C. Jun

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An approach to long-range electron transfer mechanisms in metalloproteins: <i>In situ</i> scanning tunneling microscopy with submolecular resolution

Proceedings of the National Academy of Sciences of the United States of America, Feb 16, 1999

In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows intere... more In situ scanning tunneling microscopy (STM) of redox molecules, in aqueous solution, shows interesting analogies and differences compared with interfacial electrochemical electron transfer (ET) and ET in homogeneous solution. This is because the redox level represents a deep indentation in the tunnel barrier, with possible temporary electronic population. Particular perspectives are that both the bias voltage and the overvoltage relative to a reference electrode can be controlled, ref lected in spectroscopic features when the potential variation brings the redox level to cross the Fermi levels of the substrate and tip. The blue copper protein azurin adsorbs on gold(111) via a surface disulfide group. Well resolved in situ STM images show arrays of molecules on the triangular gold(111) terraces. This points to the feasibility of in situ STM of redox metalloproteins directly in their natural aqueous medium. Each structure also shows a central brighter contrast in the constant current mode, indicative of 2-to 4-fold current enhancement compared with the peripheral parts. This supports the notion of tunneling via the redox level of the copper atom and of in situ STM as a new approach to long-range electron tunneling in metalloproteins.

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In Situ Scanning Tunneling Microscopy of a Redox Molecule as a Vibrationally Coherent Electronic Three-Level Process

The Journal of Physical Chemistry A, 1998

We provide a theoretical frame for in situ scanning tunneling microscopy (STM) of adsorbate molec... more We provide a theoretical frame for in situ scanning tunneling microscopy (STM) of adsorbate molecules with low-lying redox levels strongly coupled to the environmental nuclear motion. The STM process is viewed as a coherent two-step electron transfer (ET) involving electron exchange between the local redox level and the manifolds of electronic levels in the substrate and tip. The notion coherence is here taken to imply that the intermediate electron or hole state after the first ET step does not fully relax vibrationally before the second ET step. These views and the theoretical formalism are appropriate to in situ STM of large transition metal complexes and redox metalloproteins. The formalism offers two kinds of spectroscopic features. One is the relation between the tunnel current and the bias voltage at fixed overvoltage of either the tip or the substrate relative to a reference electrode. The other one is the tunnel current dependence on the overvoltage, at fixed bias voltage. Recent data on tunneling current patterns for adsorbed or covalently tethered metalloporphyrins and the blue single-copper protein azurin are discussed in terms of the formalism.

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The Effect of Conformational Dynamics and Phase Transitions on Electron and Atom Group Transfer Processes

Proceedings in Life Sciences, 1987

Large-amplitude motion of molecular fragments in widely different time ranges in protein molecule... more Large-amplitude motion of molecular fragments in widely different time ranges in protein molecules is reflected in a variety of molecular and environmental features presently being uncovered. Techniques which have provided information about protein dynamics include x-ray crystallographic [1-3] and Mossbauer spectral properties [4], NMR relaxation of suitable probe nuclei [5,6], fluorescence quenching [7], and time resolved resonance Raman spectroscopy [8].

Effect of Overpotential on the Electronic Tunnel Factor in Diabatic Electrochemical Processes

The Journal of Physical Chemistry, 1994

ABSTRACT

Optical autoionization resonance theory as an approach to electron transfer via adsorbed atoms at metal—solution interfaces

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1985

Abstract Electron transfer between an ion in solution and an impurity atom adsorbed at a metal el... more Abstract Electron transfer between an ion in solution and an impurity atom adsorbed at a metal electrode is sometimes faster than direct electron transfer between an ion and a metal. This process displays close analogies to Fano autoionization resonances in atoms excited to formally bound states broadened by coupling to continuum states. On the basis of this analogy we have derived current—voltage relationships for electron transfer via adsorbed impurity atoms. The most striking effect is that the current passes through a maximum at overvoltages approximately coinciding with the nuclear reorganization enery, then drops, and rises again at still higher voltages. This pattern is quite different from that of direct electron transfer and is caused by the “interference” of metal and impurity wave functions in certain energy ranges. The effect is generally expected only for activationless process, i.e. for large overvoltages, where the current variation directly reflects the behaviour of the pre-exponential factor in the current expressions. The impurity level also modifies the Gibbs energy of nuclear activation due to the solvent configuration dependence of the electron density at the adatoms. This effect is commonly small and in contrast to the electronic structural effects, leads to smooth current-voltage relations.

A theory of simple electrochemical processes in solid solutions

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1977

The formalism of currently applied multiphonon electron transfer theory for heterogeneous chemica... more The formalism of currently applied multiphonon electron transfer theory for heterogeneous chemical reactions is adapted to a model system consisting of an electrode in contact with a solid solution of depolarizer ions at fixed positions. On the basis of the resulting current-time relationship it is shown that important information about the electronic factor in the reaction probability expressions can be obtained. This suggests a new class of diagnostic experiments the results of which are also directly applicable to electron transfer reactions in liquid media.

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A semiclassical approach to concerted proton transfer in condensed media

Journal of the Chemical Society, Faraday Transactions 2, 1982

Page 1. J. Chem. SOC., Faraday Trans. 2, 1982,78,1497-1512 A Semiclassical Approach to Concerted ... more

Dynamics of fast optical band-shape time evolution of three-center electron transfer systems

The Journal of Physical Chemistry, 1995

We provide here a simple description of the coherent time evolution of a coordinate point or conf... more We provide here a simple description of the coherent time evolution of a coordinate point or configuration distribution on an excited state potential energy surface, following excitation by a classical &like pulse. The configuration is probed by another &like pulse at a later time. The time evolution of the probe pulse absorption follows patterns which depend in characteristic ways on the probability of transition to other surfaces crossing the surface primarily excited, the frequency of the exciting light, and the friction of motion on the potential surfaces. The formalism is analytical and appropriate for use on the primary ultrafast charge separation involving special pair and auxiliary bacteriochlorophyll and bacteriopheophytin in the bacterial photosynthetic reaction center. In this respect the formalism also offers clues to the high-energy superexchange or lowenergy coherently populated nature of the intermediate state chlorophyll.

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Fluctuations and Coherence in Long-Range and Multicenter Electron Transfer

Advances in Chemical Physics

Page 1. FLUCTUATIONS AND COHERENCE IN ELECTRON TRANSFER LONG-RANGE AND MULTICENTER GITTE IVERSEN&... more

Theory of Interrelated Electron and Proton Transfer Processes

A simple theory of elementary act of interrelated reactions of electron and proton transfer is de... more A simple theory of elementary act of interrelated reactions of electron and proton transfer is developed. Mechanisms of synchronous and multistage transfer and coherent transitions via a dynamically populated intermediate state are discussed. Formulas for rate constants of adiabatic and nonadiabatic reactions are derived.

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Scanning tunnelling microscopy currents through large adsorbate molecules as a molecular three-centre electronic process

Surface and Coatings Technology, 1994

Abstract We have investigated theoretically the tunnel features and curerent-voltage relations of... more Abstract We have investigated theoretically the tunnel features and curerent-voltage relations of scanning microscopy (STM) processes involving large adsorbate molecules in which the electronic levels are strongly coupled to the environmental nuclear motion. The theoretical formalism resembles electrochemical electron transfer theory but differs in both conceptual and formal respects. The tunnel features of high energy adsorbate levels can be approached by multilevel equations of motion or by simpler tunnel theory extended to fluctuating barriers. Low energy adsorbate levels induce several mechanisms where the levels are temporarily populated. The mechanisms extend to weak (diabetic) and strong (adiabatic) adsorbate-electrode interaction and full or partial vibrational relaxation in the intermediate state of the adsorbate electron or hole population. Some perspectives related to fluctuationally induced STM current pulses and Coulomb blockade monitored by STM are discussed.

Second-Order Surface Phase Transitions in Electrode Kinetics

The Journal of Physical Chemistry, 1996

A theory, based on the Landau-Ginzburg formalism, shows that remarkable singularities in currents... more A theory, based on the Landau-Ginzburg formalism, shows that remarkable singularities in currents of electrode charge transfer reactions occur near the critical potentials where second-order surface phase transitions take place. This happens if the fluctuations of the order parameter, which describes the transition, are exponentially coupled to the reaction system via fluctuating tunneling or activation barriers. Coupling depending on the sign of the order parameter is considered; the corresponding singularities in Arrhenius and Tafel plots for electrode currents are predicted, and the perspectives for their experimental investigation are discussed.

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Dynamic Ionic Strength Effects in Fast Bimolecular Electron Transfer between a Redox Metalloprotein of High Electrostatic Charge and an Inorganic Reaction Partner

The Journal of Physical Chemistry B, 2000

The ionic strength dependence of the bimolecular electron transfer (ET) reaction between Clostrid... more The ionic strength dependence of the bimolecular electron transfer (ET) reaction between Clostridium pasteurianum rubredoxin(III) and photochemically generated [Ru(bpy) 3 ] + has been investigated. The reaction is fast and close to the diffusion-controlled limit. Dynamic ionic strength effects on all kinetics parameters (work terms, driving force, and reorganization free energy) have been incorporated in the data analysis; the effects on the intermolecular work terms are large and dominate in the driving force region close to the activationless limit. The variation in ET rate constant over the 0.005-2.0 M ionic strength range is quantitatively consistent with the high negative charge (-9e where e is the unit electric charge) and size (crystallographic radius ≈ 12 Å) of rubredoxin(III). If low ionic strength (0.005-0.01 M) data are omitted, the variation in rates suggests a somewhat smaller charge on the protein (-4e to-5e).

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Mechanisms of in Situ Scanning Tunnelling Microscopy of Organized Redox Molecular Assemblies

The Journal of Physical Chemistry A, 2001

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Resonance and environmental fluctuation effects in STM currents through large adsorbed molecules

Surface Science, 1992

Scanning tunnelling microscopy (STM) involving electron tunnelling through large adsorbate molecu... more Scanning tunnelling microscopy (STM) involving electron tunnelling through large adsorbate molecules with discrete electronic levels accessible at low bias voltage, exhibits conceptual and physical analogies to other thermal and optical multi-level electronic processes. The analogies are most conspicuous if the adsorbate levels are strongly coupled to the environmental molecular, conformational or solvent nuclear motion but interact weakly with the conducting substrate and tip. These conditions would be appropriate for example for adsorbed large transition metal complexes or redox metalloproteins. In these limits electronic-vibrational coupling induces resonance between the local adsorbate level and either the substrate or the tip levels, and the STM current-voltage relations can be approached by methods known from the theory of related electronic transitions such as long-range molecular electron transfer and multi-photon optical processes. We provide a new theoretical frame for STM processes in this limit. The formalism rests on perturbative coupling of the adsorbate levels to the substrate and tip. Specific models incorporate strong coupling to the adsorbate and environmental nuclear motion, vibrational relaxation features, and the continuous electronic spectra of the substrate and tip. All these features are directly and transparently reflected in the current-voltage relations of the STM process.

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Fluctuational tunnel effects and vibrational dispersion in primary electron transfer processes of bacterial photosynthesis

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1998

Abstract We have investigated forward electron transfer (ET) from reduced bacteriopheophytin (bph... more Abstract We have investigated forward electron transfer (ET) from reduced bacteriopheophytin (bph − ) to the primary quinone (Q A ), and the recombination ET from Q A − to the oxidized special pair (bch) 2 + in the photosynthetic reaction centre of Rh . sphaeroides . The same reactant, Q A , is here engaged in two ET reactions of widely different distances. The processes can also be followed over broad temperature ranges. Focus is on two elements not commonly considered in ET theory. One is continuous environmental dielectric dispersion which is both formally and physically important. The other one is environmental fluctuational modulation of the tunnel factor which is important when the donor and acceptor are separated by environmental matter. The analysis shows, first that a broad dielectric dispersion is in line with the ET data up to ≈180°K. Fluctuational modulation of the tunnel factor is, secondly, unimportant in shorter-range forward ET from bph − to Q A (13 A centre-to-centre distance) but could be important in the much longer-range recombination ET from Q A − to (bch) 2 + (28 A).

Simple schemes in chemical electron transfer formalism beyond single-mode quadratic forms: environmental vibrational dispersion and anharmonic nuclear motion

Physical Chemistry Chemical Physics, 1999

Page 1. Simple schemes in chemical electron transfer formalism beyond single-mode quadratic forms... more

Resonance interference in a three-level system with dynamic coupling of the intermediate state to a vibrational mode

Molecular Physics, 1996

Coherent electronic transitions are analysed in a three-level system where the intermediate level... more Coherent electronic transitions are analysed in a three-level system where the intermediate level is strongly coupled to a classical nuclear mode the dynamics of which is explicitly incorporated. Such a configuration is representative of scanning tunnelling microscopy through a molecular adsorbate. Solution of the equations of motion gives a drop in the overall transition probability per unit time (current) from the initial to the final state when these two states are in resonance. This observation differs from resonance effects obtained by second-order perturbation theory in stationary nuclear environments, and is associated with the motion of the intermediate state level through the resonance region.

Light-driven molecular machine at ITIES

Journal of Physics: Condensed Matter, 2007

... Alexei A Kornyshev1, Marina Kuimova1, Alexander M Kuznetsov1,2, Jens Ulstrup3 and Michael Urb... more ... Alexei A Kornyshev1, Marina Kuimova1, Alexander M Kuznetsov1,2, Jens Ulstrup3 and Michael Urbakh4 ... used in such architectures [36]. Together with a variety of other molecular architectures, these have led to nanoscale replicas of mechanical &amp;#x27;rotors&amp;#x27;, &amp;#x27;gears&amp;#x27;, &amp;#x27;paddle wheels ...

Electron transfer behaviour of biological macromolecules towards the single-molecule level

Journal of Physics: Condensed Matter, 2003

Page 1. Electron transfer behaviour of biological macromolecules towards the single-molecule leve... more

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