Development of a compact electron ion coincidence analyzer using a coaxially symmetric mirror electron energy analyzer and a miniature polar-angle-resolved time-of-flight ion mass spectrometer with four concentric anodes.

A compact electron ion coincidence (EICO) analyzer that uses a coaxially symmetric mirror electron energy analyzer and a miniature polar-angle-resolved time-of-flight ion mass spectrometer with four concentric anodes was developed for surface science and surface analysis. The apparatus is especially useful in the study of ion desorption stimulated by an Auger process because information on the mass, yield, desorption polar angle, and kinetic energy of ions can be obtained for the selected core-ionization-final-states or the selected Auger-final-states. The analyzer can be used also for analysis of the configuration of specific surface molecules because the desorption polar angles reflect the direction of surface bonds. The EICO analyzer was evaluated by measuring polar-angle-resolved-ion yield spectra and coincidence spectra of Auger-electron and polar-angle-resolved H(+) from condensed water.

Construction and evaluation of a miniature electron ion coincidence analyzer mounted on a conflat flange with an outer diameter of 114 mm.

We have developed a miniature electron ion coincidence (EICO) analyzer mounted on a conflat flange with an outer diameter of 114 mm. It consists of a cylindrical mirror analyzer (CMA), a time-of-flight ion mass spectrometer (TOF-MS), a commercially available linear motion feed through, and a tilt adjustment mechanism. Each sample surface was irradiated by synchrotron radiation, and the energies of emitted electrons were analyzed and detected by the CMA, while desorbed ions were collected by the TOF-MS in coincidence with the electrons. The performance of the EICO analyzer was tested by measuring the Auger-electron H+ photoion coincidence spectrum of condensed water at 4a1 <-- O 1s resonance.

Transcriptional regulation of the Drosophila rfc1 gene by the DRE-DREF pathway.

The DNA replication-related element (DRE) is a common 8-bp sequence (5'-TATCGATA) found in the promoters of many DNA replication-related genes, to which DRE-binding factor (DREF) specifically binds to activate transcription. Replication factor C (RFC) is an essential five-subunit complex in DNA replication, the largest subunit being RFC140. We first identified the gene (rfc1) encoding the Drosophila RFC140 (dRFC140) protein and then isolated a mutant. The phenotypes suggested that the gene is essential for cell-cycle progression, and immunocytochemical studies also indicated a relation between its expression and the cell cycle. The rfc1 gene contains three DRE-like sequences in its 5'-flanking region, one of them perfectly matching DRE and the other two demonstrating a match in seven of eight nucleotides. These sequences were named DRE1 (-63 to -69), DRE2 (-378 to -385), and DRE3 (-1127 to -1134), respectively. Immunostaining of polytene chromosomes in third-instar larvae using anti-DREF sera detected a specific band in 82E2 of 3R chromosome, containing the rfc1 gene region. Band-mobility shift assays using Drosophila Kc cell nuclear extracts revealed that DREF binds to DRE1, -2, and -3 in vitro, and chromatin immunoprecipitation using anti-DREF IgG confirmed that this occurs in vivo. Luciferase transient expression assays in S2 cells further suggested that DREs in the rfc1 promoter are involved in transcriptional regulation of the gene. Moreover, rfc1 promoter activity was reduced by 38% in DREF double-stranded RNA-treated S2 cells. These results indicate that DREF positively regulates the rfc1 promoter.

Transcriptional regulation of the Drosophila orc2 gene by the DREF pathway.

DNA replication-related element (DRE) and the DRE-binding factor (DREF) play an important role in regulating DNA replication-related genes such as PCNA and DNA polymerase alpha in Drosophila. We have previously reported that overexpression of DREF in developing eye imaginal discs induced ectopic DNA synthesis and apoptosis, which results in rough eyes. To identify genetic interactants with the DREF gene, we have carried out a screen for modifiers of the rough eye phenotype. One of the suppressor genes identified was the Drosophila orc2 gene. A search for known transcription factor recognition sites revealed that the orc2 gene contains three DREs, named DRE1 (+14 to +21), DRE2 (-205 to -198), and DRE3 (-709 to -702). Band mobility shift analysis using Kc cell nuclear extracts detected the specific complex formed between DREF and the DRE1 or DRE2. Specific binding of DREF to genomic region containing the DRE1 or DRE2 was further demonstrated by chromatin immunoprecipitation assays, suggesting that these are the genuine complexes formed in vivo. The luciferase assay in Kc cells indicated that the DRE sites in the orc2 promoter are involved in a transcriptional regulation of the orc2 gene. The results, taken together, demonstrate that the orc2 gene is under the control of DREF pathway.

Polarized near-edge x-ray-absorption fine structure spectroscopy of C60-functionalized 11-amino-1-undecane thiol self-assembled monolayer: molecular orientation and evidence for C60 aggregation.

Near-edge x-ray-absorption fine structure (NEXAFS) spectroscopy was adopted to probe the unoccupied electronic states of C60 anchored onto an organized assembly of 11-amino-1-undecane thiol on Au(111). The polarization dependence of the intensity of pi* resonance associated with C60 pi network revealed the self-assembled monolayer (SAM) system to be oriented with an average molecular tilt angle of 57 degrees with respect to the surface normal. Invoking the absence of solid-state band dispersion effects and in comparison to solid C60 and /or 1-ML C60/Au(111), the electronic structure of the resulting assembly was found dominated by spectral position shift and linewidth and intensity changes of the lowest unoccupied molecular orbital (LUMO), LUMO+1, and LUMO+2 orbitals. The latter implied hybridization between N Pz of -NH2 group of thiolate SAM and pi levels of C60, resulting in a nucleophilic addition with a change in the symmetry of C60 from Ih to C1 in the SAM. Occurrence of a new feature at 285.3 eV in the NEXAFS spectrum, assigned previously to pi* graphitic LUMO, signified the formation of aggregated clusters, (C60)n of C60 monomer. Low tunneling current scanning tunneling microscopy confirmed them to be spherical and stable aggregates with n approximately 5.

Electronic delocalization in discotic liquid crystals: a joint experimental and theoretical study.

Discotic liquid crystals emerge as very attractive materials for organic-based (opto)electronics as they allow efficient charge and energy transport along self-organized molecular columns. Here, angle-resolved photoelectron spectroscopy (ARUPS) is used to investigate the electronic structure and supramolecular organization of the discotic molecule, hexakis(hexylthio)diquinoxalino[2,3-a:2',3'-c]phenazine, deposited on graphite. The ARUPS data reveal significant changes in the electronic properties when going from disordered to columnar phases, the main feature being a decrease in ionization potential by 1.8 eV following the appearance of new electronic states at low binding energy. This evolution is rationalized by quantum-chemical calculations performed on model stacks containing from two to six molecules, which illustrate the formation of a quasi-band structure with Bloch-like orbitals delocalized over several molecules in the column. The ARUPS data also point to an energy dispersion of the upper pi-bands in the columns by some 1.1 eV, therefore highlighting the strongly delocalized nature of the pi-electrons along the discotic stacks.

Simulation study of angle-resolved photoemission spectra and intramolecular energy-band dispersion of a poly(tetrafluoroethylene) oligomer film.

Theoretical simulations of the angle-resolved ultraviolet photoemission spectra (ARUPS) for the oligomer of poly(tetrafluoroethylene) [(CF(2))(n); PTFE] were performed using the independent-atomic-center approximation combined with ab initio molecular orbital calculations. Previously observed normal-emission spectra for the end-on oriented sample (with long-chain axis perpendicular to the surface) showed the incident photon-energy (hnu) dependence due to the intramolecular energy-band dispersion along the one-dimensional chain, and the present simulations successfully reproduced this hnu dependence of the observed spectra. We employed the experimentally observed helical structure for PTFE oligomers for the simulations. We also calculated the density of states (DOS) for the planar zigzag structure, and examined the changes in the electronic structure due to the difference in the molecular structure by comparing the DOS for the helical and planar zigzag structures. Only a small change in the DOS was found between these structures, showing little change of the electronic structure between these conformations. We also evaluated the inner potential V(0), which is the parameter defining the energy origin of the free-electron-like final state, and checked the validity of the value of -10 eV estimated in our previous study using the experimentally observed hnu dependence of the peak intensity. The estimation of V(0) was performed by pursuing the best agreement between the energy-band dispersion [E=E(k)] relation along the chain direction obtained from the simulated spectra and the experimentally deduced one. An excellent agreement in the topmost band was achieved when the assumed inner potential V(0) was set at about zero. This value of V(0) is much different from the value of V(0)=-10 eV in the previous study, suggesting the invalidity of the previous assumption at the estimation of V(0) from the peak intensity variation with hnu. Using the presently obtained V(0), we could derive more reliable E=E(k) dispersion relation from the observed ARUPS spectra. The comparison of this newly derived relation gave good agreement with theoretically calculated E=E(k) relations, in contrast to the poor agreement for the previous results with V(0)=-10 eV.