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Ten important findings and research results in the chemical field in 2014
Time:2018-06-04 Source: Inner Mongolia Chengxin Yongan Chemical Co., Ltd.
No.1 Periodic Table of the Elements: A New Record of Oxidized States Realized in the Compounds of Bismuth
The oxidation state indicates the degree to which an atom in the compound has been oxidized. Before 2014, the highest known oxidation state of the compounds was +8. Only compounds with a few elements such as lanthanum, cerium, and lanthanum were present. Among them, lanthanum was particularly unusual because theoretically it could be further oxidized. +9 oxidation state. This year, researchers from Germany, Canada and China’s Fudan University and Tsinghua University have successfully made theoretical predictions a reality through close cooperation. They started from the simple substance of helium and successfully prepared osmium tetroxide (IrO4+) by gas phase reaction. In this ion, the oxidation state of niobium reaches +9, which is the highest record of oxidation state so far.
No.2 Microscopy Technology: Micrograph of the First Hydrogen Bond Was Questioned
Left: Atomic force microscopic photograph of 8-hydroxyquinoline on copper surface at low temperature, black region shows the existence of hydrogen bond; Right: Atomic force micrograph of tetramer of bis(4-pyridyl)acetylene. Although this molecule does not have a hydrogen bond between each other, similar "hydrogen bond" structures are still shown on the picture.
Hydrogen bonds are a special type of interaction between molecules. Their strength lies between the covalent and van der Waals forces. Hydrogen bonds are widely involved in many important phenomena—especially in life phenomena. Therefore, it is of great significance to study hydrogen bonding. In 2013, a research group from China had used atomic force microscopy to observe hydrogen bonds between molecules such as 8-hydroxyquinoline. This was the first time that hydrogen bonds were observed directly, and this caused widespread concern. However, this year, researchers from Finland and the Netherlands published papers in the Physical Review Letters, questioning the study. They used atomic force microscopy to observe the tetramer of this molecule, bis(4-pyridyl)acetylene. In a tetramer, there are no hydrogen bonds between the nitrogen atoms of two adjacent molecules, but they also observe similar "hydrogen bond" structures. Therefore, they believe that the previously reported hydrogen bond images may only be the artifacts produced by the AFM scanning the sample. This study reminds relevant personnel that extra care must be taken when using microscopic techniques to observe objects on the nanometer scale.
No.3 Materials Science: Unexpected new properties of graphene
Graphene is a thin film of one atom thick composed of carbon atoms and is often referred to as a two-dimensional material. Since the 2010 Nobel Prize in physics, Andrei of the University of Manchester, United Kingdom. Heim and Constantine. Since Novoshorov succeeded in separating graphene for the first time in 2004, the study of graphene has become a very popular field. It is hoped that this new material will replace traditional materials in many applications.
In 2014, some new studies on graphene gave people a deeper understanding of this new type of material. One of the studies showed that the chemical properties of graphene may not be as stable as people previously thought. A common method for preparing graphene is to first oxidize graphite to obtain graphite oxide, and then reduce it. Researchers from the United States have found that graphene prepared by this method can rapidly decompose into carbon dioxide and water under the conditions of ultraviolet irradiation and titanium dioxide nanoparticle catalysis. Another study showed that although previous researchers thought that various atoms or molecules were difficult to pass through graphene, protons could pass it well. Therefore, graphene may be used as a proton-conducting membrane in fuel cells.
No.4 Computational Chemistry: Promoting Experiments Through Models
In 2014, researchers took a solid step toward the ultimate goal of computational chemistry—the use of theory to discover new chemical reactions. Researchers from Stanford University in the United States have developed a new system of computational chemistry called the "ab initio nanoreactor." In a virtual environment, this "nanometer reactor" mixes and compresses the molecules of the reactants, and then uses quantum mechanical methods to calculate the reaction process and reaction products. Using this method, the researchers predicted the products of some chemical reactions that cannot be verified in the lab due to the need for high temperature and high pressure. Although this new computational chemistry system needs further improvements, it is still an important advance in the field of computational chemistry.
No.5 Organic Synthesis: Salts Can Affect Root-Side Coupling Reactions
The effect of inorganic salts on the root-neck coupling reaction: top left: When the organozinc reagent is attached to two fatty alkyl groups, the reaction cannot proceed with or without the presence of inorganic salts; top right: when the organozinc reagent is attached to two aromatic groups The reaction can be performed without the addition of inorganic salts: Next: When the organozinc reagent is attached to a fatty alkyl or aromatic group and a halogen atom, the reaction must take place in the presence of an inorganic salt.
Negishi cross-coupling reaction was discovered by the Japanese chemist and one of the winners of the Nobel Prize in Chemistry in 2010, Negishi Kanetaki, referring to the reaction of halogenated alkanes with organozinc reagents to form new organic compounds under the catalysis of transition metals. The root-neck coupling reaction has been used to synthesize many important organic compounds since it was discovered in 1977. Researchers from Canada after more than 10 years of research found that inorganic salts such as lithium chloride can significantly affect the root-shore coupling reaction. Depending on the structure of the organozinc reagents, the reaction must be carried out in the presence of inorganic salts in some cases. In some cases, inorganic salts may be used without the participation of inorganic salts. In some cases, the presence or absence of inorganic salts may also be achieved. No reaction can occur. The researchers explained that the root-neutral coupling reaction is going to work properly, the polarity of the organozinc reagent and the solvent must be matched, and adding inorganic salts can help achieve this goal. This study can help researchers better control the progress of the reaction and reduce the production of unnecessary by-products.
No.6 Nanotechnology: Preparation of High Purity Carbon Nanotubes
When the polycyclic aromatic hydrocarbons on the platinum surface are heated, they are folded to form carbon nanotubes. Through this method, researchers can control the size of carbon nanotubes very well.
Single-walled carbon nanotubes are considered to have potential applications in many fields, but for a long time, the preparation of high-purity carbon nanotubes is an urgent problem to be solved. At present, the commonly used methods can only obtain a mixture of carbon nanotubes with different sizes and different chiralities, thereby affecting the electrical conductivity of the carbon nanotubes. This year, two research groups have made major breakthroughs in the preparation of high-purity carbon nanotubes. Professor Li Yan of Peking University and co-workers use tungsten-cobalt alloy nanocrystals as "seeds" to guide the growth of carbon nanotubes at high temperatures. Using this method, they increased the purity of carbon nanotubes from 55% to 92%. Researchers from Germany and Switzerland used polycyclic aromatic hydrocarbons as raw materials for the synthesis of carbon nanotubes. At high temperatures, these aromatic molecules fold and extend to form carbon nanotubes. By this means, they can get a single carbon nanotube at a time.
No.7 Synthetic Biology: Bacteria received an extended genetic code
Chemical structure of synthetic d5SICS-dNaM base pairs; Bottom: If DNA bases are expanded from 2 to 4 to 3 to 6 species, the possible combination of codons will increase from 64 to 216, so it is possible to add some new Amino acid molecules are introduced into the protein.
Adenine (A) and thymine (T) and guanine (G) and cytosine (C) are two pairs of four bases in our well-known DNA. All living things on Earth use these four bases to organize the genetic code to control protein synthesis. In 2014, scientists from the Scripps Research Institute in the United States introduced DNA containing the non-naturally occurring bases of d5SICS and dNaM into living bacteria and found that DNA containing new bases can be found in bacteria. Normal copy.
This pair of new bases does not interact with the A-T and G-C base pairs through hydrogen bonds, but rather through hydrophobic interactions. Although DNA containing new base pairs has been shown to direct protein synthesis in vitro, replication in vivo is the first report. If DNA containing a new base pair can be transcribed into messenger RNA in vivo, we will be able to use it to synthesize new protein structures in the future.
No.8 Structural Biology: First Determination of Protein Structure by Electron Microscopy
An ultra-high resolution electron micrograph of the mitochondrial ribosome large subunit of yeast. The structures marked with blue, red, and yellow represent the same structure as the ribosome of bacteria, the same structure as the mitochondria of mammals, and the structure unique to yeast.
The precise determination of the structure of proteins and other biological macromolecules has always been a patent for X-ray diffraction, but this year, several researchers from the Cambridge Molecular Biology Laboratory in the UK have identified the structure of proteins for the first time by means of electron microscopy alone. Through improved electron microscopy, they succeeded in obtaining images of the yeast mitochondrial ribosomal large subunit with a resolution of 3.2 angstroms (1 angstrom is one tenth of one nanometer, one billionth of a meter, atomic radius Generally around 1 angstrom). Since there is no need for complex and tedious purification and crystallization processes like X-ray diffraction, new electron microscopy technology is expected to help researchers better understand the structure of biological macromolecules.
No.9 Polymer Science: A Novel Plastic with Chirality
Researchers from Cornell University in the United States have developed a novel metal cobalt-containing compound that can catalyze the reaction of two molecules, succinic anhydride and propylene oxide, to obtain a polymer. Propylene oxide molecules are chiral, which means that they actually have two different structures. They mirror each other like human hands, but they cannot overlap. When propylene oxide and succinic anhydride generate macromolecules under the action of this novel catalyst, the chirality is maintained, which means that we can obtain two kinds of polymers that are mirror images of each other. Interestingly, the melting point of these two polymer materials is 79oC, but after mixing at a ratio of 1:1, due to the special interaction, the melting point is increased to 120oC, and the crystallization rate is also greatly accelerated. It is very beneficial to the production and processing of plastic products. In addition, this new type of plastic can be biodegraded, and succinic anhydride and propylene oxide are common chemical raw materials, so it is hopeful that large-scale applications will be achieved in the near future.
No.10 Solar Cell: Perovskite Solar Cell Continues to Make Progress
Solar cells have always been regarded as an important form of renewable energy. Currently commercialized silicon solar cells can convert about 25% of solar energy into electrical energy, but they are expensive. Solar cells based on polymers and other materials are relatively cheap, but their conversion efficiency is only about 10%. In recent years, a new type of solar cell, perovskite solar cells, has received extensive attention from researchers. Perovskite-type solar cells do not use perovskite (CaTiO3), but the substance used to convert solar energy has a chemical composition of the general formula ABX3, and the crystal structure is similar to that of perovskite, which has the advantages of low cost and energy. The advantages of high conversion efficiency. At present, the most commonly used material for perovskite solar cells is (CH3NH3)PbI3. Earlier this year, it was reported that the conversion efficiency of perovskite solar cells has reached 16%, and by the end of this year, researchers have already achieved 20 % conversion rate. Due to the toxicity of lead-containing compounds, researchers at the Northwestern University in the United States proposed that similar compounds derived from tin instead of lead can also be used to produce perovskite solar cells. Also this year, researchers from Oxford University in the United Kingdom published a paper saying that composites of carbon nanotubes and polymers can effectively improve the stability of perovskite solar cells.