Subnanosecond Time Scale Research Articles

Superexchange-Mediated Charge Separation and Charge Recombination in Covalently Linked Donor - Bridge - Acceptor Systems

Evidence is presented in support of the concept that electron transfer (ET) between a pair of chromophores may take place efficiently over large distances (>10 Å) by the mediation of an intervening saturated hydrocarbon medium. For example, ET is found to take place on a sub-nanosecond timescale through saturated norbornylogous bridges greater than 13 Å in length, by a superexchange (through-bond coupling) mechanism. The dependence of the ET dynamics on the bridge length and configuration are consistent with the operation of a superexchange mechanism. The distinction between molecular wire behaviour and superexchange-mediated ET is made. The distance dependence of ET dynamics through different types of bridges—saturated and unsaturated hydrocarbon bridges, proteins, and duplex DNA—is discussed and explained. Strategies for prolonging the lifetimes of charge-separated states are explored and discussed. In general, long-lived charge-separated species have been generated using giant multichromophoric systems in which the charges are separated by large distances, often exceeding 20 Å. In contrast, it is shown that very long-lived charge-separated states, possessing the triplet multiplicity, may be generated using short ‘dwarf’ dyads, in which the charges are less than 6 Å apart. Charge recombination in these species is slowed by the difference in electron spin multiplicity between the charge-separated state and the ground state.

15N relaxation study of the cold shock protein CspB at various solvent viscosities.

For a detailed NMR study of the dynamics of the cold shock protein CspB from Bacillus subtilis, we determined (15)N transverse and longitudinal relaxation rates and heteronuclear nuclear Overhauser effects at different solvent viscosities. Up to a relative viscosity of 2, which is equivalent to 27% ethylene glycol (EG), the overall correlation time follows the linear Stokes-Einstein equation. At a relative viscosity of 6 (70% EG) the correlation time deviates from linearity by 30%, indicating that CspB tumbles at a higher rate as expected from the solvent viscosity probably due to a preferential binding of water molecules at the protein surface. The corresponding hydrodynamic radii, determined by NMR diffusion experiments, show no variation with viscosity. The amplitudes of intramolecular motions on a sub-nanosecond time scale revealed by an extended Lipari-Szabo analysis were mainly independent of the solvent viscosity. The lower limit of the NMR 'observation window' for the internal correlation time shifts above 0.5 ns at 70% EG, which is directly reflected in the experimentally derived internal correlation times. Chemical exchange contributions to the transverse relaxation rates derived from the Lipari-Szabo approach coincide with the experimentally determined values from the transverse (1)H-(15)N dipolar/(15)N chemical shift anisotropy relaxation interference. These contributions originate from fast protein folding reactions on a millisecond timescale, which get retarded at increased solvent viscosities.

Chemical activation in OH radical-oxidation of 1-n-alkenes

Statistical kinetic calculations, using RRKM-master equation analysis and phase space theory, were performed to determine the importance of chemical activation in the subsequent evolution of the β-hydroxy-1-alkoxy radicals produced in the troposphere OH-oxidation of 1-n-alkenes via the exothermic reaction R–CH(OH)–CH2O2 + NO → R–CH(OH)–CH2O2NO* → R–CH(OH)–CH2O + NO2; the series of radicals from β-hydroxy-ethoxy to -1-hexoxy was considered. At 298 K and 1 atm the fraction of promptly reacting alkoxy radical (on a subnanosecond time-scale) decreases from 75% for the C3-radical to 20% for the C6-radical, the C2-radical being a particular case (higher dissociation barrier height) with only 30% of prompt dissociation. The thermal unimolecular rate constants of these alkoxy radicals were determined by RRKM calculations of the fall-off curves. From the totality of these results it is deduced: (i) the troposphere impact of chemical activation is important for C2-hydroxy-alkoxy radical and specially in the upper troposphere (ii) for C3 chain length radicals, a chemical activation, by favouring the unimolecular reactions, decreases the fraction of O2 reaction, the major effect being predicted for C4 radical. For all radicals except C2 radical the unimolecular reactions are predicted to be preponderant, and at low temperature the isomerisation, when possible from a –CH2– group, is the major way of reaction.

Counterion Condensation and Conformational Transitions of Polyelectrolytes Characterized by EPR Spectroscopy

Counterion condensation of multivalent, charged spin probes to highly charged cationic and anionic polyelectrolytes is characterized by CW and FT EPR spectroscopy. Line broadening and deviation from Lorentzian line shape in the EPR spectra of the spin probes are observed upon addition of the polyelectrolyte. These effects are due to dynamic electrostatic attachment of the counterions with exchange between the condensed and free states on a subnanosecond time scale. The spectral changes can be separated into a contribution due to slowdown of rotational dynamics and a contribution due to enhanced spin exchange. A drastic increase of the spin-exchange contribution is observed upon increasing the concentration of two anionic spin probes in aqueous solutions of the cationic polyelectrolyte poly(diallyldimethylammonium chloride), PDADMAC. This can be traced back to a counterion-induced chain collapse which is, however, not observed in mixtures of water with organic solvents of either higher (N-methylpropionamid...

The secondary response distortion in transient absorption spectroscopy

Transient absorption spectroscopy has been used for many years to record the kinetics and spectra of transient chemical species following a short photolysis or radiation pulse. Linearity of the detector is always important, but cannot always be assumed for experiments on a submicrosecond timescale, and should never be assumed on a subnanosecond timescale. In addition, fast photodiode detectors often exhibit a delayed secondary response, which depends on the wavelength of excitation. In this article we demonstrate the distortions introduced by secondary detector response with some examples from pulse radiolysis. A method for calibration is demonstrated using the broad visible/near-infrared absorption of solvated electrons in water. A standard decay shape is constructed from stroboscopic measurements at short time, and from the (400–800 nm) response of an EG&G FND100Q silicon diode at times greater than 10 ns. The calibration is applied to the FND100Q silicon diode, and to GMP566 germanium and GAP520 InGaAs diodes manufactured by Germanium Power Devices, Inc. Correction of the latter diode is needed to record a visible/near infrared spectrum of solvated electrons in heavy water at elevated temperatures.

Coherent magnetization rotation and phase control by ultrashort optical pulses in CrO(2) thin films.

We have applied photoexcitation by ultrashort laser pulses to single crystal thin CrO(2) films to trigger coherent transient magnetization rotation on a subnanosecond time scale, in macroscale single domains. Moreover, by applying the photoexcitation by pairs of temporally separated pump pulses, the transient precession of the magnetization can be phase controlled, depending on the time separation between the pulses. The mechanism behind the photoexcitation originates from the modulation of the magnetocrystalline anisotropy by nonthermal hot electron spins.

Study of magnetic domains by magnetic soft x-ray transmission microscopy*

X-ray magnetic circular dichroism serves as a strong element-specific magnetic contrast mechanism in full-field transmission soft x-ray microscopy to image micromagnetic domain structures. A lateral resolution down to 25 nm is provided by Fresnel zone plates used as optical elements. Recording the images in varying external magnetic fields and the sensitivity to the direction of the magnetization allows for detailed studies of static magnetization reversal processes in magnetic thin films and nanopatterned elements. Results on highly magnetostrictive Terfenol-D layers are reported. The experimental findings of the switching processes in soft magnetic permalloy rectangular structures are consistent with micromagnetic simulations. The pulsed time structure of polarized synchrotron radiation allows for a stroboscopic imaging of spin dynamics on a sub-nanosecond timescale.

Investigating the phase-dependent photochemical reaction dynamics of chlorine dioxide using resonance Raman spectroscopy

Recent progress in understanding the phase-dependent reactivity demonstrated by halooxides is outlined. Specifically, resonance Raman intensity analysis (RRIA) and time-resolved resonance Raman (TRRR) studies of chlorine dioxide (OClO) photochemistry in solution are presented. Using RRIA, it has been determined that the excited-state structural evolution that occurs along the asymmetric-stretch coordinate in the gas phase is restricted in solution. The absence of evolution along this coordinate results in the preservation of groundstate symmetry in the excited state. The role of symmetry in defining the reaction coordinate and the solvent-solute interactions responsible for modification of the excited-state potential energy surface are discussed. TRRR studies are presented which demonstrate that geminate recombination of the primary photoproducts resulting in the reformation of ground-state OClO is a central feature of OClO photochemistry in solution. These studies also demonstrate that a fraction of photoexcited OClO undergoes photoisomerization to form ClOO, with the ground-state thermal decomposition of this species resulting in Cl production on the subnanosecond timescale. Finally, time-resolved anti-Stokes experiments are presented which demonstrate that the OClO vibrational-relaxation dynamics are solvent dependent. The current picture of OClO photochemistry derived from these studies is discussed, and future directions for study are outlined.

Ultrafast spectroscopy reveals subnanosecond peptide conformational dynamics and validates molecular dynamics simulation.

Femtosecond time-resolved spectroscopy on model peptides with built-in light switches combined with computer simulation of light-triggered motions offers an attractive integrated approach toward the understanding of peptide conformational dynamics. It was applied to monitor the light-induced relaxation dynamics occurring on subnanosecond time scales in a peptide that was backbone-cyclized with an azobenzene derivative as optical switch and spectroscopic probe. The femtosecond spectra permit the clear distinguishing and characterization of the subpicosecond photoisomerization of the chromophore, the subsequent dissipation of vibrational energy, and the subnanosecond conformational relaxation of the peptide. The photochemical cis/trans-isomerization of the chromophore and the resulting peptide relaxations have been simulated with molecular dynamics calculations. The calculated reaction kinetics, as monitored by the energy content of the peptide, were found to match the spectroscopic data. Thus we verify that all-atom molecular dynamics simulations can quantitatively describe the subnanosecond conformational dynamics of peptides, strengthening confidence in corresponding predictions for longer time scales.

Manipulating the production and recombination of electrons during electron transfer: Femtosecond control of the charge-transfer-to-solvent (CTTS) dynamics of the sodium anion.

The scavenging of a solvated electron represents the simplest possible electron-transfer (ET) reaction. In this work, we show how a sequence of femtosecond laser pulses can be used to manipulate an ET reaction that has only electronic degrees of freedom: the scavenging of a solvated electron by a single atom in solution. Solvated electrons in tetrahydrofuran are created via photodetachment using the charge-transfer-to-solvent (CTTS) transition of sodide (Na(-)). The CTTS process ejects electrons to well-defined distances, leading to three possible initial geometries for the back ET reaction between the solvated electrons and their geminate sodium atom partners (Na(0)). Electrons that are ejected within the same solvent cavity as the sodium atom (immediate contact pairs) undergo back ET in approximately 1 ps. Electrons ejected one solvent shell away from the Na(0) (solvent-separated contact pairs) take hundreds of picoseconds to undergo back ET. Electrons ejected more than one solvent shell from the sodium atom (free solvated electrons) do not recombine on subnanosecond time scales. We manipulate the back ET reaction for each of these geometries by applying a "re-excitation" pulse to promote the localized solvated electron ground state into a highly delocalized excited-state wave function in the fluid's conduction band. We find that re-excitation of electrons in immediate contact pairs suppresses the back ET reaction. The kinetics at different probe wavelengths and in different solvents suggest that the recombination is suppressed because the excited electrons can relocalize into different solvent cavities upon relaxation to the ground state. Roughly one-third of the re-excited electrons do not collapse back into their original solvent cavities, and of these, the majority relocalize into a cavity one solvent shell away. In contrast to the behavior of the immediate pair electrons, re-excitation of electrons in solvent-separated contact pairs leads to an early time enhancement of the back ET reaction, followed by a longer-time recombination suppression. The recombination enhancement results from the improved overlap between the electron and the Na(0) one solvent shell away due to the delocalization of the wave function upon re-excitation. Once the excited state decays, however, the enhanced back ET is shut off, and some of the re-excited electrons relocalize even farther from their geminate partners, leading to a long-time suppression of the recombination; the rates for recombination enhancement and relocalization are comparable. Enhanced recombination is still observed even when the re-excitation pulse is applied hundreds of picoseconds after the initial CTTS photodetachment, verifying that solvent-separated contact pairs are long-lived, metastable entities. Taken together, all these results, combined with the simplicity and convenient spectroscopy of the sodide CTTS system, allow for an unprecedented degree of control that is a significant step toward building a full molecular-level picture of condensed-phase ET reactions.

NMR Solution Structure, Backbone Mobility, and Homology Modeling ofc-Type Cytochromes from Gram-Positive Bacteria

The solution structure of oxidized cytochrome c(553) (71 amino acid residues) from the Gram-positive bacterium Bacillus pasteurii is here reported and compared with the available crystal structure. The solution structure is obtained from 1609 meaningful NOE data (22.7 per residue), 76 dihedral angles, and 59 pseudocontact shifts. The root mean square deviations from the average structure are 0.25+/-0.07 and 0.59+/-0.13 A for the backbone and all heavy atoms, respectively, and the quality assessment of the structure is satisfactory. The solution structure closely reproduces the fold observed in the crystal structure. The backbone mobility was then investigated through amide (15)N relaxation rate and (15)N-(1)H NOE measurements. The protein is rigid in both the sub-nanosecond and millisecond time scales, probably due to the relatively large heme:number of amino acids ratio. Modeling of eight c-type cytochromes from other Gram-positive bacteria with a high sequence identity (>30 %) to the present cytochrome c(553) was performed. Analysis of consensus features accounts for the relatively low reduction potential as being due to extensive heme hydration and indicates residues 34-35, 44-46, 69-72, and 75 as a conserved hydrophobic patch for the interaction with a protein partner. At variance with mitochondrial c-type cytochrome, this protein does not experience pH-dependent coordination equilibria. The reasons for this difference are analyzed.

A 15N NMR mobility study on the dicalcium P43M calbindin D9k and its mono-La3+-substituted form.

Calbindin D(9k) is a dicalcium binding protein consisting of two helix-loop-helix EF-hand motifs joined together by a flexible linker region where one metal ion can bind to each of the two loops. A proline residue at position 43 in the linker region displays cis-trans isomerism in the wild-type (WT) protein. Such isomerism appeared to be removed by substituting the proline with a glycine or a methionine in the P43G or P43M mutant. We have extended the available mobility studies on the P43M mutant through amide (15)N R(1), R(2), and R(1)(rho)() measurements. This has revealed unexpected conformational equilibria on the millisecond time scale involving residues 38, 42-44, and 46 in the linker region and residues 18 and 19 in calcium binding site I with similar energy barriers. These data are discussed in comparison with those available for the WT, as well as the apo-, mono-, and disubstituted P43G mutant. Quantification of water-amide proton exchange rates using saturation transfer and qualitative application of (15)N-(CLEANEX-PM)-FHSQC shows the values are in agreement with high mobility for the above-mentioned residues. Cross correlation between N-H dipole-dipole relaxation and (15)N CSA relaxation indicates that some of these mobility differences may extend to the sub-nanosecond time scale. Similar data were also obtained for the derivative where the calcium ion in the C-terminal loop was replaced with lanthanum. The results presented here show that, contrary to expectations, there are significant differences in dynamics between the dicalcium state of P43G and P43M and that these differences are not confined to the flexible linker region containing the point mutation. They also demonstrate that substitution of a lanthanide ion for calcium, which is a common procedure, does not significantly alter the mobility of the native protein.

Site-specific characterization of the association of xylooligosaccharides with the CBM13 lectin-like xylan binding domain from Streptomyces lividans xylanase 10A by NMR spectroscopy.

Endo-beta-1,4-xylanase 10A (Xyn10A) from Streptomyces lividans includes an N-terminal catalytic module and a 130-residue C-terminal family 13 carbohydrate-binding module (CBM13). This latter domain adopts a beta-trefoil structure with three potential binding sites (alpha, beta, and gamma) for a variety of small sugars, xylooligosaccharides, and xylan polymers. To investigate the role of this multivalency in carbohydrate binding, we have used NMR spectroscopy to characterize the interaction of isolated CBM13 with a series of sugars. We have assigned resonances from the main chain nuclei of CBM13 using heteronuclear NMR experiments. Analysis of (15)N NMR relaxation data using the extended model free formalism reveals that CBM13 tumbles as an oblate ellipsoid (D( parallel)/D( perpendicular) = 0.80 +/- 0.02) and that its backbone is relatively rigid on the sub-nanosecond time scale. In particular, the three binding sites show no distinct patterns of increased internal mobility. Ligand-induced chemical shift changes in the (1)H-(15)N HSQC spectra of CBM13 were monitored as a function of increasing concentrations of L-arabinose, lactose, D-xylose, xylobiose, xylotetraose, and xylohexaose. Patterns of shift perturbations for well-resolved resonances demonstrate that all of these sugars associate independently with the three binding sites of CBM13. On the basis of the site-specific association constants derived from a quantitative analysis of these titration data, we show that L-arabinose, lactose, and D-xylose preferentially bind to the alpha site of CBM13, xylobiose binds equally well to all three sites, and xylotetraose and xylohexaose prefer binding to the beta site. Inspection of the crystallographic structure of CBM13 [Notenboom, V., Boraston, A. B., Williams, S. J., Kilburn, D. G., and Rose, D. R. (2002) Biochemistry 41, 4246-4254] provides a rationalization for these results.

Association Complexes between Cationic Metallophthalocyanines and Anionic Metalloporphyrins II: Ultrafast Studies of Excited State Dynamics

Femtosecond transient absorption studies were conducted for self-assemblies between oppositely charged metal-substituted 18-crown-6 tetrasubstituted phthalocyanines (McrPc) and metal-substituted meso-(4-sulfophenyl)-porphine (MTPPS) or meso-(4-carboxylphenyl)-porphine (MTPPC). Excitation could be carried out at 400 nm (Ti-Sapphire second harmonic), which populates the porphyrin-localized S 2 state or directly into the CT band (690), and was achieved by changing the pump pulse wavelength with an optical parametric amplifier. Each complex showed the transient features and kinetics that were independent of the excitation wavelength. After 400 nm excitation, all complexes displayed rapid conversion to the low-lying charge-transfer state. Studies of the CuP/CuPc complex showed no significant decay of the transients on the subnanosecond time scale. However, investigations of the complexes containing different transition metals showed that deactivation of the complex excited state occurs through metal-centered (d,d) states. For the mixed metal/free-base complexes, the excited-state relaxation occurred through the metallotetrapyrrole component regardless of whether it was porphyrin or phthalocyanine. In these compounds, the charge transfer state deactivated to form the metal-centered (d,d) state within 2 ps, with lifetimes that varied somewhat with the metal center. This latter state repopulated the ground state with a lifetime of ca. 13 ps (NiP/NiPc), 200 ps (NiP/CuPc), 8 ps (CuP/NiPc), and 7 ps (FbP/CoPc). These metal-to-ground state rates were similar to those measured for the monomeric metallotetrapyrroles.

Picosecond large angle reorientation of the magnetization in Ni81Fe19 circular thin-film elements

Large angle picosecond reorientation of the magnetization has been studied in circular Ni81Fe19 thin-film elements of 30 μm diameter and 500 Å thickness by means of an optical pump–probe technique. The sample was pumped by an optically triggered magnetic field pulse and probed by a time resolved magneto-optical Kerr effect measurement. The temporal profile of the pulsed field and the in-plane uniaxial anisotropy of the element were first determined from measurements made in large static fields where the magnetization exhibited small amplitude ferromagnetic resonance oscillations. Measurements of large amplitude oscillations were then made in a smaller static field that was still larger than the in-plane uniaxial anisotropy field and sufficient to saturate the sample. Using the measured temporal profile of the pulsed field, the Landau–Lifshitz–Gilbert equation was used to model the motion of the magnetization as a coherent rotation process. The same values of the anisotropy and damping constants provided an adequate simulation of both the high and low field data. The magnetization was found to move through an angle of up to about 30° on subnanosecond time scales. The dependence of the reorientation upon the direction of the static applied field and observed deviations from the coherent precession model are discussed.

High-frequency behavior and damping of Fe-Co-N-based high-saturation soft magnetic films

Magnetization dynamics measurements at subnanosecond time scale have been performed on Fe-Co-N high-saturation soft magnetic films with Permalloy nanolayer seeds and having a saturation magnetization of 1.9 MA/m (1900 emu/cm/sup 3/). The damping parameter /spl alpha/ varies from 0.011 to 0.018, depending on applied bias field. The peak frequencies of the imaginary permeability spectra and the zero-crossing frequencies of the real permeability spectra cannot be fitted with a fixed value of anisotropy field, indicating that the Kittel equation is only qualitatively valid for these films. A phenomenological damping criterion is established based on a small-signal solution of the Landau-Lifshitz-Gilbert equation: critical damping occurs in a soft magnetic film when the damping parameter is /spl alpha/=2//spl radic/(/spl chi//sub 0/), where /spl chi//sub 0/ is the initial permeability. The experimentally observed damping parameters are smaller than the critical value for the range of bias fields employed. The Fe-Co-N-based films have a ferromagnetic resonance frequency of 2 GHz at zero-bias field, showing great promise for applications in write heads and integrated inductors in a frequency range >1 GHz.

CdTe-Based Auston Switch for Optically-Driven Integrated Optics Devices

We report on the implementation and characterisation of Auston switches based on semi-insulating CdTe, aimed at optically driving integrated optics modulators. In view of applications, switching of voltages around a few volts in sub-nanosecond or picosecond time scale is required, while minimizing optical energy. Most efficient operation is obtained at λ = 810 nm, using In : CdTe, where 6 V are switched by use of 2.5 nJ pulses in the nanosecond regime. Intrinsic sub-nanosecond response times are evident and from experimental results activating switching energies down to 50 pJ per pulse can be estimated for the device, when switching at 10 GHz, corresponding to 500 mW pulse peak power.

Canonical Adiabatic Free Energy Sampling (CAFES): A Novel Method for the Exploration of Free Energy Surfaces

We present a novel method, canonical adiabatic free energy sampling (CAFES) that allows for the efficient exploration of the free energy surface of a subsystem (S) embedded in an environment (E) using mol. dynamics simulations. The dynamics of S is decoupled from the environment by introducing fictitious masses that ensure that S evolves slowly and adiabatically on the potential of mean force generated by E. In addn., the decoupling enables the use of different temps. for the two parts of the system without introducing an irreversible heat flow. Using a higher temp. for the subsystem, a high efficiency for the sampling of rare events on the phys. free energy surface is obtained. The performance of this approach is demonstrated with a conformational anal. of a Gly-Ala dipeptide in aq. soln. Rare conformational transitions, which naturally occur on a millisecond time scale, are obsd. within a few nanoseconds of a classical mol. dynamics simulation. The same method has also been applied in a hybrid Car-Parrinello/classical mol. dynamics investigation of the proton-catalyzed conversion of 2-bromoethanol to dibromoethane in water. Using CAFES, the anchimeric assistance of the bromine atom and the occurrence of a bromonium ion intermediate, a process which involves a barrier of ca. 23 kcal/mol, is obsd. spontaneously on the subnanosecond time scale. [on SciFinder (R)]

Role of protolytic interactions in photo-aging processes of carminic acid and carminic lake in solution and painted layers

In this paper absorption and fluorescence spectra and emission quantum yields and lifetimes of the red colorants, carminic acid and its metal complex, carminic lake, were studied in solution and on painted surfaces. Accelerated photo-aging of carminic acid and lake was investigated in solution, in the presence and absence of a binder (arabic gum) commonly used in water-colour painting, while natural ageing was followed for several months on water-colour painted paper. The study of carminic acid in water as a function of pH showed that the absorption spectrum changes with pH. Four acid–base dissociation steps were detected and the corresponding pKs were determined from spectrophotometric and fluorimetric titrations. The fluorescence quantum yields (in the 10−2–10−4 range) and the lifetimes (on the sub-nanosecond timescale, 90–1000 ps) were markedly dependent on the pH of the medium. Excited state pK*s were calculated by means of the Forster cycle. The acidity decreased upon excitation for the first deprotonation step involving the –COOH group (ΔpK* = −1.9), but increased slightly for the successive deprotonation steps involving three phenolic hydroxy groups (ΔpK* = 0.6, 2.0 and 0.2, respectively). The results obtained from the aging experiments indicate that both carminic acid and lake are bleached during irradiation. While the binder prevents lake from fading, it destabilises the carminic acid. These findings are discussed in the light of the interactions of the dye with the solvent and matrix.

Backbone Dynamics of Plastocyanin in Both Oxidation States: SOLUTION STRUCTURE OF THE REDUCED FORM AND COMPARISON WITH THE OXIDIZED STATE

A model-free analysis based on (15)N R(1), (15)N R(2), and (15)N-(1)H nuclear Overhauser effects was performed on reduced (diamagnetic) and oxidized (paramagnetic) forms of plastocyanin from Synechocystis sp. PCC6803. The protein backbone is rigid, displaying a small degree of mobility in the sub-nanosecond time scale. The loops surrounding the copper ion, involved in physiological electron transfer, feature a higher extent of flexibility in the longer time scale in both redox states, as measured from D(2)O exchange of amide protons and from NH-H(2)O saturation transfer experiments. In contrast to the situation for other electron transfer proteins, no significant difference in the dynamic properties is found between the two redox forms. A solution structure was also determined for the reduced plastocyanin and compared with the solution structure of the oxidized form in order to assess possible structural changes related to the copper ion redox state. Within the attained resolution, the structure of the reduced plastocyanin is indistinguishable from that of the oxidized form, even though small chemical shift differences are observed. The present characterization provides information on both the structural and dynamic behavior of blue copper proteins in solution that is useful to understand further the role(s) of protein dynamics in electron transfer processes.