Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session L27: Focus Session: Solvation of Ions and Electrons I |
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Sponsoring Units: DCP Chair: Mary T. Rodgers, Wayne State University Room: 204B |
Wednesday, March 4, 2015 8:00AM - 8:36AM |
L27.00001: Comprehensive thermochemistry for the hydration of copper ions Invited Speaker: Peter Armentrout Cross sections for the threshold collision-induced dissociation (TCID) of Cu$^{2+}$(H$_{2}$O)$_{n}$, where n $=$ 8 -- 10, and of CuOH$^{+}$(H$_{2}$O)$_{n}$, where n $=$ 1 -- 4, are measured using a guided ion beam tandem mass spectrometer. In both cases, the primary dissociation pathway is found to be loss of a single water molecule followed by the sequential loss of additional water molecules. In the Cu$^{2+}$ complexes, charge separation to form CuOH$^{+}$(H$_{2}$O)$_{3}$ and H$^{+}$(H$_{2}$O)$_{3}$ is also observed and CuOH$^{+}$(H$_{2}$O) competitively loses both H$_{2}$O and OH. The data are analyzed using a statistical model after accounting for internal and kinetic energy distributions, multiple collisions, and kinetic shifts to obtain 0 K bond dissociation energies (BDEs). In addition, BDEs for the loss of OH from CuOH$^{+}$(H$_{2}$O)$_{n}$ where n $=$ 0 -- 4 are derived using the experimental BDEs for dissociation of CuOH$^{+}$(H$_{2}$O)$_{n}$ and literature values for Cu$^{+}$(H$_{2}$O)$_{n}$. Experimental BDEs are compared to theoretical BDEs determined at several levels of theory with reasonable agreement. Structural information regarding complexes of CuOH$^{+}$(H$_{2}$O)$_{n}$, where n $=$ 2 -- 9, are also obtained using infrared photodissociation spectroscopy (IRPD) in the OH stretching region and comparison to theoretical spectra. The IRPD spectra of all complexes where n $\ge $ 3 are consistent with structures generally having a coordination number (CN) of 4 although CuOH$^{+}$(H$_{2}$O)$_{7}$ exhibits bands characteristic of both CN $=$ 4 and CN $=$ 5 isomers. [Preview Abstract] |
Wednesday, March 4, 2015 8:36AM - 8:48AM |
L27.00002: Collision induced dissociation study of azobenzene and its derivatives: computational and experimental results Mohammadreza Rezaee, Robert Compton Experimental and computational investigation have been performed in order to study the bond dissociation energy of azobenzene and its derivatives using collision induced dissociation method as well as other energy and structural characteristics. The results have been verified by comparing with results obtained from computational quantum chemistry. We used different density functional methods as well as the M\"{o}ller-Plesset perturbation theory and the coupled cluster methods to explore geometric, electronic and the spectral properties of the sample molecules. Geometries were calculated and optimized using the 6-311$++$G(2d,2p) basis set and the B3LYP level of theory and these optimized structures have been subjected to the frequency calculations to obtain thermochemical properties by means of different density functional, M\"{o}ller-Plesset, and coupled cluster theories to obtain a high accuracy estimation of the bond dissociation energy value. The results from experiments and the results obtained from computational thermochemistry are in close agreement. [Preview Abstract] |
Wednesday, March 4, 2015 8:48AM - 9:00AM |
L27.00003: Hydration Structures and Thermodynamic Properties of Cationized Biologically Relevant Molecules, M$^{+}$(Indole)(H$_{2}$O)$_{\mathrm{n}}$ (M $=$ Na, K; n $=$ 3-6) Haochen Ke, James Lisy The balance between various noncovalent interactions plays a key role in determining the hydration structures and thermodynamic properties of biologically relevant molecules in biological mediums. Such properties of biologically relevant molecules are closely related to their often unique biological functionalities. The indole moiety is a basic functional group of many important neurotransmitters and hormones and has been used as tractable model for more complex biomolecules. The cationized indole water cluster is a perfect system for the quantitative and systematic study of the competition and cooperation of noncovalent interactions, as electrostatic interactions can be adjusted by introducing different monovalent cations and hydrogen bonding interactions can be adjusted by varying the level of hydration. IRPD spectra with isotopic (H/D) analysis helped unravel the overlapping N-H and O-H stretching modes, a major challenge of earlier studies. Thermodynamic analysis using relative Gibbs free energies, for energy ordering, together with spectral analysis provided unambiguous assignment of spectral features and structural configurations. A systematic hydration model with an in-depth account of noncovalent interactions is presented. [Preview Abstract] |
Wednesday, March 4, 2015 9:00AM - 9:36AM |
L27.00004: How big is the hydrated electron? Thermodynamics of electron solvation and its partial molar volume Invited Speaker: David Bartels Several models for the hydrated electron solvation structure have been proposed, which all can do a reasonable job of reproducing the room temperature optical spectrum. As Larsen, Glover and Schwartz [1] demonstrated, tweaking the electron-water pseudopotential can completely change the structure from a cavity to a non-cavity geometry. Deciding between the competing models then requires comparison with other observables. The resonance Raman spectrum and the temperature dependence of the optical spectrum can be cited as evidence in favor of a non-cavity structure [2]. In the present work we will re-examine the thermodynamics of hydration [3]. In particular, we will present new experimental and simulation results for the partial molar volume, which can bear directly on the cavity vs. non-cavity controversy. \\[4pt] [1] Larsen, R.E., W.J. Glover, and B.J. Schwartz, Does the Hydrated Electron Occupy a Cavity? Science, 2010. 329(5987): p. 65-69.\\[0pt] [2] Casey, J.R., A. Kahros, and B.J. Schwartz, To Be or Not to Be in a Cavity: The Hydrated Electron Dilemma. Journal of Physical Chemistry B, 2013. 117(46): p. 14173-14182.\\[0pt] [3] Bartels, D.M., et al., Pulse radiolysis of supercritical water. 3. Spectrum and thermodynamics of the hydrated electron. Journal of Physical Chemistry A, 2005. 109(7): p. 1299-1307. [Preview Abstract] |
Wednesday, March 4, 2015 9:36AM - 9:48AM |
L27.00005: Theoretical studies of nonvalence correlation-bound anions Vamsee Voora, Kenneth Jordan Nonvalence correlation-bound anion states have been investigated using state-of-the-art ab initio methodologies as well as by model potential approaches. In nonvalence correlation-bound anion states the excess electron occupies a very extended orbital with the binding to the molecule or cluster being dominated by long-range correlation effects. Failure of conventional Hartree-Fock reference based approaches for treating these anionic states is discussed. Ab initio approaches that go beyond Hartree-Fock orbitals, such as Green's function, and equation-of-motion methods are used to characterize nonvalence correlation-bound anion states of a variety of systems including C$_{60}$ and C$_6$F$_6$. Edge-bound nonvalence correlation-bound anionic states are established for polycyclic aromatics. Accurate one-electron model potential approaches, parametrized using the results of ab initio calculations, are described. The model potentials are used to study nonvalence correlation-bound anion states of large water clusters as well as ``superatomic'' states of fullerene systems.\\[4pt] [1] V. K. Voora, and K. D. Jordan, {\em Nano Lett.}, {\bf 2014}, {\em 14 }(8), pp 4602-4606. [Preview Abstract] |
Wednesday, March 4, 2015 9:48AM - 10:24AM |
L27.00006: Solute-Solvent Structural Changes that Accompany Ion Dehydration in Electrospray Ionization (ESI) as Revealed by Cryogenic (80 K) Ion Mobility-Mass Spectrometry (IM-MS) Invited Speaker: David Russell Peptide/protein conformer preferences are dictated by intra- and intermolecular interactions. Because of the large number of degrees-of-freedom in bulk solvent networks and the dynamic nature of hydrogen bonds, experimental studies of specific interactions of individual conformational states are difficult. Gas phase studies of solvent-free biomolecules provide a potential solution to this problem because inter- and intramolecular interactions are effectively decoupled. However, a potential concern is that during the transition from solution to gas phase the molecules encounter unique environments that can potentially affect their conformer preference. A number of studies have demonstrated that peptide/protein ions generated by ESI can retain memory of their solution structures, including retention of biological activity, suggesting that gaseous ions can be kinetically trapped in local minima along their potential energy surface owing to evaporative cooling and relatively slow rates of isomerization; however, the effect of charge state and extent to which non-covalent interactions are affected remains unresolved. Here, we discuss recent cryogenic (80 K) IM-MS studies that capture the evaporative dynamics of a series of model peptide ions. Cryogenic-IM affords new insights as to the multiplicity of peptide ion conformations and how solute-solvent interactions alter both solute and solvent structures. [Preview Abstract] |
Wednesday, March 4, 2015 10:24AM - 10:36AM |
L27.00007: Mapping the UV Photophysics of Platinum Metal Complexes Bound to Nucleobases Ananya Sen, Caroline Dessent We report the first UV laser spectroscopic study of isolated gas-phase complexes of Platinum metal complex anions bound to a nucleobase as model systems for exploring at the molecular level the key photophysical processes involved in photodynamic therapy. Spectra of the $Pt^{IV}\left( {CN} \right)_{6}^{2-} \bullet Uracil$ and $Pt^{II}\left( {CN} \right)_{4}^{2-} \bullet Uracil$ complexes were acquired across the 220$-$320 nm range using mass-selective photodepletion and photofragment action spectroscopy. The spectra of both complexes reveal prominent UV absorption bands that we assign primarily to excitation of the Uracil $\pi -\pi $* localized chromophore. Distinctive UV photofragments are observed for the complexes, with $Pt^{IV}\left( {CN} \right)_{6}^{2-} \bullet Uracil$ photoexcitation resulting in complex fission, while $Pt^{II}\left( {CN} \right)_{4}^{2-} \bullet Uracil$ photoexcitation initiates a nucleobase proton-transfer reaction across 4.4$-$5.2 eV and electron detachment above 5.2 eV. The observed photofragments are consistent with ultrafast decay of a Uracil localized excited state back to the electronic ground state followed by intramolecular vibrational relaxation and ergodic complex fragmentation. In addition, we present recent results to explore how the photophysics of the Platinum complex-nucleobase clusters evolves as a function of nucleobase. Results are presented for $Pt^{II}\left( {CN} \right)_{4}^{2-} \bullet Uracil$ complexed to Cytosine, Thymine and Adenine, reveal distinctive decay dynamics which we attribute to the intrinsic decay dynamics of the nucleobase. [Preview Abstract] |
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