Resonance Raman and molecular orbital studies of the effects of deuteration on the vibrational structure of the p-benzosemiquinone radical anion

Schüler, Robert H.; Tripathi, G. N. R.; Prebenda, M. F.; Chipman, Daniel M.

doi:10.1021/j150644a010

Cited by 48 publications

(33 citation statements)

References 3 publications

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“…The resonance Raman frequency is significantly higher than that reported for the CO stretching vibration of free Q .À (1435 cm À1 ), in which the CO bond order is estimated from the Raman data to be 1.5, [23] but lower than Scheme 1. Electron transfer reactions of 1 and 2 to give complexes 3 and 4, respectively.…”

Section: Introductioncontrasting

confidence: 58%

Coordination of Semiquinone and Superoxide Radical Anions to the Zinc Ion in SOD Model Complexes that Act as the Key Step in Disproportionation of the Radical Anions

Ohtsu

Fukuzumi

2001

Chem. Eur. J.

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Reactions of imidazolate-bridged CuII-ZnII heterodinuclear and CuII-CuII homodinuclear complexes, [CuIIZnII(bdpi)(CH3CN)2](ClO4)3 x 2CH3CN (1) and [CuII2(bdpi)(CH3CN)2](ClO4)3 x CH3CN x 3H2O (2) (Hbdpi = 4,5-bis(di(2-pyridylmethyl)aminomethyl)imidazole), with the p-benzosemiquinone radical anion (Q*-) have been examined to provide mechanistic insight into the role of the ZnII ion in copper-zinc superoxide dismutase (Cu,Zn-SOD). The addition of less than one equivalent of Q*- to a deaerated solution of 1 or 2 in propionitrile at -80 degrees C results in the oxidation of Q*- accompanied by the appearance of a new absorption band at 585 nm due to the CuI-Q complex (3 or 4), the absorbance of which increases linearly with the increase in Q*- concentration. Both the resonance Raman spectra of 3 and 4 exhibit a strong resonance-enhanced Raman band at 1580 cm(-1), which can be assigned to a CO stretching vibration in the CuI-Q complexes. Further addition of Q*- to a deaerated solution of 3 in propionitrile results in the reduction of Q*-, whereas no reduction of Q*- occurs with 4, which does not contain the ZnII ion. Thus, the coordination of Q*- to the ZnII ion is essential for the reduction of Q*- by the CuI ion in 3. The coordination of O2*- and Q*- to the ZnII ion has been confirmed by the electronic and ESR spectra of the O2*- and Q*- complexes with mononuclear ZnII complexes, [ZnII[MeIm(Py)2](CH3CN)](ClO4)2 (5) and [ZnII[MeIm(Me)2](H2O)](ClO4)2 (6) (MeIm(Py)2 = (1-methyl-4-imidazolylmethyl)bis(2-pyridylmethyl)amine, MeIm(Me)2 = (1-methyl-4-imidazolylmethyl)bis(6-methyl-2-pyridylmethyl)amine). The binding energies of O2*- with the ZnII ion in 5 and 6 have been evaluated from the deviation of the g values of the ESR spectra from the free spin value.

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Section: Introductioncontrasting

confidence: 58%

Coordination of Semiquinone and Superoxide Radical Anions to the Zinc Ion in SOD Model Complexes that Act as the Key Step in Disproportionation of the Radical Anions

Ohtsu

Fukuzumi

2001

Chem. Eur. J.

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“…Raman spectra which revealed some of the totally symmetric fundamentals, [11][12][13][14][15] but only the strongest band in the IR spectrum, at around 1500 cm…”

Section: Introductionmentioning

confidence: 99%

Vibronic spectra of the p-benzoquinone radical anion and cation: a matrix isolation and computational study

Piech

Bally

Ichino

et al. 2014

Phys. Chem. Chem. Phys.

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The electronic and vibrational absorption spectra of the radical anion and cation of p-benzoquinone (PBQ) in an Ar matrix between 500 and 40 000 cm À1 are presented and discussed in detail. Of particular interest is the radical cation, which shows very unusual spectroscopic features that can be understood in terms of vibronic coupling between the ground and a very low-lying excited state. The infrared spectrum of PBQ + exhibits a very conspicuous and complicated pattern of features above 1900 cm A notable exception is the antisymmetric CQO stretching vibration, which contributes significantly to the vibronic coupling, but has nevertheless quite small intensity in the cation spectrum. This surprising feature is rationalized on the basis of a simple perturbation analysis.

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“…Green salts with formulae NaC 6 Cl 4 O 2 and KC 6 Cl 4 O 2 precipitated from cold acetone but quickly decomposed upon heating. During the last fifty years perhalogenosemiquinones were studied by various techniques: EPR, [4][5][6] UV/Vis 7 and IR/Raman spectroscopy [8][9][10][11] and computational methods. [12][13][14][15] Several charge-transfer systems involving tetrachloro-1,4-benzoquinone (Cl 4 Q) [16][17][18][19][20] and tetrabromo-1,4-benzoquinone (Br 4 Q), 21,22 where radical anions can be stabilised under appropriate conditions, have also been designed.…”

Section: Introductionmentioning

confidence: 99%

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

et al. 2011

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Crystal structures of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates and their solvent-free salts are determined. p-Semiquinone anion radical reveals enhanced aromaticity of the ring compared to the quinone. A pair of p-stacked radical anion (psemiquinone) rings occurs in crystal structures of potassium and rubidium salts of tetrachlorosemiquinone anion acetone solvates and their potassium tetrabromo analogue. The ring centroid separation distances are about 3.2 Å and carbon-carbon contacts between the contiguous rings are 0.3 Å shorter than the sum of van der Waals radii. The spin-coupling of the two unpaired electrons between the two anion radical rings (forming a stacked dimer) correlates with the diamagnetic property of the crystals. Magnetic properties of alkali salts of tetrahaolgenosemiquinone anion radical acetone solvates were examined by electron paramagnetic resonance spectroscopy. IntroductionQuinones and semiquinone radicals undergo easily reversible oxidation-reduction reactions and they are excellent electron carriers. Due to influence of the functional groups, quinones may have various values of the standard redox potential. The oxidation potential of the quinones with electron-donating groups such as -OH, is lower, and with electronwithdrawing groups such as -Cl and -NO2, the potential becomes higher. These unique electron properties of quinones are exploited for syntheses, both, in laboratory and by nature in vivo. 1,2 Substituents on the quinoid ring modify electron density affecting oxidation potential and stability of the semiquinone radical (Scheme 1). Perhalogenated benzoquinones are easily reduced and their radicals are rather stable; four electronegative substituents make electron density in the ring significantly lower. Sodium and potassium salts of tetrachlorosemiquinone anion radical were first prepared in 1912 by Torrey and Hunter 3 by reaction of alkali iodide and tetrachloroquinone in acetone. Green salts with formulae NaC 6 C l4 O 2 and KC 6 C l4 O 2 precipitated from cold acetone but quickly decomposed upon heating. During the last fifty years perhalogenosemiquinones were studied by various techniques: EPR, 4-6 UV/Vis 7 and IR/Raman spectroscopy [8][9][10][11] and computational methods. [12][13][14][15] Several charge-transfer systems involving tetrachloro-1,4-benzoquinone (Cl4Q) [16][17][18][19][20] and tetrabromo-1,4-benzoquinone (Br4Q), 21,22 where radical anions can be stabilised under appropriate conditions, have also been designed. A crystallographic study of tetrachlorosemiquinone radical anion-in its well-known potassium salt3-was attempted in a Rudjer Bo_skovi_c Institute, Bijeni_cka 54, HR-10000 Zagreb, Croatia. E-mail: kmolcano@irb.hr Molčanov, K., , "Stabilisation of tetrabromo-and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals", CrystEngComm, Vol.13, No.16, 1973 23 using a film method (Weissenberg camera). However, due to an extremely weak diffraction of poor crystals the authors could only determine unit cells of...

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Resonance Raman and molecular orbital studies of the effects of deuteration on the vibrational structure of the p-benzosemiquinone radical anion

Cited by 48 publications

References 3 publications

Coordination of Semiquinone and Superoxide Radical Anions to the Zinc Ion in SOD Model Complexes that Act as the Key Step in Disproportionation of the Radical Anions

Coordination of Semiquinone and Superoxide Radical Anions to the Zinc Ion in SOD Model Complexes that Act as the Key Step in Disproportionation of the Radical Anions

Vibronic spectra of the p-benzoquinone radical anion and cation: a matrix isolation and computational study

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

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