Searching for nitroxyl modulators in Arabidopsis thaliana - a new paradigm of redox signaling in plant.

Through extensive research, nitroxyl (HNO) has emerged as a newly recognized redox signal in plant developmental and stress responses. The interplay between nitric oxide (●NO) and HNO entails a complex network of signaling molecules and regulatory elements sensitive to the environment's specific redox conditions. However, functional implications for HNO in cell signaling require more detailed studies, starting with identifying HNO-level switches.

From Simple Palladium(II) Monomers to 2D Heterometallic Sodium-Palladium(II) Coordination Networks with 2-Halonicotinates.

The 2D heterometallic sodium-palladium(II) coordination polymers with 2-halonicotinates [2-chloropyridine-3-carboxylate (2-chloronicotinate), 2-Clnic and 2-bromopyridine-3-carboxylate (2-bromonicotinate), 2-Brnic], {[Na(HO)(μ-HO)PdCl(μ-2-Clnic-')]} (), and {[Na(HO)(μ-HO)PdBr(μ-2-Brnic-')]·2HO} () were prepared in aqueous solutions under the presence of NaHCO, while palladium(II) monomers with the neutral 2-chloronicotinic and 2-bromonicotinic acid ligands, [PdCl(2-ClnicH-)]·2DMF () and [PdCl(2-BrnicH-)]·2DMF (), were prepared in DMF/water mixtures (DMF = ,'-dimethylformamide). The zigzag chains of water-bridged sodium ions are in turn bridged by [PdCl(2-Clnic)] moieties in or by [PdBr(2-Brnic)] moieties in , leading to the formation of the infinite 2D coordination networks of or . The DFT calculations showed the halosubstituents type (Cl Br) does not have an influence on the formation of either or isomers.

Structural insight into halide-coordinated [FeSXY] clusters (X, Y = Cl, Br, I) by XRD and Mössbauer spectroscopy.

Iron sulphur halide clusters [FeSBr] and [FeSXY] (X, Y = Cl, Br, I) were obtained in excellent yields (77 to 78%) and purity from [Fe(CO)], elemental sulphur, I and benzyltrimethylammonium (BTMA) iodide, bromide and chloride. Single crystals of (BTMA)[FeSBr] (1), (BTMA)[FeSBrCl] (2), (BTMA)[FeSClI] (3), and (BTMA)[FeSBrI] (4) were isostructural to the previously reported (BTMA)[FeSI] (5) (monoclinic, ). Instead of the chloride cubane cluster [FeSCl], we found the prismane-shaped cluster (BTMA)[FeSCl] (6) (1̄).

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.

Structural characterization of the water-soluble porphyrin complexes [Fe(TPPS) (NO)] and [μ-O-([Fe(TPPS)])].

Iron water-soluble porphyrins have been long used as biomimetic compounds for modelling the active sites found in heme-enzymes. In this regard, the anionic porphyrin [Fe(TPPS)] and its coordination complexes have been repeatedly chosen as suitable water-soluble platforms for bioinorganic chemistry studies. In this work we report for the first time the crystal structure of the water-soluble nitrosyl complex [Fe(TPPS) (NO)] along with that of oxodimeric ferric species [μ-O-([Fe(TPPS)])].

HS/Thiols, NO, and NO/HNO: Interactions with Iron Porphyrins.

In the past decade, gasotransmitters NO and HS have been thoroughly studied in biological contexts, as their biosynthesis and physiological effects became known. Moreover, an additional intricate 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.

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

The chemical reactivity of NO and its role in several biological processes seem well established. Despite this, the chemical reduction of NO toward HNO has been historically discarded, mainly because of the negative reduction potential of NO. However, this value and its implications are nowadays under revision.

Azanone (HNO): generation, stabilization and detection.

HNO (nitroxyl, azanone), joined the 'biologically relevant reactive nitrogen species' family in the 2000s. Azanone is impossible to store due to its high reactivity and inherent low stability. Consequently, its chemistry and effects are studied using donor compounds, which release this molecule in solution and in the gas phase upon stimulation.

Redox and Antioxidant Modulation of Circadian Rhythms: Effects of Nitroxyl, N-Acetylcysteine and Glutathione.

The circadian clock at the hypothalamic suprachiasmatic nucleus (SCN) entrains output rhythms to 24-h light cycles. To entrain by phase-advances, light signaling at the end of subjective night (circadian time 18, CT18) requires free radical nitric oxide (NO•) binding to soluble guanylate cyclase (sGC) heme group, activating the cyclic guanosine monophosphate (cGMP)-dependent protein kinase (PKG). Phase-delays at CT14 seem to be independent of NO•, whose redox-related species were yet to be investigated.

Updating NO/HNO interconversion under physiological conditions: A biological implication overview.

Azanone (HNO/NO), also called nitroxyl, is a highly reactive compound whose biological role is still a matter of debate. A key issue that remains to be clarified regarding HNO and its biological activity is that of its endogenous formation. Given the overlap of the molecular targets and reactivity of nitric oxide (NO•) and HNO, its chemical biology was perceived to be similar to that of NO• as a biological signaling agent.

Cobalt Corroles as Electrocatalysts for Water Oxidation: Strong Effect of Substituents on Catalytic Activity.

Two Co(III) complexes ( and ) of new corrole ligands (5,15-bis(-methylcarboxyphenyl)-10-(-methylcarboxyphenyl)corrole) and (5,15-bis(-nitrophenyl)-10-(-methylcarboxyphenyl)corrole) with two apical pyridine ligands have been synthesized and thoroughly characterized by cyclic voltammetry, UV-vis-NIR, and EPR spectroscopy, spectroelectrochemistry, single-crystal X-ray diffraction studies, and DFT methods. Complexes and possess much lower oxidation potentials than cobalt(III)--pentafluorophenylcorrole (Co(tpfc)) and similar corroles containing pentafluorophenyl (CF) substituents, thus allowing access to high oxidation states of the former metallocorroles using mild chemical oxidants. The spectroscopic (UV-vis-NIR and EPR) and electronic properties of several oxidation states of these complexes have been determined by a combination of the mentioned methods.

The Underlying Mechanism of HNO Production by the Myoglobin-Mediated Oxidation of Hydroxylamine.

Azanone (HNO, nitroxyl) is a highly reactive molecule that, in the past few years, has drawn significant interest because of its pharmacological properties. However, the understanding of how, when, and where endogenous HNO is produced remains a matter of discussion. In this study, we examined the ability of myoglobin to produce HNO via the peroxidation of hydroxylamine with HO using both experimental and computational approaches.

Synthesis, structure and reactivity of NO, NO˙ and NO pincer PCN-Rh complexes.

Synthesis of a pincer-type linear nitrosyl complex [Rh(PCN)(NO)] (3) is described. The product and all intermediates involved were fully characterized by FTIR, NMR, cyclic voltammetry and X-ray crystallography. Attempts at obtaining (3) from its chlorinated precursor Rh(PCN)(NO)Cl (2) revealed that a relative stabilization of this complex ion is introduced by the BArF counteranion, as other counteranions-PF, BF and triflate-proved to coordinate to the metal center.

NO/HS "Crosstalk" Reactions. The Role of Thionitrites (SNO) and Perthionitrites (SSNO).

The redox chemistry of HS with NO and other oxidants containing the NO group is discussed on a mechanistic basis because of the expanding interest in their biological relevance, with an eye open to the chemical differences of HS and thiols RSH. We focus on the properties of two "crosstalk" intermediates, SNO (thionitrite) and SSNO (perthionitrite, nitrosodisulfide) based in the largely controversial status on their identity and chemistry in aqueous/nonaqueous media, en route to the final products NO, NO, NHOH/NH, and S. Thionitrous acid, generated either in the direct reaction of NO + HS or through the transnitrosation of RSNO's (nitrosothiols) with HS at pH 7.

Water-Soluble Nitroxyl Porphyrin Complexes FeTPPSHNO and FeTPPSNO Obtained from Isolated FeTPPSNO

The first biomimetic water-soluble Fe-porphyrin nitroxyl complexes were obtained and characterized by UV-vis in protonated and deprotonated forms by reduction of previously isolated and characterized FeTPPSNO. The p involved in the Fe-HNO ⇄ Fe-NO + H equilibrium was estimated to be around 9.7.

Synthesis, structural elucidation and antiradical activity of a copper (II) naringenin complex.

Coupling the extraction and derivatization of flavonoids to the Citrus processing industry is attractive from both the environmental and economic points of view. In the present work, the flavonoid naringin, obtained by "green" extraction with a water:ethanol mixture from waste grapefruit industry, was hydrolyzed to obtain naringenin. This flavonoid was used to synthesize the complex trans-di(aqua) bis(7-hydroxy-2-(4-hydroxyphenyl)-4-oxo-5-chromanolato) copper (II).

Synthesis and structural characterisation of unprecedented primary N-nitrosamines coordinated to iridium(iv).

The redox chemistry of the N-nitrosamine complexes [IrCl5(RN(H)N[double bond, length as m-dash]O)]2- (R = benzyl or n-butyl) was studied in detail. One-electron oxidations at around 200 mV vs. ferrocene/ferrocenium were reversible in cyclic voltammograms.

NO˙ disproportionation by a {RhNO} pincer-type complex.

The reactivity of the {RhNO} complex [Rh(PCPBu)(NO)]˙ (1˙) with NO˙ was studied. A disproportionation reaction takes place in which NO is released quantitatively, while the complex Rh(PCPBu)(NO)(NO) (2), with coordinated nitrite, is formed. The new complex 2 was fully characterized by multinuclear NMR techniques, IR and X-ray diffraction.

HNO Is Produced by the Reaction of NO with Thiols.

Azanone (nitroxyl, HNO) is a highly reactive compound whose biological role is still a matter of debate. One possible route for its formation is NO reduction by biological reductants. These reactions have been historically discarded due to the negative redox potential for the NO,H+/HNO couple.

Solvation and Proton-Coupled Electron Transfer Reduction Potential of NO to HNO in Aqueous Solution: A Theoretical Investigation.

In this work, quantum mechanical calculations and Monte Carlo statistical mechanical simulations were carried out to investigate the solvation properties of HNO in aqueous solution and to evaluate the proton-coupled one electron reduction potential of NO to HNO, which is essential missing information to understand the fate of NO in the biological medium. Our results showed that the HNO molecule acts mainly as a hydrogen bond donor in aqueous solution with an average energy of -5.5 ± 1.

Rapid generation of HNO induced by visible light.

We present a new method for controlled generation of HNO, based on the combination of a pH photoactuator induced by visible light with an HNO donor activated by pH increase. This method avoids the use of UV light, and in the future could be extended by using an IR photoactuator.

Dimerization, redox properties and antioxidant activity of two manganese(III) complexes of difluoro- and dichloro-substituted Schiff-base ligands.

Two mononuclear Mn complexes [Mn(3,5-Fsalpn)(HO)][B(CH)]·2HO (1·2HO) and [Mn(3,5-Clsalpn)(OAc)(HO)]·HO (2·HO), where Hsalpn=1,3-bis(salicylidenamino)propane, have been prepared and characterized. The crystal structure of 1·HO shows that this complex forms μ-aqua dimers with a short Mn⋯Mn distance of 4.93Å.