Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session P25: DCP Prize SessionFocus Prize/Award
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Sponsoring Units: DCP Chair: David Nesbitt, University of Colorado Room: 288 |
Wednesday, March 15, 2017 2:30PM - 2:42PM |
P25.00001: Gas-Phase Folding of Small Glutamine Containing Peptides: Sidechain Hydrogen Bonding Stabilizes $\beta $-turns. Patrick S. Walsh, Karl N. Blodgett, Carl McBurney, Samuel H. Gellman, Timothy S. Zwier Glutamine is vitally important to a class of neurodegenerative diseases called poly-glutamine (poly-Q) repeat diseases such as Huntington's Disease (HD). Recent studies have revealed a pathogenic pathway that proceeds through misfolding of poly-Q regions into characteristic $\beta $-turn/$\beta $-hairpin structures that are highly correlated with toxicity. The inherent conformational preferences of small glutamine containing peptides (Ac-Q-Q-NHBn and Ac-A-Q-NHBn) were studied using conformation-specific IR and UV spectroscopies, with the goal of probing the delicate interplay between three competitive hydrogen bonding motifs: backbone-backbone, sidechain-backbone, and sidechain-sidechain hydrogen bonds. Laser desorption, coupled with a supersonic expansion, was used to introduce the non-thermally labile sample into the gas-phase. Resonant ion-dip infrared (RIDIR) spectroscopy is a powerful tool for recording the vibrational spectra of single conformational isomers and was used here to reveal the innate structural preferences of the glutamine containing peptides. Experimental results are compared against density functional calculations to arrive at firm conformational assignments. Our results demonstrate a striking preference for $\beta $-turn formation in the non-polar environment of the gas-phase. [Preview Abstract] |
Wednesday, March 15, 2017 2:42PM - 3:18PM |
P25.00002: Cold chemistry with cold molecules Invited Speaker: Yuval Shagam Low temperature chemistry has been predicted to be dominated by quantum effects, such as shape resonances, where colliding particles exhibit wave-like behavior and tunnel through potential barriers. Observation of these quantum effects provides valuable insight into the microscopic mechanism that governs scattering processes. Our recent advances in the control of neutral supersonic molecular beams, namely merged beam experiments, have enabled continuous tuning of collision energies from the classical regime at room temperature down to 0.01 kelvin, where a quantum description of the dynamics is necessary. I will discuss our use of this technique to study how the dynamics change when molecules participate in collisions, demonstrating the crucial role the molecular quantum rotor plays. We have found that at low temperatures rotational state of the molecule can strongly affect collision dynamics considerably changing reaction rates, due to the different symmetries of the molecular wavefunction. [Preview Abstract] |
Wednesday, March 15, 2017 3:18PM - 3:54PM |
P25.00003: In the Footsteps of Irving Langmuir: Physical Chemistry in Service of Society Invited Speaker: Emily Carter The approach that Irving Langmuir took during his scientific career in industry at General Electric exemplifies the best that we chemical physicists/physical chemists can offer the world. His name is associated with very fundamental concepts and phenomena (e.g., the Langmuir isotherm, Langmuir-Blodgett films) along with practical inventions (e.g., the Langmuir probe, Langmuir trough). He worked at the interface of physics, chemistry, and engineering, with much of his important work devoted to understanding surface and interface phenomena. I have -- unintentionally -- followed in his footsteps, trained as a physical chemist who now leads the engineering school at Princeton. In this talk, I will give examples from my research as to how fundamental physical chemistry techniques and concepts -- based largely on quantum mechanics -- can be harnessed to help the world transition to a sustainable energy future. In the footsteps of Irving, surface and interfacial phenomena will figure prominently in the examples chosen. [Preview Abstract] |
Wednesday, March 15, 2017 3:54PM - 4:30PM |
P25.00004: Earle K. Plyler Prize Lecture: The Three Pillars of Ultrafast Molecular Science - Time, Phase, Intensity Invited Speaker: Albert Stolow We discuss the probing and control of molecular wavepacket dynamics in the context of three main `pillars' of light-matter interaction: time, phase, intensity. Time: Using short, coherent laser pulses and perturbative matter-field interactions, we study molecular wavepackets with a focus on the ultrafast non-Born-Oppenheimer dynamics, that is, the coupling of electronic and nuclear motions. Time-Resolved Photoelectron Spectroscopy (TRPES) is a powerful ultrafast probe of these processes in polyatomic molecules because it is sensitive both electronic and vibrational dynamics [1, 2]. Ideally, one would like to observe these ultrafast processes from the molecule's point of view -- the Molecular Frame -- thereby avoiding loss of information due to orientational averaging. This can be achieved by Time-Resolved Coincidence Imaging Spectroscopy (TRCIS) which images 3D recoil vectors of both photofragments and photoelectrons, in coincidence and as a function of time, permitting direct Molecular Frame imaging of valence electronic dynamics during a molecular dynamics [3]. Phase: Using intermediate strength non-perturbative interactions, we apply the second order (polarizability) Non-Resonant Dynamic Stark Effect (NRDSE) to control molecular dynamics without any net absorption of light [4]. NRDSE is also the interaction underlying molecular alignment and applies to field-free 1D of linear molecules and field-free 3D alignment of general (asymmetric) molecules [5]. Using laser alignment, we can transiently fix a molecule in space, yielding a more general approach to direct Molecular Frame imaging of valence electronic dynamics during a chemical reaction [6, 7]. Intensity: In strong (ionizing) laser fields, a new laser-matter physics emerges for polyatomic systems [8] wherein both the single active electron picture and the adiabatic electron response, both implicit in the standard 3-step models, can fail dramatically. This has important consequences for all attosecond strong field spectroscopies of polyatomic molecules, including high harmonic generation (HHG) [9]. We discuss an experimental method, Channel-Resolved Above Threshold Ionization (CRATI), which directly unveils the electronic channels participating in the attosecond molecular strong field ionization response [10]. \textbf{[1]} Nature \underline {401}, 52, (1999). \textbf{[2]} Chemical Reviews \underline {104}, 1719 (2004). \textbf{[3]} Science \underline {311}, 219 (2006). \textbf{[4]} Science \underline {314}, 278 (2006). \textbf{[5] }Physical Review Letters \underline {94}, 143002 (2005); \underline {97}, 173001 (2006). \textbf{[6]} Science \underline {323}, 1464 (2009). \textbf{[7] }Nature Physics \underline {7}, 612 (2011). \textbf{[8]} Physical Review Letters \underline {86}, 51 (2001); \underline {93}, 203402 (2004); \underline {93}, 213003 (2004). \textbf{[9]} Science \underline {322}, 1207 (2008). \textbf{[10]} Science \underline {335}, 1336 (2012); Physical Review Letters \underline {110}, 023004 (2013) [Preview Abstract] |
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