EPR and proton ENDOR study of the solution equilibria of bis(2-ethyl-2-hydroxybutanoato(2-))oxochromate(V) and bis(2-hydroxy-2-methylbutanoato(2-))oxochromate(V)

Branca, Mario; Dessì, Alessandro; Micera, Giovanni; Sanna, Daniele

doi:10.1021/ic00057a015

Cited by 20 publications

(30 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…This is established by the pH, [Cr(V)] and [Cr(V)]/[qaH 5 ] dependencies, and the distinct A iso values ( A iso ( IIIa ) = 17.2 × 10 -4 cm -1 ; A iso ( IIIb ) = 16.4 × 10 -4 cm -1 ). The A iso values are similar to those observed in the EPR spectra from aqueous solutions of Na[Cr(O)(ehba) 2 ]·H 2 O ( A iso = 17.2 × 10 -4 cm -1 ; A iso = 16.1 × 10 -4 cm -1 ) and Na[Cr(O)(hmba) 2 ]·H 2 O ( A iso = 17.4 × 10 -4 cm -1 ; A iso = 16.3 × 10 -4 cm -1 ), which have been assigned previously to the presence of more than one geometric isomer per Cr(V)-2-hydroxy acid complex. , The presence of a maximum of three geometric isomers for Cr(V)-2-hydroxy acid complexes arises from the interchange of the alcoholato and/or the carboxylato donors about the distorted trigonal bipyramid . The possibility of an equilibrium existing between mononuclear and polymeric species, where coordination features qaH bridging two Cr(V) ions via the 2-hydroxy acid group ( O 1 , O 7 ) and either the 4,5- ( O 4 , O 5 ) ( IX ) or 3,4- ( O 3 , O 4 ) diol groups ( X ) were eliminated due to the EPR spectral invariance upon changing the concentrations of qaH 5 and Cr(V) at a constant [qaH 5 ]/[Cr(V)] ratio and a constant pH value.…”

Section: Discussionsupporting

confidence: 85%

“…Despite many attempts, crystals of K[Cr(O)(qaH 3 ) 2 ]·H 2 O suitable for X-ray structural analysis have not been obtained as yet. It is possible that the complex may exist in the solid state as more than one geometric isomer as has been observed for similar complexes in solution. , The XAFS structure of [Cr(O)(qaH 3 ) 2 ] - is also consistent with a bis(2-hydroxy acid) coordination mode. , The solid-state EPR spectra of the Cr(V)-2-hydroxy acid complexes, K[Cr(O)(qaH 3 ) 2 ]·H 2 O, Na[Cr(O)(hmba) 2 ]·H 2 O and Na[Cr(O)(ehba) 2 ]·H 2 O, exhibit a single broad signal (Figure , upper graphic) with comparable g iso values (Table ). The signal line widths vary among the spectra, in the following order of highest to lowest: K[Cr(O)(qaH 3 ) 2 ]·H 2 O > Na[Cr(O)(hmba) 2 ]·H 2 O > Na[Cr(O)(ehba) 2 ]·H 2 O.…”

Section: Resultsmentioning

confidence: 78%

“…The possibility of the multiple species in the case of Na[Cr(O)(hmba) 2 ]·H 2 O (hmba has a chiral carbon) arising from chiral species, Na[Cr(O)( R -hmba) 2 ]·H 2 O or Na[Cr(O)( S -hmba) 2 ]·H 2 O, is discounted, since very similar spectra are obtained from solutions of Na[Cr(O)(hmba) 2 ]·H 2 O and the achiral complex, Na[Cr(O)(ehba) 2 ]·H 2 O. The two signals observed in the aqueous solution EPR spectra of Na[Cr(O)(L) 2 ]·H 2 O (L = hmba, ehba) have been assigned as being due to geometric isomers, , and it is expected that geometric isomers are similarly observed for K[Cr(O)(qaH 3 ) 2 ]·H 2 O.…”

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Competition between 1,2-Diol and 2-Hydroxy Acid Coordination in Cr(V)-Quinic Acid Complexes: Implications for Stabilization of Cr(V) Intermediates of Relevance to Cr(VI)-Induced Carcinogenesis

Codd

Lay

1999

J. Am. Chem. Soc.

View full text Add to dashboard Cite

For the speciation of Cr(V) intermediates formed during the intracellular reduction of Cr(VI) to be understood, the intramolecular competition between 1,2-diol and 2-hydroxy acid coordination to Cr(V) as a function of pH has been studied in quinic acid complexes. The Cr(V)-2-hydroxy acid complex, K[Cr(O)(qaH3)2]·H2O (qaH5 = 1R,3R,4R,5R-1,3,4,5-tetrahydroxycyclohexanecarboxylic acid, I), has been isolated and characterized. In aqueous solutions at pH values <4.0, K[Cr(O)(qaH3)2]·H2O gives two EPR signals (g iso = 1.9787, A iso = 17.2 × 10-4 cm-1; g iso = 1.9791, A iso = 16.4 × 10-4 cm-1). The relative intensities of the signals are independent of [qaH5]/[Cr(V)], and of increasing [qaH5] and [Cr(V)] at constant [qaH5]/[Cr(V)] and pH values. These signals are consistent with those found with well-characterized Cr(V)-2-hydroxy acid complexes and are assigned to two geometric isomers of the [Cr(O)(O 1,O 7-qaH3)2]- linkage isomer. Both the 2-hydroxy acid (O 1,O 7) and vic-diol (cis-O 3,O 4; trans-O 4,O 5) groups of qaH5 are viable Cr(V) donors. In the reduction of Cr(VI) by GSH in the presence of an excess of qaH5, the EPR spectra are similar to that of K[Cr(O)(qaH3)2]·H2O at low pH values (<4.0). At intermediate pH values (pH 5−7.5) additional signals appear (g iso = 1.9791, g iso = 1.9794, g iso = 1.9799), which have EPR spectral data consistent with the presence of Cr(V)-qa linkage isomers, featuring one of each donor type (1 × 2-hydroxy acid; 1 × diol). By using EPR spectral simulation, we deduced that the cis-diol linkage isomer, [Cr(O)(O 1,O 7-qaH3)(O 3,O 4-qaH2)]2-, is an order of magnitude more thermodynamically stable to intramolecular ligand exchange compared to the trans-diol linkage isomer, [Cr(O)(O 1,O 7-qaH3)(O 4,O 5-qaH2)]2-. At pH values >7.5, the Cr(V)-qa EPR spectra reveal two triplets (g iso = 1.9800, g iso = 1.9802), which are ascribed to geometric isomers of a bis-diol Cr(V)-qa complex, [Cr(O)(O 3,O 4-qaH2)2]3-. The concentration of the trans-diol isomer, [Cr(O)(O 4,O 5-qaH2)2]3-, is predicted to be negligible. This assignment is supported by the similarity of the EPR spectral data with those formed in the Cr(VI) reduction by GSH in the presence of the related polyol (cis-O 3,O 4; trans-O 4,O 5) ligand, shikimic acid (3R,4R,5R-3,4,5-trihydroxycyclohexenecarboxylic acid, II), which does not possess a 2-hydroxy acid moiety. The relative intensities of the EPR signals of the Cr(V)-sa species (g iso = 1.9800, g iso = 1.9801), ascribed to geometric isomers of [Cr(O)(O 3,O 4-saH)2]3-, are independent of increasing pH and of [saH4] at pH values >4.0. The results show that 2-hydroxy acid ligands are favored with respect to 1,2-diols for stabilizing Cr(V) at low pH values relevant to phagocytosis of insoluble chromates (pH ∼4), but the opposite is the case when soluble chromates are taken up by the cells at pH = 7.4. Both classes of ligands compete effectively for complexation of Cr(V) compared to glutathione at all pH values studied.

show abstract

Section: Discussionsupporting

confidence: 85%

Section: Resultsmentioning

confidence: 78%

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Competition between 1,2-Diol and 2-Hydroxy Acid Coordination in Cr(V)-Quinic Acid Complexes: Implications for Stabilization of Cr(V) Intermediates of Relevance to Cr(VI)-Induced Carcinogenesis

Codd

Lay

1999

J. Am. Chem. Soc.

View full text Add to dashboard Cite

show abstract

“…Here K is the Fermi-contact term and ge = 2.0023. Equations (5) and (6) derived from those above show the relationship between K = la/PI M I(A)/PI [when ((8) -8,) is fairly small] (6) ( A ) and a. Note that the thus estimated P values of the nitridochromium complexes in Table 1 are substantially smaller than those of the oxochromium complexes.…”

Section: The Values Adoptedmentioning

confidence: 96%

Spectroscopic studies of a square-pyramidal nitridochromium(V) complex

Azuma¹,

Ozawa²,

Tsuboyama³

1994

J. Chem. Soc., Dalton Trans.

View full text Add to dashboard Cite

The Institute of Physical and Chemical Research (RIKEN) , Wako, Saitama 35 I -0 I , JapanThe E S R and UV/VlS spectra have been studied for solutions of [ N N -bis( pyridine-2-carbonyl) -0phenylenediamido] nitridochromium(v) having a square-pyramidal (CrN,) chromophore. The g and , , Cr hyperfine coupling tensors ( A ) are axially symmetric. An analysis of the A tensor indicated a 3d,, ground-state Kramers doublet. Fairly high d,-p, interaction in the CEN formally triple bond was also revealed. The striking stability of this complex can be attributed to the remarkable d,-p, covalency of the CEN bond. None of the d-d* transitions has been observed in the region of h 2 600 nm at room temperature. Bands at 25 000 and 29 000 cm-' have been tentatively assigned to charge-transfer transitions. The considerable difference between the A1(53Cr), a(=Cr), gL and gi,o values of nitridoand those of 0x0-chromium(v) complexes have been explained in terms of the different extents of covalency in the CEN and Cr=O multiple bonds.

show abstract

“…Similar to NMR, these EPR techniques can be used to study the Cr based catalyst systems under a variety of conditions (variable temperatures, variable pressures, in solution, etc), providing information not only on the principle oxidation states involved but also a structural description on the complexes in solution. To date most of the available EPR literature pertaining to Cr complexes has focussed on Cr(III) 23, 24 and Cr(V) 25 compounds, and to a much lesser extent on low spin Cr(I). 26 Bruckner et al, 24 have recently monitored the structure and valence state of a Cr(III) oligomerization system via in situ EPR.…”

Section: Introductionmentioning

confidence: 99%

A cw EPR and ENDOR investigation on a series of Cr(i) carbonyl complexes with relevance to alkene oligomerization catalysis: [Cr(CO)4L]+ (L = Ph2PN(R)PPh2, Ph2P(R)PPh2)

et al. 2010

View full text Add to dashboard Cite

The preparation and characterisation of the Cr(I) complexes [Cr(CO)(4)L](+) (L = Ph(2)PN(R)PPh(2), Ph(2)P(R)PPh(2)), which are used as pre-catalysts for the selective oligomerization of ethylene, are reported. The electronic properties and structural features of these complexes in frozen solution have been established via continuous wave X-band Electron Paramagnetic Resonance (cw-EPR) and continuous wave (1)H, (14)N and (31)P Electron Nuclear Double Resonance (cw-ENDOR) spectroscopy. The EPR spectra are dominated by the g anisotropy, with notably large (P)A couplings from the two equivalent (31)P nuclei. The spin Hamiltonian parameters (g(perpendicular) (g(xx) = g(yy)) > g(e) > g(parallel) (g(zz))) are consistent with a low-spin d(5) system possessing C(2v) symmetry, with a SOMO where the metal contribution is primarily d(xy) for all complexes. The isotropic Fermi contact term ((P)a(iso), determined by EPR and ENDOR) was found to be largest for complexes containing ligands e, d, f and g, indicating that the (31)P 3 s character in the SOMO is higher for the PNP type ligands than the PCP type. Subtle structural differences in the complexes were also identified through variations in the Deltag shifts (identified by EPR), and through differences in the phenyl ring conformations (identified by (1)H ENDOR). Attempts to correlate trends in EPR-derived parameters with data measured for catalysis using these pre-catalysts are also made, but no clear connections were found.

show abstract

EPR and proton ENDOR study of the solution equilibria of bis(2-ethyl-2-hydroxybutanoato(2-))oxochromate(V) and bis(2-hydroxy-2-methylbutanoato(2-))oxochromate(V)

Abstract: EPR and !H ENDOR Study of the Solution Equilibria of Bis(2-ethyl-2-hydroxybutanoato(2-) )oxochromate(V) and Bis(2-hydroxy-2-methylbutanoato(2-))oxochromate(V)

Cited by 20 publications

References 0 publications

Competition between 1,2-Diol and 2-Hydroxy Acid Coordination in Cr(V)-Quinic Acid Complexes: Implications for Stabilization of Cr(V) Intermediates of Relevance to Cr(VI)-Induced Carcinogenesis

Competition between 1,2-Diol and 2-Hydroxy Acid Coordination in Cr(V)-Quinic Acid Complexes: Implications for Stabilization of Cr(V) Intermediates of Relevance to Cr(VI)-Induced Carcinogenesis

Spectroscopic studies of a square-pyramidal nitridochromium(V) complex

A cw EPR and ENDOR investigation on a series of Cr(i) carbonyl complexes with relevance to alkene oligomerization catalysis: [Cr(CO)4L]+ (L = Ph2PN(R)PPh2, Ph2P(R)PPh2)

Contact Info

Product

Resources

About