Influence of Amino Acid Side Chains on Long-Distance Electron Transfer in Peptides: Electron Hopping via “Stepping Stones” (original) (raw)
Related papers
ChemInform Abstract: Electron Transfer in Peptides
ChemInform, 2015
In this review, we discuss the factors that influence electron transfer in peptides. We summarize experimental results from solution and surface studies and highlight the ongoing debate on the mechanistic aspects of this fundamental reaction. Here, we provide a balanced approach that remains unbiased and does not favor one mechanistic view over another. Support for a putative hopping mechanism in which an electron transfers in a stepwise manner is contrasted with experimental results that support electron tunneling or even some form of ballistic transfer or a pathway transfer for an electron between donor and acceptor sites. In some cases, experimental evidence suggests that a change in the electron transfer mechanism occurs as a result of donoracceptor separation. However, this common understanding of the switch between tunneling and hopping as a function of chain length is not sufficient for explaining electron transfer in peptides. Apart from chain length, several other factors such as the extent of the secondary structure, backbone conformation, dipole orientation, the presence of special amino acids, hydrogen bonding, and the dynamic properties of a peptide also influence the rate and mode of electron transfer in peptides. Electron transfer plays a key role in physical, chemical and biological systems, so its control is a fundamental task in bioelectrochemical systems, the design of peptide based sensors and molecular junctions. Therefore, this topic is at the heart of a number of biological and technological processes and thus remains of vital interest.
Development of a Model System for the Study of Long Distance Electron Transfer in Peptides
Advanced Synthesis & Catalysis, 2008
We have designed and synthesized a peptide model in which stepwise electron transfer (ET) through amino acid side chains could be observed. An injection system, which generates an electron hole upon laser irradiation, was connected directly to the aromatic side chain of a modified C-terminal amino acid. This electron acceptor could be observed by transient absorption spectroscopy. The N-terminal amino acid tyrosine acts as an electron donor, giving a different signal in the transient absorption spectrum. Additional non-natural oxidizable aromatic amino acids were synthesized as spectroscopic sensors to detect oxidized amino acid side chains as chemical intermediates in long range ET.
Electron transfer in peptides and proteins
Chemical Society Reviews, 2009
Proteins and peptides use their amino acids as medium for electron-transfer reactions that occur either in single-step superexchange or in multistep hopping processes. Whereas the rate of the single-step electron transfer dramatically decreases with the distance, a hopping process is less distance dependent. Electron hopping is possible if amino acids carry oxidizable side chains, like the phenol group in tyrosine. These side chains become intermediate charge carriers. Because of the weak distance dependency of hopping processes, fast electron transfer over very long distances occurs in multistep reactions, as in the enzyme ribonucleotide reductase.
Journal of the American Chemical Society, 2003
The charge-transfer transition energies and the electronic-coupling matrix element, |HDA|, for electron transfer from aminopyridine (ap) to the 4-carbonyl-2,2′-bipyridine (cbpy) in cbpy-(gly)n-ap (gly ) glycine, n ) 0-6) molecules were calculated using the Zerner's INDO/S, together with the Cave and Newton methods. The oligopeptide linkages used were those of the idealized protein secondary structures, the R-helix, 310-helix, -strand, and polyproline I-and II-helices. The charge-transfer transition energies are influenced by the magnitude and direction of the dipole generated by the peptide secondary structure. The electronic coupling |H DA| between (cbpy) and (ap) is also dependent on the nature of the secondary structure of the peptide. A plot of 2‚ln|HDA| versus the charge-transfer distance (assumed to be the dipole moment change between the ground state and the charge-transfer states) showed that the polyproline II structure is a more efficient bridge for long-distance electron-transfer reactions ( ) 0.7 Å -1 ) than the other secondary structures ( ≈ 1.3 Å -1 ). Similar calculations on charged dipeptide derivatives, [CH3CONHCH2CONHCH3] +/-, showed that peptide-peptide interaction is more dependent on conformation in the cationic than in the anionic dipeptides. The R-helix and polyproline II-helix both have large peptide-peptide interactions (|HDA| > 800 cm -1 ) which arise from the angular dependence of their π-orbitals. Such an interaction is much weaker than in the -strand peptides. These combined results were found to be consistent with electrontransfer rates experimentally observed across short peptide bridges in polyproline II (n ) 1-3). These results can also account for directional electron transfer observed in an R-helical structure (different ET rates versus the direction of the molecular dipole).
Electron Transfer in Peptides with Cysteine and Methionine as Relay Amino Acids
Angewandte Chemie International Edition, 2009
Recently, we developed a peptide system 1 which allows the detection of a multistep hopping process in electron-transfer (ET) reactions through peptides. [1] As the rate for a singlestep ET reaction between an electron donor (D) and an electron acceptor (A) decreases exponentially with the distance, [2] long-range ET is fast only if a multistep hopping process occurs. According to this mechanism, the overall distance between D and A is split into shorter and, therefore, faster ET steps. Relay amino acids act as stepping stones for these multistep reactions by acting as intermediate charge carriers. [1] Until now, only aromatic amino acids such as tyrosine and tryptophan have been discussed as relay amino acids. We now show that the aliphatic amino acids cysteine and methionine can also function as relay amino acids in ET through peptides.
Journal of Photochemistry and Photobiology A-chemistry, 1994
Intramolecular electron-transfer studies across a series of peptides ranging from dipeptides to longer peptides with secondary structure (such as polyproline II and a 17-amino acid α helix) have been carried out. Metal ammine and bipyridine complexes have been used as donors and acceptors in these studies. These studies show that the rate of electron transfer is sensitive to the peptide structure and conformation, even for dipeptide bridges. For peptides with secondary structure, the connectivity of the donor and acceptor to the peptide is also important for the observation of long-range electron transfer. For example, for (bpy)2RuIIL(Pro)n-apyRuIII(NH3)5 (n = 9) (bpy2,2′ bipyridine, L4-carboxy-4′-methyl-2,2′-bipyridine, apy-4-aminopyridine), an electron transfer rate 2 × 104 s−1 was observed, while intramolecular electron transfer could not be observed for the α helix bridge in (bpy)2RuIIL[α-helical peptide]-(His)2RuIII(NH3)4 (α-helical peptide Ala-Glu-(Ala)3Lys-Glu(Ala) 3Lys-His(Ala)3His-Ala).Comparative intramolecular electron-transfer experiments were also conducted with two cytochrome c derivatives: one modified at His 33 by [-Ru(NH3)4isn] and one modified at Met 65 by [-Fe(CN)5]. Although the His 33 and Met 65 sites are located at similar distances from the heme, and the two metal complexes possess similar reorganization energies and driving force, different rates of electron transfer varying by about 1000 were observed for the electron transfer from the heme to the metal complex.The experiments presented show that the shortest through-space distance is not always the most important determinent of the rate of electron transfer, and other factors such as the peptide structure and conformation and the connectivity of the donor and acceptor to the peptide bridge are very important.
The Search for Relay Stations. Long-distance Electron Transfer in Peptides
CHIMIA International Journal for Chemistry, 2013
Nature uses peptide aggregates as soft materials for electron transfer over long distances. These reactions occur in a multistep hopping reaction with various functional groups as relay stations that are located in the side chain and in the backbone of the peptides.
ChemElectroChem, 2020
Understanding the distance dependence of electron transfer (ET) through peptides is a topic of continuous interest. We studied a series of donor-bridge-acceptor (D-B-A) systems. The peptide bridges (B) were oligomers of the strongly helicogenic αaminoisobutyric acid, and were prepared in different lengths to form 0, 1, 2, 3, 4, or 5 intramolecular H-bonds. D was a phthalimide group and A was a perester. The study was carried out in DMF, acetonitrile, and dichloromethane. Cyclic voltammetry (CV) and convolution analysis of the model donors and acceptor yielded the relevant thermodynamic information, whereas homogenous redox catalysis provided information on the competitive intermolecular ET. CV analysis of the D-B-A systems showed that, independently of the solvent used, the intramolecular ET occurs by a superexchange mechanism strongly affected by intramolecular H-bonds and the extend of conjugation of the peptide bridge with D and A.