scholarly journals Selective 13C labelling reveals the electronic structure of flavocoenzyme radicals

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Erik Schleicher ◽  
Stephan Rein ◽  
Boris Illarionov ◽  
Ariane Lehmann ◽  
Tarek Al Said ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Blue Light ◽  
Density Functional ◽  
Double Resonance ◽  
Density Functional Theory Calculations ◽  
Microwave Frequency ◽  
Fine Tuning ◽  
Electron Nuclear Double Resonance ◽  
Intermediate Radical ◽  
Wide Range

AbstractFlavocoenzymes are nearly ubiquitous cofactors that are involved in the catalysis and regulation of a wide range of biological processes including some light-induced ones, such as the photolyase-mediated DNA repair, magnetoreception of migratory birds, and the blue-light driven phototropism in plants. One of the factors that enable versatile flavin-coenzyme biochemistry and biophysics is the fine-tuning of the cofactor’s frontier orbital by interactions with the protein environment. Probing the singly-occupied molecular orbital (SOMO) of the intermediate radical state of flavins is therefore a prerequisite for a thorough understanding of the diverse functions of the flavoprotein family. This may be ultimately achieved by unravelling the hyperfine structure of a flavin by electron paramagnetic resonance. In this contribution we present a rigorous approach to obtaining a hyperfine map of the flavin’s chromophoric 7,8-dimethyl isoalloxazine unit at an as yet unprecedented level of resolution and accuracy. We combine powerful high-microwave-frequency/high-magnetic-field electron–nuclear double resonance (ENDOR) with 13C isotopologue editing as well as spectral simulations and density functional theory calculations to measure and analyse 13C hyperfine couplings of the flavin cofactor in DNA photolyase. Our data will provide the basis for electronic structure considerations for a number of flavin radical intermediates occurring in blue-light photoreceptor proteins.

scholarly journals A priori calculations of the free energy of formation from solution of polymorphic self-assembled monolayers

2015 ◽  
Vol 112 (45) ◽  
pp. E6101-E6110 ◽  
Author(s):  
Jeffrey R. Reimers ◽  
Dwi Panduwinata ◽  
Johan Visser ◽  
Yiing Chin ◽  
Chunguang Tang ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Density Functional ◽  
A Priori ◽  
Pyrolytic Graphite ◽  
Density Functional Theory Calculations ◽  
Self Assembled Monolayer ◽  
Atomic Structures ◽  
Wide Range ◽  
Entropy Effects ◽  
Self Assembled

Modern quantum chemical electronic structure methods typically applied to localized chemical bonding are developed to predict atomic structures and free energies for meso-tetraalkylporphyrin self-assembled monolayer (SAM) polymorph formation from organic solution on highly ordered pyrolytic graphite surfaces. Large polymorph-dependent dispersion-induced substrate−molecule interactions (e.g., −100 kcal mol−1 to −150 kcal mol−1 for tetratrisdecylporphyrin) are found to drive SAM formation, opposed nearly completely by large polymorph-dependent dispersion-induced solvent interactions (70–110 kcal mol−1) and entropy effects (25–40 kcal mol−1 at 298 K) favoring dissolution. Dielectric continuum models of the solvent are used, facilitating consideration of many possible SAM polymorphs, along with quantum mechanical/molecular mechanical and dispersion-corrected density functional theory calculations. These predict and interpret newly measured and existing high-resolution scanning tunnelling microscopy images of SAM structure, rationalizing polymorph formation conditions. A wide range of molecular condensed matter properties at room temperature now appear suitable for prediction and analysis using electronic structure calculations.

Interfacial defect engineering and Photocatalysis Properties of hBN/MX2(M = Mo, W, and X = S, Se) Heterostructures

2021 ◽  
Author(s):  
Zhihai Sun ◽  
Jiaxi Liu ◽  
Ying Zhang ◽  
Ziyuan Li ◽  
Leyu Peng ◽  
...  
Keyword(s):  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Band Alignment ◽  
Type I ◽  
Defect Engineering ◽  
Wide Range ◽  
Interfacial Defects ◽  
Significant Research ◽  
P Type ◽  
The Impact

Abstract Van der Waals (VDW) heterostructures have attracted significant research interest due to their tunable interfacial properties and potential in a wide range of applications such as electronics, optoelectronic, and heterocatalysis. In this work, the impact of interfacial defects on the electronic structures and photocatalytic properties of hBN/MX2(M = Mo, W, and X = S, Se) are studied using density functional theory calculations. The results reveal that the band alignment of hBN/MX2 can be adjusted by introducing vacancies and atomic doping. The type-I band alignment of the host structure was maintained in the heterostructure with n-type doping in the hBN sublayer. Interestingly, the band alignment changed to the type-II heterostructrue as VB defect and p-type doping was introduced in the hBN sublayer. This could be profitable for the separation of photo-generated electron−hole pairs at the interfaces and is highly desired for heterostructure photocatalysis. In addition, two Z-type heterostructures including hBN(BeB)/MoS2, hBN(BeB)/MoSe2, and hBN(VN)/MoSe2 were achieved, showing reducing band gap and ideal redox potential for water splitting. Our results reveal the possibility of engineering the interfacial and photocatalysis properties of hBN/MX2 heterostructures via interfacial defects.

scholarly journals Time-Resolved X-ray Operando Observations of Lithiation Gradients across the Cathode Matrix and Individual Oxide Particles during Fast Cycling of a Li-Ion Cell

2021 ◽  
Author(s):  
Tianlong Zheng ◽  
Jing He ◽  
Pingwei Cai ◽  
Xi Liu ◽  
Duojie Wu ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Specific Surface ◽  
Surface Area ◽  
Specific Surface Area ◽  
High Performance ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Carbon Paper ◽  
Free Energy Barrier ◽  
Active Components

Abstract Self-supporting three-dimensional (3D) transition metal electrodes have been considered for designing high-performance non-noble metal oxygen evolution reaction (OER) catalysts owing to their advantages such as binder-free, good mass transfer, and large specific surface area. However, the poor conductivity of ((oxy)hydr)oxides and the difficulty in adjusting their electronic structure limit their application. As an alternative strategy, instead of constituting the array electrode by the active components themselves, we herein report 3D Co(OH)2@MnO2 heterostructure decorated carbon nanoarrays grown directly on carbon paper (Co(OH)2@MnO2-CNAs). This unique structure can not only enhance electrical conductivity but also provide a larger specific surface area, and facilitate electrolyte diffusion and ion transport. The core-shell heterostructured Co(OH)2@MnO2 formed via incorporation with MnO2 facilitates the transition of CoII to CoIII in Co(OH)2 and it increases the storage of oxidative charge in the catalyst, leading to an OER activity with benchmark RuO2 and good stability. Density functional theory calculations suggest that the improved OER performance can be attributed to the formation of the heterojunction structure, resulting in the modulation of the electronic structure of Co atoms and the reduction of the free energy barrier of the rate-determining step for the OER.

Solution Tetrahydrobiopterin Radical vs. the Enzyme-Bound Radical: A Paramagnetic Reconciliation

2021 ◽  
Vol 16 ◽  
Author(s):  
Yaser Nejaty Jahromy
Keyword(s):  
Nitric Oxide ◽  
Density Functional ◽  
Double Resonance ◽  
Nicotinamide Adenine Dinucleotide Phosphate ◽  
Cation Radical ◽  
Spectral Simulation ◽  
Electron Nuclear Double Resonance ◽  
Paramagnetic Resonance ◽  
Isotropic Hyperfine Coupling ◽  
The 1960S

Background: Nitric oxide synthase (NOS) catalyzes the formation of nitric oxide (NO) and citrulline from L-arginine, dioxygen (O2), and nicotinamide adenine dinucleotide phosphate (NADPH) in a two-step reaction, with the enzyme-bound intermediate Nω-hydroxy-L-arginine (NHA). Previous electron paramagnetic resonance (EPR) studies of NOS reaction have shown that (6R, 1'R, 2'S)-6-(l',2'-dihydroxypropyl)-5,6,7,8-tetrahydropterin (H4B) acts as a single electron donor in both steps of the reaction, resulting in the transient generation of a tetrahydropterin cation radical (H4B•+). Results: H4B•+ can also be chemically generated in strongly acidic solutions. EPR studies of chemically generated H4B•+ and similar pterin radicals date back to the 1960s. However, the reported paramagnetic parameters of H4B•+ in NOS do not seem to match the corresponding reported parameters for either H4B•+ or other pterin centered radicals chemically generated in solution. In particular, the rather isotropic hyperfine coupling of ca. 45 MHz for 1H6 of H4B•+ in NOS is at least 15 MHz larger than that of H4B•+ or any other previously studies pterin solution radical. In the work reported here, a combination of 9.5 - 9.8 GHz contentious wave (cw-) EPR, 34GHz 1H electron nuclear double resonance (ENDOR), spectral simulation and Density Functional Theory (DFT) calculations were used to investigate this seeming discrepancy. Conclusion: We demonstrated that the differences in the paramagnetic parameters of the chemically generated H4B radicals in solutions and those of the H4B radicals in NOS are consistent with the presence of two different conformers of the same cation radical in the two media.

scholarly journals Electronic Structure of the Aqueous Vanadyl Ion Probed by 9 and 94 GHz EPR and Pulsed ENDOR Spectroscopies and Density Functional Theory Calculations

1999 ◽  
Vol 103 (48) ◽  
pp. 10627-10631 ◽  
Author(s):  
Christopher V. Grant ◽  
William Cope ◽  
James A. Ball ◽  
Guenter G. Maresch ◽  
Betty J. Gaffney ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Functional Theory ◽  
Vanadyl Ion

Tuning the electronic structure properties of MoS2 monolayers with carbon doping

2019 ◽  
Vol 21 (21) ◽  
pp. 11168-11174 ◽  
Author(s):  
Wiliam Ferreira da Cunha ◽  
Ramiro Marcelo dos Santos ◽  
Rafael Timóteo de Sousa Júnior ◽  
Renato Batista Santos ◽  
Geraldo Magela e Silva ◽  
...  
Keyword(s):  
Density Functional Theory ◽  
Electronic Structure ◽  
Electronic Properties ◽  
Density Functional ◽  
Density Functional Theory Calculations ◽  
Carbon Doping ◽  
Functional Theory ◽  
Structural And Electronic Properties ◽  
Mos2 Monolayers ◽  
Structure Properties

The structural and electronic properties of MoS2 sheets doped with carbon line domains are theoretically investigated through density functional theory calculations.

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