Electron Transfer In Peptides Research Articles

Formation of Silver Nanoparticles by Electron Transfer in Peptides and c-Cytochromes.

The reduction of Ag+ ions to Ag0 atoms is a highly endergonic reaction step, only the aggregation to Agn clusters leads to an exergonic process. These elementary chemical reactions play a decisive role if Ag nanoparticles (AgNPs) are generated by electron transfer (ET) reactions to Ag+ ions. We studied the formation of AgNPs in peptides by photoinduced ET, and in c-cytochromes by ET from their Fe2+ /hemes. Our earlier photoinduced experiments in peptides had demonstrated that histidine prevents AgNP formation. We have now observed that AgNPs can be easily synthesized with less-efficient Ag+ -binding amino acids, and the rate increases in the order lysine<asparagine<aspartate<serine. The ability of Fe2+ /hemes of c-cytochromes to reduce Ag+ to AgNPs was studied in an enzymatic experiment and with living bacteria Geobacter sulfurreducens (Gs).

Mechanically Controlled Electron Transfer in a Single-Polypeptide Transistor

Proteins are of interest in nano-bio electronic devices due to their versatile structures, exquisite functionality and specificity. However, quantum transport measurements produce conflicting results due to technical limitations whereby it is difficult to precisely determine molecular orientation, the nature of the moieties, the presence of the surroundings and the temperature; in such circumstances a better understanding of the protein electron transfer (ET) pathway and the mechanism remains a considerable challenge. Here, we report an approach to mechanically drive polypeptide flip-flop motion to achieve a logic gate with ON and OFF states during protein ET. We have calculated the transmission spectra of the peptide-based molecular junctions and observed the hallmarks of electrical current and conductance. The results indicate that peptide ET follows an NC asymmetric process and depends on the amino acid chirality and α-helical handedness. Electron transmission decreases as the number of water molecules increases, and the ET efficiency and its pathway depend on the type of water-bridged H-bonds. Our results provide a rational mechanism for peptide ET and new perspectives on polypeptides as potential candidates in logic nano devices.

Peptides as Bio-inspired Molecular Electronic Materials.

Understanding the electronic properties of single peptides is not only of fundamental importance to biology, but it is also pivotal to the realization of bio-inspired molecular electronic materials. Natural proteins have evolved to promote electron transfer in many crucial biological processes. However, their complex conformational nature inhibits a thorough investigation, so in order to study electron transfer in proteins, simple peptide models containing redox active moieties present as ideal candidates. Here we highlight the importance of secondary structure characteristic to proteins/peptides, and its relevance to electron transfer. The proposed mechanisms responsible for such transfer are discussed, as are details of the electrochemical techniques used to investigate their electronic properties. Several factors that have been shown to influence electron transfer in peptides are also considered. Finally, a comprehensive experimental and theoretical study demonstrates that the electron transfer kinetics of peptides can be successfully fine tuned through manipulation of chemical composition and backbone rigidity. The methods used to characterize the conformation of all peptides synthesized throughout the study are outlined, along with the various approaches used to further constrain the peptides into their geometric conformations. The aforementioned sheds light on the potential of peptides to one day play an important role in the fledgling field of molecular electronics.

ChemInform Abstract: Electron Transfer in Peptides

AbstractReview: 76 refs.

Frontispiece: Electron Transfer in Peptides: On the Formation of Silver Nanoparticles

Frontispiece: Electron Transfer in Peptides: On the Formation of Silver Nanoparticles

Electron transfer in peptides: on the formation of silver nanoparticles.

Some microorganisms perform anaerobic mineral respiration by reducing metal ions to metal nanoparticles, using peptide aggregates as medium for electron transfer (ET). Such a reaction type is investigated here with model peptides and silver as the metal. Surprisingly, Ag(+) ions bound by peptides with histidine as the Ag(+)-binding amino acid and tyrosine as photoinducible electron donor cannot be reduced to Ag nanoparticles (AgNPs) under ET conditions because the peptide prevents the aggregation of Ag atoms to form AgNPs. Only in the presence of chloride ions, which generate AgCl microcrystals in the peptide matrix, does the synthesis of AgNPs occur. The reaction starts with the formation of 100 nm Ag@AgCl/peptide nanocomposites which are cleaved into 15 nm AgNPs. This defined transformation from large nanoparticles into small ones is in contrast to the usually observed Ostwald ripening processes and can be followed in detail by studying time-resolved UV/Vis spectra which exhibit an isosbestic point.

Electron transfer in peptides.

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 donor-acceptor 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.

Unraveling the interplay of backbone rigidity and electron rich side-chains on electron transfer in peptides: the realization of tunable molecular wires.

Electrochemical studies are reported on a series of peptides constrained into either a 310-helix (1–6) or β-strand (7–9) conformation, with variable numbers of electron rich alkene containing side chains. Peptides (1 and 2) and (7 and 8) are further constrained into these geometries with a suitable side chain tether introduced by ring closing metathesis (RCM). Peptides 1, 4 and 5, each containing a single alkene side chain reveal a direct link between backbone rigidity and electron transfer, in isolation from any effects due to the electronic properties of the electron rich side-chains. Further studies on the linear peptides 3–6 confirm the ability of the alkene to facilitate electron transfer through the peptide. A comparison of the electrochemical data for the unsaturated tethered peptides (1 and 7) and saturated tethered peptides (2 and 8) reveals an interplay between backbone rigidity and effects arising from the electron rich alkene side-chains on electron transfer. Theoretical calculations on β-strand models analogous to 7, 8 and 9 provide further insights into the relative roles of backbone rigidity and electron rich side-chains on intramolecular electron transfer. Furthermore, electron population analysis confirms the role of the alkene as a “stepping stone” for electron transfer. These findings provide a new approach for fine-tuning the electronic properties of peptides by controlling backbone rigidity, and through the inclusion of electron rich side-chains. This allows for manipulation of energy barriers and hence conductance in peptides, a crucial step in the design and fabrication of molecular-based electronic devices.

The Search for Relay Stations. Long-distance Electron Transfer in Peptides

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.

ChemInform Abstract: The Influence of Secondary Structure on Electron Transfer in Peptides

AbstractReview: 22 refs.

The Influence of Secondary Structure on Electron Transfer in Peptides

A series of synthetic peptides containing 0–5 α-aminoisobutyric acid (Aib) residues and a C-terminal redox-active ferrocene was synthesised and their conformations defined by NMR and circular dichroism. Each peptide was separately attached to an electrode for subsequent electrochemical analysis in order to investigate the effect of peptide chain length (distance dependence) and secondary structure on the mechanism of intramolecular electron transfer. While the shorter peptides (0–2 residues) do not adopt a well defined secondary structure, the longer peptides (3–5 residues) adopt a helical conformation, with associated intramolecular hydrogen bonding. The electrochemical results on these peptides clearly revealed a transition in the mechanism of intramolecular electron transfer on transitioning from the ill-defined shorter peptides to the longer helical peptides. The helical structures undergo electron transfer via a hopping mechanism, while the shorter ill-defined structures proceeded via an electron superexchange mechanism. Computational studies on two β-peptides PCB-(β3Val-β3Ala-β3Leu)n–NHC(CH3)2OOtBu (n = 1 and 2; PCB = p-cyanobenzamide) were consistent with these observations, where the n = 2 peptide adopts a helical conformation and the n = 1 peptide an ill-defined structure. These combined studies suggest that the mechanism of electron transfer is defined by the extent of secondary structure, rather than merely chain length as is commonly accepted.

Electron Transfer in Peptides: The Influence of Charged Amino Acids

Charging off: The ammonium group in the peptide shown leads to a tenfold increase of the electron-transfer rate compared to that in a fully protected system. This is explained by Coulomb's law and the Marcus theory. Detailed facts of importance to specialist readers are published as ”Supporting Information”. Such documents are peer-reviewed, but not copy-edited or typeset. They are made available as submitted by the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

ChemInform Abstract: Electron Transfer in Peptides and Proteins

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Electron Transfer in Peptides with Cysteine and Methionine as Relay Amino Acids

Caught on the hop: In multistep electron transfer (ET) reactions through peptides, aliphatic amino acids can also act as relay stations. With cysteine, the reaction occurs as a proton-coupled electron transfer (PCET) with water used as a mediator for the proton transfer (see picture).

Electron transfer in peptides and proteins

Electron transfer (ET) processes in proteins drive the energy conversion processes in cells and are also involved in metabolic catalysis. In this tutorial review, the models explaining ET through peptides and proteins are discussed and the biological relevance of ET is elucidated.

Solvent Reorganization Energy of Intramolecular Electron Transfer in Peptides Involving Tryptophan and Tyrosine

Intramolecular electron transfer from tyrosine to tryptophan has been investigated by ab initio calculation associated with a proper consideration of solvent effect by continuum model. The solvent reorganization energy is estimated to be 87.36 kJ/mol for the ET in Trp-Pro-Tyr system and 105.80 kJ/mol for Trp-(Pro)2-Tyr.

Electron transfer in peptides and proteins

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.

Development of a Model System for the Study of Long Distance Electron Transfer in Peptides

AbstractWe 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.

Concepts and models in bioinorganic chemistry

Foreword. Preface. List of Contributors. Abbreviations. 1 The Biodistribution of Metal Ions (Robert J. P. Williams). 1.1 Introduction. 1.2 Rates of Exchange. 1.3 The Limitations of Water as a Solvent. 1.4 Equilibrium: Values of Binding Constants. 1.5 Quantitative Metal Ion Equilibria: Donor Strength. 1.6 The Effect of Size and Charge of Metal Ions. 1.7 The Effect of Electron Affi nity. 1.8 Control over Ligand Concentration. 1.9 The Compartments of Organisms. 1.10 Transport. 1.11 The Irreversible Binding of Fe, Co, Ni, Mg, and Mo (W). 1.12 Vanadium, Molybdenum, and Tungsten. 1.13 Rates of Exchange. 1.14 Summary. 2 Medicinal Inorganic Chemistry (Katherine H. Thompson and Chris Orvig). 2.1 Introduction. 2.2 Key Developments. 2.3 Summary of Key Concepts. 2.4 Selected Current Research Directions. 2.5 Open Questions. 3 The Chemical Toxicology of Metals and Metalloids (Graham N. George). 3.1 Introduction. 3.2 Arsenic. 3.3 Mercury. 3.4 Chromium. 3.5 The Promise of New Techniques. 4 Theoretical Modeling of Redox Processes in Enzymes and Biomimetic Systems (Arianna Bassan, Tomasz Borowski, Marcus Lundberg, and Per E. M. Siegbahn). 4.1 Introduction. 4.2 Computational Model. 4.3 Nonheme Iron Active Sites That Perform Alkane Hydroxylation and Olefin Oxidation. 4.4 Keto Acid-Dependent Dioxygenases and Their Synthetic Analogues. 4.5 Copper Complexes in Enzymes and Synthetic Systems. 4.6 Manganese Complexes That Oxidize Water to Dioxygen. 4.7 Conclusions. 5 Charge Transport in Biological Molecules (Yitao Long and Heinz-Bernhard Kraatz). 5.1 Introduction. 5.2 Electron Transfer in Proteins. 5.3 Electron Transfer in Peptides. 5.4 Charge Transfer in DNA. 5.5 Summary and Open Questions. 6 Bioorganometallic Chemistry (Nils Metzler-Nolte and Kay Severin). 6.1 Introduction. 6.2 Organometallic Complexes in Nature. 6.3 Synthetic Organometallic Complexes with Bioligands. 6.4 Organometallic Pharmaceuticals. 6.5 Analytical Bioorganometallic Chemistry. 6.6 Bioorganometallic Catalysis. 6.7 Conclusions and Outlook. 7 The Bioinorganic Side of Nucleic Acid Chemistry: Interactions with Metal Ions (Bernhard Lippert and Jens Muller). 7.1 Introduction: Nucleic Acids and Metals. 7.2 Modeling Metal-Nucleic Acid Interactions. 7.3 Take-Home Message. 7.4 Open Questions and Perspectives. 8 Nuclease and Peptidase Models (Srecko I. Kirin, Roland Kramer, and Nils Metzler-Nolte). 8.1 Introduction. 8.2 Mechanistic Considerations. 8.3 Substrates for Model Studies. 8.4 Peptidase Models. 8.5 Nuclease Models. 8.6 Applications. 9 Metalloporphyrins, Metalloporphyrinoids, and Model Systems (Bernhard Krautler and Bernhard Jaun). 9.1 Introduction: Biological Background. 9.2 Model Systems and Model Compounds to Understand Biological Function. 9.3 Summary of Key Concepts. 9.4 Open Questions and the Direction of Future Research. 10 Model Complexes for Vanadium-Containing Enzymes (Dieter Rehder). 10.1 Biological Background and Motivation. 10.2 Model Compounds. 10.3 Summary of Key Concepts. 10.4 Open Questions and the Direction of Future Research. 11 Model Complexes for Molybdenum- and Tungsten-Containing Enzymes (John H. Enemark and J. Jon A. Cooney). 11.1 Biological Background and Motivation. 11.1.1 Introduction 238 11.2 Model Compounds. 11.3 Summary. 11.4 Open Questions. 12 Structural and Functional Models for Oxygen-Activating Nonheme Iron Enzymes (Timothy A. Jackson and Lawrence Que, Jr.). 12.1 Biological Background and Motivation. 12.2 Dinuclear Iron Centers. 12.3 Diiron Models. 12.4 Monoiron Active Sites with a 2-His-1-Carboxylate Facial Triad Motif. 12.5 Monoiron Models. 12.6 Summary of Key Concepts. 12.7 Open Questions and the Direction of Future Research. 13 Model Chemistry of the Iron-Sulfur Protein Active Sites (George A. Koutsantonis). 13.1 Introduction. 13.2 Basic Iron and Sulfur Chemistry. 13.3 Common Iron-Sulfur Geometries. 13.4 Required Protein and Peptide Coordination Environments. 13.5 Syntheses of Model Compounds. 13.6 Properties of Analogues and Their Relation to Protein-Bound Clusters. 13.7 Conclusions. 14 Model Complexes of Ni-Containing Enzymes (Todd C. Harrop and Pradip K. Mascharak). 14.1 Introduction. 14.2 Urease. 14.3 NiFe Hydrogenase. 14.4 Carbon Monoxide Dehydrogenase/Acetyl Coenzyme A Synthase (CODH/ACS). 14.5 Conclusions. 15 Hydrogenases and Model Complexes (Robert H. Morris). 15.1 Introduction. 15.2 What are Hydrogenases? 15.3 Nickel-Iron (NiFe-Hase) and Nickel-Iron-Selenium (NiFeSe-Hase) Hydrogenases. 15.4 Iron-Iron Hydrogenases. 15.5 Similarities and Differences between NiFe-Hase and FeFe-Hase. 15.6 Synthetic Complexes that Model Hydrogenases. 15.7 Conclusions. 15.8 Open Questions and the Direction of Future Research. 16 Model Complexes for Copper-Containing Enzymes (Yunho Lee and Kenneth D. Karlin). 16.1 Introduction. 16.2 Biological Background: Copper Proteins and Motivation for Biomimetic Studies. 16.3 Model Compounds. 16.4 Summary of Key Concepts. 16.5 Open Questions and Directions for Future Research. 17 Model Complexes for Zinc-Containing Enzymes (Nicolai Burzlaff). 17.1 Introduction. 17.2 Mononuclear Zinc Enzymes and Models. 17.3 Dinuclear Zinc Enzymes and Models. 17.4 Conclusions. Subject Index.

Peptide Electron Transfer: More Questions than Answers

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.