scholarly journals Role of hydrogen bond alternation and charge transfer states in photoactivation of the Orange Carotenoid Protein

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Igor A. Yaroshevich ◽  
Eugene G. Maksimov ◽  
Nikolai N. Sluchanko ◽  
Dmitry V. Zlenko ◽  
Alexey V. Stepanov ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Hydrogen Bond ◽  
Charge Transfer ◽  
Electric Field ◽  
Quantum Chemical ◽  
Time Resolved ◽  
Bond Alternation ◽  
Orange Carotenoid Protein ◽  
The Impact

AbstractHere, we propose a possible photoactivation mechanism of a 35-kDa blue light-triggered photoreceptor, the Orange Carotenoid Protein (OCP), suggesting that the reaction involves the transient formation of a protonated ketocarotenoid (oxocarbenium cation) state. Taking advantage of engineering an OCP variant carrying the Y201W mutation, which shows superior spectroscopic and structural properties, it is shown that the presence of Trp201 augments the impact of one critical H-bond between the ketocarotenoid and the protein. This confers an unprecedented homogeneity of the dark-adapted OCP state and substantially increases the yield of the excited photoproduct S*, which is important for the productive photocycle to proceed. A 1.37 Å crystal structure of OCP Y201W combined with femtosecond time-resolved absorption spectroscopy, kinetic analysis, and deconvolution of the spectral intermediates, as well as extensive quantum chemical calculations incorporating the effect of the local electric field, highlighted the role of charge-transfer states during OCP photoconversion.

scholarly journals Restraining Surface Charge Accumulation and Enhancing Surface Flashover Voltage through Dielectric Coating

Coatings ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 750
Author(s):  
Jixing Sun ◽  
Sibo Song ◽  
Xiyu Li ◽  
Yunlong Lv ◽  
Jiayi Ren ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Electric Field ◽  
Electric Fields ◽  
Transition Process ◽  
Metallic Particle ◽  
Particle Charging ◽  
Insulating Surfaces ◽  
Surface Flashover ◽  
Charging Time ◽  
The Impact

A conductive metallic particle in a gas-insulated metal-enclosed system can charge through conduction or induction and move between electrodes or on insulating surfaces, which may lead to breakdown and flashover. The charge on the metallic particle and the charging time vary depending on the spatial electric field intensity, the particle shape, and the electrode surface coating. The charged metallic particle can move between the electrodes under the influence of the spatial electric field, and it can discharge and become electrically conductive when colliding with the electrodes, thus changing its charge. This process and its factors are mainly affected by the coating condition of the colliding electrode. In addition, the interface characteristics affect the particle when it is near the insulator. The charge transition process also changes due to the electric field strength and the particle charging state. This paper explores the impact of the coating material on particle charging characteristics, movement, and discharge. Particle charging, movement, and charge transfer in DC, AC, and superimposed electric fields are summarized. Furthermore, the effects of conductive particles on discharge characteristics are compared between coated and bare electrodes. The reviewed studies demonstrate that the coating can effectively reduce particle charge and thus the probability of discharge. The presented research results can provide theoretical support and data for studying charge transfer theory and design optimization in a gas-insulated system.

The Nature of the Hydrogen Bond in DNA Base Pairs: The Role of Charge Transfer and Resonance Assistance

1999 ◽  
Vol 5 (12) ◽  
pp. 3581-3594 ◽  
Author(s):  
Célia Fonseca Guerra ◽  
F. Matthias Bickelhaupt ◽  
Jaap G. Snijders ◽  
Evert Jan Baerends
Keyword(s):  
Hydrogen Bond ◽  
Charge Transfer ◽  
Base Pairs ◽  
Dna Base ◽  
Dna Base Pairs

Lateral deformations of a crystal of potassium acid phthalate in an external electric field

2021 ◽  
Vol 54 (5) ◽  
pp. 1317-1326
Author(s):  
Arsen Petrenko ◽  
Nataliya Novikova ◽  
Alexander Blagov ◽  
Anton Kulikov ◽  
Yury Pisarevskii ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Electrical Conductivity ◽  
Electric Field ◽  
External Electric Field ◽  
Applied Field ◽  
X Ray Diffraction ◽  
Time Resolved ◽  
X Ray ◽  
Potassium Acid Phthalate ◽  
Acid Phthalate

The anisotropy of deformations in potassium acid phthalate crystals arising under the action of an external electric field up to 1 kV mm−1 applied along the [001] polar axis was studied using X-ray diffraction methods at room temperature. Electrical conductivity was measured and rocking curves for reflections 400, 070 and 004 were obtained by time-resolved X-ray diffractometry in Laue and Bragg geometries. Two saturation processes were observed from the time dependences of the electrical conductivity. A shift in the diffraction peaks and a change in their intensity were found, which indicated a deformation of the crystal structure. Rapid piezoelectric deformation and reversible relaxation-like deformation, kinetically similar to the electrical conductivity of a crystal, were revealed. The deformation depended on the polarity and strength of the applied field. The deformation was more noticeable in the [100] direction and was practically absent in the [001] direction of the applied field. X-ray diffraction analysis revealed a disordered arrangement of potassium atoms, i.e. additional positions and vacancies. The heights of potential barriers between the positions of K+ ions and the paths of their possible migration in the crystal structure of potassium acid phthalate were determined. The data obtained by time-resolved X-ray diffractometry and X-ray structure analysis, along with additional electrophysical measurements, allow the conclusion that the migration of charge carriers (potassium cations) leads to lateral deformation of the crystal structure of potassium phthalate in an external electric field.

Influence of Electron-withdrawing Substituents on Photoelectrochemical Surface Phenomena at Phthalocyanine Thin Film Electrodes

1999 ◽  
Vol 03 (06) ◽  
pp. 444-452 ◽  
Author(s):  
TORSTEN OEKERMANN ◽  
DERCK SCHLETTWEIN ◽  
NILS I. JAEGER ◽  
DIETER WÖHRLE
Keyword(s):  
Charge Transfer ◽  
Steady State ◽  
Electrolyte Concentration ◽  
Surface States ◽  
Surface Phenomena ◽  
Time Resolved ◽  
Photogenerated Electrons ◽  
Millisecond Range ◽  
Electron Withdrawing Substituents

The influence of electron-withdrawing substituents on the photoelectrochemical properties of phthalocyanines is shown in a comparison between hexadecafluorophthalocyaninatozinc(II) ( F 16 PcZn ) and the unsubstituted phthalocyaninatozinc(II) ( PcZn ). The role of surface states in the photoelectrochemistry of both materials has been investigated by time-resolved photocurrent measurements in the millisecond range. The charging and discharging of surface states could clearly be seen as spikes at the beginning and the end of illumination. Surface states were filled with photogenerated electrons at PcZn and with photogenerated holes at F 16 PcZn . In the steady state under illumination only cathodic photocurrents were detected at PcZn , while at F 16 PcZn both cathodic and anodic photocurrents were observed. An adsorption step of electroactive species prior to the charge transfer was derived from the dependence of the steady state photocurrents on the electrolyte concentration for both materials. The concentration dependence of the charging and discharging currents, however, showed that charge transfer from surface states to the electrolyte occurs at PcZn , while at F 16 PcZn the surface states only represent recombination centres.

scholarly journals On the Role of Hydrogen Bond Strength and Charge Transfer of a Diels-Alder Reaction On-Water: Semiempirical and Free Energy Calculations.

2021 ◽  
Author(s):  
Andrés Henao Aristizàbal ◽  
Yomna Gohar ◽  
René Whilhelm ◽  
Thomas D. Kühne
Keyword(s):  
Hydrogen Bond ◽  
Free Energy ◽  
Charge Transfer ◽  
Hydrogen Bonds ◽  
Density Functional ◽  
Alder Reaction ◽  
Free Energy Calculations ◽  
Diels Alder ◽  
Diels Alder Reaction

Accelerated chemistry at the interface with water has received increasing attention. The mechanisms behind the enhanced reactivity On-Water are not yet clear. In this work we use a Langevin scheme in the spirit of second generation Car-Parrinello to accelerate the second-order density functional Tight-Binding (DFTB2) method in order to investigate the free energy of two Diels-Alder reaction On-Water: the cycloaddition between cyclopentadiene and ethyl cinnamate or thionocinnamate. The only difference between the reactants is the substitution of a carbonyl oxygen for a thiocarbonyl sulfur, making possible the distinction between them as strong and weak hydrogen-bond acceptors. We find a different mechanism for the reaction during the transition states and uncover the role of hydrogen bonds along with the reaction path. Our results suggest that acceleration of Diels-Alder reactions do not arise from an increased number of hydrogen bonds at the transition state and charge transfer plays a significant role. However, the presence of water and hydrogen-bonds is determinant for the catalysis of these reactions.

scholarly journals CHEMISORPTION OF ENROFLOXACIN ON RUTILE-TIO2 (110) SURFACE: A THEORETICAL INVESTIGATION

2019 ◽  
Vol 57 (4) ◽  
pp. 449
Author(s):  
Trung Tien Nguyen ◽  
Tri Ngoc Nguyen ◽  
Dai Quoc Ho
Keyword(s):  
Hydrogen Bond ◽  
Chemical Analysis ◽  
Dft Calculations ◽  
Quantum Chemical ◽  
Adsorption Process ◽  
Stable Configuration ◽  
Quantum Chemical Analysis ◽  
Rutile Tio2 ◽  
The Stability

We investigated the adsorption of enrofloxacin (ENR) antibiotic on rutile-TiO2 (r-TiO2­) (110) surface using DFT calculations. Stable configurations of the adsorption of ENR on r-TiO2 (110) were observed. The origin and role of interactions in stablizing the configurations are thoroughly analyzed using NBO and AIM analyses. Obtained results indicate that the adsorption process is characterized as a strong chemisorption with an associated energy of ca. -35.1 kcal.mol-1 for the most stable configuration. Quantum chemical analysis shows that the stability of configurations is mainly determined by >C=O∙∙∙Ti5f electrostatic interaction along with supplement of H∙∙∙Ob hydrogen bond.

scholarly journals A deep insight into the ion foreshock with the help of test particle two-dimensional simulations

2020 ◽  
Vol 38 (6) ◽  
pp. 1217-1235
Author(s):  
Philippe Savoini ◽  
Bertrand Lembège
Keyword(s):  
Electric Field ◽  
Shock Front ◽  
Test Particle ◽  
Field Component ◽  
Upstream Region ◽  
Mirror Reflection ◽  
Two Dimensional ◽  
Shock Profiles ◽  
The Impact

Abstract. Two-dimensional (2D) test particle simulations based on shock profiles issued from 2D full particle-in-cell (PIC) simulations are used in order to analyze the formation processes of ions back streaming within the upstream region after interacting with a quasi-perpendicular curved shock front. Two different types of simulations have been performed based on (i) a fully consistent expansion (FCE) model, which includes all self-consistent shock profiles at different times, and (ii) a homothetic expansion (HE) model in which shock profiles are fixed at certain times and artificially expanded in space. The comparison of both configurations allows one to analyze the impact of the front nonstationarity on the back-streaming population. Moreover, the role of the space charge electric field El is analyzed by either including or canceling the El component in the simulations. A detailed comparison of these last two different configurations allows one to show that this El component plays a key role in the ion reflection process within the whole quasi-perpendicular propagation range. Simulations provide evidence that the different field-aligned beam (FAB) and gyro-phase bunched (GPB) populations observed in situ are essentially formed by a Et×B drift in the velocity space involving the convective electric field Et. Simultaneously, the study emphasizes (i) the essential action of the magnetic field component on the GPB population (i.e., mirror reflection) and (ii) the leading role of the convective field Et in the FAB energy gain. In addition, the electrostatic field component El is essential for reflecting ions at high θBn angles and, in particular, at the edge of the ion foreshock around 70∘. Moreover, the HE model shows that the rate BI% of back-streaming ions is strongly dependent on the shock front profile, which varies because of the shock front nonstationarity. In particular, reflected ions appear to escape periodically from the shock front as bursts with an occurrence time period associated to the self-reformation of the shock front.

The role of pyrimidine nucleobase excimers in DNA photophysics and photoreactivity

2009 ◽  
Vol 81 (9) ◽  
pp. 1695-1705 ◽  
Author(s):  
Israel González-Ramírez ◽  
Teresa Climent ◽  
Juan José Serrano-Pérez ◽  
Remedios González-Luque ◽  
Manuela Merchán ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Quantum Chemical ◽  
Electronic States ◽  
Conical Intersections ◽  
Chemical Studies ◽  
Quantum Chemical Studies ◽  
Dna Nucleobases ◽  
Surface Crossings

Quantum chemical studies using the accurate CASPT2//CASSCF procedure show that π-stacked interactions in biochromophores such as pyrimidine (Pyr) DNA/RNA nucleobases pairs yield excimer-like situations which behave as precursors of processes like charge transfer (CT) or photoreactivity and are the source of the emissive properties in DNA. Examples are the CT between adjacent DNA nucleobases in a strand of oligonucleotides and the photodimerization taking place in cytosine (C) pairs leading to cyclobutanecytosine (CBC) mutants. These processes take place through nonadiabatic photochemical mechanisms whose evolution is determined by the presence and accessibility of conical intersections (CIs) and other surface crossings between different electronic states.

Role of electron-transfer quenching of chlorophyll fluorescence by carotenoids in non-photochemical quenching of green plants

2005 ◽  
Vol 33 (4) ◽  
pp. 858-862 ◽  
Author(s):  
A. Dreuw ◽  
G.R. Fleming ◽  
M. Head-Gordon
Keyword(s):  
Electron Transfer ◽  
Chlorophyll Fluorescence ◽  
Charge Transfer ◽  
Excited States ◽  
Quantum Chemical ◽  
Photochemical Quenching ◽  
Quenching Mechanism ◽  
High Level ◽  
Non Photochemical Quenching

NPQ (non-photochemical quenching) is a fundamental photosynthetic mechanism by which plants protect themselves against excess excitation energy and the resulting photodamage. A discussed molecular mechanism of the so-called feedback de-excitation component (qE) of NPQ involves the formation of a quenching complex. Recently, we have studied the influence of formation of a zeaxanthin–chlorophyll complex on the excited states of the pigments using high-level quantum chemical methodology. In the case of complex formation, electron-transfer quenching of chlorophyll-excited states by carotenoids is a relevant quenching mechanism. Furthermore, additionally occurring charge-transfer excited states can be exploited experimentally to prove the existence of the quenching complex during NPQ.

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