New low-spin Co(II) complexes with novel tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane ligand: electron transfer kinetics and spectroscopic characterization of Co(II)P6 and Co(II)P3S3 ions in aqueous solution

2001 ◽  
Vol 79 (9) ◽  
pp. 1344-1351 ◽  
Author(s):  
Satoshi Iwatsuki ◽  
Kenji Obeyama ◽  
Nobuyoshi Koshino ◽  
Shigenobu Funahashi ◽  
Kazuo Kashiwabara ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Spin State ◽  
Kinetic Studies ◽  
Spectroscopic Characterization ◽  
Electronic Configuration ◽  
Exchange Reactions ◽  
Teller Distortion ◽  
Jahn Teller ◽  
Controlled Potential

Substitution-inert Co(II) complexes with tripodal 1,1,1-tris(dimethylphosphinomethyl)ethane were produced in aqueous solution by the controlled-potential electrolysis. EPR studies indicated that the Co(II)P6 and Co(II)P3S3 species are in the low-spin t62ge1g state. The analyses of the absorption spectra of the Co(II) species in solution indicated significant Jahn–Teller distortion in Co(II)P6 and Co(II)P3S3 ions as expected for the low-spin d7 electronic configuration, while less distortion was observed for the Co(II)S6 ion. Kinetic studies of the redox reactions involving these Co(III/II) species confirmed that the electron self-exchange reactions for the Co(III/II)P6 and Co(III/II)P3S3 couples are relatively fast (kex ~ 1 × 104 dm3 mol–1 s–1), which is consistent with the results for other low-spin – low-spin Co(III/II) couples. It was concluded that the nephelauxetic effect of the P-donor atom stabilizes the low-spin state in Co(II), and that the rather rapid electron exchange rates for these Co(III/II) couples were explained by the lack of the spin reorganization process required for the ordinary low-spin – high-spin Co(III/II) couples.Key words: cobalt(III/II), spin state, EPR study, kinetics, electron transfer.

The quantitative Jahn-teller distortion of the Cu2+ site in aqueous solution by xanes spectroscopy

1989 ◽  
Vol 132 (1-2) ◽  
pp. 295-302 ◽  
Author(s):  
J. Garcia ◽  
M. Benfatto ◽  
C.R. Natoli ◽  
A. Bianconi ◽  
A. Fontaine ◽  
...  
Keyword(s):  
Aqueous Solution ◽  
Xanes Spectroscopy ◽  
Teller Distortion ◽  
Jahn Teller ◽  
Jahn Teller Distortion

Kinetics of self-exchange of bis(1,4,7-trithiacyclononane)iron(III)/(II) in acetonitrile and in acidic aqueous solution

1990 ◽  
Vol 68 (12) ◽  
pp. 2228-2233 ◽  
Author(s):  
Hideo Doine ◽  
Thomas W. Swaddle
Keyword(s):  
Aqueous Solution ◽  
Electron Transfer ◽  
Ionic Strength ◽  
Line Broadening ◽  
Acidic Water ◽  
Exchange Reactions ◽  
Acidic Aqueous Solution ◽  
Spontaneous Reduction ◽  
Kinetics Of ◽  
C Nmr

The rate constant kex of the [Formula: see text] self-exchange reaction cannot be measured in most common solvents because of spontaneous reduction of the [Formula: see text] ion, which is also sensitive to photolysis by visible light. However, in CD3CN at −41 to −19 °C, reproducible proton-decoupled 13C NMR line broadening measurements are possible, and give kex = (5.3 ± 0.3) × 104 kg mol−1s−1 at 0 °C, ΔH* = 10.3 ± 1.8 kJ mol−1, and ΔS* = −116 ± 7 J K−1 mol−1, at ionic strength I = 0.1 mol kg−1. Proton NMR line broadening experiments are marginally practicable in very acidic water (2.0 mol kg−1 D2SO4/D2O) near 0 °C, and give kex = 3.2 × 106 kg mol−1 s−1 at 1 °C. The relative kex values of these and other low-spin/low-spin FeIII/II self-exchange reactions follow the predictions of the Marcus–Hush theory at least qualitatively. The effect of ionic strength, however, is less than predicted, probably because of the formation of less reactive anion–cation pairs. Keywords: electron transfer kinetics, crown thioether complexes.

Thermal effects in polyelectrolyte ion exchange reactions: the Jahn–Teller effect

1988 ◽  
Vol 66 (4) ◽  
pp. 974-978 ◽  
Author(s):  
Kang Sun ◽  
George E. Boyd
Keyword(s):  
Ion Exchange ◽  
Thermal Effects ◽  
Divalent Cations ◽  
Transition Element ◽  
Electronic Configuration ◽  
Standard State ◽  
Transition Elements ◽  
Exchange Reactions ◽  
Cubic Symmetry ◽  
Jahn Teller

Microcalorimetric determinations were made of the thermal effects accompanying the exchange of the divalent cations of Mn, Fe, Co, Ni, Cu, and Zn in dilute aqueous perchlorate solutions with Mg2+ ion initially bound in a crosslinked polyelectrolyte gel. The calorimetric measurements, together with microchemical equilibrium distribution determinations with the same cations, were employed to estimate the standard state Gibbs energy, enthalpy, and entropy changes associated with their ion exchange reactions.All the transition elements were selectively absorbed relative to Mg2+ with the sequence being: Mn < Fe < Co < Ni > Cu > Zn, showing divalent Ni(II) cation to possess the greatest affinity for the polyelectrolyte phase. The sequence of standard state reaction enthalpy change, ΔH0, revealed that Ni2+ also was the most exothermic of all 3d transition element cations. However, the ΔH0 values became more negative in the order: Mn < Fe < Co < Ni > Cu < Zn, showing that Cu2+ ion behaved anomalously in being less negative than expected. This behavior (and that in the ΔS0 values also) suggested that a destabilization of the octahedrally coordinated Cu2+ in aqueous solutions must occur, possibly because of Jahn–Teller effects on its d9 electronic configuration when the cation is placed in an environment of cubic symmetry. Because of a thermodynamic compensation of the magnitudes of ΔH0 and ΔS0, the position of Cu2+ in the ΔG0 value sequence was regular.

Flavin radicals, conformational sampling and robust design principles in interprotein electron transfer: the trimethylamine dehydrogenase-electron-transferring flavoprotein complex

2004 ◽  
Vol 71 ◽  
pp. 1-14
Author(s):  
David Leys ◽  
Jaswir Basran ◽  
François Talfournier ◽  
Kamaldeep K. Chohan ◽  
Andrew W. Munro ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Kinetic Studies ◽  
Molecular Assembly ◽  
Conformational Sampling ◽  
Trimethylamine Dehydrogenase ◽  
Key Residues ◽  
Electron Transferring Flavoprotein ◽  
Electron Transfer Complex

TMADH (trimethylamine dehydrogenase) is a complex iron-sulphur flavoprotein that forms a soluble electron-transfer complex with ETF (electron-transferring flavoprotein). The mechanism of electron transfer between TMADH and ETF has been studied using stopped-flow kinetic and mutagenesis methods, and more recently by X-ray crystallography. Potentiometric methods have also been used to identify key residues involved in the stabilization of the flavin radical semiquinone species in ETF. These studies have demonstrated a key role for 'conformational sampling' in the electron-transfer complex, facilitated by two-site contact of ETF with TMADH. Exploration of three-dimensional space in the complex allows the FAD of ETF to find conformations compatible with enhanced electronic coupling with the 4Fe-4S centre of TMADH. This mechanism of electron transfer provides for a more robust and accessible design principle for interprotein electron transfer compared with simpler models that invoke the collision of redox partners followed by electron transfer. The structure of the TMADH-ETF complex confirms the role of key residues in electron transfer and molecular assembly, originally suggested from detailed kinetic studies in wild-type and mutant complexes, and from molecular modelling.

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