The Experts below are selected from a list of 294 Experts worldwide ranked by ideXlab platform

Jin Wang - One of the best experts on this subject based on the ideXlab platform.

  • curl flux coherence and population landscape of molecular systems nonequilibrium quantum steady state Energy Charge transport and thermodynamics
    arXiv: Chemical Physics, 2015
    Co-Authors: Zhedong Zhang, Jin Wang
    Abstract:

    We established a theoretical framework in terms of the curl flux, population landscape, and coherence for non-equilibrium quantum systems at steady state, through exploring the Energy and Charge transport in molecular processes. The curl quantum flux plays the key role in determining transport properties and the system reaches equilibrium when flux vanishes. The novel curl quantum flux reflects the degree of non-equilibriumness and the time-irreversibility. We found an analytical expression for the quantum flux and its relationship to the environmental pumping (non-equilibriumness quantified by the voltage away from the equilibrium) and the quantum tunneling. Furthermore, we investigated another quantum signature, the coherence, quantitatively measured by the non-zero off diagonal element of the density matrix. Besides the environment-assistance which can give dramatic enhancement of coherence and quantum flux with high voltage at a fixed tunneling strength, the quantum flux is promoted by the coherence in the regime of small tunneling while reduced by the coherence in the regime of large tunneling, due to the non-monotonic relationship between the coherence and tunneling. In view of the system as a quantum heat engine, we studied the non-equilibrium thermodynamics and established the analytical connections of curl quantum flux to the transport quantities such as Energy (Charge) transfer efficiency, chemical reaction efficiency, Energy dissipation, heat and electric currents observed in the experiments. We observed a perfect transfer efficiency in chemical reactions at high voltage (chemical potential difference). Our theoretical predicted behavior of the electric current with respect to the voltage is in good agreements with the recent experiments on electron transfer in single molecules.

  • curl flux coherence and population landscape of molecular systems nonequilibrium quantum steady state Energy Charge transport and thermodynamics
    Journal of Chemical Physics, 2014
    Co-Authors: Zhedong Zhang, Jin Wang
    Abstract:

    We established a theoretical framework in terms of the curl flux, population landscape, and coherence for non-equilibrium quantum systems at steady state, through exploring the Energy and Charge transport in molecular processes. The curl quantum flux plays the key role in determining transport properties and the system reaches equilibrium when flux vanishes. The novel curl quantum flux reflects the degree of non-equilibriumness and the time-irreversibility. We found an analytical expression for the quantum flux and its relationship to the environmental pumping (non-equilibriumness quantified by the voltage away from the equilibrium) and the quantum tunneling. Furthermore, we investigated another quantum signature, the coherence, quantitatively measured by the non-zero off diagonal element of the density matrix. Populations of states give the probabilities of individual states and therefore quantify the population landscape. Both curl flux and coherence depend on steady state population landscape. Besides the environment-assistance which can give dramatic enhancement of coherence and quantum flux with high voltage at a fixed tunneling strength, the quantum flux is promoted by the coherence in the regime of small tunneling while reduced by the coherence in the regime of large tunneling, due to the non-monotonic relationship between the coherence and tunneling. This is in contrast to the previously found linear relationship. For the systems coupled to bosonic (photonic and phononic) reservoirs the flux is significantly promoted at large voltage while for fermionic (electronic) reservoirs the flux reaches a saturation after a significant enhancement at large voltage due to the Pauli exclusion principle. In view of the system as a quantum heat engine, we studied the non-equilibrium thermodynamics and established the analytical connections of curl quantum flux to the transport quantities such as Energy (Charge) transfer efficiency, chemical reaction efficiency, Energy dissipation, heat and electric currents observed in the experiments. We observed a perfect transfer efficiency in chemical reactions at high voltage (chemical potential difference). Our theoretical predicted behavior of the electric current with respect to the voltage is in good agreements with the recent experiments on electron transfer in single molecules.

  • curl flux coherence and population landscape of molecular systems nonequilibrium quantum steady state Energy Charge transport and thermodynamics
    Journal of Chemical Physics, 2014
    Co-Authors: Zhedong Zhang, Jin Wang
    Abstract:

    We established a theoretical framework in terms of the curl flux, population landscape, and coherence for non-equilibrium quantum systems at steady state, through exploring the Energy and Charge transport in molecular processes. The curl quantum flux plays the key role in determining transport properties and the system reaches equilibrium when flux vanishes. The novel curl quantum flux reflects the degree of non-equilibriumness and the time-irreversibility. We found an analytical expression for the quantum flux and its relationship to the environmental pumping (non-equilibriumness quantified by the voltage away from the equilibrium) and the quantum tunneling. Furthermore, we investigated another quantum signature, the coherence, quantitatively measured by the non-zero off diagonal element of the density matrix. Populations of states give the probabilities of individual states and therefore quantify the population landscape. Both curl flux and coherence depend on steady state population landscape. Besides ...

Olle Bjorkman - One of the best experts on this subject based on the ideXlab platform.

  • adenine nucleotides and the xanthophyll cycle in leaves
    Planta, 1994
    Co-Authors: Adam M Gilmore, Olle Bjorkman
    Abstract:

    The effects of varying the steady-state rate of non-cyclic photosynthetic electron transport on the leaf adenylate Energy Charge and the epoxidation state of the xanthophyll-cycle pigments were determined in leaves of cotton (Gossypium hirsutum L.) and the mangrove (Aegialitis annulata R.Br.). Different photosynthetic rates were obtained by varying the intercellular CO2 concentration and/or the leaf temperature, and in some cases, by changing the leaf conductance to CO2 diffusion. Also determined were the effects of these treatments on the changes in the adenylate Energy Charge and the epoxidation state of the xanthophyll-cycle pigments that occur after darkening of the leaves. The leaf adenylate pool remained close to equilibrium with the adenylate kinase both in the light at steady state and during dark relaxation. The adenylate Energy Charge increased as the photosynthetic rate decreased and maximal levels were obtained when CO2 assimilation and, therefore, non-cyclic electron flow were maximally inhibited. This implies that, in nature, photophosphorylation may provide Energy needed for ion-pumping and biosynthetic and repair processes, even under stress conditions that severely restrict or prevent photosynthetic gas exchange. High levels of de-epoxidized violaxanthin in the light did not necessarily indicate or depend on a high adenylate Energy Charge. Dithiothreitol, an inhibitor of the violaxanthin de-epoxidase a nd ascorbate peroxidase, did not inhibit the adenylate Energy Charge in the light. Thus we conclude that coupled electron transport during inhibited CO2 fixation was not driven by a dithiothreitol-sensitive Mehler ascorbate-peroxidase reaction. The changes in the adenylate Energy Charge and xanthophyll re-epoxidation that follow when leaves were darkened are strongly affected by the preceding photosynthetic rate. Postillumination fluctuations in adenylate Energy Charge, both at 15 ° and 27 °C, were most pronounced when the preceding photosynthetic rate was minimal and least pronounced when this rate was maximal. Temperature had a considerably greater influence in the dark on xanthophyll re-epoxidation than on the pattern of adenylate relaxation.

  • adenine nucleotides and the xanthophyll cycle in leaves ii comparison of the effects of co2 and temperature limited photosynthesis on photosystem ii fluorescence quenching the adenylate Energy Charge and violaxanthin de epoxidation in cotton
    Planta, 1994
    Co-Authors: Adam M Gilmore, Olle Bjorkman
    Abstract:

    The relationships among the leaf adenylate Energy Charge, the xanthophyll-cycle components, and photosystem II (PSII) fluorescence quenching were determined in leaves of cotton (Gossypium hirsutum L. cv. Acala) under different leaf temperatures and different intercellular CO 2 concentrations (C i ). Attenuating the rate of photosynthesis by lowering the C i at a given temperature and photon flux density increased the concentration of high-Energy adenylate phosphate bonds (adenylate Energy Charge) in the cell by restricting ATP consumption (A.M. Gilmore, O. Bjorkman 1994, Planta 192, 526-536)

Michael R. Wasielewski - One of the best experts on this subject based on the ideXlab platform.

  • interrogating the intramolecular Charge transfer state of a julolidine anthracene donor acceptor molecule with femtosecond stimulated raman spectroscopy
    Journal of Physical Chemistry Letters, 2010
    Co-Authors: Jenny V. Lockard, Annie Butler Ricks, Michael R. Wasielewski
    Abstract:

    The nature of the lowest-Energy Charge-transfer (CT) excited state of the donor−acceptor molecule, 3,5-dimethyl-4-(9-anthracenyl)julolidine (DMJ−An) is investigated using femtosecond stimulated Raman spectroscopy. Transient Raman spectra are presented with subpicosecond time resolution, and peaks are assigned based on the published Raman modes of the reference molecule phenyl anthracene. The results indicate that the CT excited state is dominated by a fully Charge separated radical ion pair state with minimal contribution from the local anthracene π−π* state.

  • Energy Charge and spin transport in molecules and self assembled nanostructures inspired by photosynthesis
    ChemInform, 2006
    Co-Authors: Michael R. Wasielewski
    Abstract:

    Electron transfer in biological molecules provides both insight and inspiration for developing chemical systems having similar functionality. Photosynthesis is an example of an integrated system in which light harvesting, photoinduced Charge separation, and catalysis combine to carry out two thermodynamically demanding processes, the oxidation of water and the reduction of carbon dioxide. The development of artificial photosynthetic systems for solar Energy conversion requires a fundamental understanding of electron-transfer reactions between organic molecules. Since these reactions most often involve single-electron transfers, the spin dynamics of photogenerated radical ion pairs provide important information on how the rates and efficiencies of these reactions depend on molecular structure. Given this knowledge, the design and synthesis of large integrated structures to carry out artificial photosynthesis is moving forward. An important approach to achieving this goal is the development of small, functional building blocks, having a minimum number of covalent bonds, which also have the appropriate molecular recognition sites to facilitate self-assembly into a complete, functional artificial photosynthetic system.

Hai Liu - One of the best experts on this subject based on the ideXlab platform.

  • quality deterioration of cut carnation flowers involves in antioxidant systems and Energy status
    Scientia Horticulturae, 2014
    Co-Authors: Hai Liu, Lili Song, Yanli You, Jian Sun, Yueming Jiang
    Abstract:

    Abstract Adenosine triphosphate (ATP) has played an important role in regulating senescence of horticultural crops. The physiological mechanism of exogenous ATP to affect the senescence of cut carnation during vase life was investigated. Fresh cut carnation flowers were treated with distilled water (control), 0.1 mM adenosine triphosphate (ATP) or 0.5 mM 2,4-dinitrophenol (DNP, an agent for uncoupling oxidative phosphorylation) and then held at 25 °C up to nine days. Exogenous ATP supply increased flower size, maintained fresh weight, extended vase life, reduced ethylene production rate and maintained membrane integrity. ATP treatment also reduced activities of phospholipase D (LD) and lipoxygenase (LOX), enhanced activities of superoxide dismutase (SOD) and catalase (CAT) and increased endogenous contents of ATP and adenosine diphosphate (ADP) and Energy Charge level at the later vase life. In comparison to control, exogenous application of DNP accelerated ethylene production and reduced vase life, increased membrane permeability, MDA content and activities of PLD and LOX and reduced activities of SOD and CAT. Furthermore, contents of ATP and ADP and Energy Charge level decreased in the DNP-treated flowers during vase life. Thus, exogenous ATP supply could maintain membrane integrity, increase antioxidant system and improve endogenous Energy level, thereby suppressing ethylene production and retarding the senescence of cut carnation flower during vase life.

  • cold storage duration affects litchi fruit quality membrane permeability enzyme activities and Energy Charge during shelf time at ambient temperature
    Postharvest Biology and Technology, 2011
    Co-Authors: Hai Liu, Lili Song, Yanli You, Xuewu Duan, Yueming Jiang, D C Joyce, Muhammad Ashraf
    Abstract:

    Storage and transport of litchi fruit at low temperature is widely practiced commercially. In this study, no pericarp browning was evident at out-turn on litchi fruit stored for 10 and 20 days at cold temperature of 3–5 °C, but fruit stored for 10 days at 3–5 °C gradually browned after 12 h of shelf time at ambient temperature of 25 °C, with the browning index (BI) being elevated to 2.5 at 24 h of shelf life. Furthermore, fruit stored for 30 days began to rot and had a decay incidence of about 30% after 24 h on the shelf. The temperature increment from 3–5 to 25 °C induced marked increases in activities of lipase, phospholipase D (PLD) and lipoxygenase (LOX). Litchi fruit stored for 10 days at 3–5 °C followed by the shelf time at 25 °C had lower activities of lipase, PLD and LOX, and also lower levels of membrane permeability, than did fruit stored for 20 and 30 days. Energy level of the pericarp tissue of cold-stored litchi fruit was similarly dependent on storage time at 3–5 °C plus shelf time at 25 °C. Adenosine triphosphate (ATP) content and adenylate Energy Charge (AEC) level in pericarp tissues decreased as cold storage progressed. However, ATP and adenosine diphosphate (ADP) contents, and the AEC levels, in cold-stored litchi fruit increased during shelf time at 25 °C, reaching a peak after 6 h, and then decreasing. Fruit stored for 30 days at 3–5 °C had much lower ATP content and AEC level than fruit stored for 10 and 20 days. Increased activities of lipase, PLD and LOX, and Energy shortage in cold-stored pericarp tissues during subsequent shelf time at 25 °C suggest that the deterioration of membrane integrity and loss of compartmentation gives rise to accelerated browning and fruit quality deterioration.

Francis Dsouza - One of the best experts on this subject based on the ideXlab platform.

  • high Energy Charge separated states by reductive electron transfer followed by electron shift in the tetraphenylethylene aluminum iii porphyrin fullerene triad
    Journal of Physical Chemistry C, 2019
    Co-Authors: Niloofar Zarrabi, Adam J. Matula, Christia Agatemo, Gary N Lim, Ando J Ayard, Victo S Atista, Francis Dsouza, Prashanth K. Poddutoori
    Abstract:

    A high-potential supramolecular triad (TPE-AlPor ← Im-C60) composed of aluminum(III) porphyrin (AlPor), fullerene (C60), and tetraphenylethylene (TPE) has been constructed. The fullerene and tetraphenylethylene units are bound axially to opposite faces of the porphyrin plane via coordination and covalent bonds, respectively. The ground and excited-state properties of the triad and reference dyads are studied using steady-state and time-resolved spectroscopic techniques. The transient data show that photoexcitation results in Charge separation from tetraphenylethylene to the excited singlet state of the porphyrin (1AlPor*), generating a high-Energy (2.14 eV) Charge-separated state, (TPE)•+-(AlPor)•–, in toluene. A subsequent electron migration from the AlPor–• to fullerene generates a second high-Energy (1.78 eV) Charge-separated state (TPE)•+-AlPor ← Im-(C60)•–. The lifetime of the Charge separation is about 25 ns. The high Energy stored in the form of Charge-separated states along with their reasonable l...

  • high potential perfluorinated phthalocyanine fullerene dyads for generation of high Energy Charge separated states formation and photoinduced electron transfer studies
    ChemPhysChem, 2014
    Co-Authors: Sushanta K Das, Andrew Mahler, Angela K Wilson, Francis Dsouza
    Abstract:

    High oxidation potential perfluorinated zinc phthalocyanines (ZnF(n)Pcs) are synthesised and their spectroscopic, redox, and light-induced electron-transfer properties investigated systematically by forming donor-acceptor dyads through metal-ligand axial coordination of fullerene (C60) derivatives. Absorption and fluorescence spectral studies reveal efficient binding of the pyridine- (Py) and phenylimidazole-functionalised fullerene (C60Im) derivatives to the zinc centre of the F(n)Pcs. The determined binding constants, K, in o-dichlorobenzene for the 1:1 complexes are in the order of 10(4) to 10(5) M(-1); nearly an order of magnitude higher than that observed for the dyad formed from zinc phthalocyanine (ZnPc) lacking fluorine substituents. The geometry and electronic structure of the dyads are determined by using the B3LYP/6-31G* method. The HOMO and LUMO levels are located on the Pc and C60 entities, respectively; this suggests the formation of ZnF(n)Pc(.+)-C60Im(.-) and ZnF(n)Pc(.+)-C60Py(.-) (n=0, 8 or 16) intra-supramolecular Charge-separated states during electron transfer. Electrochemical studies on the ZnPc-C60 dyads enable accurate determination of their oxidation and reduction potentials and the Energy of the Charge-separated states. The Energy of the Charge-separated state for dyads composed of ZnF(n)Pc is higher than that of normal ZnPc-C60 dyads and reveals their significance in harvesting higher amounts of light Energy. Evidence for Charge separation in the dyads is secured from femtosecond transient absorption studies in nonpolar toluene. Kinetic evaluation of the cation and anion radical ion peaks reveals ultrafast Charge separation and Charge recombination in dyads composed of perfluorinated phthalocyanine and fullerene; this implies their significance in solar-Energy harvesting and optoelectronic device building applications.