Anomalous Hammett’s plot in the quenching of Ru(bpy)32+ phosphorescence by p-substituted phenols

Ahumada, Manuel; Lissi, Eduardo; Calderón, Cristian

doi:10.1016/j.jphotochem.2016.03.026

Cited by 3 publications

(4 citation statements)

References 13 publications

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“…Instead, this positive slope supports our hypothesis that PT has a more dominant role than ET during the oxidation of protonated phenols by permanganate . Specifically, for the PCET mechanism, it has been shown previously that a considerable negative charge could accumulate on the reactive center, resulting in larger rate constants for compounds with stronger electron-withdrawing properties. - …”

Section: Resultssupporting

confidence: 86%

Neutral Phenolic Contaminants Are Not Necessarily More Resistant to Permanganate Oxidation Than Their Dissociated Counterparts: Importance of Proton-Coupled Electron Transfer

Chen,

Dong,

et al. 2023

Environ. Sci. Technol.

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Despite decades of research on phenols oxidation by permanganate, there are still considerable uncertainties regarding the mechanisms accounting for the unexpected parabolic pH-dependent oxidation rate. Herein, the pH effect on phenols oxidation was reinvestigated experimentally and theoretically by highlighting the previously unappreciated proton transfer. The results revealed that the oxidation of protonated phenols occurred via proton-coupled electron transfer (PCET) pathways, which can switch from ETPT (electron transfer followed by proton transfer) to CEPT (concerted electron–proton transfer) or PTET (proton transfer followed by electron transfer) with an increase in pH. A PCET-based model was thus established, and it could fit the kinetic data of phenols oxidation by permanganate well. In contrast with what was previously thought, both the simulating results and the density functional theory calculation indicated the rate of CEPT reaction of protonated phenols with OH– as the proton acceptor was much higher than that of deprotonated phenols, which could account for the pH–rate profiles for phenols oxidation. Analysis of the quantitative structure–activity relationships among the modeled rate constants, Hammett constants, and pK a values of phenols further supports the idea that the oxidation of protonated phenols is dominated by PCET. This study improves our understanding of permanganate oxidation and suggests a new pattern of reactivity that may be applicable to other systems.

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Section: Resultssupporting

confidence: 86%

Neutral Phenolic Contaminants Are Not Necessarily More Resistant to Permanganate Oxidation Than Their Dissociated Counterparts: Importance of Proton-Coupled Electron Transfer

Chen,

Dong,

et al. 2023

Environ. Sci. Technol.

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“…However, no regular trends with the triplet state properties were shown. A bell-like Hammett’s plot was obtained for the ruthenium bipyridine complex, in which phosphorescence was quenched using para-substituted phenols in a bimolecular process . The unusual plot shape originated from two quenching mechanisms: a phenolate to Ru(II) electron transfer (p K a ≪ pH) and a proton-coupled electron transfer (p K a > pH) when protonated phenol predominates.…”

Section: Introductionmentioning

confidence: 99%

“…A bell-like Hammett's plot was obtained for the ruthenium bipyridine complex, in which phosphorescence was quenched using para-substituted phenols in a bimolecular process. 40 The unusual plot shape originated from two quenching mechanisms: a phenolate to Ru(II) electron transfer (pK a ≪ pH) and a proton-coupled electron transfer (pK a > pH) when protonated phenol predominates. The kinetics of proton removal from water by 5-substituted NH 2 , OMe, H, Cl, Br, and CN quinolines have been recently studied using ultrafast transient absorption spectroscopy.…”

Section: Introductionmentioning

confidence: 99%

Substituent Effect in the First Excited Triplet State of Monosubstituted Benzenes

Dobrowolski

Karpińska

2020

ACS Omega

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The structure of 30 monosubstituted benzenes in the first excited triplet T1 state was optimized with both unrestricted (U) and restricted open shell (RO) approximations combined with the ωB97XD/aug-cc-pVTZ basis method. The substituents exhibited diverse σ- and π-electron-donating and/or -withdrawing groups. Two different positions of the substituents are observed in the studied compounds in the T1 state: one distorted from the plane and the other coplanar with a quinoidal ring. The majority of the substituents are π-electron donating in the first group while π-electron withdrawing in the second one. Basically, U- and RO-ωB97XD approximations yield concordant results except for the B-substituents and a few of the planar groups. In the T1 state, the studied molecules are not aromatic, yet aromaticity estimated using the HOMA (harmonic oscillator model of aromaticity) index increases from ca. −0.2 to ca. 0.4 with substituent distortion, while in the S1 state, they are only slightly less aromatic than in the ground state (HOMA ≈0.8 vs ≈1.0, respectively). Unexpectedly, the sEDA(T1) and pEDA(T1) substituent effect descriptors do not correlate with analogous parameters for the ground and first excited singlet states. This is because in the T1 state, the geometry of the ring changes dramatically and the sEDA(T1) and pEDA(T1) descriptors do not characterize only the functional group but the entire molecule. Thus, they cannot provide useful scales for the substituents in the T1 states. We found that the spin density in the T1 states is accumulated at the Cipso and Cp atoms, and with the substituent deformation angle, it nonlinearly increases at the former while decreases at the latter. It appeared that the gap between singly unoccupied molecular orbital and singly occupied molecular orbital (SUMO-SOMO) is determined by the change of the SOMO energy because the former is essentially constant. For the nonplanar structures, SOMO correlates with the torsion angle of the substituent and the ground-state pEDA(S0) descriptor of the π-electron-donating substituents ranging from 0.02 to 0.2 e. Finally, shapes of the SOMO-1 instead of SOMO frontier orbitals in the T1 state somehow resemble the highest occupied molecular orbital ones of the S0 and S1 states. For several planar systems, the shape of the U- and RO-density functional theory-calculated SOMO-1 orbitals differs substantially.

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“…2, Ksv = (6.5 ± 0.1) × 10 7 M -1 ), using the reported fluorescence lifetime for HSA (τ0 ≈ 4.6 ns). 33 This kq value is several orders of magnitude higher than the diffusion controlled limit in water ≈ 1 x 10 10 M -1 s -1 , 34 which implies nanoparticle and HSA ground-state complex formation. Ultracentrifugation experiments, which have been described to be a useful tool to estimated binding of proteins to nanostructures, 35 were carried out to determine the amount of bound protein to nanosilver.…”

mentioning

confidence: 95%

Protein capped nanosilver free radical oxidation: role of biomolecule capping on nanoparticle colloidal stability and protein oxidation

et al. 2018

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Anomalous Hammett’s plot in the quenching of Ru(bpy)32+ phosphorescence by p-substituted phenols

Cited by 3 publications

References 13 publications

Neutral Phenolic Contaminants Are Not Necessarily More Resistant to Permanganate Oxidation Than Their Dissociated Counterparts: Importance of Proton-Coupled Electron Transfer

Neutral Phenolic Contaminants Are Not Necessarily More Resistant to Permanganate Oxidation Than Their Dissociated Counterparts: Importance of Proton-Coupled Electron Transfer

Substituent Effect in the First Excited Triplet State of Monosubstituted Benzenes

Protein capped nanosilver free radical oxidation: role of biomolecule capping on nanoparticle colloidal stability and protein oxidation

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