Electrocatalytic Oxidation of Tyrosine by Parallel Rate-Limiting Proton Transfer and Multisite Electron−Proton Transfer

Fecenko, Christine J.; Meyer, Thomas J.; Thorp, H. Holden

doi:10.1021/ja1015266

Cited by 12 publications

(34 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Similar investigations have been carried out with the proton acceptor dispersed in nonaqueous (17,18) or aqueous (19,20) solutions.…”

mentioning

confidence: 66%

“…We used the clever implementation of the method proposed in ref. 41, which uses an indium-tin-oxide electrode, prepared as described in SI Appendix, that slows down the direct oxidation of phenol at the electrode and makes the catalytic enhancement of the current more apparent. The value found for the rate constant, k þ ¼ 3 × 10 5 M −1 s −1 , confirms the photochemical result, which may, however, be considered as more accurate in view of the remaining overlap between catalytic current and direct oxidation current in the redox catalytic technique.…”

Section: Resultsmentioning

confidence: 99%

See 1 more Smart Citation

Intrinsic reactivity and driving force dependence in concerted proton–electron transfers to water illustrated by phenol oxidation

Bonin

Costentin

Louault

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

109

View full text Add to dashboard Cite

Three experimental techniques, laser flash photolysis, redox catalysis, and stopped-flow, were used to investigate the variation of the oxidation rate constant of phenol in neat water with the driving force offered by a series of electron acceptors. Taking into account a result previously obtained with a low-driving force electron acceptor thus allowed scanning more than half an electronvolt driving force range. Variation of the rate constant with pH showed the transition between a direct phenol oxidation reaction at low pH, where the rate constant does not vary with pH, and a stepwise reaction involving the prior deprotonation of phenol by OH − , characterized by a unity-slope variation. Analyses of the direct oxidation kinetics, based on its variation with the driving force and on the determination of H/D isotope effects, ruled out a stepwise mechanism in which electron transfer is followed by the deprotonation of the initial cation radical at the benefit of a pathway in which proton and electron are transferred concertedly. Derivation of the characteristics of counterdiffusion in termolecular reactions allowed showing that the concerted process is under activation control. It is characterized by a remarkably small reorganization energy, in line with the electrochemical counterpart of the reaction, underpinning the very peculiar behavior of water as proton acceptor when it is used as the solvent.photochemistry | proton-coupled electron transfer | water as proton acceptor

show abstract

“…Similar investigations have been carried out with the proton acceptor dispersed in nonaqueous (17,18) or aqueous (19,20) solutions.…”

mentioning

confidence: 66%

Section: Resultsmentioning

confidence: 99%

Intrinsic reactivity and driving force dependence in concerted proton–electron transfers to water illustrated by phenol oxidation

Bonin

Costentin

Louault

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

109

View full text Add to dashboard Cite

show abstract

“…An example is shown in Eq. 6 with HPO 4 2− as the proton acceptor base (20,21 The appearance of a base-dependent pathway in water oxidation suggests a similar microscopic origin with O-atom transfer from ½Ru V ðMebimpyÞðbpyÞðOÞ 3þ to H 2 O accompanied by proton transfer to the added base, Eq. 7.…”

Section: Discussionmentioning

confidence: 95%

“…3 and the rate constants in Table 1 Table 1 also illustrate that k B increases with the proton acceptor ability of the base (ΔG o0 ¼ −RTpK a ). A related effect has been documented for electron-proton transfer oxidation of tyrosine arising from the effect of enhanced basicity on ΔG o0 for the concerted electron-proton transfer step (20,21).…”

Section: ∕2mentioning

confidence: 96%

Concerted O atom–proton transfer in the O—O bond forming step in water oxidation

Chen

Concepcion

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

311

384

View full text Add to dashboard Cite

As the terminal step in photosystem II, and a potential half-reaction for artificial photosynthesis, water oxidation (2H 2 O → O 2 þ 4e − þ 4H þ ) is key, but it imposes a significant mechanistic challenge with requirements for both 4e − ∕4H þ loss and O-O bond formation. Significant progress in water oxidation catalysis has been achieved recently by use of single-site Ru metal complex catalysts such as ½RuðMebimpyÞðbpyÞðOH 2 Þ 2þ [Mebimpy ¼ 2,6-bisð1-methylbenzimidazol-2-ylÞpyridine; bpy ¼ 2,2 0 -bipyridine]. When oxidized from Ru II -OH 2 2þ to Ru V ¼ O 3þ , these complexes undergo O-O bond formation by O-atom attack on a H 2 O molecule, which is often the rate-limiting step. Microscopic details of O-O bond formation have been explored by quantum mechanical/molecular mechanical (QM/MM) simulations the results of which provide detailed insight into mechanism and a strategy for enhancing catalytic rates. It utilizes added bases as proton acceptors and concerted atom-proton transfer (APT) with O-atom transfer to the O atom of a water molecule in concert with proton transfer to the base (B). Base catalyzed APT reactivity in water oxidation is observed both in solution and on the surfaces of oxide electrodes derivatized by attached phosphonated metal complex catalysts. These results have important implications for catalytic, electrocatalytic, and photoelectrocatalytic water oxidation.water split | O-O coupling | base effect | isotope effect I n natural photosynthesis, and in many schemes for artificial photosynthesis, water oxidation (is a key reaction with requirements for both 4e − ∕4H þ loss and O -O bond formation. Significant progress in water oxidation catalysis has been achieved recently by using single-site molecular catalysts (1-8). This includes elucidation of a mechanism in Ce (IV) catalyzed water oxidation by ½RuðtpyÞðbpmÞðOH 2 Þ 2þ and ½RuðtpyÞðbpzÞðOH 2 Þ 2þ (tpy ¼ 2; 2 0 ∶6 0 ; 2 00 -terpyridine; bpm ¼ 2; 2 0 -bipyrimidine; bpz ¼ 2; 2 0 -bipyrazine), Scheme 1 (1). Although undergoing multiple turnovers unchanged, these catalysts are relatively slow with O-O bond formation, often the rate-limiting step. In Scheme 1, O-atom transfer from ½Ru V ðtpyÞðbpmÞðOÞ 3þ to H 2 O is rate limiting and occurs with kð0.1 M HNO 3 ; 25°CÞ ¼ 8.9 × 10 −3 s −1 (5). To put rate into perspective, in a practical solar energy conversion scheme, a turnover rate on the millisecond or submillisecond time scale is required to match or exceed the rate of solar insolation. Achieving rates of this magnitude poses a considerable challenge (9).A useful strategy for achieving faster rates in metal complex catalysts exists based on an interplay between mechanism and systematic synthetic modifications. Ligand variations can be used to modify redox potentials, increase driving force, and decrease barriers (6). Mechanistic insight can uncover previously undescribed reaction pathways. We report here the use of a previously unidentified pathway to achieve greatly enhanced rates of electrocatalytic water oxidation for the catalyst, ½RuðMebim...

show abstract

“…Thorp and Meyer found that the increase of such catalyzed current is proportional to the concentration of phosphate buffer, from which two mechanisms were proposed: electron and proton transfer (EPT) or proton transfer followed by electron transfer (PT-ET) [49,50]. As depicted in Scheme 2D, the formation of ArOH-OP(OH)-O 2 2À initiates two different pathways: electrons and protons were retained jointly (EPT, left) or progressively (PT-ET, right), indicating the possibility of multi-site electroproton transfer [102].…”

Section: Dppz]mentioning

confidence: 99%

Electrocatalytic oxidation of tyrosines shows signal enhancement in label-free protein biosensors

Wei

Famouri

Guo

2012

TrAC Trends in Analytical Chemistry

View full text Add to dashboard Cite

Label-free electrochemical (EC) protein biosensors that derive electrical signal from redox-active amino acid (AA) residues can avoid disruption of delicate protein structures, and thus provide a great opportunity to reveal valid information about protein functions. However, the challenge is that such a signal is usually very limited due to the sluggish EC reaction of free AAs on most common electrodes and slow electron-transfer rates from the deeply-buried AA residues in a protein to the electrode. Signal enhancement therefore becomes crucial. We first survey recent progress in this area.We present a signal-enhancing system that relies on the electrocatalytic oxidation of tyrosine mediated by osmium bipyridine or phenoxazine complexes. We describe several applications of label-free protein EC biosensors based on this detection principle for the analysis of protein functions, including the monitoring of protein-conformation change, study of ligand/protein binding, and detection of protein oxidative damage and protein phosphorylation.We describe related works on protein-function analysis using other signal-enhancing methods. The results suggest that labelfree EC protein biosensors are suitable for the rapid survey of protein functions due to their fast response, ease of integration, cost effectiveness and convenience. Proof-of-concept work on the application of our system is paving the way for bio-analytical detections and protein-function analysis in future work. ª

show abstract

Electrocatalytic Oxidation of Tyrosine by Parallel Rate-Limiting Proton Transfer and Multisite Electron−Proton Transfer

Abstract: We report here corrected values for k -1 for back proton transfer in the mechanism in Scheme 1. The initial values did not include the total concentration of tyrosine in the calculated rate constants. We also report a corrected value for k red . The corrected Table 1 is given here.

Cited by 12 publications

References 0 publications

Intrinsic reactivity and driving force dependence in concerted proton–electron transfers to water illustrated by phenol oxidation

Intrinsic reactivity and driving force dependence in concerted proton–electron transfers to water illustrated by phenol oxidation

Concerted O atom–proton transfer in the O—O bond forming step in water oxidation

Electrocatalytic oxidation of tyrosines shows signal enhancement in label-free protein biosensors

Contact Info

Product

Resources

About