Aggregation makes fluorescent probes better and brighter

Fluorescence, the phenomenon where a molecule re-emits light upon absorption of electromagnetic radiation, is used in biological imaging to visualise structures, processes and diseases. Emission of these fluorescent molecules, known as fluorophores, in the near-infrared region is particularly advantageous, allowing for enhanced tissue penetration and reduced photodamage. Near-infrared (NIR) fluorophores are therefore attractive probes for bioimaging but are currently limited with problems such as low brightness or quenching of the emission by aggregation.

To overcome this aggregation-caused quenching effect, researchers in China turned to fluorophores that have aggregation-induced emission (AIE) properties. Aggregation-induced emission (AIE) is a concept where molecules only fluoresce upon aggregation in concentrated solutions, and not in dilute solutions where they can freely rotate. The researchers therefore designed their fluorophore to contain the molecular rotor tetraphenylethene, that can induce AIE effects and therefore boost and brighten the fluorescence.

The researchers prepared a suite of fluorophores using a central donor-acceptor-donor core, with methoxy-tetraphenylethene (MTPE) as the donor and thieno[3,4,-b]pyrazine (TP) as the acceptor. Substituents on the TP acceptor were varied, and the effects on aggregation and the fluorescence were investigated. Density functional theory calculations gave the researchers insight into the molecular conformations of the fluorophores, as shown in Figure 1. The 3 variants all showed twisted geometries (top row, Figure 1), indicating high degrees of rotation, which could then be restricted through aggregation and give rise to the desired AIE effects. Additionally, the calculations measured electronic distributions, confirming high degrees of electron conjugation in the molecules (see the HOMO diagrams, Figure 1) that are essential for fluorescence.

DFT results of AIE fluorophores

Figure 1: Results from density functional theory calculations to show molecular geometries and electron conjugation within the suite of fluorophores

The fluorescence characteristics of the variants were measured by absorption and emission/photoluminescence spectra. The absorption spectra in DMSO (Figure 2a) shows absorptions between 518 and 543 nm, with the most red-shifted (longer wavelength) absorption displayed for the most conjugated variant (MTPE-TP3). The effect of aggregation on the fluorescence was measured by adding water (in which the fluorophores showed poor solubility) to the DMSO solutions, and the resulting photoluminescence intensities showed an increase with higher water fractions. This increase in brightness (i.e. intensity) is explained by the water affecting aggregation of the fluorophores and inducing the AIE effect (Figures 2b and c).

Fluorescence spectra and aggregation effects of AIE fluorophores

Figure 2: a) Absorption spectra of the fluorophore variants; b) photoluminescence spectra of the most conjugated variant, MTPE-TP3 with different water fractions; c) corresponding photoluminescence intensity plotted against water fractions for all three variants. d) to f) additionally indicate the effect of increased viscosity (and aggregation) upon glycerol addition to the fluorophores.

The researchers also formulated nanoparticles for each fluorophore variant to allow for better water solubility and therefore biocompatibility. They found that the absorption and emission of the nanoparticles became both brighter and more red-shifted and were now within the near-infrared range for favourable biological imaging. In vitro and in vivo testing of these nanoparticles in breast cancer cells and tumour-bearing mice verified that the AIE-nanoparticles are suitable for biological imaging, and indicate their potential to assist with tumour diagnosis in future clinical settings.

 

To find out more, please read:

Simultaneously boosting the conjugation, brightness and solubility of organic fluorophores by using AIEgens

Ji Qi, Xingchen Duan, Yuanjing Cai, Shaorui Jia, Chao Chen, Zheng Zhao, Ying Li, Hui-Qing Peng, Ryan T. K. Kwok, Jacky W. Y. Lam, Dan Ding  and  Ben Zhong Tang

Chem. Sci., 2020, 11, 8438-8447

 

About the blogger:

Dr. Samantha Apps is a Postdoctoral Research Associate in the Lu Lab at the University of Minnesota, USA, and obtained her PhD in 2019 from Imperial College London, UK. She has spent the last few years, both in her PhD and postdoc, researching synthetic nitrogen fixation and transition metal complexes that can activate and functionalise dinitrogen. Outside of the lab, you’ll likely find her baking at home, where her years of synthetic lab training has sparked a passion in kitchen chemistry too.

 

 

 

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HOT Articles: August

We are pleased to share a selection of our referee-recommended HOT articles for August. We hope you enjoy reading these articles and congratulations to all the authors whose articles are featured! As always, Chemical Science is free to read & download. You can find our full 2020 HOT article collection here.

 

Nucleation mechanisms and speciation of metal oxide clusters
Enric Petrus, Mireia Segado and Carles Bo
Chem. Sci., 2020, 11, 8448-8456
DOI: 10.1039/D0SC03530K, Edge Article

Boron tribromide as a reagent for anti-Markovnikov addition of HBr to cyclopropanes
Matthew H. Gieuw, Shuming Chen, Zhihai Ke, K. N. Houk and Ying-Yeung Yeung
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC02567D, Edge Article

Free-standing metal–organic framework (MOF) monolayers by self-assembly of polymer-grafted nanoparticles
Kyle Barcus and Seth M. Cohen
Chem. Sci., 2020, 11, 8433-8437
DOI: 10.1039/D0SC03318A, Edge Article

Recent advances of group 14 dimetallenes and dimetallynes in bond activation and catalysis
Franziska Hanusch, Lisa Groll and Shigeyoshi Inoue
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC03192E, Minireview

Dissipative self-assembly, competition and inhibition in a self-reproducing protocell model
Elias A. J. Post and Stephen P. Fletcher
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC02768E, Edge Article

A bipedal DNA nanowalker fueled by catalytic assembly for imaging of base-excision repairing in living cells
Meng-Mei Lv, Jin-Wen Liu, Ru-Qin Yu and Jian-Hui Jiang
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC03698F, Edge Article

Exploring modular reengineering strategies to redesign the teicoplanin non-ribosomal peptide synthetase
Milda Kaniusaite, Robert J. A. Goode, Julien Tailhades, Ralf B. Schittenhelm and Max J. Cryle
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC03483E, Edge Article

Engineering micromechanics of soft porous crystals for negative gas adsorption
Simon Krause, Jack D. Evans, Volodymyr Bon, Irene Senkovska, Sebastian Ehrling, Paul Iacomic, Daniel M Többens, Philip L. Llewellyn, Dirk Wallacher, Manfred S. Weiss, Bin Zheng, Pascal G. Yot, Guillaume Maurin, François-Xavier Coudert and Stefan Kaskel
Chem. Sci., 2020, Accepted Manuscript
DOI: 10.1039/D0SC03727C, Edge Article

Simultaneous Manifestations of Metallic Conductivity and Single-Molecule Magnetism in a Layered Molecule-based Compound
Yongbing Shen, Masahiro Yamashita, Brian. K. Breedlove, Carmen Herrmann, Kaiji Uchida, Goulven Cosquer, Manabu Ishikawa, Akihiro Otsuka, Shinji K Yoshina, Takefumi Yoshida, Hideki Yamochi, Seiu Katagiri, Hiroshi Ito and Haitao Zhang
Chem. Sci., 2020, Accepted Manuscript
DOI: 10.1039/D0SC04040A, Edge Article

Chemical Science, Royal Society of Chemistry

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New RSC Desktop Seminar Series

COVID-19 has rendered in-person events to be suspended or cancelled, disrupting connections around the globe. The impact of these cancellations on the sharing of information and ideas, especially in the research landscape, has been dramatic.

In an effort to help researchers to stay connected to advances in chemical research and share support we are proud to announce the RSC’s latest online-only seminar series.

Introducing RSC Desktop Seminars!

Welcome to the latest RSC Desktop Seminars, sponsored by Chemical Science, ChemComm and Chem Soc Rev. Each session will highlight two speakers, one journal board member and an early career researcher in the same field.

The RSC Desktop Seminar Series is an effort to not only replace in-person research seminars during the current pandemic situation but to also expand access for researchers around the world looking to connect to some of the leading minds in the chemical sciences. While these RSC Desktop Seminars are taking place in the Eastern US time zone working hours, we encourage any and all interested to register and attend!

Next Up:

8 September 2020 15:00 BST / 10:00 EDT
15:05: “FLP Chemistry: A metal-free approach to the activation of strong bonds”
Professor Doug Stephan
– Professor of Chemistry at Toronto University and Editorial Board Chair of Chemical Communications
15:55:“Phosphorus-Ylides: Powerful Ligands for the Stabilisation of Reactive Main Group Compounds”
Professor Viktoria Däschlein-Gessner
– Professor of Inorganic Chemistry at Ruhr-Universität Bochum

Find out more & register

RSC Desktop Seminar 8Sept

 

Upcoming RSC Desktop Seminars in this Series:

15 September 2020 15:00 BST / 10:00 EDT
15:05: “Polymers that mimic natural saccharides for applications in drug delivery
Professor Heather Maynard – Dr Myung Ki Hong Professor in Polymer Science in the Department of Chemistry and Biochemistry and the California NanoSystems Institute at UCLA and Associate Editor of Chemical Science
15:55:Tailoring Polymer Dispersity by Controlled Radical Polymerization
Dr Athina Anastasaki – Assistant Professor in the Materials Department at ETH Zurich and Editorial Board Member of Polymer Chemistry

Find out more &  register

~~~

22 September 2020 15:00 BST / 10:00 EDT
15:05: “Towards catalytic methane functionalization with Pt complexes
Professor Jennifer Love – Professor of Chemistry at University of Calgary and Editorial Board Chair of Chem Soc Rev
15:55:Synthetic modeling of the heterobinuclear Mo/Cu active site in aerobic carbon monoxide dehydrogenase (CODH)
Professor Neal Mankad – Associate Professor of Chemistry at the University of Illinois at Chicago

Find out more & register

~~~

Previous Seminars:

1 September 2020 15:00 BST / 10:00 EDT
15:05: “Mechanically Chiral Molecules: Synthesis and Applications”
Professor Steven Goldup
– Professor of Chemistry at University of Southampton and Associate Editor of Chemical Science
15:55: “The synthesis and unexpected behaviour of knotted molecules”
Dr Fabien Cougnon
– Research Associate in the Department of Organic Chemistry at University of Geneva

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16th Annual Tri-Institutional Chemical Biology Symposium, 1st September 2020

Chemical Science is pleased to be sponsoring the 16th Annual Tri-Institutional Chemical Biology Symposium along with RSC Chemical Biology and Organic & Biomolecular Chemistry. The event will take place virtually on the 1st of September, 2020, 09:00-18:30 EDT.

This event showcases research at the forefront of chemical biology, and is sponsored and organized by the Tri-Institutional PhD Program in Chemical Biology (TPCB), a joint graduate program of Memorial Sloan Kettering Cancer Center, The Rockefeller University, and Weill Cornell Medicine in New York City.

Register for this free event here by the 28th of August 2020

Undergraduate students interested in chemical biology are especially encouraged to attend.

Poster submissions are welcomed from all attendees, including early college high school students, undergraduates, postbaccalaureate students, research assistants and technicians, graduate students, postdoctoral fellows, research staff, and faculty. Posters will be presented live by video in parallel meeting rooms, and judged by TPCB faculty members and keynote speakers for a selection of poster awards sponsored by TPCB and their promotional partners, including Chemical Science, RSC Chemical Biology and Organic & Biomolecular Chemistry.

For more information, please visit the Tri-Institutional Chemical Biology Symposium event page.

TPCB has been strongly committed to diversity and inclusion since its inception. It welcomes scientists from underrepresented minority groups and disadvantaged backgrounds, and those with disabilities. It does not tolerate racism, discrimination, or harassment of any kind. All attendees are expected to maintain the highest standards of professional conduct throughout the symposium.

 

Chemical Science, Royal Society of Chemistry

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HOT Articles: July

We are pleased to share a selection of our referee-recommended HOT articles for July. We hope you enjoy reading these articles and congratulations to all the authors whose articles are featured! As always, Chemical Science is free to read & download. You can find our full 2020 HOT article collection here.

 

Exohedral functionalization vs. core expansion of siliconoids with Group 9 metals: catalytic activity in alkene isomerization
Nadine E. Poitiers, Luisa Giarrana, Volker Huch, Michael Zimmer and David Scheschkewitz
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC02861D

Deoxygenative α-alkylation and α-arylation of 1,2-dicarbonyls
Shengfei Jin, Hang T. Dang, Graham C. Haug, Viet D. Nguyen, Hadi D. Arman and Oleg V. Larionov
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC03118F

Cellular uptake and targeting of low dispersity, dual emissive, segmented block copolymer nanofibers
Steven T. G. Street, Yunxiang He, Xu-Hui Jin, Lorna Hodgson, Paul Verkade and Ian Manners
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC02593C

Mechanochemical synthesis of glycine oligomers in a virtual rotational diamond anvil cell
Brad A. Steele, Nir Goldman, I-Feng W. Kuo and Matthew P. Kroonblawd
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC00755B

Total synthesis of endiandric acid J and beilcyclone A from cyclooctatetraene
Oussama Yahiaoui, Adrian Almass and Thomas Fallon
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC03073B

Template effects of vesicles in dynamic covalent chemistry
Carlo Bravin and Christopher A. Hunter
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC03185B

Simultaneously boosting the conjugation, brightness and solubility of organic fluorophores by using AIEgens
Ji Qi, Xingchen Duan, Yuanjing Cai, Shaorui Jia, Chao Chen, Zheng Zhao, Ying Li, Hui-Qing Peng, Ryan T. K. Kwok, Jacky W. Y. Lam, Dan Ding and Ben Zhong Tang
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC03423A

Enhanced enzymatic activity exerted by a packed assembly of a single type of enzyme
Huyen Dinh, Eiji Nakata, Kaori Mutsuda-Zapater, Masayuki Saimura, Masahiro Kinoshita and Takashi Morii
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC03498C

Structure-activity relationships in well-defined conjugated oligomer photocatalysts for hydrogen production from water
Catherine M. Aitchison, Michael Sachs, Marc Little, Liam Wilbraham, Nick J. Brownbill, Chris Kane, Frédéric Blanc, Martijn Zwijnenburg, James Durrant, Reiner Sebastian Sprick and Andrew Cooper
Chem. Sci., 2020, Accepted Manuscript
DOI: 10.1039/D0SC02675A
Chemical Science, Royal Society of Chemistry

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Biradical bismuth makes its debut

Low-valent compounds are attractive in chemical synthesis and catalysis due to their highly reactive nature. Carbenes are the archetypal example, where the carbon atom is divalent with two valence electrons, but group 15 analogues have also gained recent interest as reactive intermediates in fundamental transformations. These low-valent compounds (E-R), where the group 15 atom (E) has an oxidation state of +1 and is bound to just one additional atom, are extremely reactive and therefore challenging to isolate. The lighter congeners of nitrogen and phosphorus (as nitrenes, N-R, and phosphinidenes, P-R) have been isolated, but the heavier homologues are much more difficult to access and tend to undergo degradation. Stabilisation through adduct formation with Lewis bases had previously allowed for the formation of the heaviest group 15 bismuth homologue, and these stabilised bismuthinidenes showed potential in electrocatalytic and photophysical applications. Researchers in Germany and Switzerland have now reported for the first time the generation of a free and non-stabilised organometallic bismuthinidene compound, methylbismuth (BiMe), in the gas phase (Figure 1).

Low valent group 15 structures

Figure 1: Structures and examples of low-valent group 15 compounds, with their electronic ground state configuration

The researchers targeted the non-stabilised organometallic bismuthinidene using a top-down approach, by breaking the Bi-C bonds of the higher valent and well-defined BiMe3 precursor (Scheme 1). They achieved this by pyrolysis of BiMe3, with subsequent analysis by photoelectron-photoion coincidence spectroscopy (PEPICO), that allows the recording of photoionisation mass spectra to detect ions produced by the pyrolysis. As shown by the photoionisation mass spectra in Figure 2, pyrolysis resulted in methyl loss through Bi-C homolytic cleavage, with higher pyrolysis power (bottom trace) showing full conversion of BiMe3 with by of m/z = 254. Stepwise methyl loss down to atomic bismuth was observed with m/z = 209 for Bi+, but notably BiMe+ was observed at m/z = 224, indicating bismuthinidene formation.

BiMe generation

Scheme 1: Stepwise methyl abstraction from BiMe3 to generate bismuthinidene BiMe in the  gas phase by flash pyrolysis

Photoionisation mass spectra for BiMe

Figure 2: Photoionisation mass spectra showing methyl loss in the conversion of BiMe3 to BiMe by pyrolysis. Top trace = without pyrolysis, middle trace = low pyrolysis power, bottom trace = high pyrolysis power

The researchers further probed the electronic nature of the generated bismuthinidene by additional photoelectron spectroscopy and simulations. An ionisation energy of 7.88 eV was determined, and indicated the triplet (biradical) ground state (structure 3 in Scheme 1) as the lowest energy structure. This contrasts to the lighter N and P congeners, where the methylene species are the most energetically favoured (like 5 in Scheme 1). The researchers also conducted experiments to investigate the stepwise methyl abstraction via BiMe2, determining a bond dissociation energy of 210 kJ mol-1 for the first Bi-C homolytic cleavage and demonstrating that this methyl abstraction could also be achieved under moderate reaction conditions. Overall, this report indicates that non-stabilised bismuthinidenes can be generated, with the potential for future exploitation as reactive intermediates in synthetic chemistry.

 

To find out more, please read:

Methylbismuth: an organometallic bismuthinidene biradical

Deb Pratim Mukhopadhyay, Domenik Schleier, Sara Wirsing, Jacqueline Ramler, Dustin Kaiser, Engelbert Reusch, Patrick Hemberger, Tobias Preitschopf, Ivo Krummenacher, Bernd Engels,* Ingo Fischer* and Crispin Lichtenberg*

Chem. Sci., 2020, Advance Article

 

About the blogger:

Dr. Samantha Apps is a Postdoctoral Research Associate in the Lu Lab at the University of Minnesota, USA, and obtained her PhD in 2019 from Imperial College London, UK. She has spent the last few years, both in her PhD and postdoc, researching synthetic nitrogen fixation and transition metal complexes that can activate and functionalise dinitrogen. Outside of the lab, you’ll likely find her baking at home, where her years of synthetic lab training has sparked a passion in kitchen chemistry too.

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Self-adjusting MOFs

Recent decades have established that metal-organic frameworks (MOFs) are a pretty cool class of materials, with potential applications across a range of fields. In particular, their high porosities make them extremely attractive for storing a variety of gases, including possible fuels like methane and hydrogen. Two primary strategies have emerged to store H2 and CH4 in MOFs – synthesizing materials with unsaturated metals that can strongly bind to the target and synthesizing materials with small pores where multiple weak interactions combine to produce strong binding. Of course, these MOFs are designed with a single specific target in mind, making them synthetically complex and useful for storing only one type of molecule. Ideally, new MOFs with relatively straightforward syntheses that can bind multiple targets could be developed.

Figure 1. (a) Single crystal X-ray diffraction structure of 1–H2O. (b,c) View of the pores of 1–H2O showing binding pocket.

Scientists in the United States took a hybrid approach, creating MOFs with small, but flexible binding pockets. While the concept feels relatively straightforward and intuitive, it’s of course more complicated in practice. The MOF needs to hit a Goldilocks zone in terms of flexibility, where only a small number of select targets will bind rather than a wide range of gases. The researchers accomplished this by using an actinide (depleted uranium) as the metal nodes for their MOF as its tendency to adopt high coordination numbers should result in smaller pockets and limit possible rearrangements of the flexible linker. Also, the descriptor “as it is only mildly radioactive” is something I hadn’t read about a material before and rather caught my attention. The crystalline material, referred to as 1-H2O (Figure 1), was straightforwardly synthesized in an autoclave and isolated in relatively high yields. It features pores with two pockets that are capped by the bowl-shaped linkers. As synthesized, the pockets are occupied by water molecules that can be removed by heating the MOF under a dynamic vacuum.

Figure 2. (a) Neutron powder diffraction structure of D2 adsorbed at site I in 1–D2. (b) Neutron powder diffraction structure of CD4 adsorbed at site I in 1–CD4. (c) Powder X-ray diffraction structure of DMF adsorbed inside the pore of U(bdc)2.

The MOF maintains its structural integrity after water removal, actually expanding slightly. This indicates that the MOF will contract upon binding, locking the target into place in the pocket. The researchers found that the MOF rapidly uptakes both H2 and CH4 at low temperatures, but the precise nature of the binding pocket adjustments can’t be determined by gas adsorption studies. To probe the structural details, the researchers turned to neutron powder diffraction to probe the binding of deuterated molecules to the MOF (Figure 2). The obtained structures show clear, cooperative effects that cause the adjustments to the binding pocket. The multiple different interactions allow the flexible structure to fit the two different adsorbates of interest, binding them both strongly. This work demonstrates the utility and versatility of flexible MOFs for adsorbing different gases with design principles that should be transferrable to non-radioactive materials.

To find out more, please read:

Self-adjusting binding pockets enhance H2 and CH4 adsorption in a uranium-based metal–organic framework

Dominik P. Halter, Ryan A. Klein, Michael A. Boreen, Benjamin A. Trump, Craig M. Brown and Jeffrey R. Long

Chem. Sci., 2020, Advance Article

About the blogger:

Dr. Beth Mundy is a recent PhD in chemistry from the Cossairt lab at the University of Washington in Seattle, Washington. Her research focused 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 Articles: June

We are pleased to share a selection of our referee-recommended HOT articles for June. We hope you enjoy reading these articles and congratulations to all the authors whose articles are featured! As always, Chemical Science is free to read & download. You can find our full 2020 HOT article collection here.

 

Mapping protein–polymer conformations in bioconjugates with atomic precision
Kevin M. Burridge, Ben A. Shurina, Caleb T. Kozuszek, Ryan F. Parnell, Jonathan S. Montgomery, Jamie L. VanPelt, Nicholas M. Daman, Robert M. McCarrick, Theresa A. Ramelot, Dominik Konkolewicz and Richard C. Page
Chem. Sci., 2020, 11, 6160-6166
DOI: 10.1039/D0SC02200D

D0SC02200D

 

Methylbismuth: an organometallic bismuthinidene biradical
Deb Pratim Mukhopadhyay, Domenik Schleier, Sara Wirsing, Jacqueline Ramler, Dustin Kaiser, Engelbert Reusch, Patrick Hemberger, Tobias Preitschopf, Ivo Krummenacher, Bernd Engels, Ingo Fischer and Crispin Lichtenberg
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC02410D

10.1039/D0SC02410D

 

Formicamycin biosynthesis involves a unique reductive ring contraction
Zhiwei Qin, Rebecca Devine, Thomas J. Booth, Elliot H. E. Farrar, Matthew N. Grayson, Matthew I. Hutchings and Barrie Wilkinson
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC01712D

 

Unravelling the intricate photophysical behavior of 3-(pyridin-2-yl)triimidazotriazine AIE and RTP polymorphs
Elena Lucenti, Alessandra Forni, Andrea Previtali, Daniele Marinotto, Daniele Malpicci, Stefania Righetto, Clelia Giannini, Tersilla Virgili, Piotr Kabacinski, Lucia Ganzer, Umberto Giovanella, Chiara Botta and Elena Cariati
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC02459G

10.1039/D0SC02459G

 

Molecular-level insight in supported olefin metathesis catalysts by combining surface organometallic chemistry, high throughput experimentation, and data analysis
Jordan De Jesus Silva, Marco A. B. Ferreira, Alexey Fedorov, Matthew S. Sigman and Christophe Copéret
Chem. Sci., 2020, Advance Article
DOI: 10.1039/D0SC02594A

D0SC02594A

 

Conformationally Adaptable Macrocyclic Receptors for Ditopic Anions: Analysis of Chelate Cooperativity in Aqueous Containing Media
Stuart N. Berry, Lei Qin, William Lewis and Katrina A. Jolliffe
Chem. Sci., 2020, Accepted Manuscript
DOI: 10.1039/D0SC02533J

10.1039/D0SC02533J

Templating S100A9 amyloids on Aβ fibrillar surfaces revealed by charge detection mass spectrometry, microscopy, kinetic and microfluidic analyses
Jonathan Pansieri, Igor Iashchishyn, Hussein Fakhouri, Lucija Ostojić, Mantas MM Malisauskas, Greta Musteikyte, Vytautas Smirnovas, Matthias M. Schneider, Tom Scheidt, Catherine K. Xu, Georg Meisl, Ehut Gazit, Rodolphe Antoine and Ludmilla A. Morozova-Roche
Chem. Sci., 2020, Accepted Manuscript
DOI: 10.1039/C9SC05905A

10.1039/C9SC05905A
 

Chemical Science, Royal Society of Chemistry

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Welcome to Associate Editor Shu-Li You

We would like to wish a very warm welcome to our new Chemical Science Associate Editor Professor Shu-Li You!

 

 

Professor Shu-Lli You was born in Henan, China, and received his BSc in chemistry from Nankai Univ. in 1996. He obtained his PhD from Shanghai Institute of Organic Chemistry (SIOC) in 2001 under the supervision of Prof. Lixin Dai before doing postdoctoral studies with Prof. Jeffery Kelly at The Scripps Research Institute. From 2004, he worked at the Genomics Institute of the Novartis Research Foundation as a PI before returning to SIOC as a Professor in 2006. He is currently appointed as the director of the State Key Laboratory of Organometallic Chemistry of SIOC, and the deputy director of SIOC.

His research interests mainly focus on asymmetric C-H functionalization and catalytic asymmetric dearomatization (CADA) reactions. He is a Fellow of the Royal Society of Chemistry, and the recipient of RSC Merck Award (2015) and Ho Leung Ho Lee Foundation Prize for Scientific and Technological Innovation (2016).

 

Browse a selection of Shu-Li’s work below:

Chiral phosphoric acid-catalyzed asymmetric dearomatization reactions
Zi-Lei Xia, Qing-Feng Xu-Xu, Chao Zheng and Shu-Li You
Chem. Soc. Rev., 2020, 49, 286-300
DOI: C8CS00436F, Review Article

Catalytic asymmetric dearomatization (CADA) reaction-enabled total synthesis of indole-based natural products
Chao Zheng and Shu-Li You
Nat. Prod. Rep., 2019, 36, 1589-1605
DOI: C8NP00098K, Review Article

Palladium-catalyzed intermolecular allenylation reactions of 2,3-disubstituted indoles and allenyl carbonate
Yizhan Zhai, Shu-Li You and Shengming Ma
Org. Biomol. Chem., 2019, 17, 7128-7130
DOI: C9OB01435G, Communication

Highly efficient synthesis and stereoselective migration reactions of chiral five-membered aza-spiroindolenines: scope and mechanistic understanding
Qing-Feng Wu, Chao Zheng, Chun-Xiang Zhuo and Shu-Li You
Chem. Sci., 2016, 7, 4453-4459
DOI: C6SC00176A, Edge Article
Chemical Science, Royal Society of Chemistry

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Porous supports for hemes to mimic enzymatic transformations

Nature is the ultimate molecular designer. The complex structures of proteins are crucial for allowing the many processes that support life, including the many chemical transformations that occur. A diverse array of biological reactions are catalysed by iron porphyrin active sites (also known as hemes), and rely on the local protein environments to envelop and stabilise the reactive intermediates that can form in the process. Whilst chemists can easily synthesise iron porphyrins to imitate the reactive centre, mimicking the surrounding protein superstructure is less trivial.

Metal-organic frameworks (MOFs) represent one strategy (as an alternative to proteins) to support iron porphyrins for chemical catalysis. These frameworks can precisely separate each heme unit, thereby sequestering each active site in a similar fashion to a protein, and the porous nature allows for diffusion of reagents into the catalyst. Importantly, the pore environment can be precisely controlled and modified, allowing for enhancements to the catalytic activity of the supported heme.

Researchers in the US have now reported a new method to modify a heme-containing metal-organic framework to enhance the catalytic activity towards C-H bond activation. They studied the porphyrinic Zr-based framework, PCN-224, where the porphyrin is suspended between Zr6 nodes (Figure 1).  Exchange of the formate and benzoate ligands around the Zr6 node in PCN-224 was achieved by initial treatment with acetic anhydride to give acetate ligands in the new material (PCN-224’, 1), and further reactivity with methanol resulted in Zr-hydroxy ligands (2) – see insert to Figure 1. Additionally, iron was installed into the modified framework 1 by reaction with FeCl3 and base, to give 1FeCl. Here, an FeCl was installed in each porphyrin unit in the MOF, and further hydroxylation reactivity (similar to the 1 to 2 transformation) resulted in the formation of 2FeCl.

PCN-224 framework

Figure 1. The structure of the PCN-224 framework. Insert (below) shows modifications to PCN-224 to give 1 and 2, with varying ligands around the Zr6 node (in green).

The modified PCN-224 frameworks were characterised by various techniques. Powder X-ray diffraction showed the retention of bulk crystallinity of the material upon ligand substitution. UV-Vis and 57Fe Mössbauer spectroscopy confirmed iron coordination within the porphyrin units of the framework. Importantly, the modification of the Zr6 ligands was structrually confirmed by single-crystal X-ray analysis, and DRIFTS spectra showed the expected O-H stretches for the hydroxy ligands in 2 and 2FeCl. The porosity of the framework was maintained upon the modifications, as shown by surface area measurements, making the new materials ideal candidates for catalytic testing.

PCN-224 catalytic activity

Figure 2. A chart showing the catalytic activity of the heme-frameworks (1FeCl and 2FeCl) compared to the molecular iron porphyrin complex ((TPP)FeCl) for cyclohexane oxidation.

The researchers studied the effects of the framework modifications using the catalytic oxidation of cyclohexane as a model reaction. The researchers compared the oxidation of cyclohexane with iodosylbenzene in CH2Cl2 using either the molecular iron porphyrin complex, or the metallated porphyrin frameworks 1FeCl or 2FeCl. Whilst low yields of oxidation products (cyclohexanol, cyclohexanone and chlorocyclohexane) were observed for the molecular iron porphyrin complex, higher yields of 68% and 26% were noted for the frameworks 1FeCl and 2FeCl, with corresponding turnovers of 14 and 5, respectively (Figure 2). The higher catalytic activity for the acetylated framework (1FeCl) was attributed to the lack of acidic protons within the framework that would impair any oxidation reactivity at the heme centre. Ultimately, the results show an enhancement to the catalysis when the heme is supported and protected, demonstrating that MOFs are ideal supports for modelling enzymatic reactions.

To find out more, please read:

Enhancing catalytic alkane hydroxylation by tuning the outer coordination sphere in a heme-containing metal–organic framework

David Z. Zee and T. David Harris

Chem. Sci., 2020, 11, 5447-5452

 

About the blogger:

Dr. Samantha Apps is a Postdoctoral Research Associate in the Lu Lab at the University of Minnesota, USA, and obtained her PhD in 2019 from Imperial College London, UK. She has spent the last few years, both in her PhD and postdoc, researching synthetic nitrogen fixation and transition metal complexes that can activate and functionalise dinitrogen. Outside of the lab, you’ll likely find her baking at home, where her years of synthetic lab training has sparked a passion in kitchen chemistry too.

 

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