment Molecular Orbital

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Pyrazolo[1,5-a]Pyrimidine: Synthesis and Regiospecific Electrophilic Substitution in the Pyrazole and/or Pyrimidine Rings

Canadian Journal of Chemistry ◽

10.1139/v75-016 ◽

1975 ◽

Vol 53 (1) ◽

pp. 119-124 ◽

Cited By ~ 18

Author(s):

Brian Maurice Lynch ◽

Misbahul Ain Khan ◽

Suresh Chandra Sharma ◽

Huk Chia Teo

Keyword(s):

Nitric Acid ◽

Molecular Orbital ◽

Nitro Compound ◽

Acidic Medium ◽

Electrophilic Substitution ◽

Ring System ◽

Molecular Orbital Calculations ◽

Coupling Constant ◽

Pyrimidine Synthesis ◽

Conjugate Acid

A general cyclization route to pyrazolo[1,5-a]pyrimidines from 3-aminopyrazole and 1,3-dicarbonyl compounds is applied to synthesis of the parent ring system. In nitration of this species the orientation of substitution is strongly reagent dependent. Mixed nitric and sulfuric acids yield the 3-nitro compound, whereas nitric acid in acetic anhydride yields the 6-nitro compound. Brominations yield 3-bromo and 3,6-dibromo species.The majority reacting species in the strongly acidic medium is identified as the 1-protonated entity by conjoint use of approximate molecular orbital calculations and the variation of coupling constant patterns accompanying protonation. The molecular orbital calculations predict successive 3- and 6-substitution by electrophiles in pyrazolo[l,5-a]pyrimidine and its conjugate acid, and an addition–elimination sequence is proposed to account for the observed 6-nitration.

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