Strain wave pathway to semiconductor-to-metal transition revealed by time-resolved X-ray powder diffraction.

One of the main challenges in ultrafast material science is to trigger phase transitions with short pulses of light. Here we show how strain waves, launched by electronic and structural precursor phenomena, determine a coherent macroscopic transformation pathway for the semiconducting-to-metal transition in bistable Ti3O5 nanocrystals. Employing femtosecond powder X-ray diffraction, we measure the lattice deformation in the phase transition as a function of time. We monitor the early intra-cell distortion around the light absorbing metal dimer and the long range deformations governed by acoustic waves propagating from the laser-exposed Ti3O5 surface. We developed a simplified elastic model demonstrating that picosecond switching in nanocrystals happens concomitantly with the propagating acoustic wavefront, several decades faster than thermal processes governed by heat diffusion.

Cooperative elastic switching vs. laser heating in [Fe(phen)2(NCS)2] spin-crossover crystals excited by a laser pulse.

Spin-crossover crystals show multi-step responses to femtosecond light excitation. The local molecular photo-switching from low to high spin states occurs on sub-picosecond timescale. It is followed by additional conversion due to elastic (ns) and thermal (µs) effects. In [Fe(phen)2(NCS)2] crystals discussed herein, the thermal switching can be made unobtrusive for the investigation of cooperative elastic switching. We evidence a cooperative transformation induced by lattice expansion through elastic coupling between molecules in the crystal, where up to 3 molecules are transformed per photon.

Out-of-equilibrium dynamics of photoexcited spin-state concentration waves.

The spin crossover compound [FeIIH2L2-Me][PF6]2 presents a two-step phase transition. In the intermediate phase, a spin state concentration wave (SSCW) appears resulting from a symmetry breaking (cell doubling) associated with a long-range order of alternating high and low spin molecular states. By combining time-resolved optical and X-ray diffraction measurements on a single crystal, we study how such a system responds to femtosecond laser excitation and we follow in real time the erasing and rewriting of the SSCW.

Successive dynamical steps of photoinduced switching of a molecular Fe(III) spin-crossover material by time-resolved x-ray diffraction.

We investigate the out-of-equilibrium switching dynamics of a molecular Fe(III) spin-crossover solid triggered by a femtosecond laser flash. The time-resolved x-ray diffraction and optical results show that the dynamics span from subpicosecond local photoswitching followed by volume expansion (nanosecond) and thermal switching (microsecond). We present a physical picture of the consecutive steps in the photoswitching of molecular materials.

Impulsive solvent heating probed by picosecond x-ray diffraction.

The time-resolved diffraction signal from a laser-excited solution has three principal components: the solute-only term, the solute-solvent cross term, and the solvent-only term. The last term is very sensitive to the thermodynamic state of the bulk solvent, which may change during a chemical reaction due to energy transfer from light-absorbing solute molecules to the surrounding solvent molecules and the following relaxation to equilibrium with the environment around the scattering volume. The volume expansion coefficient alpha for a liquid is typically approximately 1 x 10(-3) K(-1), which is about 1000 times greater than for a solid. Hence solvent scattering is a very sensitive on-line thermometer. The decomposition of the scattered x-ray signal has so far been aided by molecular dynamics (MD) simulations, a method capable of simulating the solvent response as well as the solute term and solute/solvent cross terms for the data analysis. Here we present an experimental procedure, applicable to most hydrogen containing solvents, that directly measures the solvent response to a transient temperature rise. The overtone modes of OH stretching and CH3 asymmetric stretching in liquid methanol were excited by near-infrared femtosecond laser pulses at 1.5 and 1.7 microm and the ensuing hydrodynamics, induced by the transfer of heat from a subset of excited CH3OH* to the bulk and the subsequent thermal expansion, were probed by 100 ps x-ray pulses from a synchrotron. The time-resolved data allowed us to extract two key differentials: the change in the solvent diffraction from a temperature change at constant density, seen at a very short time delay approximately 100 ps, and a term from a change in density at constant temperature. The latter term becomes relevant at later times approximately 1 mus when the bulk of liquid expands to accommodate its new temperature at ambient pressure. These two terms are the principal building blocks in the hydrodynamic equation of state, and they are needed in a self-consistent reconstruction of the solvent response during a chemical reaction. We compare the experimental solvent terms with those from MD simulations. The use of experimentally determined solvent differentials greatly improved the quality of global fits when applied to the time-resolved data for C2H4I2 dissolved in methanol.

Recombination of photodissociated iodine: a time-resolved x-ray-diffraction study.

A time-resolved x-ray-diffraction experiment is presented that aims to study the recombination of laser-dissociated iodine molecules dissolved in CCl4. This process is monitored over an extended time interval from pico- to microseconds. The variations of atom-atom distances are probed with a milliangstrom resolution. A recent theory of time-resolved x-ray diffraction is used to analyze the experimental data; it employs the correlation function approach of statistical mechanics. The most striking outcome of this study is the experimental determination of time-dependent I-I atom-atom distribution functions. The structure of the CCl4 solvent changes simultaneously; the solvent thus appears as a reaction partner rather than an inert medium hosting it. Thermal expansion of the system is nonuniform in time, an effect due to the presence of the acoustic horizon. One concludes that a time-resolved x-ray diffraction permits real-time visualization of solvent and solute motions during a chemical reaction.

Ultrafast x-ray diffraction of transient molecular structures in solution.

We report direct structural evidence of the bridged radical (CH2ICH2.) in a polar solution, obtained using time-resolved liquid-phase x-ray diffraction. This transient intermediate has long been hypothesized to explain stereo-chemical control in many association and/or dissociation reactions involving haloalkanes. Ultrashort optical pulses were used to dissociate an iodine atom from the haloethane molecule (C2H4I2) dissolved in methanol, and the diffraction of picosecond x-ray pulses from a synchrotron supports the following structural dynamics, with approximately 0.01 angstrom spatial resolution and approximately 100 picosecond time resolution: The loss of one iodine atom from C2H4I2 leads to the C-I-C triangular geometry of CH2ICH2.. This transient C2H4I then binds to an iodine atom to form a new species, the C2H4I-I isomer, which eventually decays into C2H4 + I2. Solvent dynamics were also extracted from the data, revealing a change in the solvent cage geometry, heating, and thermal expansion.

Copper(II)-mediated oxidative coupling of 2-aminonaphthalene homologues. Competition between the straight dimerization and the formation of carbazoles.

Whereas the Cu(II)-mediated oxidative coupling of 2-aminonaphthalenes 7a and 7b results in the clean formation of 1,1'-binaphthyls 13a and 13b, respectively, their higher homologues and congeners 8-12 have been found to exhibit a different reaction pattern. Thus, 2-aminoanthracene (8) gave a approximately 1:1 mixture of the expected bianthryl derivative 15 and the carbazole 16, whereas the 9-aminophenanthrene (10), 3-phenyl-1-aminonaphthalene (11), and 2-aminochrysene (12) produced almost exclusively the corresponding carbazoles 19, 20, and 21, respectively. By contrast, the isomeric 3-aminophenanthrene (9) gave rise to the azo compound 17 as a result of the preferential oxidation on the nitrogen. The carbazoles have been shown to arise directly from the coupling reactions rather than from the primarily formed binaphthyls. Alternatively, carbazole 19 can also be prepared from 1b on reaction with hydrazine. On the other hand, treatment of 3a with hydrazine resulted in the formation of a approximately 2:7 mixture of amine 11 and arylhydrazine 22. 2,2'-Diamino-1,1'-bianthryl (15) has been resolved into enantiomers via cocrystallization with (-)-N-benzylcinchonidinium chloride and shown to have (R)-(-)-15 configuration by X-ray crystallography.

The changes of biological markers and treatment efficacy in schizophrenia.

1. In a group of schizophrenic patients, the effect and selected parameters of biological markers were evaluated during the index hospitalisation in the acute phase of schizophrenia (n = 30) and then after one year of ambulatory treatment. 2. During the acute treatment, a significant drop in symptomatology was recorded in average; an analogical tendency was observed further on, too. Apart from that, a significant change was observed in 5/41 parameters being monitored (the pair t-test): I) decrease in the total NES score, II) decrease in the sensorial integration subscale NES score, III) increase in psychomotor speed, IV) decrease in auditory reaction time, V) increase in basal cortisol. 3. In the comparison of the successfully (severity of illness after one year = 1, 2) and unsuccessfully (severity of illness after one year > or =3) treated patients in the beginning of treatment in the acute phase, the unsuccessful group had a significantly higher score of negative symptomatology, and by the end of the acute treatment, again, a significantly higher score of negative symptomatology, a higher total PANSS score and a greater severity of illness. 4. In the acute phase, the successful group had a significantly better score in individual items of the Contemporary Memory Scale and a significantly worse performance and goal-aimed concentration in the Bourdon test than the unsuccessfully treated one; apart from that, it had a significantly higher cortisol level after dexamethasone, which was also reflected in the lower percentage rate of dexamethasone nonsupression. 5. In the course of the year, a drop in the total NES score for the individual subscales occurred; a significant drop was observed in the sensory integration subscale. The worse concentration items improved significantly in the successful group in contrast to the unsuccessful group, where they showed a downgrade tendency. Changes in Contemporary Memory Scale were negligible and mostly below statistical significance. Apart from that, a drop in basal cortisolemia occurred in the successful group and an increase in cortisolemia after administering dexamethasone was registered in the unsuccessful group. 6. The more successful group had a significantly lower NES score, a significantly better visual reaction time and a smaller forgetting item (in percentiles) after the one-year period.

Development and disappearance of tolerance to induction of interferon and tumor necrosis factor response in athletes treated with natural immunostimulant.

The effect of nonspecific immunostimulation was examined in 15 basketball players subjected to extensive physical effort. The Tolpa* Torf Preparation (TTP*), a natural immunostimulating drug, was applied orally, one 5 mg tablet daily, in two 21-day cycles, separated by 2-week hiatus. Blood samples were collected 4 times, after each of two TTP* cycles and after the first and second hiatus. Whole blood assay was used to determine the spontaneous and induced production of interferon (IFN) and tumor necrosis factor (TNF). The levels of the cytokines were measured by microbioassays. TTP* stimulated synthesis of IFN and TNF in the whole blood cultures. However, after the oral administraton of TTP* for 3 weeks the leukocytes of the athletes developed hyporeactivity to IFN induction by TTP* and to a lesser extent to another "superinducer"--a mixture of phytohemagglutinin and bacterial lipopolysaccharide. The hyporeactivity state disappeared spontaneously within 2 weeks. In contrast, the tolerance to TNF induction did not develop during the TTP* administration. The increase of immunoglobulins, mainly of IgM and IgG classes and an acute phase protein--alpha1-antitrypsin, was observed at the late phase of the treatment. We suggest that the cytokine levels may be early markers for immunoprophylaxis. Furthermore, high production of IFN and TNF may be associated with extensive physical effort.