Ultraviolet Resonance Raman Spectroscopy and General Valence Force Field Analysis of Phenolate and Phenoxyl Radical

Mukherjee, Arka; McGlashen, Michael L.; Spiro, Thomas G.

doi:10.1021/j100014a007

Cited by 86 publications

(151 citation statements)

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“…The frequency shifts observed for the modes n 7a and n 19a are in qualitative agreement with a recent study on uncoordinated phenolate by Mukherjee et al [35] These authors used an empirical force field, fitted to the experimental data for phenolate as well as their deuterated and 13 C-labeled isotopomers. Based on this force field they calculated the normal modes for the 17 O-labeled phenolate yielding shifts of À 5 and À 3 cm À1 for the modes n 7a and n 19a , respectively.…”

supporting

confidence: 89%

“…In the high frequency region (Figure 4), all of the spectra display a prominent band at about 1600 cm À1 that is readily assigned to the n 8a mode according to Wilsons notation adapted to substituted benzenes. [35] This mode includes predominantly the CC stretching coordinates (C ortho C meta ), as suggested from previous normal mode analyses.…”

mentioning

confidence: 76%

“…This latter band is attributed to the mode n 19a , which, according to normal mode analyses, should also exhibit a contribution from the CÀO stretch. [35,37] However, the distribution of the CÀO stretching coordinate is simply reversed compared with the uncoordinated phenoxyl radicals where 17 O labeling yields shifts of À 13 and À 8 cm…”

mentioning

confidence: 99%

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The Molecular and Electronic Structure of Octahedral Tris(phenolato)iron(III) Complexes and Their Phenoxyl Radical Analogues: A Mössbauer and Resonance Raman Spectroscopic Study

et al. 1999

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Hexadentate macrocyclic ligands containing a 1,4,7-triazacyclononane backbone and three N-bound pendent-arm phenolates form extremely stable neutral complexes with Fe III Cl 3 . The octahedral complexes [Fe III L] undergo three reversible one-electron oxidation processes to yield the mono-and dications, [FeL] and [FeL] 2 , which are stable in solution for hours, whereas the trications, [FeL] 3 , are only stable in solution on the time scale of a cyclic voltammetric experiment. These oxidations are shown to be ligand-rather than metal-centered. Three coordinated phenoxyl radicals are formed successively as shown conclusively by Mössbauer spectroscopy. The neutral, mono-, di-, and tricationic species each contain an octahedral, high-spin ferric ion (S Fe 5 2), which is intramolecularly, antiferromagnetically coupled to the spin (S 1 2) of the bound phenoxyl ligands to yield an S t 2 ground state for the monocation, and an S t 3 2 ground state for the dications as shown by EPR spectroscopy. The vibrations of the coordinated phenolate are observed by resonance Raman (RR) spectroscopy by excitation in resonance with the phenolate-to-iron charge-transfer (CT) transition above 500 nm or, alternatively, of the coordinated phenoxyl by excitation in resonance with the intraligand p 3p* transition at about 410 nm. Use of 18 O isotopomers selectively labeled at the phenolic oxygen allowed the identification of the C À O stretching and Fe À O stretching and bending modes. It is shown that the substitution pattern of phenolates and phenoxyls in their respective ortho and para positions and the charge of the complexes have a pronounced influence on the vibrational modes observed.

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confidence: 89%

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confidence: 76%

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The Molecular and Electronic Structure of Octahedral Tris(phenolato)iron(III) Complexes and Their Phenoxyl Radical Analogues: A Mössbauer and Resonance Raman Spectroscopic Study

et al. 1999

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“…Furthermore, the calculated IR spectrum of phenol H3 exhibits a very intense vibration at 1161 cm −1 without matching an experimental band. This vibration has also been obtained by other DFT calculations [93,95,96,98,113]. Despite of some C-C stretch character, this vibration has C-H and O-H in-plane bending character and has been assigned to a strong band at 1177 cm −1 in the IR spectrum of phenol vapor [114,115].…”

Section: Ir Spectra: Comparison Of Calculated To Experimental Resultssupporting

confidence: 70%

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Richthofen

Feldscher

Lippert

et al. 2013

Zeitschrift Für Naturforschung B

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The vicinity of a hydrogen bond donor (O-H) and a hydrogen bond acceptor (C=O or C=N-R) in salicylaldehydes and ortho-Schiff bases results in significant structural variations compared to the monosubstituted derivatives that are reflected in the electronic structure and thus in the spectroscopic properties. This interplay between intramolecular hydrogen bonding and multicenter π-electron delocalization is the origin of the concept of resonance-assisted hydrogen bonding (RAHB). Herein, the complexity is extended from one hydrogen bond donor-acceptor pair in salicylaldehyde and ortho-Schiff bases to three hydrogen bond donor-acceptor pairs in 2,4,6-tricarbonyl-and 2,4,6-triimine-substituted phloroglucinols (1,3,5-trihydroxybenzene), respectively. To evaluate the changes in the molecular and electronic structures, we have performed a comprehensive computational, spectroscopic, and structural study starting from monosubstituted benzene derivatives as references over ortho-disubstituted derivates to the sixfold-substituted derivatives. Whereas in salicylaldehydes, ortho-Schiff bases, and 2,4,6-tricarbonyl-phloroglucinols the phenolic O-protonated tautomers represent the energy minima, the N-protonated tautomers represent the energy minima in 2,4,6-triiminephloroglucinols. The analysis provides a keto-enamine resonance structure with six exocyclic double bonds to be dominant for these species reminiscent of [6]radialenes, which were termed heteroradialenes. These heteroradialenes are non-aromatic alicycles. However, the predominance of this resonance structure does not represent a sudden change going from the 2,4,6-tricarbonyl-to the 2,4,6-triimine-phloroglucinols, but a gradual increase of analogous resonance structure contributions is observed even in salicylaldehyde and ortho-Schiff bases demonstrating some hetero-orthoquinodimethane character. These changes are, besides in the molecular structures, well reflected in the IR spectra, which can therefore be used as a simple tool to probe the electronic structures in these systems. Interruption of the delocalized π system supporting the intramolecular hydrogen bond, i. e. going from 2,4,6-triimine-to 2,4,6-triamine-substituted phloroglucinols, reestablishes an O-protonated aromatic phloroglucinol system.

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“…8D) (36,45). These three modes are characteristic of the Raman spectra of phenoxyl radicals, with the 1487 cm Ϫ1 feature being assigned to the C-O stretch on the basis of its isotope dependence in model compounds (36,46). The residual features at 1185, 1246, 1312, 1417, and 1439 cm Ϫ1 in the azide complex (Fig.…”

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confidence: 97%

Glyoxal Oxidase from Phanerochaete chrysosporium Is a New Radical-Copper Oxidase

Whittaker

Kersten

Nakamura

et al. 1996

Journal of Biological Chemistry

213

160

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A free radical-coupled copper complex has been identified as the catalytic structure in the active site of glyoxal oxidase from Phanerochaete chrysosporium based on a combination of spectroscopic and biochemical studies. The native (inactive) enzyme is activated by oxidants leading to the elimination of the cupric EPR signal consistent with formation of an antiferromagnetically coupled radical-copper complex. Oxidation also leads to the appearance of a substoichiometric free radical EPR signal with an average g value (g av ‫؍‬ 2.0055) characteristic of phenoxyl -radicals arising from a minority apoenzyme fraction. Optical absorption, CD, and spectroelectrochemical measurements on the active enzyme reveal complex spectra extending into the near IR and define the redox potential for radical formation (E 1/2 ‫؍‬ 0.64 V versus NHE, pH 7.0). Resonance Raman spectra have identified the signature of a modified (cysteinyl-tyrosine) phenoxyl in the vibrational spectra of the active complex. This radical-copper motif has previously been found only in galactose oxidase, with which glyoxal oxidase shares many properties despite lacking obvious sequence identity, and catalyzing a distinct reaction. The enzymes thus represent members of a growing class of free radical metalloenzymes based on the radical-copper catalytic motif and appear to represent functional variants that have evolved to distinct catalytic roles.The white-rot wood-metabolizing basidiomycete fungi are major degraders of lignin contributing essential chemistry to the global carbon cycle. Phanerochaete chrysosporium, the organism most extensively studied for its lignin-degrading ability, produces three classes of extracellular enzyme under ligninolytic conditions: lignin peroxidase, manganese peroxidase, and glyoxal oxidase (1, 2). In the presence of H 2 O 2 (3), lignin peroxidases oxidize and partially depolymerize lignin or lignin model compounds (4 -9). The oxidizing peroxide cosubstrate for this reaction must be generated in situ for efficient turnover of extracellular lignin peroxidase, a function performed by glyoxal oxidase, which catalyzes the oxidation of a number of aldehyde and ␣-hydroxy carbonyl compounds, reducing O 2 to H 2 O 2 in the process. The enzyme exhibits a broad substrate specificity for oxidation of simple aldehydes to the corresponding carboxylic acids, as shown by Reaction 1 (10).Two of the substrates for glyoxal oxidase (glyoxal (OHCCHO) and methylglyoxal (CH 3 COCHO)) are found in extracellular fluid of ligninolytic cultures (10) and are likely to represent physiological substrates for the enzyme in a complex extracellular metabolic scheme (9, 10). Purified glyoxal oxidase is catalytically inactive but can be activated by lignin peroxidase (11, 12), suggesting a possible extracellular regulatory circuit for the control of H 2 O 2 production by glyoxal oxidase, and lignin peroxidase activity by H 2 O 2 .P. chrysosporium glyoxal oxidase has been purified to homogeneity (11), cloned for high level expression in Aspergillus nidulans (13...

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Ultraviolet Resonance Raman Spectroscopy and General Valence Force Field Analysis of Phenolate and Phenoxyl Radical

Cited by 86 publications

References 1 publication

The Molecular and Electronic Structure of Octahedral Tris(phenolato)iron(III) Complexes and Their Phenoxyl Radical Analogues: A Mössbauer and Resonance Raman Spectroscopic Study

The Molecular and Electronic Structure of Octahedral Tris(phenolato)iron(III) Complexes and Their Phenoxyl Radical Analogues: A Mössbauer and Resonance Raman Spectroscopic Study

Electronic and Molecular Structures of Heteroradialenes: A Combined Synthetic, Computational, Spectroscopic, and Structural Study Identifying IR Spectroscopy as a Simple but Powerful Experimental Probe

Glyoxal Oxidase from Phanerochaete chrysosporium Is a New Radical-Copper Oxidase

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