Dissociation energies of AgRG (RG = Ar, Kr, Xe) and AgO molecules from velocity map imaging studies

The near ultraviolet photodissociation dynamics of silver atom rare gas dimers have been studied by velocity map imaging. AgRG (RG = Ar, Kr, Xe) species generated by laser ablation are excited in the region of the C <- X continuum leading to direct, near threshold dissociation generating Ag* (2P3/2) + RG (1S0) products. Images recorded at excitation wavelengths throughout the C <- X continuum, coupled with known atomic energy levels, permit determination of the ground X (2SIGMA+) state dissociation energies of 85.9 +/- 23.4 cm-1 (AgAr), 149.3 +/- 22.4 cm-1 (AgKr) and 256.3 +/- 16.0 cm-1 (AgXe). Three additional photolysis processes, each yielding Ag atom photoproducts, are observed in the same spectral region. Two of these are markedly enhanced in intensity upon seeding the molecular beam with nitrous oxide, and are assigned to photodissociation of AgO at the two photon level. These features yield an improved ground state dissociation energy for AgO of 15965 +/- 81 cm-1, which is in good agreement with high level calculations. The third process results in Ag atom fragments whose kinetic energy shows anomalously weak photon energy dependence and is assigned tentatively to dissociative ionization of the silver dimer Ag2

Functional characterization of C. elegans Y-box-binding proteins reveals tissue-specific functions and a critical role in the formation of polysomes

The cold shock domain is one of the most highly conserved motifs between bacteria and higher eukaryotes. Y-box-binding proteins represent a subfamily of cold shock domain proteins with pleiotropic functions, ranging from transcription in the nucleus to translation in the cytoplasm. These proteins have been investigated in all major model organisms except Caenorhabditis elegans. In this study, we set out to fill this gap and present a functional characterization of CEYs, the C. elegans Y-box-binding proteins. We find that, similar to other organisms, CEYs are essential for proper gametogenesis. However, we also report a novel function of these proteins in the formation of large polysomes in the soma. In the absence of the somatic CEYs, polysomes are dramatically reduced with a simultaneous increase in monosomes and disomes, which, unexpectedly, has no obvious impact on animal biology. Because transcripts that are enriched in polysomes in wild-type animals tend to be less abundant in the absence of CEYs, our findings suggest that large polysomes might depend on transcript stabilization mediated by CEY protein

Photofragmentation studies of metal ion-molecule complexes and metal oxides

Gas phase metal-containing complexes provide suitable systems in which to study fundamental binding motifs between a metal ion and molecules in the absence of any solvent, support or competing charge effects. In this thesis, metal-containing species are explored experimentally using infrared resonance enhanced photodissociation (IR-REPD) spectroscopy and velocity map imaging (VMI). The experimental results are further interpreted with the aid of spectral simulations based on density functional theory (DFT). These are the first studies reported using a newly built IR-REPD spectrometer equipped with a purpose-built laser ablation source to allow for the study of single metal ion-molecule complexes. The laser ablation source is shown to efficiently produce various complexes including Rh+(CO2)n, VO2+(N2O)n and Au+(CH4)n and the IR-REPD spectrometer has been characterised against a well-studied system of V+(CO2)n complexes. In order to record the IR-REPD spectra for small metal ion-molecule complexes, an argon atom is employed as the inert messenger. A combined IR-REPD spectroscopy and DFT investigation of M+(CO2)n complexes (where M = Co+, Rh+ and Ir+) reveals a common [M+(CO2)2] core structure for all three considered metal ions. Additional ligands, which are not directly bound to the central metal ion, experience lower perturbation as evident in the reduced blue-shift for the ligand in the outer coordination shells. A further IR-REPD/DFT study involving CO2 complexation around NbO2+ and TaO2+ ions reveals a strongly-bound core of four CO2 ligands around the MO2+ ion (M = Nb, Ta). A significant increase in the intermolecular bond distances for the second coordination sphere ligands coincides with a decrease in the calculated binding energies. Velocity map imaging is employed to explore the rich photodissociation dynamics of VO in the vicinity of C4Σ- - X4Σ-(v',0) vibronic transitions in VO. The final quantum state distribution was observed to be strongly dependent on the intermediate vibronic state of VO via which the dissociation threshold is reached. This work provides a refined value for the VO dissociation energy of D0(VO) = 53190 ± 261 cm-1 in excellent agreement with available literature.</p

Photofragmentation studies of metal ion-molecule complexes and metal oxides

Gas phase metal-containing complexes provide suitable systems in which to study fundamental binding motifs between a metal ion and molecules in the absence of any solvent, support or competing charge effects. In this thesis, metal-containing species are explored experimentally using infrared resonance enhanced photodissociation (IR-REPD) spectroscopy and velocity map imaging (VMI). The experimental results are further interpreted with the aid of spectral simulations based on density functional theory (DFT). These are the first studies reported using a newly built IR-REPD spectrometer equipped with a purpose-built laser ablation source to allow for the study of single metal ion-molecule complexes. The laser ablation source is shown to efficiently produce various complexes including Rh+(CO2)n, VO2+(N2O)n and Au+(CH4)n and the IR-REPD spectrometer has been characterised against a well-studied system of V+(CO2)n complexes. In order to record the IR-REPD spectra for small metal ion-molecule complexes, an argon atom is employed as the inert messenger. A combined IR-REPD spectroscopy and DFT investigation of M+(CO2)n complexes (where M = Co+, Rh+ and Ir+) reveals a common [M+(CO2)2] core structure for all three considered metal ions. Additional ligands, which are not directly bound to the central metal ion, experience lower perturbation as evident in the reduced blue-shift for the ligand in the outer coordination shells. A further IR-REPD/DFT study involving CO2 complexation around NbO2+ and TaO2+ ions reveals a strongly-bound core of four CO2 ligands around the MO2+ ion (M = Nb, Ta). A significant increase in the intermolecular bond distances for the second coordination sphere ligands coincides with a decrease in the calculated binding energies. Velocity map imaging is employed to explore the rich photodissociation dynamics of VO in the vicinity of C4Σ- - X4Σ-(v',0) vibronic transitions in VO. The final quantum state distribution was observed to be strongly dependent on the intermediate vibronic state of VO via which the dissociation threshold is reached. This work provides a refined value for the VO dissociation energy of D0(VO) = 53190 ± 261 cm-1 in excellent agreement with available literature.</p

Toll-Like Receptor Agonists Synergistically Increase Proliferation and Activation of B Cells by Epstein-Barr Virus ▿

Epstein-Barr virus (EBV) efficiently drives proliferation of human primary B cells in vitro, a process relevant for human diseases such as infectious mononucleosis and posttransplant lymphoproliferative disease. Human B-cell proliferation is also driven by ligands of Toll-like receptors (TLRs), notably viral or bacterial DNA containing unmethylated CpG dinucleotides, which triggers TLR9. Here we quantitatively investigated how TLR stimuli influence EBV-driven B-cell proliferation and expression of effector molecules. CpG DNA synergistically increased EBV-driven proliferation and transformation, T-cell costimulatory molecules, and early production of interleukin-6. CpG DNA alone activated only memory B cells, but CpG DNA enhanced EBV-mediated transformation of both memory and naive B cells. Ligands for TLR2 or TLR7/8 or whole bacteria had a weaker but still superadditive effect on B-cell transformation. Additionally, CpG DNA facilitated the release of transforming virus by established EBV-infected lymphoblastoid cell lines. These results suggest that the proliferation of EBV-infected B cells and their capability to interact with immune effector cells may be directly influenced by components of bacteria or other microbes present at the site of infection

Infrared spectroscopy of gas-phase M(+)(CO2)n (M = Co, Rh, Ir) ion-molecule complexes

The structures of gas-phase M(+)(CO2)n (M = Co, Rh, Ir; n = 2-15) ion-molecule complexes have been investigated using a combination of infrared resonance-enhanced photodissociation (IR-REPD) spectroscopy and density functional theory. The results provide insight into fundamental metal ion-CO2 interactions, highlighting the trends with increasing ligand number and with different group 9 ions. Spectra have been recorded in the region of the CO2 asymmetric stretch around 2350 cm(-1) using the inert messenger technique and their interpretation has been aided by comparison with simulated infrared spectra of calculated low-energy isomeric structures. All vibrational bands in the smaller complexes are blue-shifted relative to the asymmetric stretch in free CO2, consistent with direct binding to the metal center dominated by charge-quadrupole interactions. For all three metal ions, a core [M(+)(CO2)2] structure is identified to which subsequent ligands are less strongly bound. No evidence is observed in this size regime for complete activation or insertion reactions

Infrared Signature of Structural Isomers of Gas–Phase M⁺(N₂O)_<i>n</i> (M = Cu, Ag, Au) Ion–Molecule Complexes

Gas-phase metal ion–ligand complexes offer model environments to study molecular interactions that are key to many catalytic processes. Here, we present a combined experimental and computational study of M⁺(N₂O)_<i>n</i> [M = Cu, Ag, Au; <i>n</i> = 2–7] complexes. The spectra provide clear evidence for both nitrogen- and oxygen-bound ligands giving rise to a wide range of structural isomers for each complex studied. The evolution of the complex structures observed as well as spectral trends for each metal center are interpreted in terms of a molecular orbital binding picture and resulting calculated ligand binding energies. Given the environmental importance of nitrogen oxides, these results have implications for metal-catalyzed removal of nitrous oxide and, particularly, the prospect of initiating infrared-driven isomer-selective chemistry in size-selected complexes