Archive for August, 2017

Automated synthesis yields sugar high

An automated synthetic method designed by chemists in Germany has assembled the longest synthetic oligosaccharide ever made from monosaccharides. The method could help to up the pace of carbohydrate research by improving researchers’ access to synthetic glycans.

Source: © Royal Society of Chemistry The researchers used automated glycan assembly to make a 50mer polymannoside

Read the full article by Jennifer Newton on Chemistry World.

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Elucidating the Stability of Two Metal-Organic Frameworks toward Carbon Dioxide Sorption: A Comparative Study

Metal-organic frameworks (MOFs) are coordination networks consisting of organic ligands and metal cores. They possess crystalline structures with metal complexes as the basic building blocks. These complexes assemble together and extend periodically to form the MOF structures. MOFs represent a family of highly porous materials with ultrahigh surface area (typically >1000 m2 g-1). Other attractive characteristics for MOFs are abundant active metal cores and unique porous structures with tunable pore width, useful for gas storage applications.

Capturing carbon dioxide has evolved into an intriguing research area, mainly due to environmental concerns triggered by high levels of greenhouse gas emissions. Some MOFs have already been explored as carbon dioxide storage materials and exhibited storage capability exceeding that of conventional absorbents (e.g. amines). Aside from the absorption capacity of carbon dioxide, the performance stability over prolonged operation periods is another figure of merit for MOF-based absorbents. However, there are limited studies in this area. Now for the first time, research groups led by Zeng and Zhao from National University of Singapore compared the performance stability of two representative MOFs, HKUST-1 and UiO-66(Zr). The unit cell of the two MOFs are shown in the inset of Figure a.

The two aforementioned MOFs were subjected to 500 carbon dioxide absorbing and desorbing cycles (Figure a). The carbon dioxide uptake amount of the two MOFs was gauged at specific cycle numbers (Figure b). Whilst HKUST-1 displayed a consistent decreasing storage capacity with increasing cycle number, the capacity of UiO-66(Zr) fluctuated but remained relatively constant. The results clearly indicate that HKUST-1 is more vulnerable and instable than UiO-66(Zr) during long-term working cycles.

The authors then investigated the mechanisms associated with the different stability performances. They first observed that the surface area of HKUST-1 decreased 24% to 1270 m2 g-1 after the stability test, whereas that of UiO-66(Zr) remained relatively intact. Moisture-induced structural collapse was excluded as a possible reason by carrying out a control experiment with ultra-pure and dry hydrogen gas. The authors then exploited multi-frequency atomic force microscopy and concluded that the difference in elastic modulus of the two MOF crystals played an important role in determining the corresponding MOF durability. UiO-66(Zr) has an elastic modulus (ca. 28 GPa) much higher than that of HKUST-1 (ca. 19 GPa), meaning that the former is more elastic than the latter. The high elasticity of UiO-66(Zr) can efficiently buffer the volumetric deformation caused by carbon dioxide absorption and desorption, preventing UiO-66(Zr) crystals from structural failure.

Figure. (a) Illustration of one cycle of the carbon dioxide absorption-desorption test. The inset shows where one carbon dioxide molecule resides in the corresponding MOFs. (b) The evolution of carbon dioxide uptake capacity (blue) and surface area (black) of HKUST-1 and UiO-66(Zr).

This work is expected to provide general guidelines on studying the structural stability of other MOFs with applications associated with gas storage and separation.

 

To find out more please read:

Structure Failure Resistance of Metal-organic Frameworks toward Multiple-cycle CO2 Sorption

Zhigang Hu, Yao Sun, Kaiyang Zeng, and Dan Zhao

DOI: 10.1039/c7cc04313a

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/.

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HOT ChemComm articles for July

All of the referee-recommended articles below are free to access until 10th September 2017.

Lewis acid catalyzed diastereoselective [3+4]-annulation of donor–acceptor cyclopropanes with anthranils: synthesis of tetrahydro-1-benzazepine derivatives
Zhe-Hao Wang, Huan-Huan Zhang, Dao-Ming Wang, Peng-Fei Xua and Yong-Chun Luo
Chem. Commun., 2017, 53, 8521-8524
DOI: 10.1039/C7CC04239F, Communication

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A Non-Enzyme Cascade Amplification Strategy for Colorimetric Assay of Disease Biomarkers
Jiuxing Li, Zhuangqiang Gao, Haihang Ye, Shulin Wan, Meghan Pierce, Dianping Tangb and Xiaohu Xia
Chem. Commun., 2017,53, 9055-9058
DOI: 10.1039/C7CC04521B, Communication

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Radiofluorination of a NHC-PF5 adduct: Toward new probes for 18F PET imaging
Boris Vabre, Kantapat Chansaenpak, Mengzhe Wang, Hui Wang, Zibo Li and François P. Gabbai
Chem. Commun., 2017,53, 8657-8659
DOI:  10.1039/C7CC04402J, Communication

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New mechanistic insights into intramolecular aromatic ligand hydroxylation and benzyl alcohol oxidation initiated by the well-defined (μ-peroxo)diiron(III) complex
Mio Sekino, Hideki Furutachi, Rina Tojo, Ayumi Hishi, Hanako Kajikawa, Takatoshi Suzuki, Kaito Suzuki, Shuhei Fujinami, Shigehisa Akine, Yoko Sakata, Takehiro Ohta, Shinya Hayamic and Masatatsu Suzukid
Chem. Commun., 2017,53, 8838-8841
DOI: 10.1039/C7CC04382A, Communication

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Activation of P-H Bond by a Frustrated Lewis Pair and its Application in Catalytic Z-selective Hydrophosphonylation of Terminal Ynones
Yizhen Liu, Xiaoting Fan, Zhen Hua Li and Huadong Wang
Chem. Commun., 2017, Advance Article
DOI: 10.1039/C7CC05028C, Communication

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Lone pair-π interaction-induced generation of photochromic coordination networks with photoswitchable conductance
Jian-Zhen Liao, Jian-Fei Chang, Lingyi Meng, Hai-Long Zhang, Sa-Sa Wanga and Can-Zhong Lu
Chem. Commun., 2017, Advance Article
DOI: 10.1039/C7CC05150F, Communication

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Dissolving and Stabilizing the Precursor of Graphene in Organic Solvents

Graphene, a two-dimensional single-layer graphite sheet, has aroused worldwide attention since the last decade. Its ultrahigh electrical and thermal conductivities, high mechanical stiffness and unique band structure have attracted extensive research efforts to develop graphene-based electronics, photonics, printing materials etc. Currently, among various strategies, the wet-chemical method still remains the most practical protocol for large-scale production of graphene in laboratories. This process in general involves two steps: the oxidative exfoliation of graphite, a.k.a. Hummers’ method, followed by reduction of the oxidized graphite sheets. Graphite oxide (GO), possessing a layered structure analogous to graphite but with rich oxygen functionalities (such as hydroxyl and carboxyl groups) anchored on each layer, is the product of the first step and thus serves as a precursor of graphene.

As the aforementioned wet chemical method is usually carried out in water, GO is primarily stored as aqueous-based colloidal dispersions. However, GO is reported to be chemically unstable in water since water molecules can react with electropositive carbons of GO. Though the reaction is not rapid, it partially removes the oxygen functionalities and breaks the carbon matrix, which eventually forces GO to precipitate and reduces the shelf life of the GO precursor.

Recently, Shi and coworkers from Tsinghua University have successfully prolonged the lifetime of GO by dispersing it in organic solvents. During the last purification step of the Hummers’ method, instead of using de-ionized water, anhydrous ethanol was utilized to rinse the GO product and obtain ethanol-wetted GO. X-ray diffraction revealed that ethanol molecules existed in the inter-layer space between adjacent layers. The ethanol-wetted GO could be readily dissolved in propylene carbonate, an organic solvent, for concentrations ranging from 0.1 mg mL-1 to 40 mg mL-1 (Figures a and b). More importantly, GO could be stored in propylene carbonate for at least a month without a colour change, whilst the colour of aqueous GO dispersion discernibly darkened (Figure c). Spectroscopic studies indicated that the colour change was attributed to the loss of oxygen functionalities. The results unambiguously prove that GO in propylene carbonate is much more stable than GO in water.

Figure. (a) Dissolution of ethanol-wetted GO in propylene carbonate. (b) GO colloidal dispersions with various concentrations. (c) Color evolution of GO dispersions (1 mg mL-1) with water and propylene carbonate as solvents before and after storing for 28 days under ambient conditions.

Aside from propylene carbonate, dimethyl sulfoxide, ethylene glycol and N,N-dimethylformamide are solvents that can dissolve the ethanol-wetted GO. The successful stabilization of GO colloidal dispersions could ensure the steady production of graphene in laboratories, as well as reveal new opportunities to develop GO-based devices.

To find out more please read:

Organic Dispersions of Graphene Oxide with Arbitrary Concentrations and Improved Chemical Stability

Wencheng Du, Mingmao Wu, Miao Zhang, Guochuang Xu, Tiantian Gao, Liu Qian, Xiaowen Yu, Fengyao Chi, Chun Li and Gaoquan Shi

DOI: 10.1039/c7cc04584k

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 blog writer 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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