Scientific Publications 2001
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2001. "Bulk-Like Features in the Photoemission Spectra of Hydrated Doubly Charged Anion Clusters." Science 294(5545):1322-1325. Abstract We produced gaseous hydrated clusters of sulfate and oxalate anions {SO42(H2O)n and C2 O42(H2,O)n (n=4-40)]. Photoelectron spectra (PES) of these clusters revealed that the solute dianions were in the center of the water cluster, (H2O)n. For small clusters, the PES were characteristic of the respective solutes, but beyond the first solvation shell (n=12), features in the PES from the solutes were diminished and a new feature from ionization of water emerged, analogous to bulk aqueous solutions. For large clusters with dimensions over one nanometer, the solute photoemission features disappeared and the PES were dominated by the ionization of water as the solvent coverage increased. A smooth transition from gas-phase clusters to behavior of electrolyte solutions was clearly revealed, and the large solvated clusters can be used as molecular models to investigate the photophysics and chemistry of aqueous electrolyte solutions.
2001. "Experimental and Theoretical Investigations of the Stability, Energetics, and Structures of H₂PO₄⁻, H₂P₂O₇²⁻, and H₃P₃O₁₀²⁻ in the Gas Phase." Journal of Physical Chemistry A 105(45):10468-10474. doi:10.1021/jp013244u Abstract The stability, energetics, and structures of three common inorganic phosphate species, H₂PO₄⁻, H₂P₂O₇²⁻, H₃P₃O₁₀²⁻, and their corresponding neutral radical and monoanions, were investigated in the gas phase using photodetachment photoelectron spectroscopy and theoretical calculations. We found that H₂P₂O₇²⁻ and H₃P₃O₁₀²⁻ are stable in the gas phase with adiabatic electron binding energies of 1.16 and 2.45 eV, respectively. A very high adiabatic electron binding energy of 4.57 eV was measured for H₂PO₄⁻. The intramolecular Coulomb repulsion energies in H₂P₂O₇²⁻ (~2.7 eV) and H₃P₃O₁₀²⁻ (~2.3 eV) were estimated from photon-energy-dependent photoelectron spectra. Density-functional theory calculations were used to search the optimal geometries for both the doubly and singly charged species. We found only one minimum energy conformation for H₂P₂O₇²⁻ with two intramolecular H-bonds and C₂ symmetry and three minimum energy structures for H₃P₃O₁₀²⁻. The lowest energy structure of H₃P₃O₁₀²⁻ has three intramolecular H-bonds that do not share a common oxygen atom. The calculated electron detachment energy of H₂PO₄⁻ agrees with the experimental value well, but the calculated detachment energies for H₂P₂O₇²⁻ and H₃P₃O₁₀²⁻ are ~0.3 and ~0.7 eV smaller than the experimental values, respectively. The observed spectral features, due to removal of electrons from lone-pair oxygen orbitals in the phosphate groups, were assigned qualitatively on the basis of the theoretical calculations.
2001. "The Mu Repressor-DNA Complex Contains an Immobilized 'Wing' Within the Minor Groove." Nature Structural Biology 8(1):84-90. Abstract We have determined the solution structure of the complex between the 'winged-helix' enhancer binding domain of the Mu repressor protein and its cognate DNA site. The structure reveals an unusual use for the 'wing' which becomes immobilized upon DNA binding where it makes intermolecular hydrogen bond contacts deep within the minor groove. Although the wing is mobile in the absence of DNA, it partially negates the large entropic penalty associated with its burial by maintaining a small degree of structural order in the DNA-free state. Extensive contacts are also formed between the recognition helix and the DNA, which reads the major groove of a highly conserved region of the binding site through a single base-specific hydrogen bond and van der Waals contacts.
2001. "A Study of DNA Tethered to a Surface by an All-Atom Molecular Dynamics Simulation." Theoretical Chemistry Accounts 106(3):233-235. Abstract In order to understand the structure of DNAs and their interactions when a microarray surfaces, we performed the first all-atom molecular dynamics simulation of DNA tethered to a surface.
