Blog | Page 28 of 28

Mechanochemistry for ammonia synthesis under mild conditions

December 25, 2020 |

Chemistry Article

Ammonia, one of the most important synthetic feedstocks, is mainly produced by the Haber–Bosch process at 400–500 °C and above 100 bar. The process cannot be performed under ambient conditions for kinetic reasons. Here, we demonstrate that ammonia can be synthesized at 45 °C and 1 bar via a mechanochemical method using an iron-based catalyst. With this process the ammonia final concentration reached 82.5 vol%, which is higher than state-of-the-art ammonia synthesis under high temperature and pressure (25 vol%, 450 °C, 200 bar).

Temporary or removable directing groups enable activation of unstrained C–C bonds

September 25, 2020 |

Chemist|

Chemistry Article

Carbon–carbon (C–C) bonds make up the skeletons of most organic molecules. The selective manipulation of C–C bonds offers a direct approach to editing molecular scaffolds but remains challenging. The kinetic inertness of C–C bonds can be overcome with transition-metal catalysis, which, nevertheless, relies on a substrate being highly strained or bearing a permanent directing group (DG). The driving force for C–C activation in these cases is strain relief and the formation of a stable metallocycle, respectively. Over the past two decades, a strategy has emerged that uses temporary or removable DGs to effect C–C activation of more common and less strained compounds.

In situ electrochemical generation of nitric oxide for neuronal modulation

July 2, 2020 |

Chemist|

Chemistry Article

Understanding the function of nitric oxide, a lipophilic messenger in physiological processes across nervous, cardiovascular and immune systems, is currently impeded by the dearth of tools to deliver this gaseous molecule in situ to specific cells. To address this need, we have developed iron sulfide nanoclusters that catalyse nitric oxide generation from benign sodium nitrite in the presence of modest electric fields.

Ruthenium-catalysed multicomponent synthesis

June 16, 2020 |

Chemist|

Chemistry Article

Ruthenium-catalysed multicomponent synthesis of the 1,3-dienyl-6-oxy polyketide motif. Polyketide natural products are an important class of biologically active compounds. Although substantial progress has been made on the synthesis of repetitive polyketide motifs through the iterative application of a single reaction type, synthetic access to more diverse motifs that require more than one type of carbon–carbon bond connection remains a challenge. Here we describe a catalytic, multicomponent method for the synthesis of the privileged polyketide 1,3-dienyl-6-oxy motif. The method allows for the formation of two new carbon–carbon bonds and two stereodefined olefins.

Helium placement in the Periodic Table from a crystal structure viewpoint

June 16, 2020 |

Chemist|

Chemistry Article

Helium placement in the Periodic Table For crystallography structure. By 2019, one hundred and fifty years after Dmitry Mendeleev published the first successful version of the Periodic Table of the chemical elements, there was still no universal agreement regarding what a chemical element is. A notable indication of the ongoing ambiguity is IUPAC’s Gold Book, which allows two different versions of the term ‘chemical element. (1) a species of atoms – all atoms with the same number of protons in the atomic nucleus; (2) a pure chemical substance composed of atoms with the same number of protons in the atomic nucleus. W. H. E. Schwarz in his 2007 paper (Schwarz, 2007) argued that there are in fact three different definitions of a chemical element usually encountered: (1) a basic chemical element; (2) a metallurgical element or simple material; (3) an astrophysical spectroscopic element or elemental atom. W. B. Jensen suggested… read more

Gamma radiation shielding properties of poly methyl methacrylate

June 15, 2020 |

Chemist|

Chemistry Article

Gamma radiation shielding properties of poly (methyl methacrylate) / Bi2O3 composites. This work investigated the gamma-ray shielding performance, and the physical and mechanical properties of poly (methyl methacrylate) (PMMA) composites embedded with 0-44.0 wt% bismuth trioxide (Bi2O3) fabricated by the fast ultraviolet (UV) curing method.