Thiol-disulfide oxidoreductase PDI1;1 regulates actin structures in Oryza sativa root cells.

The polarized and dynamic actin cytoskeleton is essential for root cell growth. Here, we report the key role of thiol-disulfide oxidoreductase PDI1;1 in actin structures. Microscopic analyses revealed that after Oryza sativa roots were exposed to H2 O2 , both actin and PDI1;1 were depolarized and arranged in a meshwork. In H2 O2 -exposed cells, actin formed intermolecularly disulfide-bonded high-molecular-weight structures, which were thiol-trapped by PDI1;1. Recombinant PDI1;1 exhibited the ability to recognize actin in an in vitro binding assay. During recovery from H2 O2 exposure, the amount of disulfide-bonded high-molecular-weight structures of actin decreased over time, but deficiency of PDI1;1 inhibited the decrease. These results suggest a PDI1;1-dependent pathway that reduces disulfide bonds in high-molecular-weight structures of actin, thus promoting their degradation.

Development of Targeted Protein-Displaying Technology with a Novel Carbon Material.

This study reports a new carbon material and its specific display of targeted protein. The properties of the carbon materials fabricated with carbon black MOGUL® were analyzed. The carbon materials were spherical structures with 55.421 µm as a median value. The specific surface area, pore volume, average pore diameter, and total of the acidic functional group were 130 m2·g-1, 0.55 cm3·g-1, 17.2 nm, and 0.29 mEq·g-1, respectively. The adsorption-desorption isoform of the carbon materials showed type IV of the hysteresis loop as defined by IUPAC, indicating non-uniform mesoporous structures (2-50 nm). The distribution of the log differential pore volume also indicated non-uniform porous structures because (i) the difference between the average pore size and the most frequent pore size was significant and (ii) the σ value was larger than the average value regarding the pore sizes. However, 10-90% of the integrated values of the log differential pore volume were 57.4% of the total integrated values, and the distribution was similar to the Gauss distribution model. Although the value of the total of the acidic functional group was 2.5-5.4 times lower than the values of the HPLC columns, the carbon materials require good scaffold quality rather than good HPLC quality. Therefore, the amounts could be enough for the scaffold of biotin hydrazide. To demonstrate the property of displaying the targeted proteins, carbon materials displaying biotin hydrazide by covalent bonding were prepared and avidin-labeled horse radish peroxidase (HRP) was bound to the biotin region. The carbon materials were porous structures, so the unspecific adsorption of HRP was estimated. Then, the maintenance ratios of HRP activities were analyzed in the repeated-use-with-wash processes after each evaluation, resulting in the activities of HRP on the carbon materials being treated with biotin hydrazide being significantly maintained compared to that of the ones without biotin hydrazide. The study revealed the properties of the carbon materials and indicated the display of HRP, suggesting that the carbon materials could be a new material for displaying targeted proteins.

Sub-10-fs control of dissociation pathways in the hydrogen molecular ion with a few-pulse attosecond pulse train.

The control of the electronic states of a hydrogen molecular ion by photoexcitation is considerably difficult because it requires multiple sub-10 fs light pulses in the extreme ultraviolet (XUV) wavelength region with a sufficiently high intensity. Here, we demonstrate the control of the dissociation pathway originating from the 2pσu electronic state against that originating from the 2pπu electronic state in a hydrogen molecular ion by using a pair of attosecond pulse trains in the XUV wavelength region with a train-envelope duration of ∼4 fs. The switching time from the peak to the valley in the oscillation caused by the vibrational wavepacket motion in the 1sσg ground electronic state is only 8 fs. This result can be classified as the fastest control, to the best of our knowledge, of a molecular reaction in the simplest molecule on the basis of the XUV-pump and XUV-probe scheme.

Direct observation of an attosecond electron wave packet in a nitrogen molecule.

Capturing electron motion in a molecule is the basis of understanding or steering chemical reactions. Nonlinear Fourier transform spectroscopy using an attosecond-pump/attosecond-probe technique is used to observe an attosecond electron wave packet in a nitrogen molecule in real time. The 500-as electronic motion between two bound electronic states in a nitrogen molecule is captured by measuring the fragment ions with the same kinetic energy generated in sequential two-photon dissociative ionization processes. The temporal evolution of electronic coherence originating from various electronic states is visualized via the fragment ions appearing after irradiation of the probe pulse. This observation of an attosecond molecular electron wave packet is a critical step in understanding coupled nuclear and electron motion in polyatomic and biological molecules to explore attochemistry.

Settling time of a vibrational wavepacket in ionization.

The vibrational wavepacket of a diatomic molecular ion at the time of ionization is usually considered to be generated on the basis of the Franck-Condon principle. According to this principle, the amplitude of each vibrational wavefunction in the wavepacket is given by the overlap integral between each vibrational wavefunction and the ground vibrational wavefunction in the neutral molecule, and hence, the amplitude should be a real number, or equivalently, a complex number the phase of which is equal to zero. Here we report the observation of a non-trivial phase modulation of the amplitudes of vibrational wavefunctions in a wavepacket generated in the ground electronic state of a H2⁺ molecular ion at the time of ionization. The phase modulation results in a group delay of the specific vibrational states of order 1 fs, which can be regarded as the settling time required to compose the initial vibrational wavepacket.

Frequency-resolved optical gating technique for retrieving the amplitude of a vibrational wavepacket.

We propose a novel method to determine the complex amplitude of each eigenfunction composing a vibrational wavepacket of / molecular ions evolving with a ~10 fs time scale. We find that the two-dimensional spectrogram of the kinetic energy release (KER) of H(+)/D(+) fragments plotted against the time delay of the probe pulse is equivalent to the spectrogram used in the frequency-resolved optical gating (FROG) technique to retrieve the complex amplitude of an ultrashort optical pulse. By adapting the FROG algorithm to the delay-KER spectrogram of the vibrational wavepacket, we have successfully reconstructed the complex amplitude. The deterioration in retrieval accuracy caused by the bandpass filter required to process actual experimental data is also discussed.

Ultrafast hydrogen scrambling in methylacetylene and methyl-d3-acetylene ions induced by intense laser fields.

Three-body Coulomb explosion processes of triply charged positive ions of methylacetylene (CH(3)-C≡C-H) and its isotopomer, methyl-d(3)-acetylene (CD(3)-C≡C-H), induced by an ultrashort intense laser field (790 nm, ∼40 fs, 5.0 × 10(13) W cm(-2)) are investigated by the coincidence momentum imaging method. Two types of three-body decomposition processes accompanying the ejection of a proton are identified for methylacetylene, and six types of three-body decomposition processes accompanying the ejection of a proton or a deuteron are identified for methyl-d(3)-acetylene. From the observed momentum vectors of all the three fragment ions for each decomposition pathway, the proton and deuteron distributions are constructed in the coordinate space, and the hydrogen migration processes are investigated. It was shown that the hydrogen migration proceeds more efficiently from the methyl group than from the methine group. In addition to the decomposition pathways accompanying the migration of one H (or D) atom, the decomposition pathways accompanying the migration of two light atoms (H/D exchange and 2D migration) are identified. Furthermore, the decomposition pathways ascribable to the migration of three light atoms (H/D exchange followed by D migration) are identified, showing the high intramolecular mobilities of H and D atoms within methylacetylene and methyl-d(3)-acetylene in an intense laser field, resulting in the H/D scrambling.

Resolving vibrational wave-packet dynamics of D2(+) using multicolor probe pulses.

We demonstrate the generation and real-time observation of the vibrational wave packet of D(2)(+) by using a sub-10-fs extreme UV high-harmonic pump pulse and a three-color probe laser pulse whose wavelength ranges from near-IR to vacuum UV. This multicolor pump-probe scheme can provide us with a powerful experimental tool for investigating a variety of wave packets evolving with a time scale of ~20 fs.

Two-body Coulomb explosion in methylacetylene in intense laser fields: double proton migration and proton/deuteron exchange.

Two-body decomposition processes of methylacetylene (CH(3)CCH) and its isotopomer methyl-d(3)-acetylene (CD(3)CCH) in intense laser fields (790 nm, 40 fs, 5.0 × 10(13) W cm(-2)) are investigated by the coincidence momentum imaging (CMI). In methyl-d(3)-acetylene, a total of six decomposition pathways in which one of the C-C bonds is broken and a total of six pathways in which an atomic hydrogen ion (H(+) or D(+)) or a molecular hydrogen ion (H(2)(+), HD(+), D(3)(+), or HD(2)(+)) is ejected are identified. It is revealed from the analysis of the CMI data that the migration of two deuterons as well as the exchange between a proton and a deuteron occurs prior to the two-body decomposition of a doubly charged parent molecule.

Effect of laser parameters on ultrafast hydrogen migration in methanol studied by coincidence momentum imaging.

The effect of intensity, duration, and polarization of ultrashort laser pulses (795 nm, 40-100 fs, and 0.15-1.5 × 10(15) W/cm(2)) on the hydrogen migration in methanol is systematically investigated using Coulomb explosion coincidence momentum imaging. The ratio of the ion yield obtained for the migration pathway CH(3)OH(2+) → CH(2)(+) + OH(2)(+) with respect to the sum of the yields obtained for the migration pathway and for the nonmigration pathway CH(3)OH(2+) → CH(3)(+) + OH(+) exhibits a small (10-20%) but clear dependence on laser pulse properties, that is, the ratio decreases as the laser peak intensity increases but increases when the pulse duration increases as well as when the laser polarization is changed from linear to circular.

High energy proton ejection from hydrocarbon molecules driven by highly efficient field ionization.

We investigated the ejection of energetic protons from a series of polyatomic hydrocarbon molecules exposed to 790 nm 27 fs laser pulses. Using multiparticle coincidence imaging we were able to decompose the observed proton energy spectra into the contributions of individual fragmentation channels. It is shown that the molecules can completely fragment already at relatively low peak intensities of a few 10(14) W/cm(2), and that the protons are ejected in a concerted Coulomb explosion from unexpectedly high charge states. The observations are in agreement with enhanced ionization taking place at many C-H bonds in parallel.

Extreme ultraviolet free electron laser seeded with high-order harmonic of Ti:sapphire laser.

The 13th harmonic of a Ti:sapphire (Ti:S) laser in the plateau region was injected as a seeding source to a 250-MeV free-electron-laser (FEL) amplifier. When the amplification conditions were fulfilled, strong enhancement of the radiation intensity by a factor of 650 was observed. The random and uncontrollable spikes, which appeared in the spectra of the Self-Amplified Spontaneous Emission (SASE) based FEL radiation without the seeding source, were found to be suppressed drastically to form to a narrow-band, single peak profile at 61.2 nm. The properties of the seeded FEL radiation were well reproduced by numerical simulations. We discuss the future precept of the seeded FEL scheme to the shorter wavelength region.

Communication: Two stages of ultrafast hydrogen migration in methanol driven by intense laser fields.

Hydrogen migration in methanol induced by an intense laser field (0.2 PW/cm(2)) is investigated in real time by a pump-probe coincidence momentum imaging method. The observed temporal evolution of the kinetic energy spectra reveals that there are two distinctively different stages in the hydrogen migration processes in the singly charged methanol: ultrafast hydrogen migration occurring within the intense laser field ( approximately 38 fs) and slower postlaser pulse hydrogen migration ( approximately 150 fs).

Two-proton migration in 1,3-butadiene in intense laser fields.

Ultrafast proton migration in 1,3-butadiene in an intense laser field (40 fs, 4.5 × 10(14) W cm(-2)) is investigated by using Coulomb explosion coincidence momentum imaging. The spatial distribution maps of a migrating proton reconstructed for the two three-body Coulomb explosion pathways, C(4)H(6)(3+)→ H(+) + CH(3)(+) + C(3)H(2)(+) and C(4)H(6)(3+)→ H(+) + C(2)H(+) + C(2)H(4)(+), reveal that two protons migrate within a 1,3-butadiene molecule, prior to the three body decomposition.

Tracing ultrafast hydrogen migration in allene in intense laser fields by triple-ion coincidence momentum imaging.

Ultrafast hydrogen migration in allene (CH(2)=C=CH(2)) in intense laser fields was investigated by triple-ion coincidence momentum imaging. The migrating proton covering the entire range of an allene molecule was visualized by the momentum correlation maps and by the geometrical structure of triply charged allene reconstructed from the observed momentum vectors of fragment ions. The extent of hydrogen migration was found to play a decisive role in breaking selectively one of the two initially equivalent C-C chemical bonds that become inequivalent in the course of the hydrogen migration.

Efficient ejection of H3(+) from hydrocarbon molecules induced by ultrashort intense laser fields.

The ejection processes of hydrogen molecular ion H(3)(+) from 12 kinds of hydrocarbon molecular species, methanol, ethanol, 1-propanol, 2-propanol, acetone, acetaldehyde, methane, ethane, ethylene, allene, 1,3-butadiene, and cyclohexane, induced by intense laser fields (approximately 10(14) W/cm(2)) have been investigated by time-of-flight mass spectroscopy. The observation of the H(3)(+) production with the kinetic energy range of 3.5-5.0 eV from doubly ionized ethylene, allene, 1,3-butadiene, and cyclohexane, which have no methyl groups, showed the existence of the ultrafast hydrogen migration processes that enables three hydrogen atoms to come together to form H(3)(+) within a hydrocarbon molecule.

Attosecond nonlinear Fourier transformation spectroscopy of CO2 in extreme ultraviolet wavelength region.

The interferometric autocorrelation functions of attosecond pulse trains in the time domain were measured by detecting CO(2) (2+) as well as the atomic and molecular fragment ions generated via two-photon absorption of intense vacuum ultraviolet-extreme ultraviolet light by CO(2). It was demonstrated that the Fourier transformation of the interferometric autocorrelation functions of the respective fragment ions appearing in a time-of-flight mass spectrum exhibit spectroscopic information in the frequency domain corresponding to the two-photon photofragment excitation spectra of CO(2) and the double ionization excitation spectrum to form CO(2) (2+).

Two-body Coulomb explosion and hydrogen migration in methanol induced by intense 7 and 21 fs laser pulses.

Two-body Coulomb explosion with the C-O bond breaking of methanol induced by intense laser pulses with the duration of Delta t=7 and 21 fs is investigated by the coincidence momentum imaging method. When Delta t=7 fs, the angular distribution of recoil vectors of the fragment ions for the direct C-O bond breaking pathway, CH(3)OH(2+)-->CH(3) (+)+OH(+), exhibits a peak deflected from the laser polarization direction by 30 degrees -45 degrees , and the corresponding angular distribution for the migration pathway, CH(2)OH(2) (+)-->CH(2) (+)+H(2)O(+), in which one hydrogen migrates from the carbon site to the oxygen site prior to the C-O bond breaking, exhibits almost the same profile. When the laser pulse duration is stretched to Delta t=21 fs, the angular distributions for the direct and migration pathways exhibit a broad peak along the laser polarization direction probably due to the dynamical alignment and/or the change in the double ionization mechanism; that is, from the nonsequential double ionization to the sequential double ionization. However, the extent of the anisotropy in the migration pathway is smaller than that in the direct pathway, exhibiting a substantial effect of hydrogen atom migration in the dissociative ionization of methanol interacting with the linearly polarized intense laser field.

Interferometric autocorrelation of an attosecond pulse train in the single-cycle regime.

We report on the direct observation of the phase locking of the attosecond pulse train (APT) via interferometric autocorrelation in the extreme ultraviolet region. APT is formed with Fourier synthesis of high-order harmonic fields of a femtosecond laser pulse. Time-of-flight mass spectra of N+, resulting from the Coulomb explosion of N2 absorbing two photons of APT, efficiently yield correlated signals of APT. The measured autocorrelation trace exhibits that the duration of the pulse should be only 1.3 periods of the extreme ultraviolet carrier frequency. A few interference fringes within the short pulse duration clearly show two types of symmetry, which ensure the phase locking between pulses in APT.

Conclusive evidence of an attosecond pulse train observed with the mode-resolved autocorrelation technique.

We report on the direct observation of an attosecond pulse train with a mode-resolved autocorrelation technique. The chirp among the three harmonic fields is specified by analyzing two-photon above-threshold ionization spectra of electrons, resulting in a pulse duration that should be shorter than 450 as, which is, to our knowledge, the first determination of the chirp in the attosecond pulse train with an autocorrelation technique. These results will open the way to full characterization of an attosecond pulse train with its envelope.