Archive for the ‘Hot Articles’ Category

Don’t rely on a gut feeling: investigating microbiota/human co-metabolism

A new trend gripping popular science (and business) is personal DNA testing. A host of companies sell the idea that your genetic heritage distinguishes you, and reveals who you really are. Do you really want to know what you are on a molecular level? If it’s a numbers game, you are mostly bacterial (that’s why you’re so cultured!). Bacteria outnumber our body’s cells 1.3:1. The majority of bacteria reside in the gastrointestinal tract, contributing to a microbiota of archea, eukaryotes and viruses that have a commensal relationship with the human body.

The microbiota has been linked to many vital physiological pathways including human nutrition (harvesting further energy and nutrients), immunity, inflammation and the detoxification of xenobiotic substances. Conversely, dysregulation of such pathways has been associated with diseases such as diabetes, cancer, inflammatory bowel syndrome and cardiovascular disease. Due to the number of pathways involved, it is hoped that studying the microbiota may identify enzyme targets for therapeutics or biomarkers for disease.

However, understanding of these pathways is limited, and research progress relies on advances in analytical tools. Headed by Dr Daniel Globisch at Uppsala University in Sweden, researchers have developed an analytical method to identify O-sulphated metabolites. Microbes are capable of a suite of metabolic reactions that complement the capabilities of human enzymes, and O-sulphate functionalization is characteristic of microbe/human co-metabolism as it can be catalysed by bacterial sulphotransferase enzymes.

O-sulfate functionalised molecules can be selectively analysed using sulphatase sulfatase treatment and UPLC-MS/MS

O-sulphate functionalised molecules can be selectively analysed using sulphatase treatment and UPLC-MS/MS

The researchers developed an assay to identify O-sulphated compounds in urine and faecal samples. The assay was designed using a sulphatase enzyme capable of hydrolysing the oxygen-sulfur bond in a wide variety of arylsulphate molecules. Samples were treated with this enzyme and the resulting mixtures were analysed by UPLC-MS/MS (ultra performance liquid chromatography/tandem mass spectrometry). Results were compared with the data output of control samples without enzymatic treatment and features in the spectra with a mass change of 79.9568 m/z (loss of the sulfate group) were identified, leading to the identification of 206 O-sulphated metabolites. This is a notable result as it triples the number of sulphated metabolites currently recorded in the human metabolome database.

A number of interesting compounds were identified: ferulic acid is a metabolite produced by the microbiota thought to prevent thrombosis and artherosclerosis, and indoxyl sulfate and p-cresylsulfate are biomarkers of chronic kidney disease and cardiovascular disease, respectively. Mentioned are three molecules of the 206 uncovered, giving a glimpse of the applications that further research, armed with the right analytical tools, might discover.

To find out more please read:

New enzymatic and mass spectrometric methodology for the selective investigation of gut microbiota-derived metabolites

Caroline Ballet, Mário S. P. Correia, Louis P. Conway, Theresa L. Locher, Laura C. Lehmann, Neeraj Garg, Miroslav Vujasinović, Sebastian Deindl, J.-Matthias Löhr, Daniel Globisch.
Chem. Sci., 2018, Advance Article
DOI: 10.1039/c8sc01502c

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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How Can We Stabilize Bismuth in Potassium-Ion Batteries? Add Salts!

The large-scale manufacturing and widespread demand of consumer electronics in modern societies call for batteries with affordable prices. Potassium-ion batteries are one of the economical alternatives to lithium-ion batteries, as the cost of potassium is much lower than lithium. However, these types of batteries have yet to be commercially available, partly due to the lack of high-performance and stable anode materials. Bismuth (Bi) is a promising anode material for potassium-ion batteries, because of its substantially higher theoretical charge-storage capacity than the conventional ones. Unfortunately, its poor durability severely hinders the applicability.

Now the drawback of Bi has been successfully addressed by increasing the electrolyte concentration. This breakthrough, demonstrated by Chuan-Fu Sun and coworkers from Chinese Academy of Sciences, China, was recently published in Chemical Science.

Sun and coworkers investigated the interplay between the electrolyte concentration and the charge-storage performance stability of Bi nanoparticles (Figure 1a). They identified the optimal concentration of the solute, potassium bis(tri-fluoromethylsulfonyl)imide, to be 5 M. Under this condition, the irreversible electrolyte reduction reaction on the Bi surface experienced the highest resistance. Impeding this unwanted reaction thus elongated the lifespan of Bi electrodes. In addition, the concentrated electrolyte resulted in thin layers of the reduction products being deposited on the Bi surface. This allowed ions in the electrolyte to easily penetrate the surface coatings and interact with the encapsulated Bi nanoparticles, maintaining the intrinsically high capacity of Bi (Figure 1b). Other concentrations either led to rapid battery failure or significantly reduced capacity.

Figure 1. (a) A scanning electron microscopy image of the Bi nanoparticles. (b) The change of the Bi electrode capacity vs. charge-discharge cycle number with different electrolyte concentrations. CE: coulombic efficiency.

This work innovates the design and development of commercially viable potassium-ion batteries. The strategy of increasing the electrolyte concentration could possibly be adapted to solve electrode instability issues associated with other rechargeable batteries.

 

To find out more please read:

Concentrated Electrolytes Stabilize Bismuth-Potassium Batteries

Ruding Zhang, Jingze Bao, Yu-Huang Wang and Chuan-Fu Sun

Chem. Sci., 2018, DOI: 10.1039/c8sc01848k

 

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Physical 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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HOT Chemical Science articles for June

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.

Chiral Brønsted acid-catalyzed intramolecular SN2′ reaction for enantioselective construction of a quaternary stereogenic center
Masahiro Shimizu, Jun Kikuchi, Azusa Kondoh and Masahiro Terada
Chem. Sci., 2018,9, 5747-5757
DOI: 10.1039/C8SC01942H, Edge Article

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Deciphering the mechanism of O2 reduction with electronically tunable non-heme iron enzyme model complexes
Roshaan Surendhran, Alexander A. D’Arpino, Bao Y. Sciscent, Anthony F. Cannella, Alan E. Friedman, Samantha N. MacMillan, Rupal Gupta and David C. Lacy
Chem. Sci., 2018,9, 5773-5780
DOI: 10.1039/C8SC01621F, Edge Article

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Weak interactions but potent effect: tunable mechanoluminescence by adjusting intermolecular C–H⋯π interactions
Zongliang Xie, Tao Yu, Junru Chen, Eethamukkala Ubba, Leyu Wang, Zhu Mao, Tongtong Su, Yi Zhang, Matthew P. Aldred and Zhenguo Chi
Chem. Sci., 2018,9, 5787-5794
DOI: 10.1039/C8SC01703D, Edge Article

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Shaping excitons in light-harvesting proteins through nanoplasmonics
Stefano Caprasecca, Stefano Corni and Benedetta Mennucci
Chem. Sci., 2018, Advance Article
DOI: 10.1039/C8SC01162A, Edge Article

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Highly Luminescent Phosphine Oxide-Containing Bipolar Alkynylgold(III) Complexes for Solution-Processable Organic Light-Emitting Devices with Small Efficiency Roll-Offs
Chin-Ho Lee, Man-Chung Tang, Wai-Lung Cheung, Shiu-Lun Lai, Mei-Yee Chan and Vivian Wing-Wah Yam
Chem. Sci., 2018, Advance Article
DOI: 10.1039/C8SC02265H, Edge Article

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New enzymatic and mass spectrometric methodology for the selective investigation of gut microbiota-derived metabolites
Caroline Ballet, Mário S. P. Correia, Louis P. Conway, Theresa L. Locher, Laura C. Lehmann, Neeraj Garg, Miroslav Vujasinovic, Sebastian Deindl, J.-Matthias Löhr and Daniel Globisch
Chem. Sci., 2018, Advance Article
DOI: 10.1039/C8SC01502C, Edge Article

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Welcoming a New Member into the Aluminum Battery Family

Yu and coworkers from The University of Queensland, Australia have introduced an aluminum-selenium (Al-Se) battery as a new member of the rechargeable Al-ion battery family. This battery reported in Chemical Science exhibited a capacity of 178 mAh per gram of Se, high discharging voltage above 1.5 V and satisfactory lifetime.

Al-ion batteries have attracted increasing attention as next-generation energy-storage devices. They are potentially more affordable and safer than Li-ion batteries, due to the natural abundance and the existence of native oxide surface layers of aluminum, respectively. One of the major challenges hindering the wide application of Al-ion batteries is the lack of feasible cathode materials. Previously investigated cathodes have drawbacks of low charge-storage capacity, low discharging voltage, poor electrical conductivity or chemical instability.

Inspired by sulfur, Yu and coworkers selected selenium as a cathode material for Al-ion batteries. Selenium has substantially higher electrical conductivity and lower ionization potential than sulfur, which is expected to improve the energy-storage capacity of batteries. However, a major drawback of selenium is that the oxidation product generated upon charging batteries, Se2Cl2, can dissolve quickly in electrolytes and lead to battery failure. Solving this problem would make selenium a promising cathode for Al-ion batteries.

To resolve this issue, the authors introduced a mesoporous carbon named CMK-3, nanorods that are capable of physically adsorbing Se2Cl2. The cathode, composed of Se nanowires and CMK-3 nanoparticles, is thus anticipated to improve the lifespan of batteries, as any Se2Cl2 that is generated will be confined inside the pores of CMK-3 (Figure 1).

Figure 1. A schematic illustrating the CMK-3’s capability of trapping Se2Cl2. The chemical equation below shows how selenium reacts with aluminum during charge and discharge processes.

As expected, the performance of these Al-Se batteries was stable. They retained more than 80% of the initial capacity after 50 consecutive charge-discharge cycles at 100 mA/g (Figure 2a). Additionally, the discharging capacity of the batteries reached 178 mAh per gram of selenium at 100 mA/g, and the discharging potential was above 1.5 V (Figure 2b).

Figure 2. (a) The specific capacity of the Al-Se batteries of each cycle at different current densities. (b) The variation of battery potential with specific capacity of the 2nd, 5th, 10th, and 30th charge-discharge cycles.

These promising Al-Se batteries could encourage future work to continue progress into the development of affordable and durable Al-ion batteries.

 

To find out more please read:

Rechargeable Aluminum-Selenium Batteries with High Capacity

Xiaodan Huang, Yang Liu, Chao Liu, Jun Zhang, Owen Noonan and Chengzhong Yu

Chem. Sci., 2018, DOI: 10.1039/C8SC01054D

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Physical 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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Bioelectrochemistry with nitrogenase-loaded electrodes for nitrogen fixation

We happily breathe our dinitrogen-rich atmosphere all day, but to access nitrogen for the biosynthesis of molecules such as DNA, RNA and proteins, we rely on nitrogen fixation to reduce dinitrogen into bioavailable molecules like ammonia. In nature, nitrogen-fixing bacteria and archaea equipped with nitrogenase enzymes are responsible for providing plants with reduced nitrogen, which makes its way back to us. Nitrogenase is an enzyme complex of two proteins. The first consists of an iron-containing reductase that supplies electrons to the iron/molybdenum-containing catalytic protein, which carries out the N2 to NH3 conversion.

The Haber Bosch process, an industrial method for fixing dinitrogen into ammonia, was first applied in the early 1900’s and generated a huge supply of nitrogen-based fertilizers to synthetically provide plants with this essential nutrient. The population boom that resulted, and with it the global importance of this reaction, has yet to abate. Albeit an efficient reaction, this iron-catalysed process requires high temperatures (450 °C) and pressures (200 atm). In comparison, enzymes can operate under conditions synthetic chemists can only dream of, as researchers at the University of Utah have demonstrated in their work on the bioelectrochemical reduction of dinitrogen under ambient conditions using the catalytic nitrogenase protein.

The researchers synthesised an electrode/enzyme aggregate by trapping the nitrogenase enzyme in a hydrogel, then binding the hydrogel via π-stacking of incorporated pyrene motifs to carbon paper electrodes coated in multi-walled carbon nanotubes. If the enzyme is oriented in the hydrogel in such a way that the distance between the catalytic iron/molybdenum centre of the enzyme and the electrode is within 14 Å, direct electron transfer can take place. Direct electrical contact with enzymes allows researchers to take advantage of the high efficiency and selectivity of enzymes for conducting chemical reactions under mild conditions.

Two methods for immobilization of proteins on an electrode: the docking strategy (upper) and the hydrogel strategy (middle). Active protein is green, while inactive/denatured protein is grey. Pi-stacking of pyrene moieties to bind the hydrogel to the carbon nanotubes (lower).

Two methods for immobilization of proteins on an electrode: the docking strategy (upper) and the hydrogel strategy (middle). Active protein is green, while inactive/denatured protein is grey. π-stacking of pyrene moieties within the polymer binds the hydrogel to the carbon nanotubes (lower).

To minimise the distance between the enzyme’s redox centre and the electrode, prior strategies have focused on docking enzymes in the desired configuration; however low enzyme activities can result due to protein denaturation. The authors of this work designed a system under the hypothesis that if they focussed on preserving enzymatic activity, the statistical mixture of configurations adopted by enzymes in the hydrogel would still contain a large proportion capable of participating in direct electron transfer.

Bioelectrical activity of the electrode/nitrogenase aggregate was assessed under bubbling N2 at room temperature, and 180 nmol of NH3 (1.1 μmol/mg nitrogenase enzyme) was produced, marking the first bioelectrochemical reduction of N2 in the absence of ATP. The bioelectrical activity of laccase for the reduction of O2 was also measured using the same method. In this experiment 15% of laccase proteins remained active, compared to 0.3% using a reference method applying an enzyme docking technique. This translated to increased current densities of 390 – 1880 μA cm-2 mg-1 (depending on the enzyme concentration, 1-10 mg mL-1) compared to 45 μA cm-1 mg-1 for the reference docking method.

Without being too grandiose, synthetic nitrogen fixation is vital for the continued survival of people on the planet (how did I do?). Beyond nitrogen fixation, this research offers a general method to achieve contact between a conductive electrode and the highly complex catalytic machinery that nature offers: enzymes. Beyond synthesis, opportunities broaden; technology such as this might pave the way for the production of biosensors, biofuel cells and biomolecular electronic components.

 

 

To find out more please read:

Pyrene hydrogel for promoting direct bioelectrochemistry: ATP-independent electroenzymatic reduction of N2

David P. Hickey, Koun Lim, Rong, Cai, Ashlea R. Patterson, Mengwei Yuan, Selmihan Sahin, Sofiene Abdellaoui, Shelley D. Minteer
Chem. Sci., 2018, 9, 5172-5177
DOI: 10.1039/c8sc01638k

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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HOT Chemical Science articles for May

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.

A high spatiotemporal study of somatic exocytosis with scanning electrochemical microscopy and nanoITIES electrodes
Theresa M. Welle, Kristen Alanis, Michelle L. Colombo, Jonathan V. Sweedler and Mei Shen
Chem. Sci., 2018, Advance Article
DOI: 10.1039/C8SC01131A, Edge Article

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Diffusion across a gel–gel interface – molecular-scale mobility of self-assembled ‘solid-like’ gel nanofibres in multi-component supramolecular organogels
Jorge Ruíz-Olles and David K. Smith
Chem. Sci., 2018, Advance Article
DOI: 10.1039/C8SC01071D, Edge Article

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Fine-Tuned Organic Photoredox Catalysts for Fragmentation-Alkynylation Cascades of Cyclic Oxime Ethers
Franck Le Vaillant, Marion Garreau, Stefano Nicolai, Ganna Gryn’ova, Clemence Corminboeuf and Jerome Waser
Chem. Sci., 2018, Accepted Manuscript
DOI: 10.1039/C8SC01818A, Edge Article

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A multifunctional SERS sticky note for real-time quorum sensing tracing and inactivation of bacterial biofilm
Huangxian Ju, Jingxing Guo, Ying Liu, Yunlong Chen and Jianqi Li
Chem. Sci., 2018, Accepted Manuscript
DOI: 10.1039/C8SC02078G, Edge Article

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Rapid photoinduced charge injection into covalent polyoxometalate-bodipy conjugates
Fiona A Black, Aurélie Jacquart, Georgios Toupalas, Sandra Alves, Anna Proust, Ian P Clark, Elizabeth Gibson and Guillaume Izzet
Chem. Sci., 2018, Accepted Manuscript
DOI: 10.1039/C8SC00862K, Edge Article

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Site-selective C-C modification of proteins at neutral pH using organocatalyst-mediated cross aldol ligations
Richard J Spears, Robin Brabham, Darshita Buddhadev, Tessa Keenan, Sophie McKenna, Julia Walton, James A Brannigan, Marek Brzozowski, Anthony J Wilkinson, Michael Plevin and Martin A Fascione
Chem. Sci., 2018, Accepted Manuscript
DOI: 10.1039/C8SC01617H, Edge Article

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Surface Charge Determines Success of Encapsulating Proteins into a ZIF-8 Metal Organic Framework

Australian scientists from The University of Adelaide and Graz University of Technology recently made a breakthrough in protein chemistry. They revealed that the key to successfully encasing proteins into metal organic frameworks (MOFs, a family of highly porous organic-metal coordination molecules) was the surface charge of the proteins. Their work was recently published in Chemical Science.

Encapsulating proteins into MOFs, a process termed “biomimetic mineralisation”, is an efficient way to protect and preserve proteins. This process is typically initiated by mixing the proteins and the precursors of a MOF. The MOF starts to grow at the protein surface and eventually fully covers the protein. As the growth of the MOF begins with nucleation on the protein surface, the surface properties play an important role in controlling the rate and quality of the encapsulation. Unfortunately, the interplay between protein surface and MOF growth has not been well understood, leading to inefficient reactions that require excess MOF precursors and long reaction times.

The authors demonstrated for the first time that the surface charge is one of the key factors that affects the possibility of biomimetic mineralisation. Specifically, they discovered that proteins with strongly negative charged surfaces, such as pepsin and bovine serum albumin, were able to be spontaneously incorporated into ZIF-8 (a benchmark MOF). Conversely, those with naturally positively charged or slightly negatively charged surfaces, including haemoglobin, were incapable of forming composites with ZIF-8. The authors further showed that changing the surface charge could allow or prohibit the encapsulation. For example, after reacting the lysine groups of haemoglobin with succinic anhydride, the surface of haemoglobin became more negative and ZIF-8 could now readily wrap around the protein (Figure 1). The surface potential threshold to induce biomimetic mineralisation was determined to be -30 mV.

Figure 1. Schematic illustrations of the biomimetic mineralisation of haemoglobin and bovine serum albumin. Haemoglobin with slightly negatively charged surface is unable to form composites with ZIF-8, but becomes active after succinylation or acetylation to make its surface strongly negatively charged. On the contrary, bovine serum albumin with a strongly negatively charged surface readily combines with ZIF-8, but loses its activity when its surface becomes less negatively charged via amination.

The mechanism of the aforementioned observations was attributed to the electrostatic attraction between the protein surface and Zn2+, one of the MOF precursors. The more negatively the surface is charged, the more easily the Zn2+ will attach to and accumulate at the protein surface. The adsorbed Zn2+ ions then serve as the nucleation sites for the MOF to grow around the protein. This hypothesis is proven by a number of control experiments and also validated by computational studies.

This study highlights the surface potential of a protein as a critical factor in its ability to induce biomimetic mineralisation with MOFs. The conclusions could potentially be extended to biomolecules other than proteins (e.g. viruses and cells) to facilitate their integration with various MOFs.

 

To find out more please read:

Protein Surface Functionalisation as A General Strategy for Facilitating Biomimetic Mineralisation of ZIF-8

Natasha K. Maddigan, Andrew Tarzia, David M. Huang, Christopher J. Sumby, Stephen G. Bell, Paolo Falcaro and Christian J. Doonan

Chem. Sci., 2018 , DOI: 10.1039/c8sc00825f

About the blogger:

Tianyu Liu obtained his Ph.D. (2017) in Physical Chemistry from University of California, Santa Cruz in 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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Customised peptides via nickel/photoredox-catalysed bioconjugation

Proteins have an expansive utility in the structure, function, replication and regulation of all cells, and developing tools to study each role is to the benefit of our continued health and wellbeing. One tool is protein bioconjugation, the covalent pairing of a molecule with a protein. Molecule-protein combinations are endless, provided there are efficient methods available to couple molecules with amino acids. Among bioconjugation methods, cysteine functionalisation is a popular choice because the primary thiol is highly nucleophilic thus aiding chemoselectivity. Furthermore, cysteine is rare, reducing the likelihood of many competing, reactive residues.

Transition metal catalysed transformations are uncommon in bioconjugations, despite prominence in other areas of synthetic chemistry. This is because only the most robust methods can overcome the challenges of this chemistry: the solubility of substrates in solvents other than aqueous media, the presence of other amino acids bearing reactive functional groups, and the requirement for low temperatures, low concentrations and mild pH to preserve protein structure.

Catalytic cycle for the nickel/phororedox catalysed synthesis of cysteine bioconjugates

Catalytic cycle for the nickel/phororedox catalysed synthesis of cysteine bioconjugates

A group of researchers from the University of Pennsylvania headed by Professor Gary Molander have developed a bioconjugation method in which aryl halides are cross-coupled with cysteine residues in peptides. Two complexes catalyse the reaction in two connected cycles: the photoredox cycle by a ruthenium-bipyridine complex, and the catalytic cycle by a nickel-bipyridine complex.

The reaction is efficient at room temperature and does not require prior functional group protection. The reaction can also be performed under dilute conditions (10 mM) and on gram scale (3.5 mmol). The scope table includes more than 35 reactions coupling a broad range of aryl halides with small peptides (4 and 9 amino acids) and biologically relevant molecules such as coenzyme A and sulphur-containing pharmaceuticals.

Protecting-group free functionalisation of small peptides under dilute conditions using nickel and ruthenium photoredox catalysis for cysteine functionalization

Protecting group free functionalisation of small peptides under dilute conditions

Included in the reaction scope are a number of substrates which highlight how this work can adapt to established techniques for studying proteins. Coupling of a coumarin generates a fluorescent molecule, which could be used to study the cellular localisation of a protein. Reaction with an aryl-bound biotin derivative demonstrates that affinity tags can be coupled, and utilising aryl-containing pharmaceutical agents is relevant to the synthesis of antibody-drug conjugates.

With this research the authors have contributed a robust catalytic system, which convincingly shows the value of combining a transition metal and photoredox catalyst to functionalise cysteine residues in biomolecules. A necessary next step for this chemistry, and no small task, is to further optimise the reaction conditions for whole proteins.

Read the research article:

Scalable thioarylation of unprotected peptides and biomolecules under Ni/photoredox catalysis

Chem. Sci., 2018, DOI: 10.1039/C7SC04292B

Brandon A. Vara, Xingpin Li, Simon Berritt, Christopher R. Walters, E. James Petersson, Gary A. Molander.


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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Measuring the Strength of Hydrogen Bonds

For the first time, a group of scientists from University of California, San Diego in United States has quantitatively measured the strength of hydrogen bonds between two complex molecules. They also observed an abnormal trend regarding the bond strength in the absence and presence of electron transfer. This work contributes to the understanding of how the hydrogen bond strength changes, an important point that reveals the way biological systems function.

Hydrogen bonds are a type of electrostatic attraction between hydrogen atoms and certain highly electronegative atoms including N, O and F. These bonds help to bind individual water molecules together and keep water as liquid at room temperature, a critical condition for the origin of life.

The researchers, led by Prof. Kubiak, picked two ruthenium-based complexes joined by hydrogen bonds as their studying platform. As shown in Figure 1, the two-molecule system has three states depending on whether the ends are charged or not: the neutral state when both ends are not charged (left), the singly reduced state when only one end is negatively charged (middle), and the doubly reduced state when both ends are negatively charged (right). The group utilized infrared spectroscopy, UV-vis spectroscopy and electrochemical measurements to experimentally determine the strength of hydrogen bonds in these different redox states.

The results from the study found that the hydrogen bond energy of the neutral state and the doubly reduced state was in the range of 2.56-2.88 kcal/mol and 4.50-4.63 kcal/mol, respectively. Surprisingly, the hydrogen bond energy of the singly charged state did not lie between that of the neutral state and the doubly reduced state. It ranged from 7.78 kcal/mol to 8.31 kcal/mol, indicating the hydrogen bond is much stronger than for both the neutral and doubly-reduced states. The authors ascribed such an abnormality to the reinforcement brought by electron transfer i.e., the movement of the negative charge between the two ends.

This work is the first demonstration that hydrogen bond strength can be significantly enhanced by electron delocalization.

Figure 1. A schematic diagram showing the hydrogen bond strength of the singly reduced state (middle), the neutral state (left) and the doubly reduced states (right). [Note: In this figure, the lower the state lies, the stronger its hydrogen bond is. ET: electron transfer.]

To find out more please read:

Effects of Electron Transfer on the Stability of Hydrogen Bonds

Tyler M. Porter, Gavin P. Heim and Clifford P. Kubiak

Chem. Sci. DOI: 10.1039/c7sc03361c

About the blogger:

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

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Reductive power of hydrated electrons unleashed with green lasers


Source: © Royal Society of Chemistry
Laboratory-scale photoredox catalysis using hydrated electrons sustainably generated with a single green laser. Asc = ascorbate dianion, OER = one-electron reduced form, GS = ground state, MLCT = metal-to-ligand charge-transfer excited state

Solvated electrons are highly reductive so can force stubborn compounds to react where other reagents might fail. Now a team in Germany is generating them sustainably, using only a green laser and vitamin C. The group has used the technique to perform reactions previously impossible with a visible-light responsive catalyst.

Photons from the laser transform a ruthenium-based photocatalyst into an excited state, with a central oxidised ruthenium atom and a radical anion ligand. Vitamin C’s ascorbate dianion then quenches the excited species, producing a one-electron reduced form of the complex – where the ruthenium atom is no longer oxidised, but the ligand remains as a radical anion. Another photon can then eject the additional electron – generating the hydrated electron species that can induce reduction reactions of organic compounds, and simultaneously returns the catalyst to its ground state.

Read the full story by Jamie Durrani on Chemistry World.

 

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