- An interpretation of gated behavior: Kinetic studies of the oxidation and reduction reactions of bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) in acetonitrile
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Reduction reactions of Cu(dmp)2 2+(dmp = 2,9-dimethyl-1,10-phenanthroline) by ferrocene (Fe(Cp)2= bis(cyclopentadienyl)iron(II)), decamethylferrocene (Fe(PMCp)2= bis(pentamethylcyclopentadienyl)iron(II)), and Co(bpy)3 2+(bpy = 2,2′-bipyridine) and oxidation reactions of Cu(dmp)2 +by Ni(tacn)2 3+(tacn = 1,4,7-triazacyclononane) and Mn(bpyO2)3 3+(bpyO2= N,N′-dioxo-2,2′-bipyridine) were studied in acetonitrile for the purpose of interpreting the gated behavior involving copper(II) and -(I) species. It was shown that the electron self-exchange rate constants estimated for the Cu(dmp)2 2+/+couple from the oxidation reaction of Cu(dmp)2 +by Ni(tacn)2 3+(5.9 × 102kg mol-1s-1) and Mn(bpyO2)3 3+(2.9 × 104kg mol-1s-1) were consistent with the directly measured value by NMR (5 × 103kg mol-1s-1). In contrast, we obtained the electron self-exchange rate constant of Cu(dmp)2 2+/+as 1.6 kg mol-1s-1from the reduction of Cu(dmp)2 2+by Co(bpy)3 2+. The pseudo-first-order rate constant for the reduction reaction of Cu(dmp)2 2+by Fe(Cp)2was not linear against the concentration of excess amounts of Fe(Cp)2. A detailed analysis of the reaction revealed that the reduction of Cu(dmp)2 2+involved the slow path related to the deformation of Cu(dmp)2 2+(path B in Scheme 1). By using Fe(PMCp)2(the E° value is 500 mV more negative than that of Fe(Cp)2 +/0) as the reductant, the mixing with another pathway involving deformation of Cu(dmp)2 +(path A in Scheme 1) became more evident. The origin of the Gated Behavior is discussed by means of the energy differences between the normal and deformed Cu(II) and Cu(I) species: the difference in the crystal field activation energies corresponding to the formation of pseudo-tetrahedral Cu(II) from tetragonally distorted Cu(II) and the difference in the stabilization energies of the tetrahedral and tetragonal Cu(I) for the activation of Cu(I) species. The reduction reaction of Cu(dmp)2 2+by Fe(PMCp)2confirmed that the mixing of the two pathways takes place by lowering the energy level corresponding to the less favorable conformational change of Cu(I) species.
- Koshino, Nobuyoshi,Kuchiyama, Yoshio,Ozaki, Hiroshi,Funahashi, Shigenobu,Takagi, Hideo D.
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- Spectroelectrochemical sensing based on multimode selectivity simultaneously achievable in a single device: 14. Enhancing sensitivity of a metal complex ion by ligand exchange
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Enhancement of the sensitivity of a spectroelectrochemical sensor by ligand exchange within the sensing film during spectroelectrochemical modulation is demonstrated in this paper. This concept is illustrated with a sensor for Cu(en)22+, where en = ethylenediamine, in aqueous solution. A ligand exchange reaction increases the difference in the molar absorptivities of the two complex ions involved in spectroelectrochemical modulation, thus giving a larger optical response. The spectroelectrochemical sensor consists of a cation-selective Nafion-SiO2 composite film spin-coated onto an indium tin oxide (ITO) glass optically transparent electrode (OTE). The film was loaded with 2,9-dimethyl-1,10-phenanthroline (neocuproine, or nc) for the ligand exchange reaction. Reduction of Cu(en)2 2+ at the OTE is accompanied by ligand exchange with nc to form Cu(nc)21+, which has a molar absorptivity of 7950 M -1 cm-1 at λmax = 454 nm. Detection within the sensing film using attenuated total reflectance (ATR) at 454 nm during modulation was accomplished by potential cycling between 0.8 and -0.9 V versus Ag/AgCl. The effects of nc concentration in the film and potential scan rate on the absorbance-time profile for spectroelectrochemical modulation were studied. The calibration curve for Cu(en)22+ was linear within the range of 5 × 10-6 M to 1 × 10-3 M.
- Shtoyko, Tanya,Richardson, John N.,Seliskar, Carl J.,Heineman, William R.
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- Blue copper model complexes with distorted tetragonal geometry acting as effective electron-transfer mediators in dye-sensitized solar cells
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The electron self-exchange rate constants of blue copper model complexes, [(-)-sparteine-N,N′](maleonitriledithiolato-S,S′)copper ([Cu(SP)(mmt)])0/-, bis(2,9-dimethy-1,10-phenanthroline)copper ([Cu(dmp)2]2+/+), and bis(1,10-phenanthroline)copper ([Cu(phen)2]2+/+) have been determined from the rate constants of electron transfer from a homologous series of ferrocene derivatives to the copper(II) complexes in light of the Marcus theory of electron transfer. The resulting electron self-exchange rate constant increases in the order: [Cu(phen)2]2+/+ 0/- 2]2+/+, in agreement with the order of the smaller structural change between the copper(II) and copper(I) complexes due to the distorted tetragonal geometry. The dye-sensitized solar cells (DSSC) were constructed using the copper complexes as redox couples to compare the photoelectrochemical responses with those using the conventional I 3-/I- couple. The light energy conversion efficiency (η) values under illumination of simulated solar light irradiation (100 mW/cm2) of DSSCs using [Cu(phen)2] 2+/+, [Cu(dmp)2]2+/+, and [Cu(SP)(mmt)] 0/- were recorded as 0.1%, 1.4%, and 1.3%, respectively. The maximum η value (2.2%) was obtained for a DSSC using the [Cu(dmp)2] 2+/+ redox couple under the light irradiation of 20 mW/cm2 intensity, where a higher open-circuit voltage of the cell was attained as compared to that of the conventional I3-/I- couple.
- Hattori, Shigeki,Wada, Yuji,Yanagida, Shozo,Fukuzumi, Shunichi
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- Two Faces of the Same Coin: Coupling X-Ray Absorption and NMR Spectroscopies to Investigate the Exchange Reaction Between Prototypical Cu Coordination Complexes
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The satisfactory rationalization of complex reactive pathways in solution chemistry may greatly benefit from the combined use of advanced experimental and theoretical complementary methods of analysis. In this work, we combine X-Ray Absorption and 1H NMR spectroscopies with state-of-the-art Multivariate Curve Resolution and theoretical analyses to gain a comprehensive view on a prototypical reaction involving the variation of the oxidation state and local structure environment of a selected metal ion coordinated by organic ligands. Specifically, we investigate the 2-cyano-2-phenylpropanoic acid reduction of the octahedral complex established by the Cu2+ ion with terpyridine to the tetrahedral complex formed by Cu+ and neocuproine. Through our interdisciplinary approach we gain insights into the nature, concentration time evolution and structures of the key metal (XAS measurements) and organic (1H NMR measurements) species under reaction. We believe our method may prove to be useful in the toolbox necessary to understand the mechanisms of reactive processes of interest in solution.
- Busato, Matteo,Cenesi, Flavia,D'Angelo, Paola,Del Giudice, Daniele,Di Berto Mancini, Marika,Di Stefano, Stefano,Frateloreto, Federico,Lanzalunga, Osvaldo,Oliveira De Souza, Danilo,Tavani, Francesco
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supporting information
(2021/12/22)
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- A quantitative method for the assessment of homocysteine thiolactonase enzyme activity
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This assay elucidates an accurate, simple, and precise protocol to quantify the activity of homocysteine thiolactonase (HTase). To establish HTase activity, the enzyme samples were incubated with a 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer, which contained suitable concentrations of the homocysteine thiolactone as a substrate. To stop the enzyme's reaction, the CUPRAC reagent (Cu(Nc)22+) was added after a suitable incubation time. The reduction of Cu(II)-neocuproine complex (Cu(Nc)22+) to highly coloured Cu(I)-neocuproine complex (Cu(Nc)2+) by the produced homocysteine was quantified spectrophotometrically at 450 nm (CUPRAC method). The increase in the absorbance of the coloured Cu(I)-neocuproine complex (Cu(Nc)2+) was correlated directly to the activity of HTase. ANOVA analysis was utilised to validate the new method against homocysteine thiolactonase activity using the H+ ions liberating method in matched samples. In conclusion, according to the obtained correlation coefficient (0.9995) from the comparison of the current method with the reference method, the current method is effective in assay HTase activity with high reliability.
- Obeid, Nassr J.,Hadwan, Mahmoud Hussein
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- Hydrazine Hydrate Accelerates Neocuproine–Copper Complex Generation and Utilization in Alkyne Reduction, a Significant Supplement Method for Catalytic Hydrogenation
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Diimine (HN═NH) is a strong reducing agent, but the efficiency of diimine oxidized from hydrazine hydrate or its derivatives is still not good enough. Herein, we report an in situ neocuproine–copper complex formation method. The redox potential of this complex enable it can serve as an ideal redox catalyst in the synthesis of diimine by oxidation of hydrazine hydrate, and we successfully applied this technique in the reduction of alkynes. This reduction method displays a broad functional group tolerance and substrate adaptability as well as the advantages of safety and high efficiency. Especially, nitro, benzyl, boc, and sulfur containing alkynes can be reduced to the corresponding alkanes directly, which provides a useful complementary method to traditional catalytic hydrogenation. Besides, we applied this method in the preparation of the Alzheimer’s disease drug CT-1812 and studied the mechanism.
- Chen, Guoliang,He, Xiaoyan,Huang, Gang,Lu, Xiuhong,Wang, Jincheng,Yang, Zhenjiao,Zhang, Yongsheng,Zhang, Zeng
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supporting information
p. 17696 - 17709
(2021/12/09)
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- FerriNaphth: A fluorescent chemodosimeter for redox active metal ions
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FerriNaphth, a fluorescent chemodosimeter for FeIII, has been prepared and characterized. The probe consists of a catechol ligand linked to a naphthalimide fluorophore by an aniline nitrogen linker. Upon exposure to FeIII, the aminocatechol of FerriNaphth is oxidized to the corresponding quinone, which in its imine-one tautomer, is hydrolyzed to liberate a fluorescent aminonaphthalimide derivative. The fluorescence behavior is consistent with oxidation being promoted by metal coordination.
- Jackson, Randy K.,Shi, Yu,Yao, Xudong,Burdette, Shawn C.
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p. 4155 - 4161
(2010/07/04)
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- FerriBRIGHT: A rationally designed fluorescent probe for redox active metals
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The novel catechol-BODIPY dyad, 8-(3,4-dihydroxyphenyl)-2,6- bis(ethoxycarbonyl)-1,3,5,7-tetramethyl-4,4-difluoro-4-bora-3a, 4a-diaza-s-indacene(FerriBRIGHT) was rationally designed with the aid of computational met hods. FerriBRIGHT could be prepared by standard one-pot synthesis of BODIPY fluorophores from 3,4-bis(benzyloxy)benzaldehyde (1) and 3,5-dimethyl-4-(ethoxycarbonyl)pyrrole (3); however, isolating the dipyrrin intermediate 8-[3,4-bis(benzyloxy)phenyl]-2,6-bis(ethoxycarbonyl)-1,3,5,7- tetramethyl-4,4-diaza-s-indacene (7) prior to reaction with excess BF 3·OEt2 led to marked improvements in the isolatedoverall yield of the desired compound. In addition to these improvement s in fluorophore synthesis, microwave-assisted palladium-catalyzed hydrogenolysis of benzyl ethers was used to reduce reaction times and catalyst loading in preparation of the desired compound. When FerriBRIGHT is exposed to excess FeCl3, CuCl2, [Co(NH3)5Cl]Cl 2, 2,3-dichloro-5,6-dicyanobenzoquinone, or ceric ammonium nitrate in methanol, a significant enhancement of fluorescence is observed. FerriBRIGHT-Q, the product resulting from the oxidation of the pendant catechol to the corresponding quinone, was found to bethe emissive species. FerriBRIGHT-Q was synthesized independently, isol ated, and fully characterized to allow for direct comparison with the spectroscopic data acquired in solution. Biologically relevant reactive oxygen species, such as H2O2, ?OH, 1O2, O2?-, and bleach (NaOCl), failed to cause any changes in the emission intensity of FerriBRIGHT. In accordance with the quantum mechanical calculations, the quantumyield of fluorescence for FerriBRIGHT (Φfl ' 0) and F erriBRIGHT-Q (Φfl = 0.026, λex/ λem = 490 nm/510 nm) suggests that photoinduced electron transfer between the catechol and the BODIPY dye is attenuated upon oxidation, which results in fluorescence enhancement. Binding studies of FerriBRIGHT with Ga(NO3)3, a redox-inactive analogue of Fe(III), provided conditional binding constant log β12′) 13.3 ± 0.2 for a [Ga(FerriBRIGHT)2]- complex. A 2.8-fold enhancement of fluorescence intensity upon addition of Ga(III) to FerriBRIGHT suggests the possibility of metal ion sensing with this new class of compounds.
- Kennedy, Daniel P.,Kormos, Chad M.,Burdette, Shawn C.
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p. 8578 - 8586
(2009/10/23)
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- First investigation at elevated pressures to confirm the exact nature of the gated electron-transfer systems: Volume profiles of the gated reduction reaction and nongated reverse oxidation reaction involving a [Cu(dmp) 2(solvent)]2+/[Cu(dmp)2]+ couple (dmp = 2,9-Dimethyl-1,10-phenanthroline)
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Redox reactions involving the [Cu(dmp)2]2+/+ couple (dmp = 2,9-dimethyl-1,10-phenanthroline) in acetonitrile were examined at elevated pressures up to 200 MPa. Activation volumes were determined as -8.8 and -6.3 cm3 mol-1 for the reduction cross-reaction by [Co(bipy)3]2+ (bipy = 2,2′-bipyridine) and for the oxidation cross-reaction by [Ni(tacn)2]3+ (tacn = 1,4,7-triazacyclononane), respectively. The activation volume for the hypothetical gated mode of the self-exchange reaction estimated from the reduction cross-reaction was -13.9 cm3 mol-1, indicating extensive electrostrictive rearrangement of solvent molecules around the Cu II complex during the change in the coordination geometry before the electron-transfer step. On the other hand, the activation volume for the self-exchange reaction estimated from the oxidation cross-reaction was -2.7 ± 1.5 cm3 mol-1. Although this value was within the range that can be interpreted by the concept of the ordinary concerted process, from theoretical considerations it was concluded that the reverse (oxidation) cross-reaction of the gated reduction reaction of the [Cu(dmp) 2(CH3CN)]2+/ [Cu(dmp)2]+ couple proceeds through the product excited state while the direct self-exchange reaction between [Cu(dmp)2(CH3CN)]2+ and [Cu(dmp)2]+ proceeds through an ordinary concerted process.
- Itoh, Sumitaka,Noda, Kyoko,Yamane, Ryouhei,Kishikawa, Nobuyuki,Takagi, Hideo D.
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p. 1419 - 1425
(2008/10/09)
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- Syntheses, structural analyses and redox kinetics of four-coordinate [CuL2]2+ and five-coordinate [CuL2(solvent)] 2+ complexes (L = 6,6′-dimethyl-2,2′-bipyridineor2,9- dimethyl-l,10-phenanthroline): Completely gated reduction reaction of [Cu(dmp)2]2+ in nitromethanet
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[Cu(2,9-dimethyl-1,10-phenanthroline)2]2+ and [Cu(6,6′-bipyridine)2]2+/+ complexes with no coordinated solvent molecule were synthesized and crystal structures were analyzed. Electrochemical measurement were carried out by using a BAS 100B/W electrochemical analyzer. The coordination geometry around the Cu(I) center was in the D2d symmetry while a D2 structure was observed for the four-coordinate Cu(II) complexes. The study revealed that the D2 structure of the Cu(I) complex retained in nitromethane, although a five-coordinate Thp species, was readily formed upon dissolution of the solid in acetonitrile.
- Itoh, Sumitaka,Kishikawa, Nobuyuki,Suzuki, Takayoshi,Takagi, Hideo D.
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p. 1066 - 1078
(2007/10/03)
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- Investigation of the Nitric Oxide Reduction of the Bis(2,9-Dimethyl-1,10-phenanthroline) Complex of Copper(II) and the Structure of [Cu(dmp)2(H2O)](CF3SO3)2
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The reaction between nitric oxide (NO) and the Cu(II) complex Cu(dmp)2(H2O)2+ (1, dmp = 2,9-dimethyl-1,10-phenanthroline) has been quantitatively examined in solution. In neutral or alkaline aqueous solutions or in methanol, 1 (E1/2 = 0.58 V vs NHE in water) is reduced by NO to give the corresponding cuprous species Cu(dmp)2+ plus RONO (R = H, CH3). The analogous reaction for Cu(phen)2(H2O)2+ (2. phen = 1,10-phenanthroline) (E12 = 0.18 V) is much slower and does not go to completion. In aqueous solutions, the conjugate base of 1 reacts with NO at a slower rate. At low pH, the cuprous complex Cu(phen)2+ reacts quantitatively with NO2- in the reverse reaction to give 2 plus NO, detected with a NO-sensitive electrode. The crystal structure of the triflate salt of 1 was determined, and the cupric ion was found to be 5-coordinate with two bidentate dmp ligands and one H2O ligand. The triflate salt of 1, [Cu(dmp)2(H2O)](CF3SO3)2, crystallizes in the orthorhombic system, space group Pbca, with a = 20.531(4) A, b = 21.342(8) A, c = 15.345(5) A, V = 6723(4) A, Z = 8, and R = 0.051 (Rw = 0.053). Kinetics studies for the NO reduction of 1 show the reaction to be first order in [NO], to be slower in basic media, and to be inhibited by higher concentrations of different buffers. This behavior is rationalized in terms of a mechanism where NO must form an inner sphere complex with Cu(II), but such binding at the fifth coordination site is inhibited by prior binding to OH- or to the conjugate base of the buffer.
- Tran, Dat,Skelton, Brian W.,White, Allan H.,Laverman, Leroy E.,Ford, Peter C.
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p. 2505 - 2511
(2008/10/08)
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- Kinetics of the bis(2,9-dimethyl-1,10-phenanthroline)copper(I/II) self-exchange reaction in solution
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The rate of the Cu(dmp)2+/2+ electron-transfer reaction has been measured by 1H NMR spectroscopy in the perdeuterated solvents water (with the chloride salts), acetonitrile, and acetone (with the CF3SO3- salts). The respective kinetic parameters kex298/kg mol-1 s-1, ΔH*/kJ mol-1, and ΔS*/J K-1 mol-1, at ionic strength I/mol kg-1, are as follows: for D2O, 2.0 × 105, 24, and -63, at 0.002; for CD3CN, 4.9 × 103, 29.6, and -75, at 0.1; for (CD3)2CO, 3.0 × 103, 29.2, and -80, at 0.1. For acetonitrile and acetone, respectively, variable-pressure studies gave ΔV* = -3.4 and -7.8 cm3 mol-1. No significant concentration dependences of these parameters were observed. With these data, the measured rate of the oxidation of RuII(CF3COCHCOCF3)3- by Cu(dmp)22+ in CH3CN can be satisfactorily accounted for, by using the Marcus cross relation. There is evidence that the CuII complex contains coordinated solvent in solution; with this qualification, the characteristics of the electron-transfer reactions conform to the Marcus outer-sphere adiabatic model.
- Doine, Hideo,Yano, Yoshiko,Swaddle, Thomas W.
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p. 2319 - 2322
(2008/10/08)
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- Kinetics of oxidation of cuprous complexes of substituted phenanthroline and 2,2′-bipyridyl by molecular oxygen and by hydrogen peroxide in aqueous solution
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The kinetics and the reaction mechanism of copper(I) complexes of 5-methyl-1,10-phenanthroline, 5-chloro-1,10-phenanthroline, 5-nitro-1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, and 2,2′-bipyridyl with oxygen and hydrogen peroxide have been investigated in aqueous solutions with use of the pulse radiolysis technique. The oxidation by O2 is second order in the copper(I) complex, while the oxidation by H2O2 is first order in the copper(I) complex. Both reactions are first order in oxidants. The kinetic results of the oxidation of copper(I) complexes by oxygen are interpreted by a mechanism that proceeds via a superoxide intermediate.
- Goldstein, Sara,Czapski, Gidon
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p. 1087 - 1092
(2008/10/08)
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- Electron-transfer reactions of copper(I) and copper(III) complexes
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The reactions of bis(2,9-dimethyl-1,10-phenanthroline)copper(I), Cu1(dmp)2+, and of bis(2,9-dimethyl-4,7-diphenyl-1,10-phenanthrolinedisulfonate)cuprate(I), CuI(dpmp)23-, with copper(III)-oligopeptide complexes are quite rapid with rate constants varying from 2 × 104 M-1 s-1 to 2.5 × 108 M-1 s-1, indicating that outer-sphere electron transfer occurs. The cross exchange rate constants, k12, for the reactions CuIII(peptide) + CuIL2→k12 CuII(peptide) + CuIIL2, where L is dmp or dpmp2-, are determined for a series of copper(III) peptides, where the E°12 values vary from -0.11 to +0.32 V. The values of k12 for the reduction of copper(III) by CuI(dmp)2+ exhibit a correlation with E°12 consistent with the Marcus theory. This is not the case for the reductions with CuI(dpmp)23-, which have unusual behavior in two regards. First, the observed first-order rate constants reach limiting values as the concentration of excess reductant increases, but limiting values are not observed if Cu(III) is used in excess. Second, the k12 rate constants (obtained under conditions where the rate depends on both the Cu(III) and the Cu(I) concentrations) approach a limiting value of 106 M-1 s-1 and are independent of E°12. Neither anomalous behavior is observed for the CuI(dmp)2+ reactions with Cu(III) complexes.
- Lappin, A. Graham,Youngblood, Michael P.,Margerum, Dale W.
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p. 407 - 413
(2008/10/08)
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