Lewis Acid Coordination Redirects S-Nitrosothiol Reduction

2020 ◽  
Author(s):  
Valiallah Hosseininasab ◽  
Alison C. McQuilken ◽  
Abolghasem (Gus) Bakhoda ◽  
Jeffery A. Bertke ◽  
Qadir K. Timerghazin ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Lewis Acids ◽  
Reduction Potential ◽  
Chemical Reduction ◽  
Physiological Responses ◽  
Outer Sphere ◽  
Intramolecular Electron Transfer ◽  
Computational Studies ◽  
Reduction Potentials ◽  
Initial Reduction

<i>S</i>-Nitrosothiols (RSNOs) serve as air-stable reservoirs for nitric oxide in biology and are responsible for a myriad of physiological responses. While copper enzymes promote NO release from RSNOs by serving as Lewis acids capable of intramolecular electron-transfer, redox innocent Lewis acids separate these two functions to reveal the effect of coordination on structure and reactivity. The synthetic Lewis acid B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> coordinates to the RSNO oxygen atom in adducts RSNO-B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>, leading to profound changes in the RSNO electronic structure and reactivity. Although RSNOs possess relatively negative reduction potentials (-1.0 to -1.1 vs. NHE), B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> coordination increases their reduction potential by over 1 V into the physiologically accessible +0.1 V vs. NHE. Outer-sphere chemical reduction results in formation of the Lewis acid stabilized hyponitrite dianion <i>trans</i>-[LA–O–N=N–O–LA]<sup>2–</sup> (LA = B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>) that releases N<sub>2</sub>O upon acidification. Mechanistic and computational studies support initial reduction to the [RSNO-B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>]<sup>•/- </sup>radical-anion susceptible to N-N coupling prior to loss of RSSR.

Lewis Acid Coordination Redirects S-Nitrosothiol Reduction

2020 ◽  
Author(s):  
Valiallah Hosseininasab ◽  
Alison C. McQuilken ◽  
Abolghasem (Gus) Bakhoda ◽  
Jeffery A. Bertke ◽  
Qadir K. Timerghazin ◽  
...  
Keyword(s):  
Lewis Acid ◽  
Lewis Acids ◽  
Reduction Potential ◽  
Chemical Reduction ◽  
Physiological Responses ◽  
Outer Sphere ◽  
Intramolecular Electron Transfer ◽  
Computational Studies ◽  
Reduction Potentials ◽  
Initial Reduction

<i>S</i>-Nitrosothiols (RSNOs) serve as air-stable reservoirs for nitric oxide in biology and are responsible for a myriad of physiological responses. While copper enzymes promote NO release from RSNOs by serving as Lewis acids capable of intramolecular electron-transfer, redox innocent Lewis acids separate these two functions to reveal the effect of coordination on structure and reactivity. The synthetic Lewis acid B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> coordinates to the RSNO oxygen atom in adducts RSNO-B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>, leading to profound changes in the RSNO electronic structure and reactivity. Although RSNOs possess relatively negative reduction potentials (-1.0 to -1.1 vs. NHE), B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub> coordination increases their reduction potential by over 1 V into the physiologically accessible +0.1 V vs. NHE. Outer-sphere chemical reduction results in formation of the Lewis acid stabilized hyponitrite dianion <i>trans</i>-[LA–O–N=N–O–LA]<sup>2–</sup> (LA = B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>) that releases N<sub>2</sub>O upon acidification. Mechanistic and computational studies support initial reduction to the [RSNO-B(C<sub>6</sub>F<sub>5</sub>)<sub>3</sub>]<sup>•/- </sup>radical-anion susceptible to N-N coupling prior to loss of RSSR.

The outer-sphere oxidation of ascorbic acid by the thioureapentacyanoferrate(III) ion

1981 ◽  
Vol 59 (1) ◽  
pp. 132-137 ◽  
Author(s):  
Donal H. Macartney ◽  
Alexander McAuley
Keyword(s):  
Ascorbic Acid ◽  
Reduction Potential ◽  
Outer Sphere ◽  
Reaction Scheme ◽  
Ion Concentration ◽  
Acid Dissociation ◽  
Acid Dissociation Constant ◽  
Hydrogen Ion Concentration ◽  
Reduction Potentials ◽  
Ph Range

The oxidation of ascorbic acid by thioureapentacyanoferrate(III) has been investigated over the pH range 0.8–7.2 at an ionic strength of 1.0 M (NaClO4). The variations in the rates of oxidation with hydrogen ion concentration are consistent with a reaction scheme involving three pH-related species; ascorbic acid (H2A) (k1 = 0.111 M−1 s−1, ΔH1≠ = 5.1 kcal mol−1, ΔS≠ = −46 cal deg−1 mol−1), the ascorbic anion, (HA−) (k2 = 66 M−1s−1, ΔH2≠ = 5.4 kcal mol−1, ΔS2≠ = −32 cal deg−1 mol−1) and the ascorbic dianion, (A2−) (k3 = 8.78 × 107 M−1 s−1, ΔH3≠ = 3.1 kcal mol−1, ΔS3≠ = −12 cal deg−1 mol−1). The low reduction potential of Fe(CN)5TU2− (E0 = 0.35 V) permits the measurement of the rate of oxidation of the ascorbate dianion, not previously investigated with metal complexes. The second acid dissociation constant of ascorbic acid [Formula: see text] has been measured in 1.0 M NaClO4 over the temperature range studied. A relationship between the rate of oxidation and the reduction potentials of the ascorbic acid species is shown.

scholarly journals Coordination Behavior of [Cp″2Zr(µ1:1-As4)] towards Lewis Acids

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 2966
Author(s):  
Veronika Heinl ◽  
Gábor Balázs ◽  
Sarah Koschabek ◽  
Maria Eckhardt ◽  
Martin Piesch ◽  
...  
Keyword(s):  
Transition Metal ◽  
Metal Complexes ◽  
Transition Metal Complexes ◽  
Lewis Acid ◽  
Reaction Temperature ◽  
Lewis Acids ◽  
Computational Studies ◽  
Coordination Modes ◽  
Coordination Numbers ◽  
Coordination Behavior

The functionalization of the arsenic transfer reagent [Cp″2Zr(η1:1-As4)] (1) focuses on modifying its properties and enabling a broader scope of reactivity. The coordination behavior of 1 towards different Lewis-acidic transition metal complexes and main group compounds is investigated by experimental and computational studies. Depending on the steric requirements of the Lewis acids and the reaction temperature, a variety of new complexes with different coordination modes and coordination numbers could be synthesized. Depending on the Lewis acid (LA) used, a mono-substitution in [Cp″2Zr(µ,η1:1:1:1-As4)(LA)] (LA = Fe(CO)4 (4); B(C6F5)3 (7)) and [Cp″2Zr(µ,η3:1:1-As4)(Fe(CO)3)] (5) or a di-substitution [Cp″2Zr(µ3,η1:1:1:1-As4)(LA)2] (LA = W(CO)5 (2); CpMn(CO)2 (3); AlR3 (6, R = Me, Et, iBu)) are monitored. In contrast to other coordination products, 5 shows an η3 coordination in which the butterfly As4 ligand is rearranged to a cyclo-As4 ligand. The reported complexes are rationalized in terms of inverse coordination.

Cyanide and Azide Anion Complexation by a Bidentate Stibonium-Borane Lewis Acid

2014 ◽  
Vol 69 (11-12) ◽  
pp. 1199-1205 ◽  
Author(s):  
Casey R. Wade ◽  
François P. Gabbaï
Keyword(s):  
Lewis Acid ◽  
Lewis Acids ◽  
Natural Bond Orbital ◽  
Orbital Method ◽  
Computational Studies ◽  
Cyanide Complex ◽  
Acid Anion ◽  
Anion Complexation ◽  
Azide Ligand ◽  
Complex Features

Abstract Our ongoing interest in the chemistry of polyfunctional Lewis acids has led us to investigate the reaction of the stibonium-borane [o-(Ph2MeSb)(Mes2B)C6H4]+ (1+) with cyanide and azide, two toxic anions. Both anions react with 1+ to afford the corresponding neutral complexes 1-CN and 1-N3. Structural and computational studies show that the coordinated anion interacts with both the boron and antimony atoms of the bidentate Lewis acid. While the azide complex features a typical κ2N1 : N1 bridging azide ligand, the cyanide complex possesses a cyanoborate moiety whose cyanide interacts side-on with the stibonium center. The Lewis acid-anion interactions observed in these complexes have also been studied computationally using the Natural Bond Orbital method

Tuning the reduction potentials of benzoquinone through the coordination to Lewis acids

2021 ◽  
Vol 23 (16) ◽  
pp. 9822-9831
Author(s):  
Brena L. Thompson ◽  
Zachariah M. Heiden
Keyword(s):  
Lewis Acid ◽  
Lewis Acids ◽  
Computational Study ◽  
Acid Strength ◽  
Reduction Potentials

This computational study investigates the nature of the interaction between benzoquinone and one and two Lewis acids by examining the influence of Lewis acid strength on the ability to alter the two reduction potentials of the coordinated benzoquinone molecule.

scholarly journals Understanding How Lewis Acids Dope Organic Semiconductors: A “Complex” Story

2021 ◽  
Author(s):  
Pablo Simon Marques ◽  
Giacomo Londi ◽  
Brett Yurash ◽  
Thuc-Quyen Nguyen ◽  
Stephen Barlow ◽  
...  
Keyword(s):  
Organic Semiconductors ◽  
Lewis Acids ◽  
Computational Studies

We report on computational studies of the potential of three borane Lewis acids (LAs) (B(C6F5)3 (BCF), BF3, and BBr3) to form stable adducts and/or to generate positive polarons with three...

scholarly journals Spectral Probe for Electron Transfer and Addition Reactions of Azide Radicals with Substituted Quinoxalin-2-Ones in Aqueous Solutions

2021 ◽  
Vol 22 (2) ◽  
pp. 633
Author(s):  
Konrad Skotnicki ◽  
Slawomir Ostrowski ◽  
Jan Cz. Dobrowolski ◽  
Julio R. De la Fuente ◽  
Alvaro Cañete ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Aqueous Solutions ◽  
Absorption Spectra ◽  
Density Functional ◽  
Reduction Potential ◽  
Biological Significance ◽  
Radical Cations ◽  
Basis Sets ◽  
Double Bonds ◽  
Reduction Potentials

The azide radical (N3●) is one of the most important one-electron oxidants used extensively in radiation chemistry studies involving molecules of biological significance. Generally, it was assumed that N3● reacts in aqueous solutions only by electron transfer. However, there were several reports indicating the possibility of N3● addition in aqueous solutions to organic compounds containing double bonds. The main purpose of this study was to find an experimental approach that allows a clear assignment of the nature of obtained products either to its one-electron oxidation or its addition products. Radiolysis of water provides a convenient source of one-electron oxidizing radicals characterized by a very broad range of reduction potentials. Two inorganic radicals (SO4●−, CO3●−) and Tl2+ ions with the reduction potentials higher, and one radical (SCN)2●− with the reduction potential slightly lower than the reduction potential of N3● were selected as dominant electron-acceptors. Transient absorption spectra formed in their reactions with a series of quinoxalin-2-one derivatives were confronted with absorption spectra formed from reactions of N3● with the same series of compounds. Cases, in which the absorption spectra formed in reactions involving N3● differ from the absorption spectra formed in the reactions involving other one-electron oxidants, strongly indicate that N3● is involved in the other reaction channel such as addition to double bonds. Moreover, it was shown that high-rate constants of reactions of N3● with quinoxalin-2-ones do not ultimately prove that they are electron transfer reactions. The optimized structures of the radical cations (7-R-3-MeQ)●+, radicals (7-R-3-MeQ)● and N3● adducts at the C2 carbon atom in pyrazine moiety and their absorption spectra are reasonably well reproduced by density functional theory quantum mechanics calculations employing the ωB97XD functional combined with the Dunning’s aug-cc-pVTZ correlation-consistent polarized basis sets augmented with diffuse functions.

Lewis Acid-Promoted Suzuki Reaction using Palladium Chloride Anchored on a Polymer as a Catalyst

2008 ◽  
Vol 61 (8) ◽  
pp. 610 ◽  
Author(s):  
Guozhi Fan ◽  
Hanjun Zhang ◽  
Siqing Cheng ◽  
Zhandong Ren ◽  
Zhijun Hu ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Lewis Acid ◽  
Lewis Acids ◽  
Heterogeneous Catalysts ◽  
Suzuki Reaction ◽  
Cross Coupling ◽  
Palladium Chloride ◽  
Coupling Reactions ◽  
Cross Coupling Reactions ◽  
Recoverable Catalyst

Palladium chloride anchored on polystyrene modified by 5-amino-1,10-phenanthroline was prepared and used as an efficient recoverable catalyst for Suzuki cross-coupling reactions. The heterogeneous catalysts can be easily separated from the reaction mixture and reused for five cycles without significant Pd leaching and loss of catalytic activity. Rate enhancement in the Suzuki reaction by Lewis acids was also studied.

Synthesis of pyrrolo[1,2-a]naphthyridines by Lewis acid mediated cycloisomerization

2017 ◽  
Vol 15 (15) ◽  
pp. 3216-3231 ◽  
Author(s):  
Anika Flader ◽  
Silvio Parpart ◽  
Peter Ehlers ◽  
Peter Langer
Keyword(s):  
Lewis Acid ◽  
Lewis Acids

Functionalized pyrrolo[1,2-a]naphthyridines were synthesized by application of PtCl2 and Bi(OTf)3 as simple Lewis acids in a cycloisomerization reaction.

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