Intramolecular Electron Transfer Rate Research Articles

Intramolecular electron-transfer rates in ferrocene-derivatized glucose oxidase

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTIntramolecular electron-transfer rates in ferrocene-derivatized glucose oxidaseAntonella Badia, Rina Carlini, Arthur Fernandez, Fernando Battaglini, Susan R. Mikkelsen, and Ann M. EnglishCite this: J. Am. Chem. Soc. 1993, 115, 16, 7053–7060Publication Date (Print):August 1, 1993Publication History Published online1 May 2002Published inissue 1 August 1993https://doi.org/10.1021/ja00069a001RIGHTS & PERMISSIONSArticle Views824Altmetric-Citations117LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (875 KB) Get e-Alerts Get e-Alerts

Effects of ring tilting on rates of intramolecular electron transfer in mixed-valence 1',2',1''',2'''-tetraethyl-, 1',3',1''',3'''-tetraethyl-, and 1',2',4',1''',2''',4'''-hexaethylbiferrocenium triiodides

Relatively minor perturbations caused by Cp ring substituents in a series of mixed-valence biferrocenium cations have pronounced effects on the electronic structure and rate of intramolecular electron transfer. The X-ray structure of 1',2',1'',2'''-tetraethylbiferrocene has been determined at 298 K: C2/c, a=18.760(3) A, b=9.568(3) A, c=16.441 (3) A, β=130.494(13) o , Z=4, D calcd =1.42 g cm -1 , R f =0.038, and R wf =0.041

Dinuclear complexes of (2,2′-bipyridine)(2,2′:6′,2′'-terpyridine)-ruthenium(II) bonded through cyanide to pentaammineruthenium(II/III) groups

New dinuclear complexes, containing a Ru(trpy)(bpy)2+ moiety (bpy = 2,2′-bipyridine, trpy = 2,2′:6′,2′'-terpyridine) bonded through cyanide to Ru(NH3)inf5sup2+/3+groups have been prepared and characterized by spectroscopic and electrochemical techniques. The formation of cyanide bridges is evident from the i.r. and u.v.-vis. spectra by appearance of v(C≡N) shifts and changes in λmax with respect to the mononuclear parent complex [Ru(trpy)(bpy) (CN)]+. In the mixed-valence species RuinfbsupII—CN—RuinfasupIII(Rub = Ru bonded to bpy, Rua = Ru bonded to NH3), an intense metal-to-metal charge transfer transition is observed at λmax = 700 nm in MeCN, with Δovv1/2 = 3.6 × 103 cm−1. From these spectral data and the difference in redox potentials between both metallic centres (determined by c.v. to be ΔE1/2 = 1.19 V), a value of kth,r = 5 × 105 s-1 has been calculated for the rate of thermal intramolecular electron transfer of the reverse process: RuinasupII→ RuinbsupIII. This low value suggests an ‘inverted regime’. The complexes studied are thus interesting as models for the design of energy conversion schemes.

Intramolecular photoinduced electron transfer (PET) bond cleavage in some sulfonium salt derivatives. Effect of distance and thermodynamics on PET rate

AbstractThe rate of intramolecular photoinduced electron transfer (PET) between a naphthacene electron donor (D) and a sulfonium electron acceptor (A) was found to be dependent on the thermodynamics for PET and distance between D and A. The slopes of In kET vs through‐bond and through‐space distance plots was found to be −0·60 and −0·91 Å−1, respectively. The product distribution obtained from the photolysis of regioisomeric naphthacenyl sulfonium salt derivatives was found to be independent of distance. Photolysis of three regioisomeric naphthacenyl phenylmethyl‐p‐cyanobenzylsulfonium salts produced unsubstituted thiomethylphenylnaphthacene and mono‐, di‐ and tri‐p‐cyanobenzyl‐substituted thiomethylphenylnaphthacene. The appearance of the out‐of‐cage di‐ and trisubstituted photoproducts suggests that secondary photochemistry and intermolecular electron transfer bond‐cleavage reactions are occurring when the concentration of the sulfonium salt in acetonitrile is 10−2 and 10−3 M and the degree of conversion is high. The primary photoproduct is the mono‐substituted naphthacene derivative.

Preparation and intramolecular electron-transfer rate constant for the ruthenium-modified selenium-substituted [4Fe–4Se] high-potential protein from Chromatium vinosum and related studies

The Se-substituted [4Fe–4Se] form of the high-potential iron–sulfur protein from Chromatium vinosum(Mr≈9500, 85 amino acids) has been prepared and Ru-modified (68% yield) at the single histidine residue His 42. The purified product gives and Fe: Ru ratio close to 4:1 consistent with a single stoichiometric modification. The His 42 of the Ru-modified protein no longer reacts with O(CO2Et)2 and the sharp 1H NMR C2H resonance for His 42 at δ 8.38 is no longer present due to paramagnetic line broadening by the attached RuIII. The His 42 is bonded via Cys 43 to the active site, with an edge-to-edge distance close to 7.9 Å. Pulse-radiolysis reduction of the fully oxidised Fe4Se43+–RuIII protein with eaq– gives the metastable product Fe4Se3+–RuII. A second slower stage, corresponding to conversion of the Fe4Se43+–RuII to Fe4Se42+–RuIII is made up of intramolecular (1.30 s–1) and intermolecular (2.65 × 105 M–1 s–1) electron-transfer steps. The kintra step is of interest alongside the earlier value (18 s–1) for native [4Fe–4S] protein. The smaller reduction potential for the Fe4Se43+/2+(285 mV) as compared to Fe4S43+/2+(350 mV) couple is believed to be the major contributing factor to the slower intramolecular electron-transfer process. The Beratan–Onuchic pathways program has been used and indicates through-bond electron transfer from the Ru at His 42 to the cluster as the most favourable route. The rate constant at 25 °C (M–1 s–1) for the [Fe(CN)6]3– oxidation of the Fe4Se42+ protein has also been determined (4.5 × 103 M–1 s–1), and is less than that for native Fe4S42+ protein (2.0 × 103 M–1 s–1) at pH 7.0, /= 0.100 M (NaCl).

The effect of driving force on intramolecular electron transfer in proteins. Studies on single-site mutated azurins.

An intramolecular electron-transfer process has previously been shown to take place between the Cys3--Cys26 radical-ion (RSSR-) produced pulse radiolytically and the Cu(II) ion in the blue single-copper protein, azurin [Farver, O. & Pecht, I. (1989) Proc. Natl Acad. Sci. USA 86, 6868-6972]. To further investigate the nature of this long-range electron transfer (LRET) proceeding within the protein matrix, we have now investigated it in two azurins where amino acids have been substituted by single-site mutation of the wild-type Pseudomonas aeruginosa azurin. In one mutated protein, a methionine residue (Met44) that is proximal to the copper coordination sphere has been replaced by a positively charged lysyl residue ([M44K]azurin), while in the second mutant, another residue neighbouring the Cu-coordination site (His35) has been replaced by a glutamine ([H35Q]azurin). Though both these substitutions are not in the microenvironment separating the electron donor and acceptor, they were expected to affect the LRET rate because of their effect on the redox potential of the copper site and thus on the driving force of the reaction, as well as on the reorganization energies of the copper site. The rate of intramolecular electron transfer from RSSR- to Cu(II) in the wild-type P. aeruginosa azurin (delta G degrees = -68.9 kJ/mol) has previously been determined to be 44 +/- 7 s-1 at 298 K, pH 7.0. The [M44K]azurin mutant (delta G degrees = -75.3 kJ/mol) was now found to react considerably faster (k = 134 +/- 12 s-1 at 298 K, pH 7.0) while the [H35Q]azurin mutant (delta G degrees = -65.4 kJ/mol) exhibits, within experimental error, the same specific rate (k = 52 +/- 11 s-1, 298 K, pH 7.0) as that of the wild-type azurin. From the temperature dependence of these LRET rates the following activation parameters were calculated: delta H++ = 37.9 +/- 1.3 kJ/mol and 47.2 +/- 0.7 kJ/mol and delta S++ = -86.5 +/- 5.8 J/mol.K and -46.4 +/- 4.4 J/mol.K for [H35Q]azurin and [M44K]azurin, respectively. Using the Marcus relation for intramolecular electron transfer and the above parameters we have determined the reorganization energy, lambda and electronic coupling factor, beta. The calculated values fit very well with a through-bond LRET mechanism.

Charge separation in donor-chromophore-acceptor complexes: inverted region behavior in reverse electron transfer reactions

Time-resolved absorption studies which elucidate intramolecular electron transfer rates have been performed on a series of covalently linked Ru(bipyridine) 3 -donor-acceptor complexes. In these complexes the electron donor is a phenothiazine moiety linked to a bipyridin by a (-CH 2 -) 4 chain, and the electron acceptor is an N,N'-diquaternary-2,2'-bipyridinium moiety, linked to a bipyridine by a (-CH 2 -) 2 chain

Absence of dielectric relaxation effects on intramolecular electron transfer in porphyrin-quinone cyclophanes

We have measured photoinduced intramolecular electron transfer rates k et in two porphyrin-dichloroquinone cyclophanes varying the polarity, the temperature, and the dielectric relaxation time of the solvent. The reaction is most likely activationless or in the inverted region in all solvents. The adiabaticity parameter k = 4π V 2 eff/ khλ sτℓ for dynamic dielectric solvent control is estimated to cover the range 0.2 ⪕ k ⪕ 400. Nevertheless the rate k et was found to be almost independent of the solvent properties ( k et > 5 × 10 11 s −1) casting doubt on current ideas of dielectric relaxation effects on electron transfer.

Low activation barriers characterize intramolecular electron transfer in ascorbate oxidase.

Anaerobic reduction kinetics of the zucchini squash ascorbate oxidase (AO; L-ascorbate:oxygen oxidoreductase, EC 1.10.3.3) by pulse radiolytically produced CO2- radical ions were investigated. Changes in the absorption bands of type 1 [Cu(II)] (610 nm) and type 3 [Cu(II)] (330 nm) were monitored over a range of reactant concentrations, pH, and temperature. The direct bimolecular reduction of type 1 [Cu(II)] [(1.2 +/- 0.2) x 10(9) M-1.s-1] was followed by its subsequent reoxidation in three distinct phases, all found to be unimolecular processes with the respective specific rates of 201 +/- 8, 20 +/- 4, and 2.3 +/- 0.2 s-1 at pH 5.5 and 298 K. While at this pH no direct bimolecular reduction was resolved in the 330-nm band, at pH 7.0 such a direct process was observed [(6.5 +/- 1.2) x 10(8) M-1.s-1]. In the same slower time domains where type 1 [Cu(I)] reoxidation was monitored, reduction of type 3 [Cu(II)] was observed, which was also concentration independent and with identical rate constants and amplitudes commensurate with those of type 1 [Cu(II)] reoxidation. These results show that after electron uptake by type 1 [Cu(II)], its reoxidation takes place by intramolecular electron transfer to type 3 [Cu(II)]. The observed specific rates are similar to values reported for the limiting-rate constants of AO reduction by excess substrate, suggesting that internal electron transfer is the rate-determining step of AO activity. The temperature dependence of the intramolecular electron transfer rate constants was measured from 275 to 308 K at pH 5.5 and, from the Eyring plots, low activation enthalpies were calculated--namely, 9.1 +/- 1.1 and 6.8 +/- 1.0 kJ.mol-1 for the fastest and slowest phases, respectively. The activation entropies observed for these respective phases were -170 +/- 9 and -215 +/- 16 J.K-1.mol-1. The exceptionally low enthalpy barriers imply the involvement of highly optimized electron transfer pathways for internal electron transfer.

Electron tunneling in ruthenium-modified cytochromec

Distant Fe2+-Ru3+ electronic couplings have been extracted from intramolecular electron-transfer rates in Ru(2,2′-bipyridine)2(imidazole)(histidine-X)2+ (X = 33,39,62,72,79) derivatives of cytochromec. The rates are> 1 · 108 (79); 3.2(4) · 106 (39); 2.6(3) · 106 (33); 9.0(3) · 105 (72); 1.0(2) · 104 s−1 (62); the couplings increase according to 62 (0.006) < 72 (0.057) < 33 (0.097) < 39 (0.11) < 79 (> 0.6 cm−1). The rates (and the couplings) correlate with the lengths of σ-tunneling pathways comprised of covalent bonds, hydrogen bonds, and through-space jumps from the histidines to the heme group.

Electron-Tunneling Pathways in Cytochrome c

Distant Fe(2+)-Ru(3+) electronic couplings have been extracted from intramolecular electrontransfer rates in Ru(histidine(x)) (where X = 33, 39, 62, and 72) derivatives of cytochrome c. The couplings increase according to 62 (0.0060) < 72 (0.057) < 33 (0.097) < 39 (0.11 per wave numbers); however, this order is out of line with the histidine to heme edge-edge distances [62 (14.8) > 39 (12.3) > 33 (11.1) > 72 (8.4 angstroms)]. The rates (and the couplings) correlate with the lengths of sigma-tunneling pathways comprised of covalent bonds, hydrogen bonds, and through-space jumps from the histidines to the heme group. Space jumps greatly decrease couplings: One from Pro(71) to Met(80) extends the sigma-tunneling length of the His(72) pathway by roughly 10 covalent-bond units.

Subtle effects of solvate molecules on the rate of intramolecular electron transfer of mixed-valence complexes in the solid state

The microscopic nature of the valence-detrapping phase transition of [Fe 3 O(O 2 CCH 3 ) 6 (4-Me-py) 3 ](CHCl 3 ) (2) is studied. The constant-pressure heat capacity of a 16.3703-g sample of 2 in the 14-300 K range is presented. An apparently first-order phase transition with two C p peaks at 93.48 and 95.04 K was observed

Orbital symmetry effects on intramolecular charge recombination

Quantum yields and lifetimes were determined for charge transfer fluorescence accompanying the charge recombination, that follows photoinduced charge separation, in a series of four rigid D-bridge-A systems ( 1–4) each with overall molecular C s symmetry and an effective bridge length of eight sigma bonds. From these data the electronic coupling ( H cr) between the ground state and the charge separated state was calculated. In 2–4 charge recombination is “symmetry allowed” and for these systems H cr is consistently larger than for the “symmetry forbidden” charge recombination in 1. The results obtained indicate that such symmetry effects could modify the overall rate of intramolecular electron transfer by about one order of magnitude.

Pronounced effect of substituents on the intramolecular electron-transfer rates in mixed-valence biferrocenium triiodide complexes

Pronounced effect of substituents on the intramolecular electron-transfer rates in mixed-valence biferrocenium triiodide complexes

Single vs double bridging in inner-sphere electron transfer reactions

Stabilities of polynuclear complexes {[(en) 2Cr III(OH) 2] n M II} ( n+ 2)+ , where n = 1, 2; M II = Mn, Fe, Co, Ni, Cu, Zn, and kinetics of electron transfer between cis-[(en) 2Cr(OH 2) 2] 3+ and Cr 2+ in aqueous solution are reported. The data for this and for the analogous cobalt(III) systems are used to calculate upper limits for the rates of intramolecular electron transfer in the double-bridged binuclear mixed-valence ions [(en) 2M III(OH) 2Cr II(aq)] 3+. In at least one of the two cases, namely M III = Cr III, the rate is less than that in the single-bridged ion [(H 2O)(en) 2M III(OH)Cr II(aq)] 3+.

Photoinduced electron transfer in ruthenium-modified cytochrome c

Abstract

The effect of bending modes on the intramolecular electron-transfer rates of mixed-valence 1′,3′,1‴,3‴-tetraethyl- and 1′,2′,1‴,2‴-tetraethyl-biferrocenium triiodides

The results of an X-ray structure determination of 1′,3′,1‴,3‴-tetraethylbiferrocenium triiodide, the effects of changing the relative positions of ethyl substituents from 1′,3′,1‴,3‴ to 1′,2′,1‴,2‴ on the intramolecular electron-transfer rates of biferrocenium salts in the solid state, and a theoretical explanation of the influence of steric factors on the electron-transfer rates are reported.

Extreme environmental sensitivity of the rate of intramolecular electron transfer in mixed-valence 1',1'''-dibenzylbiferrocenium triiodide

The extreme sensitivity of the rate of intramolecular electron transfer for the mixed-valence 1',1'-dibenzylbiferrocenium cation to different environments is explored. Two different crystalline morphologies of 1',1'-dibenzylbiferronium triiodide (1) could be identified by their different crystal habits (needle and plate-like crystals). They are structurally characterized by single-crystal and powder X-ray diffraction techniques. The single-crystal X-ray structure of a parallelepiped (needle) crystal of 1 at 298 K shows that this polymorph crystallizes in the triclinic space group Pi. The unit cell parameters are a = 9.900 (1) A, b = 9.962 (1) A, c = 10.193 (2) A, CY = 112.97 (2)O, @ = 114.50 (I)O, and y = 97.80 (1)O with Z = 1. The structure is also reported for the same crystal at 135 K. An analysis of the full sphere of data again indicates Pi as the appropriate space group with unit cell constants a = 9.782 (2) A, b = 9.930 (1) A, c = 10.108 (2) A, CY = 113.08 (2)O, @ = 114.08 and y = 98.06 (1)' with 2 = 1. Refinements were carried out with 2990 (6a) and 3315 (6a) observed reflections at 298 and 135 K, respectively, to give R = 0.026 and R, = 0.037 at 298 K and R = 0.025 and R, = 0.038 at 135 K. Both the mixed-valence l', 1'-dibenzylbiferrocenium cation and triiodide anion are centrosymmetric at both temperatures. The two crystallographically equivalent metallocene moieties of the cation have dimensions intermediate between those of Fe and Fell' metallocenes. The packing of 1 consists of weakly interacting 1',1'-dibenzylbiferronium cations forming chains which are surrounded by and separated from other similar chains by the triiodide anions. The 296 K single-crystal X-ray structure of the plate-like crystals of complex 1 show that this pol morph crystallizes in the monoclinic space group P2,/n. The unit cell parameters are a = 22.286 (9) A, b = 19.413 (10) 1, c = 22.840 (5) A, and @ = 98.55 (3)O with Z = 12. Refinement was carried out with 4486 (6a) observed reflections to give R = 0.089 and R, = 0.131. There are three different l',l'- dibenzylbiferrocenium cations and three different Ip- anions in the asymmetric unit. There is not crystallographically imposed symmetry for any of the cations or anions. The temperature dependencies of the S7Fe Mossbauer spectra of the Pi and P2,/n polymorphs of complex 1 differ widely. A sample of needle crystallites has a Mossbauer spectrum characteristic of a valence detrapped mixed-valence species down to a temperature of 25 K. On the other hand, a sample of the P2,/n plate-like crystals exhibits a Mhsbauer spectrum characteristic of a valence-trapped species which remains trapped even at 300 K. It was surprising to find that mild grinding of the needle crystallites produces a valence-trapped Mossbauer signal in addition to the valence detrapped signal. Appreciable amounts of the trapped species persist for the ground Pi needles even up to 300 K. At 7 K, the EPR spectrum of a recrystallized microcrystalline sample of 1 consists of the superposition of three signals: two axial powder patterns each with its own gH and g, signals and one isotropic g = 2.16 signal. The g tensor anisotropies of the two axial signals are Ag = 1.29 and 0.76. The axial pattern with Ag = 0.76 is assigned to the Pi form, whereas, the Ag = 1.29 pattern is assigned to the P2,/n form. The two axial EPR patterns broaden with increasing temperature and the isotropic g = 2 signal gains in relative intensity, so that by 150 K it is the only signal observed. This Lorentzian g = 2.16 signal persists to high temperatures. In contrast, the variable-temperature EPR spectrum of an ethanol glass of 1 shows a single axial signal (Ag = 1.82) which broadens with increasing temperature and becomes unobservable above -77 K. The EPR properties of mixed-valence l', 1'-dibenzylbiferrocenium cation are modified by the local environments. Not only does the EPR signal change from the Pi to the P2Jn crystal forms but also there is even a sample history dependence of the g values for the two crystal forms. The g = 2.16 signal is the result of intermolecular interactions.

Micromodulation of electron-transfer rates in mixed-valence 1′,1″′-dibenzylbiferrocenium cations

X-Ray structures of 1′,1′″-disubstituted biferrocenium triiodide salts have been studied and the dramatic effects of substituents on the intramolecular electron-transfer rates are described.

Dependence of electron transfer rates on donor-acceptor angle in bis-porphyrin adducts

We have prepared a series of bis-porphyrin molecules in which the angle between the donor and acceptor porphyrins is systematically varied. In these molecules, the intramolecular electron transfer rate varies by over 1 order of magnitude as the angle changes. This variance is anticipated by symmetry arguments which focus on the nodal properties of the molecules