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A Single Nickel Site Reduces Nitrate Ions to Nitrogen Gas

03 Jun 2019

Surface runoff of agricultural or landscape areas with excessive nitrate fertilizers has resulted in increasing nitrate ion concentrations in freshwater. This issue leads to eutrophication and algae blooms that significantly threaten aquatic lives and ecosystems. Eliminating nitrate ions is thus necessary to address the nitrate-borne water pollution. Nature presents a delicate yet complicated process for turning NO₃^– into N₂ by four metalloenzymes. Is it possible to develop an artificial method with just one catalyst to drive the same process?

Lee, Baik, and coworkers at the Institute for Basic Science (IBS) and Korea Advanced Institute of Science and Technology (KAIST) answered yes. The researchers synthesized a square-planar nickel(II)-based complex, (PNP)Ni(ONO₂) (PNP = N[2-P’Pr-4-methyl-C₆H₃]₂), which converted NO₃^– to N₂ in the presence of CO and NO. Ni²⁺ is the only active site. This breakthrough has been published in Chemical Science (DOI: 10.1039/C9SC00717B).

The reaction mechanism involves four successive redox reactions among (PNP)Ni(ONO₂), CO, and NO (Figure 1). The first two steps consecutively transfer two oxygen atoms from (PNP)Ni(ONO₂) to CO at room temperature, yielding two molecules of CO₂ and a Ni-nitrosyl complex, (PNP)Ni(NO). Afterwards, the (PNP)Ni(NO) undergoes a disproportionation reaction with NO, generating (PNP)Ni(NO₂) and N₂O. The as-formed N₂O interacts with the remaining (PNP)Ni(NO) and is eventually reduced to N₂. The yield of N₂ is 46% (based on the amount of N₂O).

Figure 1. The schematic shows the artificial nitrate reduction with a Ni(II)-based complex, (PNP)Ni(ONO₂), as the catalyst. Pr: propyl group.

Besides nitrate reduction, the (PNP)Ni(ONO₂) could act as a potential alternative to the platinum-containing catalysts used in the catalytic converters of gasoline cars, because it transforms hazardous CO and NO into less toxic CO₂ and N₂.

To find out more please read:

One Metal is Enough: A Nickel Complex Reduces Nitrate Anions to Nitrogen Gas

Jinseong Gwak, Seihwan Ahn, Mu-Hyun Baik and Yunho Lee

Chem. Sci., 2019, 10, 4767-4774

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Chemistry from University of California, Santa Cruz in the United States. He is passionate about scientific communication to introduce cutting-edge research to both the general public and scientists with diverse research expertise. He is a blog writer for Chem. Commun. and Chem. Sci. More information about him can be found at http://liutianyuresearch.weebly.com/.

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Molecular Switching: from Blue Biradicals to Colorless Housanes

23 May 2019

As chemists, we typically first encounter molecular switches, the general term for any molecule that exists in at least two stable or meta-stable states, as pH indicators in introductory chemistry classes. The external factor that causes the conversion can vary from a redox event to UV light. This makes molecular switches attractive sensors for a range of chemically relevant applications. The reversible and controllable bond-making and bond-breaking also provides a system within which to interrogate the nature of chemical bonding.

Figure 1. The biradical (left) and housane (right) in solution along with their simplified chemical structures.

Chemists at the University of Rostock in Germany explored light-driven molecular switching behavior in a class of heterocyclic molecules. These can exist as either biradicals or housanes (see Figure 1 for why the name makes sense) with a bond between the two phosphorus atoms. Understanding the mechanism by which the photo-isomerization occurs is important for future applications of the biradical system in small molecule activation. The in-depth studies used the 2,6-dimethylphenyl (2Dmp) derivative, since it was the most stable of the synthesized derivatives. The researchers monitored the conversion between species by examining their dramatically different ³¹P NMR spectra, with the housane resonances between -50 and -200 ppm and the biradical resonances between 200 and 300 ppm. An additional distinguishing feature between is color: the starting biradical is blue while the housane is colorless. The researchers found that biradical converts to the housane, which has a half-life of about 7 minutes at room temperature in solution, with an almost 25% quantum yield.

Figure 2. A single crystal of the biradical. Upon irradiation, the transition to the colorless housane can be observed, along with extensive cracking of the crystal.

This switching occurs not only in solution, but also in the solid state (Figure 2). The cracking evident in the images of a single crystal is attributed to the stress caused by changes to the crystal lattice by conversion of the biradical to the housane. Despite various efforts by the team, including crystallization attempts under constant irradiation, they were unable to obtain high enough quality crystals to acquire a crystal structure of the housane. The specific isomerization mechanism was computationally modeled and showed that the photoexcitation of the biradical led to a bonding interaction and distortion, allowing for housane formation. The reverse, thermally activated process, occurs due to the intersection of the ground and excited state energies near a transition state.

Given this enhanced understanding of the isomerization mechanism, the researchers manipulated the reactivity of the biradical by adding tert-butyl isocyanide (^tBuNC). ^tBuNC catalyzed the thermal conversion of the housane back to the diradical. While the mechanism of the catalysis is unknown, it’s an exciting proof-of-concept for easily tuning molecular switching behavior.

To find out more please read:

A chemical reaction controlled by light-activatedmolecular switches based on hetero-cyclopentanediyls

Jonas Bresien, Thomas Kröger-Badge, Stefan Lochbrunner, Dirk Michalik, Henrik Müller, Axel Schultz, and Edgar Zander

Chem. Sci., 2019, 10, 3486-3493

About the blogger:

Beth Mundy is a PhD candidate in chemistry in the Cossairt lab at the University of Washington in Seattle, Washington. Her research focuses on developing new and better ways to synthesize nanomaterials for energy applications. She is often spotted knitting in seminars or with her nose in a good book. You can find her on Twitter at @BethMundySci.

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HOT Chemical Science articles for March

22 May 2019

We are happy to present a selection of our HOT articles for March. To see all of our HOT referee-recommended articles from 2019, please find the collection here.

As always, Chemical Science articles are free to access.

The antioxidant activity of polysulfides: it’s radical!

Jean-Philippe R. Chauvin, Markus Griesser and Derek A. Pratt*

Chem. Sci., 2019, 10, 4999-5010

DOI: 10.1039/C9SC00276F, Edge Article

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Anisotropic strain release in a thermosalient crystal: correlation between the microscopic orientation of molecular rearrangements and the macroscopic mechanical motion

Tomohiro Seki,* Takaki Mashimo and Hajime Ito*

Chem. Sci., 2019, 10, 4185-4191

DOI: 10.1039/C8SC05563G, Edge Article

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Alkali metal complexes of an enantiopure iminophosphonamide ligand with bright delayed fluorescence

Thomas J. Feuerstein, Bhupendra Goswami, Pascal Rauthe, Ralf Köppe, Sergei Lebedkin, Manfred M. Kappes and Peter W. Roesky*

Chem. Sci., 2019, 10, 4742-4749

DOI: 10.1039/C9SC00629J, Edge Article

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Direct observation of prion protein oligomer formation reveals an aggregation mechanism with multiple conformationally distinct species

Jason C. Sang, Ji-Eun Lee, Alexander J. Dear, Suman De, Georg Meisl, Alana M. Thackray, Raymond Bujdoso, Tuomas P. J. Knowles and David Klenerman*

Chem. Sci., 2019, 10, 4588-4597

DOI: 10.1039/C8SC05627G, Edge Article

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Using coligands to gain mechanistic insight into iridium complexes hyperpolarized with para-hydrogen

Ben. J. Tickner, Richard O. John, Soumya S. Roy, Sam J. Hart, Adrian C. Whitwood and Simon B. Duckett*

Chem. Sci., 2019, 10, Advance Article

DOI: 10.1039/C9SC00444K, Edge Article

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Direct conversion of phenols into primary anilines with hydrazine catalyzed by palladium

Zihang Qiu, Leiyang Lv, Jianbin Li, Chen-Chen Li and Chao-Jun Li*

Chem. Sci., 2019, 10, 4775-4781

DOI: 10.1039/C9SC00595A, Edge Article

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HOT Chemical Science articles for February

26 Apr 2019

We are happy to present a selection of our HOT articles for February. To see all of our HOT referee-recommended articles from 2019, please find the collection here.

As always, Chemical Science articles are free to access.

Cooperativity basis for small-molecule stabilization of protein-protein interactions

Pim J. de Vink, Sebastian A. Andrei, Yusuke Higuchi, Christian Ottmann, Lech-Gustav Milroy and Luc Brunsveld*

Chem. Sci., 2019, 10, 2869-2874

DOI: 10.1039/C8SC05242E, Edge Article

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Acyclic 1,2-Dimagnesioethanes/-ethene Derived from Magnesium(I) Compounds: Multipurpose Reagents for Organometallic Synthesis

Deepak Dange, Andrew R. Gair, Dafydd D. L. Jones, Martin Juckel, Simon Aldridge and Cameron Jones*

Chem. Sci., 2019, 10, 3208-3216

DOI: 10.1039/C9SC00200F, Edge Article

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Catalytic Radical Difluoromethoxylation of Arenes and Heteroarenes

Johnny W. Lee, Weijia Zheng, Cristian A. Morales-Rivera, Peng Liu* and Ming-Yu Ngai*

Chem. Sci., 2019, 10, 3217-3222

DOI: 10.1039/C8SC05390A, Edge Article

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Revising measurement process in the variational quantum eigensolver: Is it possible to reduce the number of separately measured operators?

Artur F. Izmaylov,* Tzu-Ching Yen and Ilya G. Ryabinkin

Chem. Sci., 2019, 10, 3746-3755

DOI: 10.1039/C8SC05592K, Edge Article

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A dinuclear ruthenium(II) phototherapeutic that targets duplex and quadruplex DNA

Stuart A. Archer, Ahtasham Raza, Fabian Dröge, Craig Robertson, Alexander J. Auty, Dimitri Chekulaev, Julia A. Weinstein, Theo Keane, Anthony J. H. M. Meijer, John W. Haycock,* Sheila MacNeil* and James A. Thomas*

Chem. Sci., 2019, 10, 3502-3513

DOI: 10.1039/C8SC05084H, Edge Article

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Facile synthesis of AIEgens with wide color tunability for cellular imaging and therapy

Wenhan Xu, Michelle M. S. Lee, Zhihan Zhang, Herman H. Y. Sung, Ian D. Williams, Ryan T. K. Kwok, Jacky W. Y. Lam, Dong Wang* and Ben Zhong Tang*

Chem. Sci., 2019, 10, 3494-3501

DOI: 10.1039/C8SC05805A, Edge Article

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HOT Chemical Science articles for January

28 Feb 2019

We are happy to present a selection of our HOT articles for January. To see all of our HOT referee-recommended articles from 2019, please find the collection here.

As always, Chemical Science articles are free to access.

Enantioselective [1,3] O-to-C rearrangement: dearomatization of alkyl 2-allyloxy/benzyloxy-1/3-naphthoates catalyzed by a chiral π–Cu(II) complex

Lu Yao, Kazuaki Ishihara*

Chem. Sci., 2019, 10, 2259-2263

DOI: 10.1039/C8SC05601C, Edge Article

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Through-space charge transfer hexaarylbenzene dendrimers with thermally activated delayed fluorescence and aggregation-induced emission for efficient solution-processed OLEDs

Xingdong Wang, Shumeng Wang, Jianhong Lv, Shiyang Shao,* Lixiang Wang,* Xiabin Jing and Fosong Wang

Chem. Sci., 2019, Advance Article

DOI: 10.1039/C8SC04991B, Edge Article

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Heterolytic bond activation at gold: evidence for gold(III) H–B, H–Si complexes, H–H and H–C cleavage

Luca Rocchigiani,* Peter H. M. Budzelaar* and Manfred Bochmann*

Chem. Sci., 2019, 10, 2633-2642

DOI: 10.1039/C8SC05229H, Edge Article

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Insights into mechanochemical reactions at the molecular level: simulated indentations of aspirin and meloxicam crystals

Michael Ferguson, M. Silvina Moyano, Gareth A. Tribello, Deborah E. Crawford, Eduardo M. Bringa, Stuart L. James,* Jorge Kohanoff* and Mario G. Del Pópolo*

Chem. Sci., 2019, Advance Article

DOI: 10.1039/C8SC04971H, Edge Article

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Structure revision of cryptosporioptides and determination of the genetic basis for dimeric xanthone biosynthesis in fungi

Claudio Greco, Kate de Mattos-Shipley, Andrew M. Bailey, Nicholas P. Mulholland, Jason L. Vincent, Christine L. Willis, Russell J. Cox* and Thomas J. Simpson*

Chem. Sci., 2019, Advance Article

DOI: 10.1039/C8SC05126G, Edge Article

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From nano-balls to nano-bowls

Helena Brake, Eugenia Peresypkina, Claudia Heindl, Alexander V. Virovets, Werner Kremer and Manfred Scheer*

Chem. Sci., 2019, Advance Article

DOI: 10.1039/C8SC05471A, Edge Article

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Learning from Nature: A Cu(II)-Porphyrin Complex Produces Oxygen Gas from Water at Ultra-Small Overpotential

25 Feb 2019

Sunlight-assisted water splitting represents a sustainable way to convert solar energy into chemical energy in hydrogen and oxygen gases. Due to its high activation energy, the oxygen evolution reaction (OER) requires large overpotential for initiation. Developing suitable OER catalysts to reduce the overpotential thus becomes instrumental for the feasibility of solar energy harvesting.

Recently, a group of scientists led by Rui Cao from Renmin University of China, and Shaanxi Normal University, China, has developed a water-soluble Cu(II)-porphyrin complex as a high-performance OER catalyst. This breakthrough has been published in Chemical Science (DOI: 10.1039/C8SC04529A).

Inspired by the molecular structure of a natural OER catalyst in the photosynthesis system – photosystem II (PSII), the researchers designed a Cu²⁺-coordination compound with a porphyrin ligand, tetrakis(4-N-methylpyridyl)porphyrin (Figure 1a), which mimics the structure of PSII. This biomimetic Cu²⁺-complex exhibits outstanding catalytic OER activity in a phosphate buffer solution at pH=7.0. The current of the cyclic voltammogram of the Cu²⁺-complex increases sharply (due to O₂ evolution) at an onset potential of 1.13 V vs. normal hydrogen electrode (Figure 1b), corresponding to an OER overpotential of 310 mV. For comparison, the cyclic voltammograms of a blank buffer solution and a CuSO₄-containing buffer solution show no pronounced current enhancement (Figure 1b), indicating the electrolyte itself and the un-coordinated Cu²⁺ cannot generate O₂ within the tested potential range. The 310 mV overpotential is approximately two times smaller than the typical values exhibited by previously reported Cu complexes.

Figure 1. (a) The molecular structure of Cu²⁺-tetrakis(4-N-methylpyridyl)porphyrin complex. (b) Cyclic voltammograms of 1 mM Cu²⁺-tetrakis(4-N-methylpyridyl)porphyrin (red), bare buffer solution (black) and buffer solution containing 1 mM CuSO₄ (green). The electrode is a piece of fluorine-doped tin oxide glass slide.

The authors ascribed the ultra-small OER overpotential to the formation of an oxidized form of the Cu²⁺-porphyrin complex. This oxidized species is generated after the complex loses one electron, and is active for O-O bond formation and subsequent O₂ evolution. The energy barrier of this one-electron-oxidation pathway is expected to be much lower than those of conventional processes involving higher-valent Cu species (e.g., Cu⁴⁺-oxo), which facilitates OER at small overpotential.

With the complete catalytic cycle of water oxidation by the Cu²⁺-porphyrin complex being fully revealed, OER will become more efficient and energy-saving.

To find out more please read:

Low Overpotential Water Oxidation at Neutral pH Catalyzed by A Copper(II) Porphyrin

Yanju Liu, Yongzhen Han, Zongyao Zhang, Wei Zhang, Wenzhen Lai, Yong Wang and Rui Cao

Chem. Sci., 2019, DOI: 10.1039/C8SC04529A

About the blogger:

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HOT Chemical Science articles for December

11 Jan 2019

We are happy to present a selection of our HOT articles over the past month. To see all of our HOT referee-recommended articles from 2018, please find the collection here.

As always, Chemical Science articles are free to access.

Reaction-free and MMP-independent fluorescent probes for long-term mitochondria visualization and tracking

Ruoyao Zhang, Guangle Niu, Xuechen Li, Lifang Guo, Huamiao Zhang, Rui Yang, Yuncong Chen, Xiaoqiang Yu and Ben Zhong Tang

Chem. Sci., 2019, Advance Article

DOI: 10.1039/C8SC05119D, Edge Article

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Monitoring metal–amyloid-β complexation by a FRET-based probe: design, detection, and inhibitor screening

Hyuck Jin Lee, Young Geun Lee, Juhye Kang, Seung Hyun Yang, Ju Hwan Kim, Amar B.T. Ghisaidoobe, Hyo Jin Kang, Sang-Rae Lee, Mi Hee Lim and Sang J. Chung

Chem. Sci., 2019, Accepted Manuscript

DOI: 10.1039/C8SC04943B, Edge Article

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Fluorinated synthetic anion carriers: experimental and computational insights into membrane partitioning and transmembrane chloride transport mechanism

Michael J. Spooner, Hongyu Li, Igor Marques, Pedro M. R. Costa, Xin Wu, Ethan N. W. Howe, Nathalie Busschaert, Stephen J. Moore, Mark E. Light, David N. Sheppard, Vítor Félix and Philip A. Gale

Chem. Sci., 2019, Accepted Manuscript

DOI: 10.1039/C8SC05155K, Edge Article

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How machine learning can assist the interpretation of ab initio molecular dynamics simulations and conceptual understanding of chemistry

Florian Häse, Ignacio Fdez. Galván, Alán Aspuru-Guzik, Roland Lindh and Morgane Vacher

Chem. Sci., 2019, Accepted Manuscript

DOI: 10.1039/C8SC04516J, Edge Article

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Synergistic Self-Seeding in One-Dimension: a Route to Patchy and Block Comicelles with Uniform and Controllable Length

Jiangping Xu, Hang Zhou, Qing Yu, Gerald Guerin, Ian Manners and Mitchell A. Winnik

Chem. Sci., 2019, Advance Article

DOI: 10.1039/C8SC04705G, Edge Article

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Optical control of the antigen translocation by syntethic photo-conditional viral inhibitors

M. Braner, N. Koller, J. Knauer, V. Herbring, S. Hank, R. Wieneke and R. Tampé

Chem. Sci., 2019, Advance Article

DOI: 10.1039/C8SC04863K, Edge Article

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Carbon Coating Promotes CO2 Reduction on Nickel Surfaces

18 Dec 2018

Reducing CO₂ into fuels such as CO or hydrocarbons is a promising strategy to reduce the net emission of greenhouse gases and mitigate climate change. The CO₂ reduction reaction, however, is an energy-costly process. Therefore, CO₂ reduction catalysts are necessary to enhance the CO₂ conversion efficiency and minimize the overall energy demand.

Researchers are developing high-performance yet inexpensive CO₂ reduction catalysts. Noble metals such as Au, Ag and Pd exhibit high CO₂-to-CO conversion efficiency, but their scarcity restricts their large-scale practicability. Metallic Fe, Co and Ni are active in reducing CO₂ and therefore, have been identified as alternatives to the noble metal catalysts.

Recently in Chem. Sci., a group of scientists led by Zhenyu Sun from Beijing University of Chemical Technology and Yousung Jung from Korea Advanced Institute of Science and Technology (KAIST) pushed the CO₂-reduction activity of Ni metal to a new height. The researchers synthesized carbon-supported Ni nanocrystals via pyrolysis of Ni-based metal organic frameworks (MOFs) in argon. The resultant Ni nanoparticles had an average diameter of ~30 nm and were embedded in N-doped carbon scaffolds (Fig. 1a). Each nanoparticle was uniformly coated with a thin layer of amorphous carbon (Fig. 1b).

Figure 1. (a) The elemental mapping of the carbon-supported Ni nanoparticles. Green dots and blue regions are Ni nanoparticles and carbon matrices, respectively. (b) The scanning transmission electron microscope image showing the thin carbon coating on a Ni nanoparticle surface. (c) The CO2-to-CO conversion efficiencies at different applied potentials. Ni-NC_ATPA@C and Ni-NC_TPA@C are carbon-supported Ni nanoparticles derived from MOFs with 2-amino-terephthalic acid and terephthalic acid organic linkers, respectively. NC_ATPA@C is the Ni-free carbon powder derived from ATPA.

The CO₂-to-CO conversion efficiencies of these Ni-C nanocomposites were the highest among all the reported carbon-supported Ni nanoparticles. The best Ni catalyst achieved a maximal efficiency of ~94% at an overpotential of 0.59 V, while previously reported Ni-C catalysts typically exhibited efficiencies lower than 25%. The significantly improved conversion efficiency was associated with the thin carbon coating. This coating prevented the Ni nanoparticles from directly contacting with aqueous electrolytes, and thus minimized hydrogen evolution reaction, a side reaction that decreased the conversion efficiency.

This work highlights the instrumental role of the surface carbon layers in promoting the CO₂-reduction activity of Ni nanoparticles. The carbon-coating strategy could be extended to other low-cost transition metals, which may lead to a variety of cost-effective CO₂-reduction catalysts.

To find out more please read:

Carbon-Supported Ni Nanoparticles for Efficient CO₂ Electroreduction

Mingwen Jia, Changhyeok Choi, Tai-Sing Wu, Chen Ma, Peng Kang, Hengcong Tao, Qun Fan, Song Hong, Shizhen Liu, Yun-Liang Soo, Yousung Jung, Jieshan Qiu and Zhenyu Sun

Chem. Sci., 2018, 9, 8775-8780

About the blogger:

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HOT Chemical Science articles for November

05 Dec 2018

We are happy to present a selection of our HOT articles over the past month. To see all of our HOT referee-recommended articles from 2018, please find the collection here.

As always, Chemical Science articles are free to access.

Carbon-supported Ni nanoparticles for efficient CO2 electroreduction

Mingwen Jia, Changhyeok Choi, Tai-Sing Wu, Chen Ma, Peng Kang, Hengcong Tao, Qun Fan, Song Hong, Shizhen Liu, Yun-Liang Soo, Yousung Jung, Jieshan Qiu and Zhenyu Sun

Chem. Sci., 2018, Advance Article

DOI: 10.1039/C8SC03732A, Edge Article

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Rare “Janus”-Faced {FeII7} Single-Molecule Magnet Exhibiting Intramolecular Ferromagnetic Interactions

Dimitris I Alexandropoulos, Kuduva R. Vignesh, Theocharis Stamatatos and Kim R. Dunbar

Chem. Sci., 2019, Accepted Manuscript

DOI: 10.1039/C8SC04384A, Edge Article

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Lytic Reactions of Drugs with Lipid Membranes

Hannah Mary Britt, Clara Antia García-Herrero, Paul W Denny, Jackie A. Mosely and John M Sanderson

Chem. Sci., 2019, Accepted Manuscript

DOI: 10.1039/C8SC04831B, Edge Article

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A Catalytic Antioxidant for Limiting Amyloid-Beta Peptide Aggregation and Reactive Oxygen Species Generation

Luiza M. F. Gomes, Atif Mahammed, Kathleen E Prosser, Jason R. Smith, Michael A. Silverman, Charles John Walsby, Zeev Gross and Tim Storr

Chem. Sci., 2019, Accepted Manuscript

DOI: 10.1039/C8SC04660C, Edge Article

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A bio-inspired approach to ligand design: folding single-chain peptoids to chelate a multimetallic cluster

Andy I. Nguyen, Ryan K. Spencer, Christopher L. Anderson and Ronald N. Zuckermann

Chem. Sci., 2018, Advance Article

DOI: 10.1039/C8SC04240C, Edge Article

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Single Ru atoms with precise coordination on a monolayer layered double hydroxide for efficient electrooxidation catalysis

Zelin Wang, Si-Min Xu, Yanqi Xu, Ling Tan, Xian Wang, Yufei Zhao, Haohong Duan and Yu-Fei Song

Chem. Sci., 2019, Advance Article

DOI: 10.1039/C8SC04480E, Edge Article

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Mutant Enzymes and Frankenstein Catalysts

04 Oct 2018

I know what you’re thinking: “Autumn is here! Who needs sunny weather and optimism? Sign me up for grey skies and vitamin D supplements!”. Oh you weren’t thinking that? Me neither. Well perhaps Halloween gives you more joy, along with the chance to see one of your colleagues dressed up like Freddy Mercury (‘Hg’ emblazoned on their chest, classic) at the departmental party?

In the spirit of Halloween, Simone Morra and Anca Pordea at the University of Nottingham have synthesized a mutant alcohol dehydrogenase enzyme turned Frankenstein catalyst, by replacing the zinc catalytic site with a covalently-bound rhodium(III) complex. The resulting mutant/transition-metal composite was used in combination with the wild-type enzyme to synthesize the chiral alcohol (S)-4-phenyl-2-butanol.

Like many hybrid systems, the purpose of combining enzymatic with transition metal catalysis is to take advantage of the benefits of each. Millions of years of evolution have produced enzymatic catalysts that function under mild conditions, in aqueous solvents, with impressive selectivity and high catalytic efficiency. But the narrow range of conditions that enzymes operate under can be disadvantageous in a synthetic setting. On the other hand, transition metal catalysts are versatile and can be easily customised, reacting with a liberty that would make the most promiscuous of enzymes blush.

Unfortunately, developing multi-component systems that utilise both transition metal and enzymatic catalysis is not as simple as combining them in a single mixture, as mutual deactivation often results. The authors found that encasing the transition metal complex in an enzyme provided a physical shield against inhibition, and preserved the activity of both the wild type enzyme and the rhodium(III) complex.

Synthesis of chiral alcohols via two interconnected cycles: the wild type enzyme (native ADH) reduces the ketone to the alcohol using NADPH as a reducing agent. NADPH is regenerated using the mutant enzyme containing a rhodium active site (chemically modified ADH) with formic acid as the terminal reductant. Alcohol dehydrogenase

Synthesis of chiral alcohols via two interconnected cycles: the wild type enzyme (native ADH) reduces the ketone using NADPH as a reducing agent. NADPH is regenerated by the mutant enzyme containing a catalytically-active rhodium complex (chemically modified ADH) with formic acid as the terminal reductant.

Two interconnected catalytic cycles were responsible for synthesis of the chiral alcohol. In the first, the wild type enzyme effected reduction of 4-phenyl-2-butanol, a process that relies on the biological reductant nicotinamide adenine dinucleotide phosphate (NADPH). In the second cycle, NADPH was recycled using the composite rhodium(III) complex/mutant enzyme, with formic acid as the stoichiometric reductant. The rate of alcohol formation was slow (turnover frequency of 0.02 s^-1) and the transition-metal catalysed process was deemed to be rate limiting (compare to turnover frequencies of 4.8 s^-1for enzymatic systems). However, near perfect enantioselectivity was obtained (>99% ee).

This research demonstrates one way that transition metal catalysts can augment the scope of co-factor-dependent enzymes. Furthermore, devising strategies to prepare metal-complex/enzyme bioconjugates might have value for small molecule synthesis due to the second coordination sphere that enzymes offer; an encased steric environment to guide the reaction outcome is a valuable approach to improving selectivity in catalytic reactions.

To find out more please read:

Biocatalyst-artifical metalloenzyme cascade based on alcohol dehydrogenase

Simone Morra, Anca Pordea.
Chem. Sci., 2018, 9, 7447-7454
DOI: 10.1039/c8sc02371a

About the author

Zoë Hearne is a PhD candidate in chemistry at McGill University in Montréal, Canada, under the supervision of Professor Chao-Jun Li. She hails from Canberra, Australia, where she completed her undergraduate degree. Her current research focuses on transition metal catalysis to effect novel transformations, and out of the lab she is an enthusiastic chemistry tutor and science communicator.

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Chemical Science Blog

Archive for the ‘Hot Articles’ Category

A Single Nickel Site Reduces Nitrate Ions to Nitrogen Gas

Molecular Switching: from Blue Biradicals to Colorless Housanes

HOT Chemical Science articles for March

HOT Chemical Science articles for February

HOT Chemical Science articles for January

Learning from Nature: A Cu(II)-Porphyrin Complex Produces Oxygen Gas from Water at Ultra-Small Overpotential

HOT Chemical Science articles for December

Carbon Coating Promotes CO2 Reduction on Nickel Surfaces

HOT Chemical Science articles for November

Mutant Enzymes and Frankenstein Catalysts

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