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.

 

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

HOT Chemical Science articles for September

All of the referee-recommended articles below are free to access.

Chemoenzymatic synthesis of heparan sulfate and heparin oligosaccharides and NMR analysis: paving the way to a diverse library for glycobiologists
Xing Zhang, Vijayakanth Pagadala, Hannah M. Jester, Andrew M. Lim, Truong Quang Pham, Anna Marie P. Goulas, Jian Liu and  Robert J. Linhardt
Chem. Sci., 2017, Advance Article
DOI: 10.1039/C7SC03541A, Edge Article

____________________________________________________

Displacement and hybridization reactions in aptamer-functionalized hydrogels for biomimetic protein release and signal transduction
Jinping Lai, Shihui Li, Xuechen Shi, James Coyne, Nan Zhao, Fengping Dong, Yingwei Mao and  Yong Wang
Chem. Sci., 2017, Advance Article
DOI: 10.1039/C7SC03023A, Edge Article

____________________________________________________

Effects of electron transfer on the stability of hydrogen bonds
Tyler M. Porter, Gavin P. Heim and Clifford P. Kubiak
Chem. Sci., 2017, Advance Article
DOI: 10.1039/C7SC03361C, Edge Article

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Scientists poke holes in zeolite theory

Theorists in the UK have studied the aluminium distribution in a number of catalytically active zeolite species, finding evidence that –Al–O–Al– linkages could exist in some zeolite species after all.1


Source: Royal Society of Chemistry
Löwenstein’s rule of ‘aluminium avoidance’ says that that –Al–O–Al– bonds are forbidden but new research hints that this motif may not be as elusive as is generally believed

Since Löwenstein first published his study on ‘the distribution of aluminium in the tetrahedra of silicates and aluminates’ in 1954,2 scientists had generally accepted that aluminium clusters cannot exist within zeolite structures. Löwenstein’s rule of ‘aluminium avoidance’ states that whenever two tetrahedra are linked by an oxygen bridge, if the centre of one is occupied by an aluminium atom, the other must be occupied by silicon. As such, Löwenstein’s rule prohibits –Al–O–Al– linkages from occurring within zeolites, and dictates that the ratio of Al:Si in zeolites must be 1:1.

Read the full story by Hannah Dunckley on Chemistry World.

1 R E Fletcher, S Ling and B Slater, Chem. Sci., 2017, DOI: 10.1039/c7sc02531a (This article is open access.)
2 W Löwenstein, Am. Mineral., 1954, 39, 92

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Drilling Holes on Metal Organic Framework Crystals with Phosphoric Acid

Synthesis of porous materials with tunable pore size remains a long-standing challenge for materials research. These materials, particularly hierarchical porous materials with copious different sized pores, are attractive candidates as catalysts, battery electrodes, and guest molecule hosts etc. An ideal synthesis protocol of hierarchical porous materials should be easy and capable of fine tuning pore size within a wide size range as well as able to preserve structural integrity. Unfortunately, it is extremely challenging for the currently developed methods to achieve the aforementioned three characteristics simultaneously.

Recently, this challenge has been addressed by Kimoon Kim and co-workers from the Institute of Basic Science and the Pohang University of Science and Technology in Republic of Korea. Their strategy targeted at metal organic frameworks (MOFs), a family of highly porous crystalline materials built by interconnected metal-organic complexes, as the starting materials. Phosphoric acid was chosen to selectively break down the building blocks and create pores with tunable diameters (Figure 1). Detailed synthesis procedures are published in Chemical Science.

Figure 1. Schematic illustration of the major steps of the demonstrated strategy.

The authors specifically chose the octahedral-shaped MIL-100(Fe) MOF crystals as an example, and demonstrated that their method could readily turn the original smooth crystals into highly porous ones merely by phosphoric acid aqueous solutions. Moreover, simply changing the concentration of phosphoric acid was able to tune the diameter of the created pores from 2.4 nm to 18.4 nm (Figure 2).

Figure 2. Scanning electron microscopy images and pore diameter distributions (showing pores larger than 2 nm only) of different MOFs: (a) the untreated MIL-100(Fe) and the acid treated MIL-100(Fe) with phosphoric acid concentration of (b) 20 mM, (c) 40 mM, (d) 60 mM and (e) 80 mM. All scale bars represent 200 nm.

Structural evolution analysis revealed that the etching process initiated preferably by cleaving the coordination bonds between metal cores and organic ligands around the hexagonal windows on (2 2 0) crystal planes. It further propagated to dig out the inner part of MIL-100(Fe), forming pores on surface.

This method is expected to be applicable to other MOFs coupled with properly selected etchants, thus making the hierarchical porous crystals with tailorable porous structures readily available to worldwide materials researchers.

To find out more please read:

Hollowing Out MOFs: Hierarchical Micro- and Mesoporous MOFs with Tailorable Porosity via Selective Acid Etching

Jaehyoung Koo, In-Chul Hwang, Xiujun Yu, Subhadeep Saha, Yonghwi Kim and Kimoon Kim

DOI: 10.1039/c7sc02886e

About the blogger:

Tianyu Liu is a Ph.D. in chemistry graduated from University of California-Santa Cruz. 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 writer for the Chem. Commun. and Chem. Sci. blog websites. More information about him can be found at http://liutianyuresearch.weebly.com/.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

HOT Chemical Science articles for August

All of the referee-recommended articles below are free to access.

Effects of Electron Transfer on the Stability of Hydrogen Bonds
Tyler M. Porter,  Gavin P, Heim and Clifford P. Kubiak
Chem. Sci., 2017, Accepted Manuscript
10.1039/C7SC03361C, Edge Article

____________________________________________________

Magnetic Control of Cellular Processes using Biofunctional Nanoparticles
Cornelia Monzel, Chiara Vicario, Jacob Piehler, Mathieu Coppey and Maxime Dahan
Chem. Sci., 2017, Accepted Manuscript
10.1039/C7SC01462G, Minireview

____________________________________________________

Hollowing out MOFs: hierarchical micro- and mesoporous MOFs with tailorable porosity via selective acid etching
Jaehyoung Koo, In-Chul Hwang, Xiujun Yu, Subhadeep Saha, Yonghwi Kima and Kimoon Kim
Chem. Sci., 2017, Advance Article
10.1039/C7SC02886E, Edge Article

____________________________________________________

Biosynthesis of methyl-proline containing griselimycins, natural products with anti-tuberculosis activity
Peer Lukat, Yohei Katsuyama, Silke C. Wenzel, Tina Binz, Claudia König, Wulf Blankenfeldt, Mark Brönstrup and Rolf Müller
Chem. Sci., 2017, Accepted Manuscript
10.1039/C7SC02622F, Edge Article

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Hydrogen bonded system faces strength test

Scientists in Spain have devised a versatile technique that uses DNA to pull apart host–guest complexes so they can measure the overall strength of hydrogen bonds in that system. The method can distinguish forces as low as 0.1–1pN.

Source: © Royal Society of Chemistry
Using a DNA reporter guarantees that the force measurements refer to a single system

Procedures to measure supramolecular interactions in the bulk, under equilibrium conditions, are well established. But nature operates out of equilibrium, so scientists want a technique to measure hydrogen bonds in conditions realistic to living systems.

Read the full story by Jennifer Newton on Chemistry World.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

An absolute acidity scale for solvents

Comprehensive solvent acidity scale could help make acid-catalysed reactions more reliable and reproducible.

Using acids from this table, buffer solutions of a well-defined composition can be prepared spanning an acidity range of over 28 pH units, which is double the pH window of water.

A collaboration between scientists in Estonia and Germany has resulted in a comprehensive solvent acidity scale spanning 28 orders of magnitude, twice as much as the classical pH scale.

Click here to read the full story on Chemistry World written by Lynn Murphy.

 

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Mimicking Biological Systems with Supramolecular Assemblies: A Step Closer

Biological systems, such as circadian rhythms and ion pumps, are generally able to respond autonomously to chemical stimuli. Such ability is at the root of certain amphiphilic molecules (i.e. molecules containing both hydrophilic and hydrophobic parts) that can change their configurations temporally at the presence of the stimulants. In recent decades, building artificial biological systems with active, adaptive and autonomous behaviours similar to natural biological systems has become a hot topic.

Supramolecular assemblies are among the most extensively explored building materials. A supramolecular assembly is a system consisting of complex molecules held together by non-covalent bonds, such as DNA. One of the major technological hurdles for developing artificial biological systems using supramolecular assemblies is to acquire assemblies with an amphiphilic nature and the ability to undergo a transient change of configuration when stimulated. The change should also be highly reversible and durable. Currently, extensive research efforts are committed to finding candidates that address the aforementioned challenge.

A research group from Jawaharlal Nehru Centre for Advanced Scientific Research in India recently made a step forward and published their work in Chemical Science. They developed an amphiphilic supramolecular motif, coined PN-VN foldamer, which could switch its conformation upon contact with oxidizing and reducing agents. As shown in Figure 1a, the skeleton of the supramolecular motif is composed of three sections. The green head is an electron donor pyranine (PN), the red tail is an electron acceptor called viologen (VN) rendering the hydrophobic nature, and the blue body is a flexible hydrophilic hexaethylene glycol that connects the electron donor and acceptor.

Figure 1. (a) The structure of the amphiphilic PN-VN foldamer. (b) Unfolded and folded states of the PN-VN foldamer correspond to sheet and vesicle morphologies, respectively.

The researchers demonstrated the assembly pattern of PN-VN foldamers (Figure 1b) by using two chemical fuels, sodium dithionite and glucose, as the stimulants. The transformation process is depicted in Figure 2a. When undisturbed, the negatively charged PN (PN3-) and the positively charged VN (VN2+) can attract each other via a charge transfer interaction, folding the entire molecular chains to vesicles. When placed in a solution containing sodium dithionite and glucose, the VN2+ terminal can be instantaneously reduced by sodium dithionite to its radical cation form (VN•+). The reduction weakens the charge transfer interaction, and subsequently unfolds PN-VN vesicles to sheets. Meanwhile, catalyzed by glucose oxidase (an enzyme), the excess glucose in the same solution can oxidize VN•+ back to its original state, resulting in the folded state that recovers vesicles. The transition is directly confirmed by transmission electron microscopy as shown in Figure 2b. Since the reduction process proceeds much faster than the oxidation process, it is observed that PN-VN vesicles first extend to sheets momentarily and gradually but automatically fold back to vesicles within minutes. The rate of the transition can be well tuned by varying the concentration of glucose oxidase.

Figure 2. (a) Schematic of the transient configuration change between vesicles and sheets. SDT: sodium dithionite; GOx: glucose oxidase. (b) Transmission electron microscopic images of the vesicles (left) and the sheets (right). Inset in the left panel shows the distribution of the wall thickness of the vesicles. Inset in the right panel is a confocal fluorescence microscopy image of a selected sheet (scale bar: 2 μm).

To find out more please read:

Temporal Switching of an Amphiphilic Self-assembly By a Chemical Fuel-driven Conformational Response

Krishnendu Jalani, Shikha Dhiman, Ankit Jain, and Subi J. George

DOI: 10.1039/c7sc01730h

About the author:

Tianyu Liu is a Ph.D. in chemistry graduated from University of California-Santa Cruz. 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 writer for the Chem. Commun. and Chem. Sci. blog websites. More information about him can be found at http://liutianyuresearch.weebly.com/.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

HOT Chemical Science articles for July

All of the referee-recommended articles below are free to access.

Solid–State Molecular Organometallic Chemistry. Single–Crystal to Single–Crystal Reactivity and Catalysis with Light Hydrocarbon Substrates
F. Mark Chadwick, Alasdair I. McKay, Antonio J. Martinez-Martinez, Nicholas H. Rees, Tobias Krämer, Stuart A. Macgregor and Andrew S. Weller
Chem. Sci., 2017, Advance Article
DOI: 10.1039/C7SC01491K, Edge Article

____________________________________________________

Efficient stabilisation of a dihydrogenphosphate tetramer and a dihydrogenpyrophosphate dimer by a cyclic pseudopeptide containing 1,4-disubstituted 1,2,3-triazole moieties
Disha Mungalpara, Arto Valkonen, Kari Rissanen and Stefan Kubik
Chem. Sci., 2017, Advance Article
DOI: 10.1039/C7SC02700A, Edge Article

____________________________________________________

Dual targeting of the cancer antioxidant network with 1,4-naphthoquinone fused Gold(I) N-heterocyclic carbene complexes
R. McCall, M. Miles, P. Lascuna, B. Burney, Z. Patel, K. J. Sidoran, V. Sittaramane, J. Kocerha, D. A. Grossie, J. L. Sessler, K. Arumugam and J. F. Arambula
Chem. Sci., 2017, Advance Article
DOI: 10.1039/C7SC02153D, Edge Article

____________________________________________________

Remote C–H insertion of vinyl cations leading to cyclopentenones
Sarah E. Cleary, Magenta J. Hensinger and Matthias Brewer
Chem. Sci., 2017, Advance Article
DOI: 10.1039/C7SC02768K, Edge Article

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)

Plotting a course to new antibiotics

Researchers in Switzerland and Italy have devised a way to chart protein-based antibiotics according to their chemistry. This map of the chemical space has allowed them to search for new compounds more intelligently and has already led to them finding a new antibiotic for a highly resistant hospital bug.

In the biochemical arms race between bacteria and medicine, novelty is key. New types of molecules, acting in new ways, can kill microbes that are resistant to our existing arsenal. Unfortunately, the world of potential molecules is huge and mostly uncharted. New antibiotics act as landmarks, signposting where other useful compounds might lie. Researchers then start exploring nearby – although in an abstract chemical space, ‘nearby’ can be a tricky concept.

Source: © Royal Society of Chemistry
Chemical space guided the discovery of antimicrobial bridged bicyclic peptides against Pseudomonas aeruginosa and its biofilms

Read the full story by Alexander Whiteside on Chemistry World.

Digg This
Reddit This
Stumble Now!
Share on Facebook
Bookmark this on Delicious
Share on LinkedIn
Bookmark this on Technorati
Post on Twitter
Google Buzz (aka. Google Reader)