Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session C51: Coherence and Quantum Aspects of Living Systems IFocus
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Sponsoring Units: DBIO Chair: Vanessa Huxter, Univ of Arizona Room: LACC 511C |
Monday, March 5, 2018 2:30PM - 3:06PM |
C51.00001: Coherence in the Bacterial Reaction Center Invited Speaker: Veronica R. Policht Photosynthetic Reaction Center (RC) protein complexes rapidly trap absorbed sunlight and convert the excitation energy into a stable charge separation with near unity quantum efficiency in wild type proteins. In the past decade a large amount of research has been devoted to understanding the phenomenon of long-lived coherent oscillatory states in RCs, as well as other photosynthetic and molecular systems. Here we present ultrafast multidimensional spectra of the W(M250)V bacterial RC, which undergoes charge separation, and discuss our recent work to understand the physical origin of the observed coherent signals and what they reveal about the electronic structure of the bacterial RC. |
Monday, March 5, 2018 3:06PM - 3:18PM |
C51.00002: Quantumness from ultrafast spectroscopy experiments Animesh Datta, George Knee, Max Marcus, Luke Smith The role of quantumness in the energy transfer process in light-harvesting complexes has long been debated. A major obstacle in verifying competing hypothesis is the complicated nature of ultrafast spectroscopy experiments. While multidimensional ultrafast optical spectroscopy has been crucial in clarifying the nature of interacting multi-chromophoric systems, the underlying mechanisms of energy transport in light-harvesting complexes remain unclear. Earlier works have shown that 2D electronic spectroscopy can provide enough information to perform quantum process tomography on the multi-chromophoric light-harvesting complexes. We build upon this methodology to provide more efficient spectroscopic techniques that can provide bounds of measures of quantumness. In particular, we show how the nature of quantum correlations can be extracted directly from measured data rather than hypothesized models. We expect our tools to be applicable to the evaluation of quantumness from other spectroscopy experiments or any other data stream in general. |
Monday, March 5, 2018 3:18PM - 3:30PM |
C51.00003: Probing Quantum Interference Effects during Electron Transfer in Bacterial Pili Proteins Peter Dahl, Sophia Yi, Patrick O'Brien, Nikhil Malvankar A cornerstone of quantum physics is the interference of electron waves arising from the superposition principle. Metallic conductivity is an effect of interference of partial electron waves multiply scattered at the ion cores of the crystal lattice. Metallic conductivity has been considered impossible in proteins. However, previously we have shown that protein nanofilaments called pili of Geobacter sulfurreducens show metallic-like conductivity [1]. In preliminary studies, we have found that pili exhibit signatures of quantum interference phenomena of weak localization, one of the unique cases where superposition principle of quantum mechanics leads to observable consequences in the macroscopic systems. Applying magnetic field increased the conductivity of pili at physiological temperatures as expected from weak localization effect in the metallic regime. In contrast, the pili conductivity decreased at lower temperatures, where pili show semiconducting behavior, as expected for the wavefunction shrinkage effect. |
Monday, March 5, 2018 3:30PM - 3:42PM |
C51.00004: Effect of initial coherence in the excitation energy transfer in Fenna-Mathews-Olson complex: Distinguishing in vitro and in vivo dynamics Davinder Singh, Shubhrangshu Dasgupta Long-lasting coherence among different excitons in a 7-site monomer exists in an in vitro Fenna-Mathews-Olson (FMO) complex. In the exisiting models to explain such coherence, however, all the features of the excitation energy transfer (EET) through such monomer have not been considered together, namely, non-Markovianlty, relative dipole orientations of the chromophores and their site-specific coupling to the local bath modes, phonon contribution, initial states, the presence of the eighth chromphore, and the sink-model of the reaction center. In this work, all these included, we numerically solve the non-Markovian master equation to study the dynamics of EET in the singly-excited subspace of eight chromophores and the sink, incoherently coupled to the other sites, in a suitably structured phonon bath. We show that a laser pulse creates an initial excitonic coherence (thanks to non-orthogonal dipole orientations among the sites), that leads to the EET much faster than it happens for an initial mixed state. It enhances the transfer efficiency as well, near to unity. Our detailed analysis challenges the existing two-channel model of EET and also exhibits a clear distinction between the dynamics of an in vitro and an in vivo FMO complex. |
Monday, March 5, 2018 3:42PM - 3:54PM |
C51.00005: Structural Basis for Metallic Conductivity in Bacterial Pili Protein Filaments Sibel Ebru Yalcin, Patrick O'Brien, Winston Huynh, Yangqi Gu, Tamas Varga, Nikhil Malvankar Electron transfer in proteins typically occurs via quantum tunneling or hopping mechanism and metallic conductivity has been considered impossible. The quantum interference of partial electron waves scattered from a periodic structure can give rise to electron delocalization and therefore metallic conductivity. Our previous studies suggested that pili protein nanofilaments of Geobacter sulfurreducens possess a periodic structure that can confer metallic-like conductivity [1]. We aim to identify the structural and molecular mechanism of metallic conductivity. Here, using a suite of complementary methods such as X-ray diffraction, Circular Dichroism, Fluorescence Microscopy and Infrared Spectroscopy, we identify the molecular architecture responsible for metallic conductivity. Our studies suggest that aromatic amino acids in pili are closely packed from each other (< 4 Å), forming pi stacking, that can cause intermolecular electron delocalization, conferring metallic conductivity to pili. We observe large conformational changes in pili that accelerate electron transfer in pili. Furthermore, our studies show that improved metallic nature in the pili correlates with the improved pi stacking. |
Monday, March 5, 2018 3:54PM - 4:06PM |
C51.00006: Pulsed generation of electronic-vibrational quantum coherences and non-classicality in biophysical and biochemical systems Fernando Gómez-Ruiz, Ferney Rodríguez, Luis Quiroga, Neil Johnson We offer an explanation for why robust quantum coherences have been observed in so many driven biophysical and biochemical systems containing large numbers of components (e.g. N≠3 akin to the LHCII aggregates found in green plants). We avoid the typical assumptions inherent in all existing theoretical analyses, by calculating the exact real-time evolution of a driven, generic, N-component system. Our results predict a new form of dynamically-driven vibronic (i.e. electronic-vibrational) quantum entanglement which arises for intermediate pulse durations in a system of general N, and {\em without} having to access the empirically challenging strong-coupling regime. These new findings offer several functional advantages for energy processing in both natural and artificial nanosystems. |
Monday, March 5, 2018 4:06PM - 4:18PM |
C51.00007: When excitons dance: mechanistic regimes of vibronic transport Doran Bennett, Pavel Maly, Sam Blau, Christoph Kreisbeck, Greg Scholes, Reink van Grondelle, Alan Aspuru-Guzik Spectroscopic signatures of vibronic coherence, the delocalization between a donor and a vibrationally excited acceptor state, have been observed in both the phycobiliprotein PC645 antenna complex and the photosystem II reaction center. The extent to which vibronic coherence enhances photosynthetic light harvesting, however, remains controversial. The challenge in determining the importance of vibronic coherence has been the absence of a clear, quantitative assignment of vibronic mechanisms across different parameter regimes. Here, we use numerically exact hierarchical equations of motion (HEOM) calculations and detailed mechanistic analysis to establish the regimes of vibronic transport appropriate for prototypical photosynthetic heterodimers. Integrating the vibronic regimes with detailed atomistic simulations of PC645 we demonstrate that rapid transport from the highest-energy states to the lowest energy pigments in this pigment-protein complex occurs via an incoherent vibronic mechanism supported by a large reorganization energy and a broad collection of high-frequency vibrations. This work lays the foundation for further exploration of vibronic mechanisms in more complex systems such as the reaction center. |
Monday, March 5, 2018 4:18PM - 4:30PM |
C51.00008: Oxidative species-induced excitonic transport in biomolecular aromatic networks Philip Kurian, Travis Craddock Oxidative stress is a pathological hallmark of degenerative disorders such as Alzheimer’s disease and cancer, which are characterized by altered forms of the microtubule-associated protein (MAP) tau. The precise role of reactive oxygen species (ROS) in the disease process, however, is poorly understood. It is known that the production of ROS by mitochondria can result in ultraweak photon emission (UPE) within cells, and surrounding biomolecules can absorb these photons via aromatic amino acids (e.g., tryptophan and tyrosine). One likely absorber is the microtubule cytoskeleton, as it forms a vast network spanning neurons, is highly co-localized with mitochondria, and shows a high density of aromatics, but DNA and the photoactive receptors in the mitochondrial membrane are also potential candidates. These networks may traffic ROS-generated endogenous photon energy for cellular signaling, or they may serve as dissipaters of such energy to protect the cell from potentially harmful effects. Recent modeling efforts based on ambient temperature experiment are presented, showing that such biopolymers can feasibly absorb and channel these photoexcitations via resonance energy transfer, on mesoscopic length scales of physiological significance. |
Monday, March 5, 2018 4:30PM - 4:42PM |
C51.00009: Effect of capacitors in the central nervous system on neural behavior Douglas Boone, Giovanna Scarel We are interested in studying the interaction of electromagnetic (EM) waves with the capacitors that are found within the nervous systems of mammals. It is widely known that the central nervous system contains capacitors which allow electrical signals to pass through and be transported to the next neuron. However, in-depth studies exploring the interaction of EM waves with the nervous system and its effect on neural behavior related to the values of the capacitance are currently sparse. The human nervous system is highly complex; therefore, the capacitance of a cell may vary over a range of several orders of magnitude, depending on the region of the body that cell is concentrated. In our work we show how, through the development of a mathematical equations combined with experimental results, we are able calculate the amount of energy transferred from EM waves to the capacitors in the nervous system. Knowing the capacitance values for cells allows us to calculate the action potential the stimulation will cause. This suggest that if we are able to quantify the transfer of energy from EM waves to a specific capacitor, we can then quantify the action potential generated for a specific neuron and predict the effect on the nervous system as well as neurological behavior. |
Monday, March 5, 2018 4:42PM - 5:18PM |
C51.00010: Metallic Conductivity in Proteins: A New Paradigm for Biological Electron Transfer Invited Speaker: Nikhil Malvankar
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