SURFACE PHOTODEGRADATION OF POLY(VINYLIDENE FLUORIDE) BY INNER-SHELL EXCITATION

Poly(vinylidene fluoride) (PVDF, –(CH2–CF2)n–) shows the effective H+ desorption induced by the irradiation of photon corresponding to the transition from carbon (C) 1s to σ(C–H)*. In order to clarify the effect of the C–H bond scission by the irradiation, near-edge X-ray absorption fine structure (NEXAFS) spectra and the kinetic energy (Ek) distribution of desorbed ion were observed. By the irradiation of photon near C 1s region, a new peak appears in the C 1s NEXAFS spectra at photon energy of 285 eV, which is about 3 eV lower than that of the lowest peak in the NEXAFS spectrum of the pristine PVDF film. The appearance of the lowest NEXAFS peak of irradiated PVDF film is assigned to the transition to π*. It indicates that the irradiation of photons near C 1s region introduces carbon–carbon double bonds into the backbone chain of PVDF. At early stage of X-ray exposure the yield of desorbed ion with low Ek (~ 2 eV) decreases rapidly. The ion with low Ek is assigned to H+ desorbed from the sp3-hybrid state, which is characteristics of the pristine PVDF. It indicates that formation of double bonds in PVDF backbone chain makes the number of sp3-hybrid state decrease. This variation occurs by irradiation of photons corresponding to the transition from C 1s to σ(C–H)* more rapidly than that to the transition to σ(C–F)*.Photodegradation, PSID, poly(vinylidene fluoride), NEXAFS

Angle-resolved photoemission measurements of ω-(n-pyrrolyl)alkanethiol self-assembled monolayers using in-situ sample preparation apparatus

An in-situ sample preparation apparatus was developed for measuring intrinsic angle-resolved ultraviolet photoemission spectra (ARUPS) from ω-(n-pyrrolyl)alkanethiol self-assembled monolayers (pyrrolyl-SAMs) on an Ag surface. The apparatus enables the preparation of the SAMs directly from the thiol solution and the measurement of ARUPS without exposing the sample to air. The spectral features of the SAMs were analyzed with the aid of ab-initio molecular orbital calculations. It was observed that the ARUPS features associated with the π bands originating from the substituent pyrrole are distinct from the features associated with the alkyl chain

Human immunodeficiency virus type-1-specific immune responses induced by DNA vaccination are greatly enhanced by mannan-coated diC14-amidine.

Use of mannan-coated N-t-butyl-N'-tetradecyl-3-tetradecylamino-propionamidine (diC14-amidine) as an adjuvant for a DNA vaccine encoding glycoprotein 160 of human immunodeficiency virus type-1 (HIV-1) enhanced the antigen-specific immune responses. The role of interferon-gamma (IFN-gamma) and interleukin-12 in the mechanism of adjuvant action was also evaluated. Coating of diC14-amidine with mannan significantly augmented the HIV-specific delayed-type hypersensitivity reaction induced by the immunogenic DNA. HIV-1-specific cytotoxic T lymphocyte activity was also markedly enhanced by the mannan-diC14-amidine cocktail. An immunomodulatory effect of this cocktail was inhibited by treatment with anti-IFN-gamma monoclonal antibody in vivo, which suggests that IFN-gamma plays an important role in inducing cell-mediated immunity by the DNA vaccine containing this adjuvant. The results of both antigen-specific immunoglobulin isotype analysis and cytokine measurement showed that the immunogenic DNA incorporated into mannan-coated diC14-amidine elicits Th1-biased immune responses.Journal ArticleResearch Support, Non-U.S. Gov'tFLWINinfo:eu-repo/semantics/publishe

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.Journal Articleinfo:eu-repo/semantics/publishe