Nitric Oxide Reacts Very Fast with Hydrogen Sulfide, Alcohols, and Thiols to Produce HNO: Revised Rate Constants

Reactivity of Thiolate and Hydrosulfide with a Mononuclear {FeNO}7 Complex Featuring a Very High N-O Stretching Frequency

Synthesis, characterization, electronic structure, and redox reactions of a mononuclear {FeNO}7 complex with a very high N-O stretching frequency in solution are presented. Nitrosylation of [(LKP)Fe(DMF)]2+ (1) (LKP = tris((1-methyl-4,5-diphenyl-1H-imidazol-2-yl)methyl)amine) produced a five-coordinate {FeNO}7 complex, [(LKP)Fe(NO)]2+ (2). While complex 2 could accommodate an additional water molecule to generate a six-coordinate {FeNO}7 complex, [(LKP)Fe(NO)(H2O)]2+ (3), the coordinated H2O in 3 dissociates to generate 2 in solution. The molecular structure of 2 features a nearly linear Fe-N-O unit with an Fe-N distance of 1.744(4) Å, N-O distance of 1.162(5) Å, and Collapse

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Affiliation(s)

Soumik Karmakar School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India
Suman Patra School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India
Koushik Pramanik School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India
Amit Adhikary Department of Chemistry, Technology Campus, University of Calcutta, JD Block, Sector III, Salt Lake, Kolkata 700098, India
Abhishek Dey School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India
Amit Majumdar School of Chemical Sciences, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Jadavpur, Kolkata 700032, India

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Endogenous plant nitroxyl, a new component of nitric oxide biology

Nitroxyl (HNO), a one-electron reduced and protonated congener of nitric oxide (•NO), was recently discovered in Arabidopsis thaliana. Due to its distinct chemical properties, we believe HNO must be further studied to determine how many physiological processes it impacts.

Discovery of endogenous nitroxyl as a new redox player in Arabidopsis thaliana

Nitroxyl (HNO) is the one-electron reduced and protonated congener of nitric oxide (•NO), owning a distinct chemical profile. Based on real-time detection, we demonstrate that HNO is endogenously formed in Arabidopsis. Senescence and hypoxia induce shifts in the redox balance, triggering HNO decay or formation mediated by non-enzymatic •NO/HNO interconversion with cellular reductants. The stimuli-dependent HNO generation supports or competes with •NO signalling, depending on the local redox environment.

The Chemistry of HNO: Mechanisms and Reaction Kinetics

Azanone (HNO, also known as nitroxyl) is the protonated form of the product of one-electron reduction of nitric oxide (^•NO), and an elusive electrophilic reactive nitrogen species of increasing pharmacological significance. Over the past 20 years, the interest in the biological chemistry of HNO has increased significantly due to the numerous beneficial pharmacological effects of its donors. Increased availability of various HNO donors was accompanied by great progress in the understanding of HNO chemistry and chemical biology. This review is focused on the chemistry of HNO, with emphasis on reaction kinetics and mechanisms in aqueous solutions.

Enzyme-responsive hybrid prodrug of nitric oxide and hydrogen sulfide for heart failure therapy

A hybrid prodrug was synthesized to realize the combined delivery of nitric oxide and hydrogen sulfide. The NO-H₂S donor can release nitric oxide and hydrogen sulfide step by step in response to the endogenous enzymes β-galactosidase and carbonic anhydrase, providing potent therapeutic efficacy for heart failure post- myocardial infarction.

Theoretical investigation of [Ru(bpy)2(HAT)]2+ (HAT = 1,4,5,8,9,12-hexaazatriphenylene; bpy = 2,2'-bipyridine): Photophysics and reactions in excited state

In this article, Density Functional Theory based calculations, including dispersion corrections, PBE0(D3BJ)/Def2-TZVP(-f), were performed to elucidate the photophysics of the [Ru(bpy)₂(HAT)]²⁺ complex in water. In addition, the thermodynamics of the charge and electron transfer excited state reactions of this complex with oxygen, nitric oxide and Guanosine-5'-monophosphate nucleotide (GMP) were investigated. The first singlet excite state, S₁, strongly couples with the second and third triplet excited states (T₂ and T₃) giving rise to a high intersystem crossing rate of 6.26 × 10¹¹ s^-1 which is ∼10⁶ greater than the fluorescence rate decay. The thermodynamics of the excited reactions revealed that all electron transfer reactions investigated are highly favorable, due mainly to the high stability of the triply charged radical cation ²PS^•3+ species formed after the electron has been transferred. Excited state electron transfer from the GMP nucleotide to the complex is also highly favorable (ΔG_sol = -92.6 kcal/mol), showing that this complex can be involved in the photooxidation of DNA, in line with experimental findings. Therefore, the calculations allow to conclude that the [Ru(bpy)₂(HAT)]²⁺ complex can act in Photodynamic therapy through both mechanisms type I and II, through electron transfer from and to the complex and triplet-triplet energy transfer, generating ROS, RNOS and through DNA photooxidation. In addition, the work also opens a perspective of using this complex for the in-situ generation of the singlet nitroxyl (¹NO^-) species, which can have important applications for the generation of HNO and may have, therefore, important impact for physiological studies involving HNO.

H2S/Thiols, NO•, and NO-/HNO: Interactions with Iron Porphyrins

In the past decade, gasotransmitters NO^• and H₂S have been thoroughly studied in biological contexts, as their biosynthesis and physiological effects became known. Moreover, an additional intricate crosstalk reaction scheme between these compounds and related species is thought to exist as part of the cascade signaling processes in physiological conditions. In this context, heme enzymes, as modeled by iron porphyrins, play a central role in catalyzing the key interconversions involved. In this work, iron porphyrin interactions with sulfide and nitric-oxide-related species are described. The stability and reactivity of mixed ternary systems are also described, and future perspectives are discussed.