Showing papers by "Mary K. Gilles published in 2005"
TL;DR: Density functional theory calculations of the XAS indicate that the observed red shift of the water transitions as a function of salt concentration arises from a strong, direct perturbation of the unoccupied molecular orbitals on water by anions, and does not require significant distortion of the hydrogen bond network beyond the first solvation shell.
Abstract: Measurements of the oxygen K-edge X-ray absorption spectrum (XAS) of aqueous sodium halide solutions demonstrate that ions significantly perturb the electronic structure of adjacent water molecules. The addition of halide salts to water engenders an increase in the preedge intensity and a decrease in the postedge intensity of the XAS, analogous to those observed when increasing the temperature of pure water. The main-edge feature exhibits unique behavior and becomes more intense when salt is added. Density functional theory calculations of the XAS indicate that the observed red shift of the water transitions as a function of salt concentration arises from a strong, direct perturbation of the unoccupied molecular orbitals on water by anions, and does not require significant distortion of the hydrogen bond network beyond the first solvation shell. This contrasts the temperature-dependent spectral variations, which result primarily from intensity changes of specific transitions due to geometric rearrangement of the hydrogen bond network.
164 citations
TL;DR: In this article, the carbon, nitrogen and oxygen K-edge spectra were measured for aqueous solutions of glycine by total electron yield near-edge X-ray absorption fine structure (TEY NEXAFS) spectroscopy.
Abstract: The carbon, nitrogen, and oxygen K-edge spectra were measured for aqueous solutions of glycine by total electron yield near-edge X-ray absorption fine structure (TEY NEXAFS) spectroscopy. The bulk solution pH was systematically varied while maintaining a constant amino acid concentration. Spectra were assigned through comparisons with both previous studies and ab initio computed spectra of isolated glycine molecules and hydrated glycine clusters. Nitrogen K-edge solution spectra recorded at low and moderate pH are nearly identical to those of solid glycine, whereas basic solution spectra strongly resemble those of the gas phase. The carbon 1s → π*CO transition exhibits a 0.2 eV red shift at high pH due to the deprotonation of the amine terminus. This deprotonation also effects a 1.4 eV red shift in the nitrogen K-edge at high pH. Two sharp preedge features at 401.3 and 402.5 eV are also observed at high pH. These resonances, previously observed in the vapor-phase ISEELS spectrum of glycine,1 have been rea...
94 citations
TL;DR: Although multiple administration schedules in vivo might induce Gd penetration into more tumor cell nuclei, a search for new Gd compounds with higher nuclear affinity is warranted before planning GdNCT in animal models or clinical trials.
Abstract: Objective: Gadolinium neutron capture therapy (GdNCT) is a potential treatment for malignant tumors based on two steps: (1) injection of a tumor-specific 157Gd compound; (2) tumor irradiation with thermal neutrons. The GdNC reaction can induce cell death provided that Gd is proximate to DNA. Here, we studied the nuclear uptake of Gd by glioblastoma (GBM) tumor cells after treatment with two Gd compounds commonly used for magnetic resonance imaging, to evaluate their potential as GdNCT agents. Methods: Using synchrotron X-ray spectromicroscopy, we analyzed the Gd distribution at the subcellular level in: (1) human cultured GBM cells exposed to Gd-DTPA or Gd-DOTA for 0–72hours; (2) intracerebrally implanted C6 glioma tumors in rats injected with one or two doses of Gd-DOTA, and (3) tumor samples from GBM patients injected with Gd-DTPA. Results: In cell cultures, Gd-DTPA and Gd-DOTA were found in 84% and 56% of the cell nuclei, respectively. In rat tumors, Gd penetrated the nuclei of 47% and 85% of ...
56 citations
01 Jan 2005
TL;DR: In this article, a post-exposure bake was performed on poly(4-t-butoxycarbonyloxystyrene) PTBOCST resist, imprinted by deep ultraviolet lithography with a line∕space pattern of 1.10μm∕0.87μm followed by a postexposed bake, and chemical contrast was obtained by measuring the x-ray absorption at an energy of 290.5 eV.
Abstract: Scanning transmission x-ray microscopy (STXM) is shown to be a powerful imaging technique that provides chemical selectivity and high spatial resolution (∼35nm) for studying chemically amplified photoresists. Samples of poly(4-t-butoxycarbonyloxystyrene) PTBOCST resist, imprinted by deep ultraviolet lithography with a line∕space pattern of 1.10μm∕0.87μm followed by a post-exposure bake, are used to demonstrate STXM imaging capabilities to extract photoresist latent images. Chemical contrast is obtained by measuring the x-ray absorption at an energy of 290.5 eV, corresponding to a carbon K shell electronic transition to the unoccupied π* molecular orbital of the PTBOCST carbonyl group. A quantitative analysis provides the spatial distribution of the fraction of the unexposed and deprotected polymers remaining after the post-exposure bake stage as well as the thickness of both regions. Both chemical and topographical contributions to the total contrast are estimated. Advantages and limitations of STXM in co...
16 citations
TL;DR: In this article, a post-exposure bake was performed on poly(4-t-butoxycarbonyloxystyrene) PTBOCST resist, imprinted by deep ultraviolet lithography with a line∕space pattern of 1.10μm∕0.87μm followed by a postexposed bake, and chemical contrast was obtained by measuring the x-ray absorption at an energy of 290.5 eV.
Abstract: Scanning transmission x-ray microscopy (STXM) is shown to be a powerful imaging technique that provides chemical selectivity and high spatial resolution (∼35nm) for studying chemically amplified photoresists. Samples of poly(4-t-butoxycarbonyloxystyrene) PTBOCST resist, imprinted by deep ultraviolet lithography with a line∕space pattern of 1.10μm∕0.87μm followed by a post-exposure bake, are used to demonstrate STXM imaging capabilities to extract photoresist latent images. Chemical contrast is obtained by measuring the x-ray absorption at an energy of 290.5 eV, corresponding to a carbon K shell electronic transition to the unoccupied π* molecular orbital of the PTBOCST carbonyl group. A quantitative analysis provides the spatial distribution of the fraction of the unexposed and deprotected polymers remaining after the post-exposure bake stage as well as the thickness of both regions. Both chemical and topographical contributions to the total contrast are estimated. Advantages and limitations of STXM in co...
14 citations