105 results on '"Bo Zhang"'
Search Results
2. A Low-Volatile and Durable Deep Eutectic Electrolyte for High-Performance Lithium–Oxygen Battery
- Author
-
Chao-Le Li, Gang Huang, Yue Yu, Qi Xiong, Jun-Min Yan, and Xin-bo Zhang
- Subjects
Colloid and Surface Chemistry ,General Chemistry ,Biochemistry ,Catalysis - Abstract
The lithium-oxygen battery (LOB) with a high theoretical energy density (∼3500 Wh kg
- Published
- 2022
3. Core-Shell Gyroid in ABC Bottlebrush Block Terpolymers
- Author
-
Shuquan Cui, Bo Zhang, Liyang Shen, Frank S. Bates, and Timothy P. Lodge
- Subjects
Colloid and Surface Chemistry ,General Chemistry ,Biochemistry ,Catalysis - Abstract
Block polymer self-assembly provides a versatile platform for creating useful materials endowed with three-dimensional periodic network morphologies that support orthogonal physical properties such as high ionic conductivity and a high elastic modulus. However, coil configurations limit conventional linear block polymers to finite ordered network dimensions, which are further restricted by slow self-assembly kinetics at high molecular weights. A bottlebrush architecture can circumvent both shortcomings owing to extended backbone configurations due to side chain crowding and molecular dynamics substantially free of chain entanglements. However, until now, network morphologies have not been reported in AB bottlebrush block copolymers, notwithstanding favorable mean-field predictions. We explored the phase behavior by small-angle X-ray scattering of 133 poly(ethylene
- Published
- 2022
4. Engineering Single-Atomic Ni-N4-O Sites on Semiconductor Photoanodes for High-Performance Photoelectrochemical Water Splitting
- Author
-
Yanxue Zhang, Chen Wang, Zhuwei Li, Licheng Sun, Zhaozhong Fan, Bo Zhang, Xiaomeng Zhang, Junfeng Gao, Jungang Hou, Panlong Zhai, Lei Ran, and Yunzhen Wu
- Subjects
Photocurrent ,business.industry ,Chemistry ,Oxygen evolution ,General Chemistry ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,Semiconductor ,Optoelectronics ,Water splitting ,Reversible hydrogen electrode ,Moiety ,Density functional theory ,business ,Absorption (electromagnetic radiation) - Abstract
Direct photoelectrochemical (PEC) water splitting is a promising solution for solar energy conversion; however, there is a pressing bottleneck to address the intrinsic charge transport for the enhancement of PEC performance. Herein, a versatile coupling strategy was developed to engineer atomically dispersed Ni-N4 sites coordinated with an axial direction oxygen atom (Ni-N4-O) incorporated between oxygen evolution cocatalyst (OEC) and semiconductor photoanode, boosting the photogenerated electron-hole separation and thus improving PEC activity. This state-of-the-art OEC/Ni-N4-O/BiVO4 photoanode exhibits a record high photocurrent density of 6.0 mA cm-2 at 1.23 V versus reversible hydrogen electrode (vs RHE), over approximately 3.97 times larger than that of BiVO4, achieving outstanding long-term photostability. From X-ray absorption fine structure analysis and density functional theory calculations, the enhanced PEC performance is attributed to the construction of single-atomic Ni-N4-O moiety in OEC/BiVO4, facilitating the holes transfer, decreasing the free energy barriers, and accelerating the reaction kinetics. This work enables us to develop an effective pathway to design and fabricate efficient and stable photoanodes for feasible PEC water splitting application.
- Published
- 2021
5. Mixed-Valence CsCu4Se3: Large Phonon Anharmonicity Driven by the Hierarchy of the Rigid [(Cu+)4(Se2–)2](Se–) Double Anti-CaF2 Layer and the Soft Cs+ Sublattice
- Author
-
Ling Chen, Xin Liu, Li-Ming Wu, Jian-Gao Li, Yan-Yan Li, Fan Li, Dong-Bo Zhang, and Ni Ma
- Subjects
Valence (chemistry) ,Condensed matter physics ,Scattering ,Phonon ,Chemistry ,Anharmonicity ,General Chemistry ,Antibonding molecular orbital ,Biochemistry ,Catalysis ,symbols.namesake ,Colloid and Surface Chemistry ,symbols ,Multiplicity (chemistry) ,Rotational–vibrational coupling ,Debye model - Abstract
Crystalline solids that exhibit inherently low lattice thermal conductivity (κlat) have attracted a great deal of attention because they offer the only independent control for pursuing a high thermoelectric figure of merit (ZT). Herein, we report the successful preparation of CsCu4Q3 (Q = S (compound 1), Se (compound 2)) with the aid of a safe and facile boron-chalcogen method. The single-crystal diffraction data confirm the P4/mmm hierarchical structures built up by the mixed-valence [(Cu+)4(Q2-)2](Q-) double anti-CaF2 layer and the NaCl-type Cs+ sublattice involving multiple bonding interactions. The electron-poor compound CsCu4Q3 features Cu-Q antibonding states around EF that facilitates a high σ value of 3100 S/cm in 2 at 323 K. Significantly, the ultralow κlat value of 2, 0.20 W/m/K at 650 K (70% lower than that of Cu2Se), is mainly driven by the vibrational coupling of the rigid double anti-CaF2 layer and the soft NaCl-type sublattice. The hierarchical structure increases the bond multiplicity, which eventually leads to a large phonon anharmonicity, as evidenced by the effective scattering of the low-lying optical phonons to the heat-carrying acoustic phonons. Consequently, the acoustic phonon frequency in 2 drops sharply from 118 cm-1 (of Cu2Se) to 48 cm-1. In addition, the elastic properties indicate that the hierarchical structure largely inhibits the transverse phonon modes, leading to a sound velocity (1571 m/s) and a Debye temperature (189 K) lower than those of Cu2Se (2320 m/s; 292 K).
- Published
- 2021
6. Conformal Macroporous Inverse Opal Oxynitride-Based Photoanode for Robust Photoelectrochemical Water Splitting
- Author
-
Bo Zhang, Shi Qiu, Xiaomeng Zhang, Panlong Zhai, Junfeng Gao, Jungang Hou, Zhuwei Li, Chen Wang, Lei Ran, and Licheng Sun
- Subjects
business.industry ,Chemistry ,Inverse ,Charge (physics) ,Heterojunction ,Conformal map ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,Colloid and Surface Chemistry ,Reversible hydrogen electrode ,Optoelectronics ,Water splitting ,Density functional theory ,business ,Current density - Abstract
Direct photoelectrochemical (PEC) water splitting is of prime importance in sustainable energy conversion systems; however, it is a big challenge to simultaneously control light harvesting and charge transport for the improvement of PEC performance. Herein, we report a three-dimensional ordered macroporous (3DOM) CsTaWO6-xNx inverse opal array as a promising candidate for the first time. To address the critical challenge, an ultrathin carbon-nitride-based layer-intercalated 3DOM CsTaWO6-xNx architecture as a conformal heterojunction photoanode was assembled. This state-of-the-art conformal heterojunction photoanode with carrier-separation efficiency up to 88% achieves a high current density of 4.59 mA cm-2 at 1.6 V versus a reversible hydrogen electrode (vs RHE) under simulated AM 1.5G illumination, which is approximately 3.4 and 17 times larger than that of pristine CsTaWO6-xNx inverse opals and powers photoelectrodes in alkaline media, corresponding to an incident photon-to-current efficiency of 32% at 400 nm and outstanding stability for PEC water splitting. Density functional theory calculations propose that the intimate interface of a conformal photoanode optimizes the charge separation and transfer, thus enhancing the intrinsic water oxidation performance. This work enables us to elucidate the pivotal importance of 3DOM architectures and conformal heterostructures and the promising contributions to excellent PEC water-splitting applications.
- Published
- 2021
7. Influence of Water and Enzyme on the Post-Transition State Bifurcation of NgnD-Catalyzed Ambimodal [6+4]/[4+2] Cycloaddition
- Author
-
Wen Wang, Bo Zhang, Chun Zhang, Yaoyukun Jiang, Zhongyue Yang, Hui Ming Ge, Xin Wang, Yong Liang, Ren-Xiang Tan, Yuan Zhou, and Yu Chen
- Subjects
Molecular Dynamics Simulation ,Biochemistry ,Molecular mechanics ,Catalysis ,Nocardia ,Lactones ,Colloid and Surface Chemistry ,Bacterial Proteins ,Computational chemistry ,Catalytic Domain ,Carbon-Carbon Lyases ,Bifurcation ,Density Functional Theory ,chemistry.chemical_classification ,Cycloaddition Reaction ,Chemistry ,Water ,General Chemistry ,Cycloaddition ,Enzyme ,Models, Chemical ,Reaction dynamics ,Femtosecond ,Biocatalysis ,Selectivity ,Protein Binding - Abstract
The enzyme NgnD catalyzes an ambimodal cycloaddition that bifurcates to [6+4]- and [4+2]-adducts. Both products have been isolated in experiments, but it remains unknown how enzyme and water influence the bifurcation selectivity at the femtosecond time scale. Here, we study the impact of water and enzyme on the post-transition state bifurcation of NgnD-catalyzed [6+4]/[4+2] cycloaddition by integrating quantum mechanics/molecular mechanics quasiclassical dynamics simulations and biochemical assays. The ratio of [6+4]/[4+2] products significantly differs in the gas phase, water, and enzyme. Biochemical assays were employed to validate computational predictions. The study informs how water and enzyme affect the bifurcation selectivity through perturbation of the reaction dynamics in the femtosecond time scale, revealing the fundamental roles of condensed media in dynamically controlling the chemical selectivity for biosynthetic reactions.
- Published
- 2021
8. Engineering Single-Atomic Ni-N
- Author
-
Xiaomeng, Zhang, Panlong, Zhai, Yanxue, Zhang, Yunzhen, Wu, Chen, Wang, Lei, Ran, Junfeng, Gao, Zhuwei, Li, Bo, Zhang, Zhaozhong, Fan, Licheng, Sun, and Jungang, Hou
- Abstract
Direct photoelectrochemical (PEC) water splitting is a promising solution for solar energy conversion; however, there is a pressing bottleneck to address the intrinsic charge transport for the enhancement of PEC performance. Herein, a versatile coupling strategy was developed to engineer atomically dispersed Ni-N
- Published
- 2021
9. A Peroxodiiron(III/III) Intermediate Mediating Both N-Hydroxylation Steps in Biosynthesis of the N-Nitrosourea Pharmacophore of Streptozotocin by the Multi-domain Metalloenzyme SznF
- Author
-
Grace E. Kenney, Molly J. McBride, Tai L. Ng, Bo Zhang, J. Martin Bollinger, Anne Marie Crooke, Christina Tysoe, Carsten Krebs, Debangsu Sil, Emily P. Balskus, and Amie K. Boal
- Subjects
Oxidase test ,biology ,Chemistry ,Stereochemistry ,General Chemistry ,Quadrupole splitting ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,Cofactor ,0104 chemical sciences ,Hydroxylation ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Biosynthesis ,biology.protein ,Moiety ,Molecule ,Pharmacophore - Abstract
The alkylating warhead of the pancreatic cancer drug streptozotocin (SZN) contains an N-nitrosourea moiety constructed from Nω-methyl-l-arginine (l-NMA) by the multi-domain metalloenzyme SznF. The enzyme's central heme-oxygenase-like (HO-like) domain sequentially hydroxylates Nδ and Nω' of l-NMA. Its C-terminal cupin domain then rearranges the triply modified arginine to Nδ-hydroxy-Nω-methyl-Nω-nitroso-l-citrulline, the proposed donor of the functional pharmacophore. Here we show that the HO-like domain of SznF can bind Fe(II) and use it to capture O2, forming a peroxo-Fe2(III/III) intermediate. This intermediate has absorption- and Mossbauer-spectroscopic features similar to those of complexes previously trapped in f erritin-like d iiron o xidases and oxygenases (FDOs) and, more recently, the HO-like fatty acid oxidase UndA. The SznF peroxo-Fe2(III/III) complex is an intermediate in both hydroxylation steps, as shown by the concentration-dependent acceleration of its decay upon exposure to either l-NMA or Nδ-hydroxy-Nω-methyl-l-Arg (l-HMA). The Fe2(III/III) cluster produced upon decay of the intermediate has a small Mossbauer quadrupole splitting parameter, implying that, unlike the corresponding product states of many FDOs, it lacks an oxo-bridge. The subsequent decomposition of the product cluster to one or more paramagnetic Fe(III) species over several hours explains why SznF was previously purified and crystallographically characterized without its cofactor. Programmed instability of the oxidized form of the cofactor appears to be a unifying characteristic of the emerging superfamily of H O-like d iiron o xidases and oxygenases (HDOs).
- Published
- 2020
10. Oxygen Dependent Purine Lesions in Double-Stranded Oligodeoxynucleotides: Kinetic and Computational Studies Highlight the Mechanism for 5′,8-Cyclopurine Formation
- Author
-
Chryssostomos Chatgilialoglu, Shudong Wang, Ru-Bo Zhang, Marios G. Krokidis, Leif A. Eriksson, and Annalisa Masi
- Subjects
Purine ,Reaction mechanism ,Aqueous solution ,Diastereomer ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Radical cyclization ,Oxygen ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Reaction rate constant ,chemistry ,Computational chemistry ,Limiting oxygen concentration - Abstract
The reaction of HO• radical with DNA is intensively studied both mechanistically and analytically for lesions formation. Several aspects related to the reaction paths of purine moieties with the formation of 5',8-cyclopurines (cPu), 8-oxopurines (8-oxo-Pu), and their relationship are not well understood. In this study, we investigated the reaction of HO• radical with a 21-mer double-stranded oligodeoxynucleotide (ds-ODNs) in γ-irradiated aqueous solutions under various oxygen concentrations and accurately quantified the six purine lesions (i.e., four cPu and two 8-oxo-Pu) by LC-MS/MS analysis using isotopomeric internal standards. In the absence of oxygen, 8-oxo-Pu lesions are only ∼4 times more than cPu lesions. By increasing oxygen concentration, the 8-oxo-Pu and the cPu gradually increase and decrease, respectively, reaching a gap of ∼130 times at 2.01 × 10-4 M of O2. Kinetic treatment of the data allows to estimate the C5' radical competition between cyclization and oxygen trapping in ds-ODNs, and lastly the rate constants of the four cyclization steps. Tailored computational studies by means of dispersion-corrected DFT calculations were performed on the CGC and TAT in their double-strand models for each cPu diastereoisomer along with the complete reaction pathways of the cyclization steps. Our findings reveal unheralded reaction mechanisms that resolve the long-standing issues with C5' radical cyclization in purine moieties of DNA sequences.
- Published
- 2020
11. First Step in Catalysis of the Radical S-Adenosylmethionine Methylthiotransferase MiaB Yields an Intermediate with a [3Fe-4S]0-Like Auxiliary Cluster
- Author
-
Arthur J. Arcinas, Carsten Krebs, Matthew I. Radle, Alexey Silakov, Bo Zhang, and Squire J. Booker
- Subjects
chemistry.chemical_classification ,Chemistry ,Stereochemistry ,chemistry.chemical_element ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Sulfur ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Biosynthesis ,Transfer RNA ,Cluster (physics) ,Moiety ,Nucleotide ,Radical SAM - Abstract
The enzyme MiaB catalyzes the attachment of a methylthio (-SCH3) group at the C2 position of N6-(isopentenyl)adenosine (i6A) in the final step of the biosynthesis of the hypermodified tRNA nucleotide 2-methythio-N6-(isopentenyl)adenosine (ms2i6A). MiaB belongs to the expanding subgroup of enzymes of the radical S-adenosylmethionine (SAM) superfamily that harbor one or more auxiliary [4Fe-4S] clusters in addition to the [4Fe-4S] cluster that all family members require for the reductive cleavage of SAM to afford the common 5'-deoxyadenosyl 5'-radical (5'-dA•) intermediate. While the role of the radical SAM cluster in generating the 5'-dA• is well understood, the detailed role of the auxiliary cluster, which is essential for MiaB catalysis, remains unclear. It has been proposed that the auxiliary cluster may serve as a coordination site for exogenously derived sulfur destined for attachment to the substrate or that the cluster itself provides the sulfur atom and is sacrificed during turnover. In this work, we report spectroscopic and biochemical evidence that the auxiliary [4Fe-4S]2+ cluster in Bacteroides thetaiotaomicron (Bt) MiaB is converted to a [3Fe-4S]0-like cluster during the methylation step of catalysis. Mossbauer characterization of the MiaB [3Fe-4S]0-like cluster revealed unusual spectroscopic properties compared to those of other well-characterized cuboidal [3Fe-4S]0 clusters. Specifically, the Fe sites of the mixed-valent moiety do not have identical Mossbauer parameters. Our results support a mechanism where the auxiliary [4Fe-4S] cluster is the direct sulfur source during catalysis.
- Published
- 2020
12. Mixed-Valence CsCu
- Author
-
Ni, Ma, Fan, Li, Jian-Gao, Li, Xin, Liu, Dong-Bo, Zhang, Yan-Yan, Li, Ling, Chen, and Li-Ming, Wu
- Abstract
Crystalline solids that exhibit inherently low lattice thermal conductivity (κ
- Published
- 2021
13. Collision, Adhesion, and Oxidation of Single Ag Nanoparticles on a Polysulfide-Modified Microelectrode
- Author
-
Bo Zhang and Peter A. Defnet
- Subjects
Silver ,Chemistry ,Metal Nanoparticles ,General Chemistry ,Biosensing Techniques ,Sodium thiosulfate ,Sulfides ,Electrochemistry ,Biochemistry ,Catalysis ,Silver nanoparticle ,chemistry.chemical_compound ,Microelectrode ,Colloid and Surface Chemistry ,Chemical engineering ,Electrode ,Particle ,Sticking probability ,Microelectrodes ,Oxidation-Reduction ,Polysulfide - Abstract
We report the collision, adhesion, and oxidation behavior of single silver nanoparticles (Ag NPs) on a polysulfide-modified gold microelectrode. Despite its remarkable success in volume analysis for smaller Ag NPs, the method of NP-collision electrochemistry has failed to analyze particles greater than 50 nm due to uncontrollable collision behavior and incomplete NP oxidation. Herein, we describe the unique capability of an ultrathin polysulfide layer in controlling the collision behavior of Ag NPs by drastically improving their sticking probability on the electrode. The ultrathin sulfurous layer is formed on gold by sodium thiosulfate electro-oxidation and serves both as an adhesive interface for colliding NPs and as a preconcentrated reactive medium to chemically oxidize Ag to form Ag2S. Rapid particle dissolution is further promoted by the presence of bulk sodium thiosulfate serving as a Lewis base, which drastically improves the solubility of generated Ag2S by a factor of 1013. The combined use of polysulfide and sodium thiosulfate allows us to observe a 25× increase in NP detection frequency, a 3× increase in peak amplitude, and more complete oxidation for larger Ag NPs. By recognizing how volumetric analysis using transmission electron microscopy (TEM) may overestimate quasi-spherical NPs, we believe we can have full NP oxidation for particles up to 100 nm. By focusing on the electrode/solution interface for more effective NP-electrode contact, we expect that the knowledge learned from this study will greatly benefit future NP collision systems for mechanistic studies in single-entity electrochemistry as well as designing ultrasensitive biochemical sensors.
- Published
- 2021
14. Stabilizing Highly Active Ru Sites by Suppressing Lattice Oxygen Participation in Acidic Water Oxidation
- Author
-
Hui-Hui Li, Cao-Thang Dinh, Youyong Li, Xinnan Mao, Shangyu Li, Robert J. Nielsen, Tao-Tao Zhuang, Changchun Ke, Bo Zhang, Peining Chen, Yongfeng Hu, William A. Goddard, Longsheng Zhang, Jehad Abed, Lie Wang, Liping Wang, Ziyun Wang, Huisheng Peng, Edward H. Sargent, Lu Wang, Rui Huang, Yimeng Min, Yunzhou Wen, Oleksandr Voznyy, and Phil De Luna
- Subjects
Absorption spectroscopy ,Chemistry ,Inorganic chemistry ,Oxygen evolution ,Oxide ,General Chemistry ,Crystal structure ,Electrolyte ,Overpotential ,010402 general chemistry ,7. Clean energy ,01 natural sciences ,Biochemistry ,Catalysis ,0104 chemical sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Hydrogen production - Abstract
In hydrogen production, the anodic oxygen evolution reaction (OER) limits the energy conversion efficiency and also impacts stability in proton-exchange membrane water electrolyzers. Widely used Ir-based catalysts suffer from insufficient activity, while more active Ru-based catalysts tend to dissolve under OER conditions. This has been associated with the participation of lattice oxygen (lattice oxygen oxidation mechanism (LOM)), which may lead to the collapse of the crystal structure and accelerate the leaching of active Ru species, leading to low operating stability. Here we develop Sr-Ru-Ir ternary oxide electrocatalysts that achieve high OER activity and stability in acidic electrolyte. The catalysts achieve an overpotential of 190 mV at 10 mA cm-2 and the overpotential remains below 225 mV following 1,500 h of operation. X-ray absorption spectroscopy and 18O isotope-labeled online mass spectroscopy studies reveal that the participation of lattice oxygen during OER was suppressed by interactions in the Ru-O-Ir local structure, offering a picture of how stability was improved. The electronic structure of active Ru sites was modulated by Sr and Ir, optimizing the binding energetics of OER oxo-intermediates.
- Published
- 2021
15. Redox Modifications in the Biosynthesis of Alchivemycin A Enable the Formation of Its Key Pharmacophore
- Author
-
Yasuhiro Igarashi, Ren-Xiang Tan, Wen Wang, Lan Wang, Shuang He Liu, Hong Jie Zhu, Bo Zhang, Hui Ming Ge, and Ghader Bashiri
- Subjects
chemistry.chemical_classification ,Chemistry ,Molecular Conformation ,RNA ,Biological activity ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,Streptomyces ,0104 chemical sciences ,Polyketide ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Enzyme ,Biosynthesis ,RNA polymerase ,Peptide bond ,Macrolides ,Pharmacophore ,Oxidation-Reduction - Abstract
Redox enzymes play a critical role in transforming nascent scaffolds into structurally complex and biologically active natural products. Alchivemycin A (AVM, 1) is a highly oxidized polycyclic compound with potent antimicrobial activity and features a rare 2H-tetrahydro-4,6-dioxo-1,2-oxazine (TDO) ring system. The scaffold of AVM has previously been shown to be biosynthesized by a hybrid polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) pathway. In this study, we present a postassembly secondary metabolic network involving six redox enzymes that leads to AVM formation. We characterize this complex redox network using in vivo gene deletions, in vitro biochemical assays, and one-pot enzymatic total synthesis. Importantly, we show that an FAD-dependent monooxygenase catalyzes oxygen insertion into an amide bond to form the key TDO ring in AVM, an unprecedented function of flavoenzymes. We also show that the TDO ring is essential to the antimicrobial activity of AVM, likely through targeting the β-subunit of RNA polymerase. As further evidence, we show that AvmK, a β-subunit of RNA synthase, can confer self-resistance to AVM via target modification. Our findings expand the repertoire of functions of flavoenzymes and provide insight into antimicrobial and biocatalyst development based on AVM.
- Published
- 2021
16. Hydrogen Donation but not Abstraction by a Tyrosine (Y68) during Endoperoxide Installation by Verruculogen Synthase (FtmOx1)
- Author
-
Noah P. Dunham, José M. Del Río Pantoja, Bo Zhang, Lauren J. Rajakovich, Benjamin D. Allen, Carsten Krebs, Amie K. Boal, and J. Martin Bollinger
- Subjects
Indoles ,Aspergillus fumigatus ,Ascorbic Acid ,General Chemistry ,Biochemistry ,Article ,Catalysis ,Dioxygenases ,Fungal Proteins ,Oxygen ,Colloid and Surface Chemistry ,Mutation ,Tyrosine ,Oxidation-Reduction ,Hydrogen - Abstract
Hydrogen-atom transfer (HAT) from a substrate carbon to an iron(IV)-oxo (ferryl) intermediate initiates a diverse array of enzymatic transformations. For outcomes other than hydroxylation, coupling of the resultant carbon radical and hydroxo ligand (oxygen rebound) must generally be averted. A recent study of FtmOx1, a fungal iron(II)- and 2-(oxo)glutarate-dependent oxygenase that installs the endoperoxide of verruculogen by adding O(2) between carbons 21 and 27 of fumitremorgin B, posited that tyrosine (Tyr or Y) 224 serves as HAT intermediary to separate the C21 radical (C21•) and Fe(III)–OH HAT products and prevent rebound. Our re-investigation of the FtmOx1 mechanism revealed, instead, direct HAT from C21 to the ferryl complex and surprisingly competitive rebound. The C21-hydroxylated (rebound) product, which undergoes deprenylation, predominates when low [O(2)] slows C21•–O(2) coupling in the next step of the endoperoxidation pathway. This pathway culminates with addition of the C21-O–O• peroxyl adduct to olefinic C27 followed by HAT to the C26• from a Tyr. The last step results in sequential accumulation of Tyr radicals, which are suppressed without detriment to turnover by inclusion of the reductant, ascorbate. Replacement of each of four candidates for the proximal C26 H• donor (including Y224) with phenylalanine (F) revealed that only the Y68F variant (i) fails to accumulate the first Tyr• and (ii) makes an altered major product, identifying Y68 as the donor. The implied proximities of C21 to the iron cofactor and C26 to Y68 support a new structural model of the enzyme-substrate complex that is consistent with all available data.
- Published
- 2019
17. Non-heme High-Spin {FeNO}6–8 Complexes: One Ligand Platform Can Do It All
- Author
-
Bo Zhang, Amy L. Speelman, Carsten Krebs, Michael Hu, E. Ercan Alp, James E. Penner-Hahn, Jiyong Zhao, Corey J. White, and Nicolai Lehnert
- Subjects
Extended X-ray absorption fine structure ,010405 organic chemistry ,Ligand ,Center (category theory) ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Redox ,Catalysis ,XANES ,0104 chemical sciences ,Metal ,chemistry.chemical_compound ,Crystallography ,Colloid and Surface Chemistry ,chemistry ,visual_art ,Mössbauer spectroscopy ,visual_art.visual_art_medium ,Heme - Abstract
Heme and non-heme iron–nitrosyl complexes are important intermediates in biology. While there are numerous examples of low-spin heme iron–nitrosyl complexes in different oxidation states, much less is known about high-spin (hs) non-heme iron–nitrosyls in oxidation states other than the formally ferrous NO adducts ({FeNO}7 in the Enemark–Feltham notation). In this study, we present a complete series of hs-{FeNO}6–8 complexes using the TMG3tren coligand. Redox transformations from the hs-{FeNO}7 complex [Fe(TMG3tren)(NO)]2+ to its {FeNO}6 and {FeNO}8 analogs do not alter the coordination environment of the iron center, allowing for detailed comparisons between these species. Here, we present new MCD, NRVS, XANES/EXAFS, and Mossbauer data, demonstrating that these redox transformations are metal based, which allows us to access hs-Fe(II)–NO–, Fe(III)–NO–, and Fe(IV)–NO– complexes. Vibrational data, analyzed by NCA, directly quantify changes in Fe–NO bonding along this series. Optical data allow for the ident...
- Published
- 2018
18. Molecular Basis for the Final Oxidative Rearrangement Steps in Chartreusin Biosynthesis
- Author
-
Suwen Zhao, Hui-Qin Huang, Fang Liu, Ren-Xiang Tan, Hui Ming Ge, Cheng Long Yang, Cheng Li Liu, Rui Hua Jiao, Bo Zhang, Yi Shuang Wang, Yong Liang, Jiapeng Zhu, and Yu Guo
- Subjects
Stereochemistry ,Antineoplastic Agents ,Flavin group ,Crystallography, X-Ray ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,Dioxygenases ,Polyketide ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Bacterial Proteins ,Biosynthesis ,Dioxygenase ,Catalytic Domain ,Benzopyrans ,Glycosides ,Binding site ,Bond cleavage ,Molecular Structure ,010405 organic chemistry ,Chartreusin ,General Chemistry ,Streptomyces ,0104 chemical sciences ,Molecular Docking Simulation ,Models, Chemical ,chemistry ,Docking (molecular) ,Multigene Family ,Mutation ,Mutagenesis, Site-Directed ,Oxidation-Reduction ,Protein Binding - Abstract
Oxidative rearrangements play key roles in introducing structural complexity and biological activities of natural products biosynthesized by type II polyketide synthases (PKSs). Chartreusin (1) is a potent antitumor polyketide that contains a unique rearranged pentacyclic aromatic bilactone aglycone derived from a type II PKS. Herein, we report an unprecedented dioxygenase, ChaP, that catalyzes the final α-pyrone ring formation in 1 biosynthesis using flavin-activated oxygen as an oxidant. The X-ray crystal structures of ChaP and two homologues, docking studies, and site-directed mutagenesis provided insights into the molecular basis of the oxidative rearrangement that involves two successive C-C bond cleavage steps followed by lactonization. ChaP is the first example of a dioxygenase that requires a flavin-activated oxygen as a substrate despite lacking flavin binding sites, and represents a new class in the vicinal oxygen chelate enzyme superfamily.
- Published
- 2018
19. A Peroxodiiron(III/III) Intermediate Mediating Both
- Author
-
Molly J, McBride, Debangsu, Sil, Tai L, Ng, Anne Marie, Crooke, Grace E, Kenney, Christina R, Tysoe, Bo, Zhang, Emily P, Balskus, Amie K, Boal, Carsten, Krebs, and J Martin, Bollinger
- Subjects
Models, Molecular ,Bacterial Proteins ,Molecular Structure ,Metalloproteins ,Hydroxylation ,Ferric Compounds ,Nitrosourea Compounds ,Streptomyces ,Streptozocin ,Article - Abstract
The alkylating warhead of the antineoplastic drug streptozotocin (SZN) contains an N-nitrosourea moiety constructed from N(ω)-methyl-l-arginine (l-NMA) by the multi-domain metalloenzyme SznF. The enzyme’s central heme-oxygenase-like (HO-like) domain sequentially hydroxylates N(δ) and N(ω’) of l-NMA. Its C-terminal cupin domain then rearranges the triply modified arginine to N(δ)-hydroxy-N(ω)-methyl-N(ω)-nitroso-l-citrulline, the proposed donor of the functional pharmacophore. Here we show that the HO-like domain of SznF can bind Fe(II) and use it to capture O(2), forming a peroxo-Fe(2)(III/III) intermediate. This intermediate has absorption- and Mössbauer-spectroscopic features similar to those of complexes previously trapped in ferritin-like diiron oxidases and oxygenases (FDOs) and, more recently, the HO-like fatty acid oxidase UndA. The SznF peroxo-Fe(2)(III/III) complex is an intermediate in both hydroxylation steps, as shown by the concentration-dependent acceleration of its decay upon exposure to either l-NMA or N(δ)-hydroxy-N(ω)-methyl-l-Arg (L-HMA). The Fe(2)(III/III) cluster produced upon decay of the intermediate has a small Mössbauer quadrupole splitting parameter, implying that, unlike the corresponding product states of many FDOs, it lacks an oxo-bridge. The subsequent decomposition of the product cluster to one or more paramagnetic Fe(III) species over several hours explains why SznF was previously purified and crystallographically characterized without its cofactor. Programmed instability of the oxidized form of the cofactor appears to be a unifying characteristic of the emerging superfamily of HO-like diiron oxidases and oxygenases (HDOs).
- Published
- 2020
20. First Step in Catalysis of the Radical
- Author
-
Bo, Zhang, Arthur J, Arcinas, Matthew I, Radle, Alexey, Silakov, Squire J, Booker, and Carsten, Krebs
- Subjects
Iron-Sulfur Proteins ,Spectroscopy, Mossbauer ,Escherichia coli Proteins ,Sulfurtransferases ,Catalysis ,Article ,Substrate Specificity - Abstract
The enzyme MiaB catalyzes the attachment of a methylthio (−SCH(3)) group at the C2 position of N(6)-(isopentenyl)adenosine (i(6)A) in the final step of the biosynthesis of the hypermodified tRNA nucleotide 2-methythio-N(6)-(isopentenyl)adenosine (ms(2)i(6)A). MiaB belongs to the expanding subgroup of enzymes of the radical S-adenosylmethionine (SAM) superfamily that harbor one or more auxiliary [4Fe-4S] clusters in addition to the [4Fe-4S] cluster that all family members require for the reductive cleavage of SAM to afford the common 5′-deoxyadenosyl 5′-radical (5′-dA(•)) intermediate. While the role of the radical SAM cluster in generating the 5′-dA(•) is well understood, the detailed role of the auxiliary cluster, which is essential for MiaB catalysis, remains unclear. It has been proposed that the auxiliary cluster may serve as a coordination site for exogenously derived sulfur destined for attachment to the substrate or that the cluster itself provides the sulfur atom and is sacrificed during turnover. In this work, we report spectroscopic and biochemical evidence that the auxiliary [4Fe–4S](2+) cluster in Bacteroides thetaiotaomicron (Bt) MiaB is converted to a [3Fe-4S](0)-like cluster during the methylation step of catalysis. Mössbauer characterization of the MiaB [3Fe-4S](0)-like cluster revealed unusual spectroscopic properties compared to those of other well-characterized cuboidal [3Fe-4S](0) clusters. Specifically, the Fe sites of the mixed-valent moiety do not have identical Mössbauer parameters. Our results support a mechanism where the auxiliary [4Fe-4S] cluster is the direct sulfur source during catalysis.
- Published
- 2020
21. Collision Dynamics during the Electrooxidation of Individual Silver Nanoparticles
- Author
-
Henry S. White, Bo Zhang, Yuwen Liu, Stephen M. Oja, Martin A. Edwards, Donald A. Robinson, and Nicholas J. Vitti
- Subjects
Chemistry ,Analytical chemistry ,Nanoparticle ,Exchange current density ,02 engineering and technology ,General Chemistry ,Electrolyte ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Biochemistry ,Catalysis ,Silver nanoparticle ,0104 chemical sciences ,Microelectrode ,Colloid and Surface Chemistry ,Chemical physics ,Electrode ,Particle ,Diffusion (business) ,0210 nano-technology - Abstract
Recent high-bandwidth recordings of the oxidation and dissolution of 35 nm radius Ag nanoparticles at a Au microelectrode show that these nanoparticles undergo multiple collisions with the electrode, generating multiple electrochemical current peaks. In the time interval between observed current peaks, the nanoparticles diffuse in the solution near the electrolyte/electrode interface. Here, we demonstrate that simulations of random nanoparticle motion, coupled with electrochemical kinetic parameters, quantitatively reproduce the experimentally observed multicurrent peak behavior. Simulations of particle diffusion are based on the nanoparticle-mass-based thermal nanoparticle velocity and the Einstein diffusion relations, while the electron-transfer rate is informed by the literature exchange current density for the Ag/Ag+ redox system. Simulations indicate that tens to thousands of particle–electrode collisions, each lasting ∼6 ns or less (currently unobservable on accessible experimental time scales), con...
- Published
- 2017
22. Mixed-Valence CsCu4Se3: Large Phonon Anharmonicity Driven by the Hierarchy of the Rigid [(Cu+)4(Se2-)2](Se-) Double Anti-CaF2 Layer and the Soft Cs+...
- Author
-
Ni Ma, Fan Li, Jian-Gao Li, Xin Liu, Dong-Bo Zhang, Yan-Yan Li, Ling Chen, and Li-Ming Wu
- Published
- 2021
- Full Text
- View/download PDF
23. Single-Molecule Electrochemistry on a Porous Silica-Coated Electrode
- Author
-
Jin Lu, Joshua C. Vaughan, Bo Zhang, Yunshan Fan, and Marco D. Howard
- Subjects
Surface Properties ,Inorganic chemistry ,Oxide ,02 engineering and technology ,010402 general chemistry ,Electrochemistry ,Photochemistry ,Indium ,01 natural sciences ,Biochemistry ,Redox ,Article ,Catalysis ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Adsorption ,Desorption ,Particle Size ,Electrodes ,Molecular diffusion ,Total internal reflection fluorescence microscope ,Tin Compounds ,Electrochemical Techniques ,General Chemistry ,Silicon Dioxide ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Electrode ,0210 nano-technology ,Oxidation-Reduction ,Porosity - Abstract
Here we report the direct observation and quantitative analysis of single redox events on a modified indium–tin oxide (ITO) electrode. The key in the observation of single redox events are the use of a fluorogenic redox species and the nanoconfinement and hindered redox diffusion inside 3-nm-diameter silica nanochannels. A simple electrochemical process was used to grow an ultrathin silica film (~100 nm) consisting of highly ordered parallel nanochannels exposing the electrode surface from the bottom. The electrode-supported 3-nm-diameter nanochannels temporally trap fluorescent resorufin molecules resulting in hindered molecular diffusion in the vicinity of the electrode surface. Adsorption, desorption, and heterogeneous redox events of individual resorufin molecules can be studied using total-internal reflection fluorescence (TIRF). The rate constants of adsorption and desorption processes of resorufin were characterized from single-molecule analysis to be (1.73 ± 0.08) × 10−4 cm·s−1 and 15.71 ± 0.76 s−1, respectively. The redox events of resorufin to the non-fluorescent dihydroresorufin were investigated by analyzing the change in surface population of single resorufin molecules with applied potential. The scan-rate-dependent molecular counting results (single-molecule fluorescence voltammetry) indicated a surface-controlled electrochemical kinetics of the resorufin reduction on the modified ITO electrode. This study demonstrates the great potential of mesoporous silica as a useful modification scheme for studying single redox events on a variety of transparent substrates such as ITO electrodes and gold or carbon film coated glass electrodes. The ability to electrochemically grow and transfer mesoporous silica films onto other substrates makes them an attractive material for future studies in spatial heterogeneity of electrocatalytic surfaces.
- Published
- 2017
24. O–H Activation by an Unexpected Ferryl Intermediate during Catalysis by 2-Hydroxyethylphosphonate Dioxygenase
- Author
-
Bo Zhang, Wilfred A. van der Donk, Lauren J. Rajakovich, J. Martin Bollinger, Laura M. K. Dassama, Spencer C. Peck, Chen Wang, Carsten Krebs, and Yisong Guo
- Subjects
0301 basic medicine ,2-hydroxyethylphosphonate ,Stereochemistry ,Molecular Conformation ,Organophosphonates ,010402 general chemistry ,Photochemistry ,01 natural sciences ,Biochemistry ,Article ,Catalysis ,Dioxygenases ,Spectroscopy, Mossbauer ,03 medical and health sciences ,Colloid and Surface Chemistry ,Dioxygenase ,Mössbauer spectroscopy ,Chemistry ,Substrate (chemistry) ,General Chemistry ,Enzymatic process ,0104 chemical sciences ,Solvent ,Kinetics ,030104 developmental biology ,Deuterium ,Biocatalysis ,Spectrophotometry, Ultraviolet ,Iron Compounds - Abstract
Activation of O–H bonds by inorganic metal-oxo complexes has been documented, but no cognate enzymatic process is known. Our mechanistic analysis of 2-hydroxyethylphosphonate dioxygenase (HEPD), which cleaves the C1–C2 bond of its substrate to afford hydroxymethylphosphonate on the biosynthetic pathway to the commercial herbicide phosphinothricin, uncovered an example of such an O–H-bond-cleavage event. Stopped-flow UV–visible absorption and freeze-quench Mössbauer experiments identified a transient iron(IV)-oxo (ferryl) complex. Maximal accumulation of the intermediate required both the presence of deuterium in the substrate and, importantly, the use of 2H2O as solvent. The ferryl complex forms and decays rapidly enough to be on the catalytic pathway. To account for these unanticipated results, a new mechanism that involves activation of an O–H bond by the ferryl complex is proposed. This mechanism accommodates all available data on the HEPD reaction.
- Published
- 2017
25. Collision, Adhesion, and Oxidation of Single Ag Nanoparticles on a Polysulfide-Modified Microelectrode.
- Author
-
Defnet, Peter A. and Bo Zhang
- Published
- 2021
- Full Text
- View/download PDF
26. Observation of Multipeak Collision Behavior during the Electro-Oxidation of Single Ag Nanoparticles
- Author
-
Nicholas J. Vitti, Yuwen Liu, Martin A. Edwards, Stephen M. Oja, Bo Zhang, Henry S. White, and Donald A. Robinson
- Subjects
Chemistry ,Analytical chemistry ,Nanoparticle ,Ag nanoparticles ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Collision ,01 natural sciences ,Biochemistry ,Catalysis ,Amperometry ,0104 chemical sciences ,Microelectrode ,Colloid and Surface Chemistry ,Chemical physics ,Electrode ,Partial oxidation ,Diffusion (business) ,0210 nano-technology - Abstract
The dynamic collision behavior of the electro-oxidation of single Ag nanoparticles is observed at Au microelectrodes using stochastic single-nanoparticle collision amperometry. Results show that an Ag nanoparticle collision/oxidation event typically consists of a series of 1 to ∼10 discrete "sub-events" over an ∼20 ms interval. Results also show that the Ag nanoparticles typically undergo only partial oxidation prior to diffusing away from the Au electrode into the bulk solution. Both behaviors are characterized and shown to exist under a variety of experimental conditions. These previously unreported behaviors suggest that nanoparticle collision and electro-dissolution is a highly dynamic process driven by fast particle-electrode interactions and nanoparticle diffusion.
- Published
- 2016
27. Non-Heme Diiron Model Complexes Can Mediate Direct NO Reduction: Mechanistic Insight into Flavodiiron NO Reductases
- Author
-
Hai T. Dong, Nicolai Lehnert, Bo Zhang, Corey J. White, and Carsten Krebs
- Subjects
Iron ,Nitrous Oxide ,010402 general chemistry ,medicine.disease_cause ,Crystallography, X-Ray ,Ligands ,Nitric Oxide ,01 natural sciences ,Biochemistry ,Catalysis ,Nitric oxide ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Biomimetic Materials ,Coordination Complexes ,medicine ,Non heme ,Enzyme family ,chemistry.chemical_classification ,010405 organic chemistry ,Pathogenic bacteria ,General Chemistry ,Combinatorial chemistry ,0104 chemical sciences ,Cold Temperature ,chemistry ,Models, Chemical ,Yield (chemistry) ,Propionate ,Cyclic voltammetry ,Oxidoreductases ,Oxidation-Reduction - Abstract
Flavodiiron nitric oxide reductases (FNORs), a common enzyme family found in various types of pathogenic bacteria, are capable of reducing nitric oxide (NO) to nitrous oxide (N2O) as a protective detoxification mechanism. Utilization of FNORs in pathogenic bacteria helps them survive and proliferate in the human body, thus causing chronic infections. In this paper, we present a new diiron model complex, [Fe2((Py2PhO2)MP)(OPr)2](OTf), with bridging propionate ligands (OPr−) that is capable of directly reducing NO to N2O in quantitative yield without the need to (super)reduce the complex. We first prepared the diferric precursor and characterized it by UV–vis, IR, NMR and Mossbauer spectroscopies, cyclic voltammetry, and mass spectrometry. This complex can then conveniently be reduced to the diferrous complex using CoCp2. Even though this diferrous complex is highly reactive, we have successfully isolated and characterized this species using X-ray crystallography and various spectroscopic techniques. Most i...
- Published
- 2018
28. Spectroscopic Evidence for the Two C–H-Cleaving Intermediates of Aspergillus nidulans Isopenicillin N Synthase
- Author
-
Gang Xing, Bo Zhang, Frank Neese, Yisong Guo, Esta Y. Tamanaha, J. Martin Bollinger, Jennifer St. Clair, Wei-Chen Chang, Eric W. Barr, Carsten Krebs, and Shengfa Ye
- Subjects
Stereochemistry ,Thiazolidine ,Isopenicillin N synthase ,Tripeptide ,010402 general chemistry ,Cleavage (embryo) ,Ring (chemistry) ,01 natural sciences ,Biochemistry ,Aspergillus nidulans ,Article ,Catalysis ,Cofactor ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Cleave ,biology ,010405 organic chemistry ,Spectrum Analysis ,Substrate (chemistry) ,General Chemistry ,0104 chemical sciences ,Oxygen ,Kinetics ,chemistry ,biology.protein ,Quantum Theory ,Oxidoreductases - Abstract
The enzyme isopenicillin N synthase (IPNS) installs the β-lactam and thiazolidine rings of the penicillin core into the linear tripeptide, L-δ-aminoadipoyl-L-Cys-D-Val (ACV), on the pathways to a number of important antibacterial drugs. A classic set of enzymological and crystallographic studies by Baldwin and co-workers established that this overall four-electron oxidation occurs by a sequence of two oxidative cyclizations, with the β-lactam ring being installed first and the thiazolidine ring second. Each phase requires cleavage of an aliphatic C–H bond of the substrate: the pro-S-CCys,β-H bond for closure of the β-lactam ring, and the CVal,β-H bond for installation of the thiazolidine ring. IPNS uses a mononuclear non-heme-iron(II) cofactor and dioxygen as co-substrate to cleave these C–H bonds and direct the ring closures. Despite the intense scrutiny to which the enzyme has been subjected, the identities of the oxidized iron intermediates that cleave the C–H bonds have been addressed only computationally; no experimental insight into their geometric or electronic structures has been reported. In this work, we have employed a combination of transient-state-kinetic and spectroscopic methods, together with the specifically deuterium-labeled substrates, A[d2-C]V and AC[d8-V], to identify both C–H-cleaving intermediates. The results show that they are high-spin Fe(III)-superoxo and high-spin Fe(IV)-oxo complexes, respectively, in agreement with published mechanistic proposals derived computationally from Baldwin’s founding work.
- Published
- 2016
29. Spectroscopic and Electrochemical Characterization of the Iron–Sulfur and Cobalamin Cofactors of TsrM, an Unusual Radical S-Adenosylmethionine Methylase
- Author
-
Sean Elliott, Squire J. Booker, Nicholas D. Lanz, Stephanie J. Maiocco, Alexey Silakov, Bo Zhang, Wendy L. Kelly, Anthony J. Blaszczyk, and Carsten Krebs
- Subjects
Iron-Sulfur Proteins ,0301 basic medicine ,S-Adenosylmethionine ,Stereochemistry ,Coenzymes ,chemistry.chemical_element ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Cobalamin ,Catalysis ,Cofactor ,law.invention ,Spectroscopy, Mossbauer ,03 medical and health sciences ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,law ,Electrochemistry ,Moiety ,Organic chemistry ,Electron paramagnetic resonance ,Indole test ,biology ,Electron Spin Resonance Spectroscopy ,Methyltransferases ,General Chemistry ,Methylation ,Sulfur ,0104 chemical sciences ,Vitamin B 12 ,030104 developmental biology ,chemistry ,biology.protein ,Methyl group - Abstract
TsrM, an annotated radical S-adenosylmethionine (SAM) enzyme, catalyzes the methylation of carbon 2 of the indole ring of L-tryptophan. Its reaction is the first step in the biosynthesis of the unique quinaldic acid moiety of thiostrepton A, a thiopeptide antibiotic. The appended methyl group derives from SAM; however, the enzyme also requires cobalamin and iron-sulfur cluster cofactors for turnover. In this work we report the overproduction and purification of TsrM and the characterization of its metallocofactors by UV-visible, electron paramagnetic resonance, hyperfine sublevel correlation (HYSCORE), and Mössbauer spectroscopies as well as protein-film electrochemistry (PFE). The enzyme contains 1 equiv of its cobalamin cofactor in its as-isolated state and can be reconstituted with iron and sulfide to contain one [4Fe-4S] cluster with a site-differentiated Fe(2+)/Fe(3+) pair. Our spectroscopic studies suggest that TsrM binds cobalamin in an uncharacteristic five-coordinate base-off/His-off conformation, whereby the dimethylbenzimidazole group is replaced by a non-nitrogenous ligand, which is likely a water molecule. Electrochemical analysis of the protein by PFE indicates a one-electron redox feature with a midpoint potential of -550 mV, which is assigned to a [4Fe-4S](2+)/[4Fe-4S](+) redox couple. Analysis of TsrM by Mössbauer and HYSCORE spectroscopies suggests that SAM does not bind to the unique iron site of the cluster in the same manner as in other radical SAM (RS) enzymes, yet its binding still perturbs the electronic configuration of both the Fe/S cluster and the cob(II)alamin cofactors. These biophysical studies suggest that TsrM is an atypical RS enzyme, consistent with its reported inability to catalyze formation of a 5'-deoxyadenosyl 5'-radical.
- Published
- 2016
30. C and N Hybrid Coordination Derived Co–C–N Complex as a Highly Efficient Electrocatalyst for Hydrogen Evolution Reaction
- Author
-
Zhongli Wang, Xueping Sun, Hai-Xia Zhong, Xin-Bo Zhang, Zheng Jiang, Dan Xu, Jun Wang, Xianfeng Hao, and Fan-Lu Meng
- Subjects
Chemistry ,Nanotechnology ,General Chemistry ,Overpotential ,Electrocatalyst ,Biochemistry ,Catalysis ,Electron transfer ,Colloid and Surface Chemistry ,Adsorption ,Chemical engineering ,Transition metal ,Water splitting ,Density functional theory - Abstract
Development of an efficient hydrogen evolution reaction (HER) catalyst composed of earth-abundant elements is scientifically and technologically important for the water splitting associated with the conversion and storage of renewable energy. Herein we report a new class of Co-C-N complex bonded carbon (only 0.22 at% Co) for HER with a self-supported and three-dimensional porous structure that shows an unexpected catalytic activity with low overpotential (212 mV at 100 mA cm(-2)) and long-term stability, better than that of most traditional-metal catalysts. Experimental observations in combination with density functional theory calculations reveal that C and N hybrid coordination optimizes the charge distribution and enhances the electron transfer, which synergistically promotes the proton adsorption and reduction kinetics.
- Published
- 2015
31. Asymmetric Total Synthesis of Propindilactone G
- Author
-
Yuefan Wang, Yuan-He Li, Ling-Min Xu, Lin You, Bo Zhang, Jia-Jun Zhang, Jiahua Chen, Xin-Ting Liang, Shouliang Yang, Qi Su, and Zhen Yang
- Subjects
Cycloaddition Reaction ,biology ,Chemistry ,Stereochemistry ,Total synthesis ,chemistry.chemical_element ,Chemistry Techniques, Synthetic ,General Chemistry ,biology.organism_classification ,Biochemistry ,Triterpenes ,Catalysis ,Terpene ,Colloid and Surface Chemistry ,Hydrogenolysis ,Propindilactone G ,Oxidation-Reduction ,Palladium ,Schisandra propinqua ,Schisandra - Abstract
A concise total synthesis of (+)-propindilactone G, a nortriterpenoid isolated from the stems of Schisandra propinqua var. propinqua, has been achieved for the first time. The key steps of the synthesis include an asymmetric Diels-Alder reaction, a Pauson-Khand reaction, a Pd-catalyzed reductive hydrogenolysis reaction, and an oxidative heterocoupling reaction. These reactions enabled the synthesis of (+)-propindilactone G in only 20 steps. As a consequence of our synthetic studies, the structure of (+)-propindilactone G has been revised.
- Published
- 2015
32. Imaging Dynamic Collision and Oxidation of Single Silver Nanoparticles at the Electrode/Solution Interface
- Author
-
Yunshan Fan, Bo Zhang, and Rui Hao
- Subjects
Silver ,Inorganic chemistry ,Metal Nanoparticles ,02 engineering and technology ,Electrolyte ,010402 general chemistry ,Electrochemistry ,01 natural sciences ,Biochemistry ,Catalysis ,Silver nanoparticle ,Corrosion ,Colloid and Surface Chemistry ,Desorption ,Electroplating ,Electrodes ,Chemistry ,General Chemistry ,Electrochemical Techniques ,Nanocell ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Solutions ,Chemical engineering ,Microscopy, Fluorescence ,Electrode ,0210 nano-technology - Abstract
The electrochemical interface is an ultrathin interfacial region between the electrode surface and the electrolyte solution and is often characterized by numerous dynamic processes, such as solvation and desolvation, heterogeneous electron transfer, molecular adsorption and desorption, diffusion, and surface rearrangement. Many of these processes are driven and modulated by the presence of a large interfacial potential gradient. The study and better understanding of the electrochemical interface is important for designing better electrochemical systems where their applications may include batteries, fuel cells, electrocatalytic water splitting, corrosion protection, and electroplating. This, however, has proved to be a challenging analytical task due to the ultracompact and dynamic evolving nature of the electrochemical interface. Here, we describe the use of an electrochemical nanocell to image the dynamic collision and oxidation process of single silver nanoparticles at the surface of a platinum nanoelectrode. A nanocell is prepared by depositing a platinum nanoparticle at the tip of a quartz nanopipette forming a bipolar nanoelectrode. The compact size of the nanocell confines the motion of the silver nanoparticle in a 1-D space. The highly dynamic process of nanoparticle collision and oxidation is imaged by single-particle fluorescence microscopy. Our results demonstrate that silver nanoparticle collision and oxidation is highly dynamic and likely controlled by a strong electrostatic effect at the electrode/solution interface. We believe that the use of a platinum nanocell and single molecule/nanoparticle fluorescence microscopy can be extended to other systems to yield highly dynamic information about the electrochemical interface.
- Published
- 2017
33. Chemically Resolved Transient Collision Events of Single Electrocatalytic Nanoparticles
- Author
-
Stephen J. Percival, Zhihui Guo, and Bo Zhang
- Subjects
Inert ,Surface Properties ,Chemistry ,Metal Nanoparticles ,Nanoparticle ,Ultramicroelectrode ,Nanotechnology ,Electrochemical Techniques ,General Chemistry ,Biochemistry ,Signal ,Catalysis ,Amperometry ,Colloid and Surface Chemistry ,Electrode ,Transient (oscillation) ,Cyclic voltammetry ,Electrodes - Abstract
Here we report the use of fast-scan cyclic voltammetry (FSCV) to study transient collision and immobilization events of single electrocatalytic metal nanoparticles (NPs) on an inert electrode. In this study, a fast, repetitive voltage signal is continuously scanned on an ultramicroelectrode and its faradaic signal is recorded. Electrocatalytically active metal NPs are allowed to collide and immobilize on the electrode resulting in the direct recording of the transient voltammetric response of single NPs. This approach enables one to obtain the transient voltammetric response and electrocatalytic effects of single catalytic NPs as they interact with an inert electrode. The use of FSCV has enabled us to obtain chemical information, which is otherwise difficult to study with previous amperometric methods.
- Published
- 2014
34. A Peroxodiiron(III/III) Intermediate Mediating Both N‑Hydroxylation Steps in Biosynthesis of the N‑Nitrosourea Pharmacophore of Streptozotocin by the Multi-domain Metalloenzyme SznF.
- Author
-
McBride, Molly J., Sil, Debangsu, Ng, Tai L., Crooke, Anne Marie, Kenney, Grace E., Tysoe, Christina R., Bo Zhang, Balskus, Emily P., Boal, Amie K., Krebs, Carsten, and Bollinger Jr., J. Martin
- Published
- 2020
- Full Text
- View/download PDF
35. Single Particle Detection by Area Amplification: Single Wall Carbon Nanotube Attachment to a Nanoelectrode
- Author
-
Bo Zhang, Jun Hui Park, Allen J. Bard, and Scott N. Thorgaard
- Subjects
Nanotubes, Carbon ,Surface Properties ,Chemistry ,Nanoparticle ,Nanotechnology ,Electrochemical Techniques ,General Chemistry ,Electrochemical detection ,Carbon nanotube ,Active electrode ,Biochemistry ,Catalysis ,law.invention ,Electron transfer ,Colloid and Surface Chemistry ,law ,Electric field ,Particle ,Ferrous Compounds ,Particle Size ,Electrodes ,Oxidation-Reduction - Abstract
We describe the electrochemical detection of single nanoparticle (NP) attachment on a nanoelectrode by the increase in the active electrode area. The attachment of gold NP-decorated single wall carbon nanotubes (Au-SWCNTs) was observed by their current-time transients for ferrocenemethanol (FcMeOH) oxidation. Since the attached Au-SWCNT increases the electroactive area available for FcMeOH oxidation, the current increases after attachment of the particle. The "staircase" shape of the current response establishes that the particles do not become deactivated for the outer-sphere electron transfer reaction after attachment. Au-SWCNTs migrate to and are held at the nanoelectrode by an electric field. However, SWCNTs that are not decorated with a gold NP produce only a sharp transient ("blip") response.
- Published
- 2013
36. Monothiol Glutaredoxins Function in Storing and Transporting [Fe2S2] Clusters Assembled on IscU Scaffold Proteins
- Author
-
Bo Zhang, Michael K. Johnson, and Priyanka Shakamuri
- Subjects
Iron-Sulfur Proteins ,Scaffold protein ,Circular dichroism ,010402 general chemistry ,01 natural sciences ,Biochemistry ,Catalysis ,03 medical and health sciences ,Colloid and Surface Chemistry ,Glutaredoxin ,Cluster (physics) ,Sulfhydryl Compounds ,Glutaredoxins ,030304 developmental biology ,0303 health sciences ,biology ,Chemistry ,Communication ,Circular Dichroism ,General Chemistry ,biology.organism_classification ,0104 chemical sciences ,Crystallography ,General purpose ,Azotobacter vinelandii ,Biophysics ,biology.protein ,Spectrophotometry, Ultraviolet ,ISCU ,Function (biology) - Abstract
In the bacterial ISC system for iron-sulfur cluster assembly, IscU acts as a primary scaffold protein, and the molecular co-chaperones HscA and HscB specifically interact with IscU to facilitate ATP-driven cluster transfer. In this work, cluster transfer from Azotobacter vinelandii [Fe(2)S(2)](2+) cluster-bound IscU to apo-Grx5, a general purpose monothiol glutaredoxin in A. vinelandii, was monitored by circular dichroism spectroscopy, in the absence and in the presence of HscA/HscB/Mg-ATP. The results indicate a 700-fold enhancement in the rate of [Fe(2)S(2)](2+) cluster transfer in the presence of the co-chaperones and Mg-ATP, yielding a second-order rate constant of 20 000 M(-1) min(-1) at 23 °C. Thus, HscA and HscB are required for efficient ATP-dependent [Fe(2)S(2)](2+) cluster transfer from IscU to Grx5. The results support a role for monothiol Grx's in storing and transporting [Fe(2)S(2)](2+) clusters assembled on IscU and illustrate the limitations of interpreting in vitro cluster transfer studies involving [Fe(2)S(2)]-IscU in the absence of the dedicated HscA/HscB co-chaperone system.
- Published
- 2012
37. The structure of formaldehyde-inhibited xanthine oxidase determined by 35 GHz [super 2]H ENDOR spectroscopy
- Author
-
Shanmugam, Muralidharan, Bo Zhang, McNaughton, Rebecca L., Kinney, R. Adam, Hille, Russ, and Hoffman, Brian M.
- Subjects
Enzyme inhibitors -- Chemical properties ,Enzyme inhibitors -- Structure ,Enzyme inhibitors -- Spectra ,Formaldehyde -- Chemical properties ,Oxidases -- Chemical properties ,Oxidases -- Structure ,Chemistry - Abstract
The formaldehyde-inhibited Mo(V) state of xanthine oxidase (I) is analyzed. [super 1]H and [super 2]H ENDOR spectra of xanthine oxidase(C[super 1,2][H.sub.2]O) in [H.sub.2]O/[D.sub.2]O buffer have shown that the active-site structure of xanthine oxidase contains a C[H.sub.2]O adduct of Mo(V) in the form of a four-membered ring with S and O linking the C to Mo and have ruled out a direct Mo-C bond.
- Published
- 2010
38. One-step seeding growth of magnetically recyclable Au@Co core-shell nanoparticles: highly efficient catalyst for hydrolytic dehydrogenation of ammonia borane
- Author
-
Jun-Min Yan, Xin-Bo Zhang, Akita, Tomoki, Haruta, Masatake, and Qiang Xu
- Subjects
Ammonia -- Chemical properties ,Borane -- Chemical properties ,Borane -- Magnetic properties ,Borane -- Thermal properties ,Cobalt alloys -- Chemical properties ,Cobalt alloys -- Magnetic properties ,Cobalt alloys -- Thermal properties ,Dehydrogenation -- Analysis ,Gold alloys -- Chemical properties ,Gold alloys -- Magnetic properties ,Gold alloys -- Thermal properties ,Chemistry - Abstract
Magnetically recyclable core-shell nanoparticles are prepared in a one-step seeding-growth process within a few minutes. They are thermally stable and have displayed higher catalytic activity toward the dehydrogenation of ammonia borane than Au-Co alloy and the pure metal counterparts.
- Published
- 2010
39. Prodrugs forming high drug loading multifunctional nanocapsules for intracellular cancer drug delivery
- Author
-
Youqing Shen, Erlei Jin, Bo Zhang, Murphy, Caitlin J., Meihua Sui, Jian Zhao, Jinqiang Wang, Jianbin Tang, Maohong Fan, Kirk, Edward Van, and Murdoch, William J.
- Subjects
Prodrugs -- Analysis ,Antimitotic agents -- Analysis ,Antineoplastic agents -- Analysis ,Chemistry - Abstract
A new concept directly using drug molecules to fabricate nanocarriers in order to minimize use of inert materials, substantially increase the drug loading content, and suppress premature burst release is described. The concept directly using drugs as part of a carrier could be applied to fabricate other highly efficient nanocarriers with a substantially reduced use of inert carrier materials and increased drug loading content without premature burst release.
- Published
- 2010
40. Electrochemical responses and electrocatalysis at single Au nanoparticles
- Author
-
Yongxin Li, Cox, Jonathan T., and Bo Zhang
- Subjects
Catalysis -- Analysis ,Gold -- Chemical properties ,Gold -- Electric properties ,Nanoparticles -- Chemical properties ,Nanoparticles -- Electric properties ,Platinum -- Chemical properties ,Platinum -- Electric properties ,Chemistry - Abstract
Steady-state electrochemical responses are obtained at single Au nanoparticles by using Pt nanoelectrodes and Au single-nanoparticle electrode (SNPE) is constructed by chemically immobilizing a single Au nanoparticle at a Si[O.sub.2]-encapsulated Pt disk nanoelectrode. The studies have shown that the electrocatalytic activity of single Au nanoparticles is measured by using SNPEs and have helped in understanding the structure-function relationship in nanoparticle-based electrocatalysis.
- Published
- 2010
41. In Situ Coupling of Strung Co4N and Intertwined N-C Fibers toward Free-Standing Bifunctional Cathode for Robust, Efficient, and Flexible Zn-Air Batteries
- Author
-
Hai-Xia Zhong, Jun-Min Yan, Di Bao, Xin-Bo Zhang, and Fan-Lu Meng
- Subjects
Oxygen evolution ,Nanotechnology ,02 engineering and technology ,General Chemistry ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Polypyrrole ,01 natural sciences ,Biochemistry ,Catalysis ,Flexible electronics ,Cathode ,0104 chemical sciences ,law.invention ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,chemistry ,law ,Nanofiber ,Electrode ,Specific energy ,0210 nano-technology ,Bifunctional - Abstract
Flexible power sources with high energy density are crucial for the realization of next-generation flexible electronics. Theoretically, rechargeable flexible zinc-air (Zn-air) batteries could provide high specific energy, while their large-scale applications are still greatly hindered by high cost and resources scarcity of noble-metal-based oxygen evolution reaction (OER)/oxygen reduction reaction (ORR) electrocatalysts as well as inferior mechanical properties of the air cathode. Combining metallic Co4N with superior OER activity and Co-N-C with perfect ORR activity on a free-standing and flexible electrode could be a good step for flexible Zn-air batteries, while lots of difficulties need to be overcome. Herein, as a proof-of-concept experiment, we first propose a strategy for in situ coupling of strung Co4N and intertwined N-C fibers, by pyrolyzation of the novel pearl-like ZIF-67/polypyrrole nanofibers network rooted on carbon cloth. Originating from the synergistic effect of Co4N and Co-N-C and the stable 3D interconnected conductive network structure, the obtained free-standing and highly flexible bifunctional oxygen electrode exhibits excellent electrocatalytic activity and stability for both OER and ORR in terms of low overpotential (310 mV at 10 mA cm(-2)) for OER, a positive half-wave potential (0.8 V) for ORR, and a stable current density retention for at least 20 h, and especially, the obtained Zn-air batteries exhibit a low discharge-charge voltage gap (1.09 V at 50 mA cm(-2)) and long cycle life (up to 408 cycles). Furthermore, the perfect bendable and twistable and rechargeable properties of the flexible Zn-air battery particularly make it a potentially power portable and wearable electronic device.
- Published
- 2016
42. Direct growth of semiconducting single-walled carbon nanotube array
- Author
-
Guo Hong, Bo Zhang, Banghua Peng, Jin Zhang, Won Mook Choi, Jae-Young Choi, Jong Min Kim, and Zhongfan Liu
- Subjects
Chemical vapor deposition -- Usage ,Nanotubes -- Structure ,Nanotubes -- Chemical properties ,Nanotubes -- Electric properties ,Quartz -- Chemical properties ,Quartz -- Electric properties ,Raman spectroscopy -- Usage ,Semiconductors -- Chemical properties ,Semiconductors -- Electric properties ,Chemistry - Abstract
A UV beam was introduced into homemade chemical vapor deposition system to obtain a well aligned SWNT array on an ST-cut quartz substrate. The SWNT array detected by Raman spectroscopy and electrical measurement showed that over 95% of the SWNT is semiconducting and could be used to solve problems in SWNT application.
- Published
- 2009
43. Room-temperature hydrogen generation from hydrous hydrazine for chemical hydrogen storage
- Author
-
Singh, Sanjay Kumar, Xin-Bo Zhang, and Qiang Xu
- Subjects
Rhodium -- Chemical properties ,Ammonium chloride -- Chemical properties ,Ammonium compounds -- Chemical properties ,Ammonium paratungstate -- Chemical properties ,Catalysis -- Analysis ,Hydrazine -- Chemical properties ,Methyl groups -- Chemical properties ,Chemistry - Abstract
Rhodium nanoparticles (NPs) have catalyzed the decomposition of hydrous hydrazine to produce hydrogen under ambient reaction conditions. Rh(0) NPs with a particle size of 5 nm prepared in the presence of hexadecyltrimethyl ammonium bromide has shown higher catalytic activity.
- Published
- 2009
44. Magnetically recyclable Fe@Pt core-shell nanoparticles and their use as electrocatalysts for ammonia borane oxidation: the role of crystallinity of the core
- Author
-
Xin-Bo Zhang, Jun-Min Yan, Song Han, Shioyama, Hiroshi, and Qiang Xu
- Subjects
Ammonia -- Chemical properties ,Crystallography -- Usage ,Iron alloys -- Structure ,Iron alloys -- Chemical properties ,Iron alloys -- Magnetic properties ,Nanoparticles -- Structure ,Nanoparticles -- Chemical properties ,Oxidation-reduction reaction -- Analysis ,Platinum -- Chemical properties ,Platinum -- Magnetic properties ,Chemistry - Abstract
Carbon-supported nanoparticles (NP) catalysts with Fe cores in different crystal states are prepared by a sequential reduction process. Iron in the amorphous state has exerted a powerful ability as the core of for the NPs, which is in contrast with its crystallized counterpart.
- Published
- 2009
45. Electrostatic-gated transport in chemically modified glass nanopore electrodes
- Author
-
Gangli Wang, Bo Zhang, Wayment, Joshua R., Harris, Joel M., and White, Henry S.
- Subjects
Electrodes -- Research ,Platinum -- Electric properties ,Platinum -- Chemical properties ,Chemistry - Abstract
The chemical modification of glass nanopore electrodes was described to impart the transport selectivity based on electrostatic forces at the pore orifice. A simple and powerful means to measure the molecular interactions at the orifice of individual nanometer scale pores by electrochemical detection using the relatively large Pt electrode at the base of the conical-shaped pore.
- Published
- 2006
46. Electrostatic-Gated Transport in Chemically Modified Glass Nanopore Electrodes
- Author
-
Joshua R. Wayment, Joel M. Harris, Bo Zhang, Gangli Wang, and Henry S. White
- Subjects
Surface Properties ,Static Electricity ,Analytical chemistry ,Biosensing Techniques ,Electrochemistry ,Biochemistry ,Catalysis ,Colloid and Surface Chemistry ,Etching (microfabrication) ,Platinum ,Chemistry ,General Chemistry ,Hydrogen-Ion Concentration ,Silanes ,Electrostatics ,Nanostructures ,Nanopore ,Microscopy, Fluorescence ,Silanization ,Electrode ,Glass ,Cyclic voltammetry ,Microelectrodes ,Oxidation-Reduction ,Porosity ,Body orifice - Abstract
Electrostatic-gated transport in chemically modified glass nanopore electrodes with orifice radii as small as 15 nm is reported. A single conical-shaped nanopore in glass, with a approximately 1 microm radius Pt disk located at the pore base, is prepared by etching the exposed surface of a glass-sealed Pt nanodisk. The electrochemical response of the nanopore electrode corresponds to diffusion of redox-active species through the nanopore orifice to the Pt microdisk. Silanization of the exterior glass surface with Cl(Me)(2)Si(CH(2))(3)CN and the interior pore surface with EtO(Me)(2)Si(CH(2))(3)NH(2) introduces pH-dependent ion selectivity at the pore orifice, a consequence of the electrostatic interactions between the redox ions and protonated surface amines. Nanopore electrodes with very small pore orifice radii (approximately 50 nm) display anion permselectively at pH4, as demonstrated by electrochemical measurement of transport through the pore orifice. Ion selective transport vanishes at pH6 or when the pore radius is significantly larger than the Debye screening length, consistent with the observed ion selectivity resulting from electrostatic interactions. The ability to introduce different surface functionalities to the interior and exterior surfaces of glass nanopores is demonstrated using fluorescence microscopy to monitor the localized covalent attachment of 5- (and 6)-carboxytetramethylrhodamine succinimidyl ester to interior pore surfaces previously silanized with EtO(Me)(2)Si(CH(2))(3)NH(2).
- Published
- 2006
47. The Structure of Formaldehyde-Inhibited Xanthine Oxidase Determined by 35 GHz 2H ENDOR Spectroscopy
- Author
-
R. Adam Kinney, Bo Zhang, Rebecca L. McNaughton, Russ Hille, Muralidharan Shanmugam, and Brian M. Hoffman
- Subjects
Xanthine Oxidase ,Protein Conformation ,Chemistry ,Electron Spin Resonance Spectroscopy ,Formaldehyde ,General Chemistry ,Photochemistry ,Biochemistry ,Article ,Catalysis ,chemistry.chemical_compound ,Colloid and Surface Chemistry ,Protein structure ,Catalytic Domain ,Organic chemistry ,Xanthine oxidase ,Spectroscopy - Abstract
The formaldehyde-inhibited Mo(V) state of xanthine oxidase (I) has been studied for four decades, yet it has not proven possible to distinguish unequivocally among the several structures proposed for this form. The uniquely large isotropic hyperfine coupling for (13)C from CH(2)O led to the intriguing suggestion of a direct Mo-C bond for the active site of I. This suggestion was supported by the recent crystal structures of glycol- and glycerol-inhibited forms of aldehyde oxidoreductase, a member of the xanthine oxidase family. (1)H and (2)H ENDOR spectra of I(C(1,2)H(2)O) in H(2)O/D(2)O buffer now have unambiguously revealed that the active-site structure of I contains a CH(2)O adduct of Mo(V) in the form of a four-membered ring with S and O linking the C to Mo and have ruled out a direct Mo-C bond. Density functional theory computations are consistent with this conclusion. We interpret the large (13)C coupling as resulting from a "transannular hyperfine interaction".
- Published
- 2010
48. Graphene nanoelectrodes: fabrication and size-dependent electrochemistry
- Author
-
Shengli Chen, Lixin Fan, Yuwen Liu, Huawei Zhong, and Bo Zhang
- Subjects
Nanostructure ,Graphene ,Chemistry ,Surface Properties ,Analytical chemistry ,Oxides ,General Chemistry ,Electrochemical Techniques ,Electrochemistry ,Biochemistry ,Catalysis ,law.invention ,Nanostructures ,Electron transfer ,Colloid and Surface Chemistry ,Hydrazines ,law ,Monolayer ,Electrode ,Graphite ,Particle Size ,Nanoscopic scale ,Electrodes - Abstract
The fabrication and electrochemistry of a new class of graphene electrodes are presented. Through high-temperature annealing of hydrazine-reduced graphene oxides followed by high-speed centrifugation and size-selected ultrafiltration, flakes of reduced graphene oxides (r-GOs) of nanometer and submicrometer dimensions, respectively, are obtained and separated from the larger ones. Using n-dodecanethiol-modified Au ultramicroelectrodes of appropriately small sizes, quick dipping in dilute suspensions of these small r-GOs allows attachment of only a single flake on the thiol monolayer. The electrodes thus fabricated are used to study the heterogeneous electron transfer (ET) kinetics at r-GOs and the nanoscopic charge transport dynamics at electrochemical interfaces. The r-GOs are found to exhibit similarly high activity for electrochemical ET reactions to metal electrodes. Voltammetric analysis for the relatively slow ET reaction of Fe(CN)6(3-) reduction produces slightly higher ET rate constants at r-GOs of nanometer sizes than at large ones. These ET kinetic features are in accordance with the defect-dominant nature of the r-GOs and the increased defect density in the nanometer-sized flakes as revealed by Raman spectroscopic measurements. The voltammetric enhancement and inhibition for the reduction of Ru(NH3)6(3+) and Fe(CN)6(3-), respectively, at r-GO flakes of submicrometer and nanometer dimensions upon removal of supporting electrolyte are found to significantly deviate in magnitude from those predicted by the electroneutrality-based electromigration theory, which may evidence the increased penetration of the diffuse double layer into the mass transport layer at nanoscopic electrochemical interfaces.
- Published
- 2013
49. Two Distinct Mechanisms for C–C Desaturation by Iron(II)- and 2-(Oxo)glutarate-Dependent Oxygenases: Importance of α-Heteroatom Assistance.
- Author
-
Dunham, Noah P., Wei-chen Chang, Mitchell, Andrew J., Martinie, Ryan J., Bo Zhang, Bergman, Jonathan A., Rajakovich, Lauren J., Bo Wang, Silakov, Alexey, Krebs, Carsten, Boal, Amie K., and Bollinger Jr., J. Martin
- Published
- 2018
- Full Text
- View/download PDF
50. Collision Dynamics during the Electrooxidation of Individual Silver Nanoparticles.
- Author
-
Robinson, Donald A., Yuwen Liu, Edwards, Martin A., Vitti, Nicholas J., Oja, Stephen M., Bo Zhang, and White, Henry S.
- Published
- 2017
- Full Text
- View/download PDF
Catalog
Discovery Service for Jio Institute Digital Library
For full access to our library's resources, please sign in.