Reproducibility of observables and coherent control in molecular photoionization: from continuous wave to ultrashort pulsed radiation

One-photon single ionization of molecules has been at the focus of several discussions concerning the reconstruction of observables obtained with ultrashort pulses from those obtained from continuous wave radiation (and vice versa). A related controversy on the conditions and observables that allow for coherent control in one-photon processes has been recently revisited (Science 2006, 313, 1257; J. Chem. Phys. 2010, 133, 151101). Our benchmark to investigate these issues is photoionization of the hydrogen molecule, where the autoionization events are the time-dependent processes in field-free evolution that could serve as a target for coherent control. We show that the variation of one-photon ionization probabilities with pulse duration are solely due to spectral effects and thus cannot be coherently controlled. We then discuss for which observables and under which conditions phase control of autoionization dynamics is possible.

Structures, energetics, and dynamics of helium adsorbed on isolated fullerene ions

Helium adsorbed on C(60)(+) and C(70)(+) exhibits phenomena akin to helium on graphite. Mass spectra suggest that commensurate layers form when all carbon hexagons and pentagons are occupied by one He each, but that the solvation shell does not close until 60 He atoms are adsorbed on C(60)(+), or 62 on C(70)(+). Molecular dynamics simulations of C(60)He(n)(+) at 4 K show that the commensurate phase is solid. Helium added to C(60)He(32)(+) will displace some atoms from pentagonal sites, leading to coexistence of a registered layer of immobile atoms interlaced with a nonregistered layer of mobile atoms.

Clocking ultrafast wave packet dynamics in molecules through UV-induced symmetry breaking

We investigate the use of UV-pump-UV-probe schemes to trace the evolution of nuclear wave packets in excited molecular states by analyzing the asymmetry of the electron angular distributions resulting from dissociative ionization. The asymmetry results from the coherent superposition of gerade and ungerade states of the remaining molecular ion in the region where the nuclear wave packet launched by the pump pulse in the neutral molecule is located. Hence, the variation of this asymmetry with the time delay between the pump and the probe pulses parallels that of the moving wave packet and, consequently, can be used to clock its field-free evolution. The performance of this method is illustrated for the H(2) molecule.

Observation of interference between two distinct autoionizing states in dissociative photoionization of H2

Dissociative photoionization (DPI) of randomly oriented H(2) molecules has been studied using linearly polarized synchrotron radiation at selected photon energies of 31, 33, and 35 eV. Large amplitude oscillations in the photoelectron asymmetry parameter β, as a function of electron energy, have been observed. The phase of these β oscillations are in excellent agreement with the results of recent close coupling calculations [Fernández and Martín, New J. Phys. 11, 043020 (2009)]. We show that the oscillations are the signature of interferences between the 1Q(1) (1)Σ(u)(+) and 1Q(2) (1)Π(u) doubly excited states decaying at different internuclear distances. The oscillations thus provide information about the classical paths followed by the nuclei. The presence of such oscillations is predicted to be a general phenomenon in DPI.

Protein kinase C phosphorylates the cAMP response element binding protein in the hypothalamic paraventricular nucleus during morphine withdrawal

BACKGROUND AND PURPOSE

Exposure to drugs of abuse or stress results in adaptation in the brain involving changes in gene expression and transcription factors. Morphine withdrawal modulates gene expression through various second-messenger signal transduction systems. Here, we investigated changes in activation of the transcription factor, cAMP-response element binding protein (CREB), in the hypothalamic paraventricular nucleus (PVN) and the kinases that may mediate the morphine withdrawal-triggered activation of CREB and the response of the hypothalamic-pituitary-adrenocortical (HPA) axis after naloxone-induced morphine withdrawal.

EXPERIMENTAL APPROACH

The effects of morphine dependence and withdrawal, phosphorylated CREB (pCREB), corticotrophin-releasing factor (CRF) expression in the PVN and HPA axis activity were measured using immunoblotting, immunohistochemistry and radioimmunoassay in controls and in morphine-dependent rats, withdrawn with naloxone and pretreated with vehicle, calphostin C, chelerythrine (inhibitors of protein kinase C (PKC) or SL-327 [inhibitor of extracellular signal regulated kinase (ERK) kinase]. In addition, changes in PKCα and PKCγ immunoreactivity were measured after 60 min of withdrawal.

KEY RESULTS

In morphine-withdrawn rats, pCREB immunoreactivity was increased within CRF immunoreactive neurons in the PVN and plasma corticosterone levels were raised. SL-327, at doses that reduced the augmented pERK levels in the PVN, did not attenuate the rise in pCREB immunoreactivity or plasma corticosterone secretion. In contrast, PKC inhibition reduced the withdrawal-triggered rise in pCREB, pERK1/2 and corticosterone secretion.

CONCLUSIONS AND IMPLICATIONS

PKC mediated, in part, both CREB activation and the HPA response to morphine withdrawal. The ERK kinase/ERK pathway might not be necessary for either activation of CREB or HPA axis hyperactivity.

Attosecond control in photoionization of hydrogen molecules

We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field. Fragment ion yields from distinguishable ionization channels oscillate with a period that is half the optical cycle of the IR field. For molecules aligned parallel to the laser polarization axis, the oscillations are reproduced in two-electron quantum simulations, and can be explained in terms of an interference between ionization pathways that involve different harmonic orders and a laser-induced coupling between the 1sσ(g) and 2pσ(u) states of the molecular ion. This leads to a situation where the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and demonstrates that we have probed the IR-induced electron dynamics with attosecond pulses.

Ultrafast nonadiabatic fragmentation dynamics of doubly charged uracil in a gas phase

A combination of time-dependent density functional theory and Born-Oppenheimer molecular dynamics methods is used to investigate fragmentation of doubly charged gas-phase uracil in collisions with 100 keV protons. The results are in good agreement with ion-ion coincidence measurements. Orbitals of similar energy and/or localized in similar bonds lead to very different fragmentation patterns, thus showing the importance of intramolecular chemical environment. In general, the observed fragments do not correspond to the energetically most favorable dissociation path, which is due to dynamical effects occurring in the first few femtoseconds after electron removal.

Role of dispersion forces in the structure of graphene monolayers on Ru surfaces

Elaborate density functional theory (DFT) calculations that include the effect of van der Waals (vdW) interactions have been carried out for graphene epitaxially grown on Ru(0001). The calculations predict a reduction of structural corrugation in the observed moiré pattern of about 25% (∼0.4 Å) with respect to DFT calculations without vdW corrections. The simulated STM topographies are close to the experimental ones in a wide range of bias voltage around the Fermi level.

Direct observation of Young’s double-slit interferences in vibrationally resolved photoionization of diatomic molecules

Vibrationally resolved valence-shell photoionization spectra of H₂, N₂ and CO have been measured in the photon energy range 20–300 eV using third-generation synchrotron radiation. Young’s double-slit interferences lead to oscillations in the corresponding vibrational ratios, showing that the molecules behave as two-center electron-wave emitters and that the associated interferences leave their trace in the angle-integrated photoionization cross section. In contrast to previous work, the oscillations are directly observable in the experiment, thereby removing any possible ambiguity related to the introduction of external parameters or fitting functions. A straightforward extension of an original idea proposed by Cohen and Fano [Cohen HD, Fano U (1966) Phys Rev 150:30] confirms this interpretation and shows that it is also valid for diatomic heteronuclear molecules. Results of accurate theoretical calculations are in excellent agreement with the experimental findings.

[Takotsubo syndrome. Usefulness of nuclear medicine studies]

Takotsubo syndrome can mimic an acute myocardial infarction. It is characterized by anginal chest pain with ST elevation in precordial leads, no coronary obstruction on angiography, and typical and reversible deformation of the left ventricular due to antero-apical ballooning with basal hyperkinesis. The pathophysiology of this syndrome is uncertain. It is probably multifactorial, cardiac adrenergic nervous dysfunction standing out in the acute phase. We report two cases performed within the diagnostic context of Takotsubo syndrome. Cardiac SPECT was performed using (123)I Metaiodobenzylguanidine (MIBG) and (99m)Tc-Tetrofosmin and the results of two cases were adrenergic denervation in the anterior wall without alterations in myocardial perfusion study. Identification of Takotsubo syndrome is of clinical importance because its management and prognosis differ significantly from that of acute myocardial infarction.

An epidemiological survey of hymenoptera venom allergy in the Spanish paediatric population

Hypersensitivity reactions to hymenoptera venom are infrequent in paediatric patients. A study was made to determine the incidence of this pathology in children, based on an epidemiological survey targeted to all members of the SEICAP (Sociedad Española de Inmunología Clínica y Alergia Pediátrica/Spanish Society of Paediatric Clinical Immunology and Allergy), and designed to collect the data on patients under 17 years of age diagnosed with hymenoptera venom allergy.

RESULTS

The data corresponding to 175 patients (135 males) were collected. The mean age was 9.9 ± 3.6 years. Seventeen percent (32 patients) were the offspring of beekeepers, and 68.9% had experienced previous stings. The causal insect was Apis melifera, implicated in 55 cases, followed by Polistes dominulus (33 cases). In 151 patients (83.9%) the condition consisted of a local reaction. The most frequent systemic response was urticaria and angio-oedema. Fourteen patients suffered anaphylactic shock. The diagnosis was based on skin test (intradermal and prick) and/or specific IgE testing. Three treatment categories were established: (a) prevention and educational measures; (b) symptomatic treatment with oral antihistamines as well as self-injectable adrenalin; and (c) immunotherapy. In this context, 135 patients underwent immunotherapy with a mean duration of 3.5 ± 1.7 years (range 2-5 years) - with excellent tolerance. The starting regimen was predominantly conventional (92 patients).

CONCLUSIONS

The results of this survey show hypersensitivity reactions to hymenoptera venom to be infrequent in paediatrics, though with a strong impact upon patient quality of life.

Use of liming in the remediation of soils polluted by sulphide oxidation: a leaching-column study

Pure CaCO(3) in ascending quantities was added to a soil to study the effect of liming after contamination by an acidic solution from the oxidation of pyrite tailings. The samples were placed in percolation columns, and soils and leachates were monitored. In the soil samples, the mineralogy, pH, CaCO(3), iron, and total content in Cu, Zn, As, Cd, and Pb were determined. The presence of CaCO(3) in the soils considerably limited their acidification, favouring the precipitation of Cu, Zn, and Cd, and promoting precipitation of iron and SO(4)(2-) ions in the form of iron hydroxysulphates and gypsum. The iron hydroxysulphates tended to retain the less mobile elements (As, and Pb) near the top of the soil. The more mobile elements (Zn, Cd and Cu) precipitated in deeper layers, directly related mainly to the CaCO(3) added and to pH. The CaCO(3) clearly did not reduce Zn and Cd toxicity effectively enough, given that the concentrations of both elements were above the toxic level in all leachates. The amounts of liming needs to be properly controlled, as excessively high pH limits As fixing, at the same time as the effectiveness of CaCO(3) is limited by coating precipitation, reducing its capacity to react with the acidic solution.

Circular dichroism in photoionization of H2

Circular dichroism is a consequence of chirality. However, nonchiral molecules can also exhibit it when the measurement itself introduces chirality, e.g., when measuring molecular-frame photoelectron angular distributions. The few such experiments performed on homonuclear diatomic molecules show that, as expected, circular dichroism vanishes when the molecular-frame photoelectron angular distributions are integrated over the polar electron emission angle. Here we show that this is not the case in resonant dissociative ionization of H2 for photons of 30-35 eV, which is the consequence of the delayed ionization from molecular doubly excited states into ionic states of different inversion symmetry.

Nitric oxide repression of Nanog promotes mouse embryonic stem cell differentiation

Exposure of mouse embryonic stem (mES) cells to high concentrations of chemical nitric oxide (NO) donors promotes differentiation, but the mechanisms involved in this process at the gene expression level are poorly defined. In this study we report that culture of mES cells in the presence of 0.25-1.0 mM diethylenetriamine nitric oxide adduct (DETA-NO) leads to downregulation of Nanog and Oct4, the two master genes involved in the control of the pluripotent state. This action of NO was also apparent in the human ES cell line, HS 181. The suppressive action of NO on Nanog gene depends on the activation of p53 repressor protein by covalent modifications, such as pSer15, pSer315, pSer392 and acetyl Lys 379. NO-induced repression of Nanog is also associated with binding of trimethylated histone H3 and pSer315 p53 to its promoter region. In addition, exposure to 0.5 mM DETA-NO induces early differentiation events of cells with acquisition of epithelial morphology and expression of markers of definitive endoderm, such as FoxA2, Gata4, Hfn1-beta and Sox 17. This phenotype was increased when cells were treated with valproic acid (VPA) for 10 days.