Review of chemical hot spots in 2018

2018 chemical hotspot

▲ New molecules are created, and synthetic unusual structures are favored

▲ Electron microscopy technology continues to develop and characterize small molecule compounds

▲ Catalysis and reaction: opening up new systems and establishing new processes

▲ Chiral research has achieved breakthroughs, and chiral chemistry has achieved significant opportunities.

▲ Machine learning and artificial intelligence to help predict molecular properties and explore new responses

▲ Synthetic biology technology promotes the development of green chemistry

▲ Chemistry and Materials Science: Porous materials help solve crystal structure problems, polymerization degradation of polymer plastics

▲ 2018 China’s chemical research output a number of representative results

Chemistry is the science of studying the composition and structure of matter, its reactions and mechanisms, its properties and its functions. Chemistry transforms the world by creating new molecules. As a traditional discipline, chemistry has a complete and rigorous research system; in the new century, it is closely intertwined with each other in the fields of life, medicine, materials, environment, energy, etc., greatly expanding its own development space. In 2018, chemistry continued to make significant progress in the creation, transformation, theory, and nature of molecules. At the same time, new technologies such as machine learning have injected new vitality into chemical research, and scientific issues in the fields of life and energy have attracted more and more. The interest of chemical researchers.

New molecular creation

The limit of challenging molecular synthesis is what chemists are most happy with. From simple small molecules to complex natural products, from ultra-stable high-temperature ceramics to reactive intermediates that can only exist for a few femtoseconds, from health-protecting drugs to materials that change life, chemists have discovered, designed, and synthesized Millions of molecules.

In addition to functional orientation, molecular creation is also favored by the scientific community, such as the highest coordination complex, the most distorted aromatic compound, and the longest single molecule. In 2018, Ishigaki of Hokkaido University in Japan made a breakthrough in the longest carbon-carbon single bond. They used the wonderful large steric hindrance substitution effect to obtain a bond length of up to 1.806 Å on the newly designed hexaarylethane molecule. The carbon-carbon single bond is about 1.2 times longer than the conventional carbon-carbon single bond bond, and the shortest non-covalent bond distance between the two carbon atoms in the molecule is 1.802 Å. On the one hand, the large aromatic substituents on the two carbons, through the steric repulsion, make the carbon-carbon single bond as long as possible, and at the same time, because of the shielding of the substituent, the carbon-carbon single bond which is too long and weak is not easily affected by other reactive groups. The offense breaks, and the weak interaction between the substituents also stabilizes the molecular structure and prevents the carbon-carbon single bond from breaking

Graphene is the most popular carbon material in the past decade, which has driven the development of the entire two-dimensional material. From the molecular level “bottom up” synthetic carbon materials (fullerene, carbon nanotubes, graphene, etc.) can obtain a variety of precise structures, which have unusual properties for further functionalization, devices Specific requirements. Moreno of the Catalonia Institute of Nanoscience and Nanotechnology in Spain and Peña of the University of Santiago de Compostela, starting from the small molecule DP-DBBA, first passed the Ullmann coupling polymerization on the high vacuum gold surface, and then At higher temperatures, cyclization and dehydroaromatization form nanobelts, and finally dehydrogenation cross-coupling, prepared graphene nanoporous array of graphene. Such porous graphene has the properties of a semiconductor, which is different from the zero band gap of ordinary graphene, and can be used for manufacturing transistor devices, as well as for molecular screening and sensing

The molecular structure obtained by X-ray single crystal diffraction is the most accurate and direct method for determining the three-dimensional structure of molecules. This method is also widely used in the structural determination of biological macromolecules such as proteins. Cryo-electron microscopy is a major breakthrough in molecular imaging in recent years, and single-particle cryo-electron microscopy has now reached atomic resolution. Traditional protein structure determination requires high-quality single crystals, and then the structure is determined by synchrotron radiation. The development of single-particle cryo-electron microscopy technology reduces the difficulty of processing protein samples. This technology has become the most powerful structural biology today. Research tool. Now, the same principle can be used for chemical small molecule imaging. The University of California, Los Angeles, Gonen, the California Institute of Technology, Stoltz team, and the Gruene team at the Swiss Paul Schell Institute independently reported on the use of rotational electron diffraction to determine small molecules. The three-dimensional structure, the resolution can be less than 1 Å, the test sample can reach the sub-micron crystal level, and the whole process can be completed in a few minutes. This is a major breakthrough in the determination of small-molecule structures. With the development of hardware and software technology, cryo-electron microscopy technology will promote the development of chemistry in the same way as spectrum, nuclear magnetic resonance, single crystal X-ray diffraction

The resolution of imaging is critical for characterizing structures and studying molecular properties. Scanning TEMs with a wide range of resolutions in chemical and materials research can achieve a resolution of 0.5 Å, which is achieved by high-angle annular dark field technology. Through laminated imaging technology and electron microscope pixel array detectors, Cornell University’s Muller team achieved a spatial resolution of 0.39 Å, which is the highest record of electron microscope resolution. This technology also overcomes the high angle annular dark field technology. The problem of high electron beam energy is required (the electron beam energy is too high to destroy the sample), and a high resolution image of the molybdenum disulfide two-dimensional material can be obtained only at 80 keV

Catalysis and reaction

The chemical reaction has created tens of millions of versatile substances that support the sustainable development of human society and the progress of civilization. Catalysis is the most important way to achieve efficient conversion. Current catalysis and reaction studies face many challenges, such as new chemical bond bonding methods, the development of inexpensive and efficient catalysts, the conversion of inert molecules with high added value under mild conditions, and the synthesis of green and atomic economies.

Artificial nitrogen fixation is a major issue in the chemical and chemical industry. The Haber-Bosch method for converting nitrogen into ammonia mainly uses a transition metal catalyst. Braunschweig of the University of Würzburg, Germany, found that a monovalent boron compound can combine with nitrogen molecules and reduce it, for the first time to achieve a non-transition metal activated nitrogen reaction. The boron in the borax contains both a lone pair of electrons and a free p-orbital, which can effectively bind and activate the nitrogen molecules. The work is expected to open up a new catalytic system like the blocked Lewis acid-base pair

The production of important chemical raw materials not only affects the downstream materials, electronics and other industries, but also closely related to the sustainable development of the economy, and the importance can even rise to the level of national strategic security. Acrylonitrile is widely used in synthetic fibers, synthetic rubbers, and synthetic resins. The production of acrylonitrile is usually carried out by ammoxidation of propylene. Beckham et al. of the National Renewable Energy Laboratory of the United States efficiently prepared acrylonitrile by using inexpensive TiO 2 solid acid as a surface catalyst and ethyl 3-hydroxypropionate as a raw material. The ethyl 3-hydroxypropionate can be obtained by microbial conversion of lignocellulose, thereby establishing a new process for large-scale production of acrylonitrile from renewable raw materials

Chiral science

Chirality is the basic property of a three-dimensional object. If an object cannot overlap with its mirror image, it is called a chiral object. These two mirror images are called enantiomers. Chirality is ubiquitous in small molecules, macromolecules, and macroscopic materials, and its development has made tremendous contributions to the advancement of human society. Most of the drugs used today are chiral drugs. Therefore, it is of great significance to study chiral molecules, acquire or create chiral substances, and is one of the most important fields of contemporary chemistry. 2018 is a year in which chiral research has made breakthroughs. From the discovery of new types of chiral isomerism, subversion of textbooks, chiral separation of external field regulation, and novel chiral materials, these breakthroughs have been given. Chiral chemistry brings significant development opportunities.

Reimers of Shanghai University, Sydney University of Engineering and Crossley of the University of Sydney proposed a new type of conformational isoform. They found one of the four stereoisomers of the compound (BF)O(BF)-quinoxalinoporphyrin. A previously unconformed conformational isoform, ie, akamptisomerization due to the intermediate bridged B-O-B bond angle reversal. This heterogeneity results in the formation of two pairs of enantiomers with a diastereomeric transition barrier of 10 4 kJ/mol. Similar to the stereoisomerism caused by the resistance of substituted biphenyl rotation, the resistive isomerism may be widely existed in a rigid planar macrocyclic system, and its photoelectric and catalytic properties need to be further explored

The vast majority of chiral compounds are carbon-centered, that is, the four groups attached to a saturated carbon atom are different. As a very classical chemical reaction, nucleophilic substitution of saturated carbon atoms usually has two mechanisms: S N 1 and S N 2 . The former is considered to be impossible to obtain a chiral product due to the formation of a planar carbon cation intermediate. Harvard University Jacobsen and others use the synergistic action of a chiral hydrogen bond donor catalyst and a Lewis acid promoter to stabilize the carbon cation intermediate formed by the S N 1 reaction mechanism under low temperature conditions, thereby reducing by-products such as rearrangement and elimination. The probability of formation, the high enantioselectivity of the reaction was successfully achieved by the control of the chiral catalyst, and the chiral quaternary carbon compound was obtained. This study broke the conclusion that the S N 1 reaction in textbooks could not be used for chiral synthesis, and solved the problem of obtaining high enantioselective products through the ion pair mechanism, which has broad application prospects

Resolution of the racemate is an important way to obtain a single stereoisomer. Despite the rapid development of asymmetric catalytic technology, most of the actual industrial production still uses a split method to prepare chiral compounds. The most common means of splitting is the crystallization splitting method, which is inexpensive and easy to mass produce. Resolution by chiral column chromatography is a common enantiomeric analysis method in the laboratory. The chiral column can also obtain a single chiral compound of a certain scale, but the cost is high. Whether asymmetric catalysis, or crystallization and chiral column resolution, these methods are in principle distinguished by the spatial differences in enantiomers. Naaman of the Weizmann Institute of Israel and Paltiel of the Hebrew University, starting with the magnetic properties of the molecule, use chiral-induced spin selectivity to achieve enantioselective recognition. The redistribution of the charge of the chiral molecule causes the electron spin orientation to exhibit enantioselectivity, thus interacting with the perpendicular magnetization substrate, the two enantiomers exhibit differences in adsorption energy, which is a chiral molecule. The separation has opened up a whole new way

In addition to drugs, chiral materials are a new growth point for chiral science research. With breakthroughs in chiral control at the molecular level, scientists have begun to focus on chiral control beyond molecular levels. The most prominent of these are chiral liquid crystal materials, especially blue phase liquid crystal materials. The Seoul National University of Seoul and the Pohang University of Engineering, Rho, use chiral amino acids and peptides to control the growth of gold nanoparticles. Because of the enantioselective interaction between the surface of the nanoparticles and the chiral amino acids and peptides, the nanoparticles are different. Sexual high-index crystal faces have different growth rates, and finally a single chiral three-dimensional gold nanoparticle can be obtained. This method essentially transfers the chirality of small organic molecules to inorganic particles of several hundred nanometers in size. The prepared gold nanoparticles have strong optical activity of chiral plasma elements and are expected to be used in the manufacture of plasma metamaterials.

Machine learning and artificial intelligence chemistry

Machine learning and artificial intelligence have become the topic of today’s scientists and technology developers. They are fierce and far-reaching, not only convenient for people’s lives, but also the overall structure and ethics of the entire human society for thousands of years. In the field of chemistry, the influence of machine learning is gradually emerging. Using machine learning, chemists can predict the nature of molecules, explore new reactions, and optimize the route of synthesis, thereby freeing up boring, “dangerous” laboratory work and creating new substances more purposefully and efficiently.

Merck’s Dreher and Doyle of Princeton University in the United States use machine learning algorithm-random forest algorithm to train a large number of Buchwald-Hartwig reaction data obtained through high-throughput experiments, and accurately predict carbon-nitrogen bond coupling reactions with multidimensional variables. which performed. Compared to conventional linear regression analysis, this algorithm has higher prediction accuracy and can be applied to less sample training or prediction outside the sample, so it is very practical for synthetic chemists

Synthetic chemists usually mix different reactants in the laboratory, convert them under certain conditions, analyze the products, see if they have what they want, then optimize the conditions or throw the original ideas into them. “Wastepaper.” Robots designed by Cronin et al. at the University of Glasgow in the United Kingdom can replace synthetic chemists in this common-sense operation, and control organic synthesis robots through the development of new machine learning algorithms, and connect them to analytical tools such as mass spectrometry, nuclear magnetic and infrared. After completing the experiment, the robot “thinks” the acquired data and decides what to do next. Such robots have initially possessed the ability to discover new reactions and synthesize new molecules, and their development is bound to have an impact on traditional laboratory synthesis research

Chemistry and life sciences

Life is essentially assembled from functional molecules, so chemistry and life sciences are inextricably linked. Whether it is a traditional discipline such as biochemistry or a rapidly developing chemical biology in the past 20 years, it is an important area where chemistry and life sciences intersect. From a chemical point of view, the intersection of life sciences, on the one hand, through the exogenous chemical substances, chemical methods or pathways, at the molecular level, the life system is precisely and dynamically modified, regulated and interpreted; on the other hand, The development and innovation of the chemical discipline itself can be promoted through the understanding and control of biological systems.

One of the winners of the 2018 Nobel Prize in Chemistry, Arnold, of the California Institute of Technology, has long been involved in the evolution of enzymes in the cross-cutting field of chemistry and life sciences. By modifying the directed evolution of proteins containing heme prosthetic groups, they achieved carbon-silicon bond and carbon-boron bond formation reactions that cannot occur in nature. In 2018, the team used the directed evolution of cytochrome P450 enzymes to achieve high-strength synthesis of dicyclobutane and cyclopropene, which is difficult for traditional organic synthesis. In addition, for the carbon-hydrogen insertion reaction of cheap metal iron-catalyzed carbene, they screened different heme proteins and mutants, and after several rounds of directed evolution, obtained good catalytic activity, high yield and high stereoselectivity. The enzyme can also directly use the cells expressing the mutant protein as a catalyst for the hydrocarbon insertion reaction of carbene. Directed evolution, as an important technology in synthetic biology, will have a major impetus to the development of green chemistry

At the University of Illinois at Urbana-Champaign, Lu also focused on the modification of enzymes, using in vitro remodeling methods. They introduced iron-sulfur clusters into cytochrome C peroxidase and constructed structural and functional mimics of sulfite reductase. It has the spectrum and binding properties of the native enzyme, and the sulfite has a higher reducing power than the native enzyme. They used synthetic metalloproteinases to achieve a multi-electron redox reaction that is difficult to accomplish with chemical catalysts

Although the evolution of living individuals depends mainly on the sequence of genetic genes, their complexity and diversity cannot be explained only by the “central rule”. Post-translational modification of proteins is a ubiquitous regulation in the life process, and its important physiological and pathological significance has been widely recognized and valued by people. By artificially modifying and labeling proteins at specific sites, the function of the protein can be studied and regulated in situ. Protein-modified chemical reactions require good biocompatibility, fast response, high selectivity, and high yield. Click chemistry is one such widely used reaction. Unlike methods that typically modify on active amino acids or introduce non-natural amino acids by gene codon expansion, Cambridge University Gaunt et al. reported a labeling method on methionine that nucleophilic reaction with thioether on methionine and high-valent iodine reagents. The product of the diazonium structure is further modified, and the method has a good expansion space

The application of chemistry in the field of life sciences is mainly analysis and testing. With the development of new technologies, in-situ, real-time, rapid and accurate acquisition of molecular information has become an important means of understanding the life process, and has greatly promoted the early diagnosis of diseases for the benefit of human health. Yanagisawa, a national longevity medical research center in Japan, used Aβ-related peptides in blood as a biomarker to measure the levels of multiple Aβ-related peptides by immunoprecipitation-mass spectrometry. The accuracy of up to 90% predicts the Aβ burden in the brain. Thereby achieving the diagnosis of Alzheimer’s disease.

Chemistry and Materials Science

Porous materials have important applications in the fields of catalysis, separation, energy, etc., from inorganic molecular sieves to organic-inorganic hybrid frameworks (metal organic framework materials MOF/zeolitic imidazole ester framework materials ZIF) to pure organic frameworks. Structure (covalent organic framework material COF), these porous materials with fixed pore size and crystal structure, clear structure-activity relationship, easy to control and expand performance, favored by chemical and materials scientists. Since the first case of the synthesis of crystalline organic frameworks using reversible boron-oxygen bonds in 2005, COF has developed rapidly and is used in the fields of catalysis, sensing, adsorption separation, and photovoltaic energy. Although most COFs have a better crystalline and regular pore structure by powder X-ray diffraction, obtaining a sufficiently large single crystal remains a daunting challenge. Wang Wei of Lanzhou University, Sun Junliang of Peking University, and Yaghi of UC Berkeley, etc., use the method of auxiliary reagent exchange to control the bonding speed of imine bonds and increase the reversibility of bonding, so that there is enough time for crystal growth to correct defects. The large-size high-quality single crystal satisfying the requirements of single crystal X-ray diffraction test was obtained, and the growth and analysis of the three-dimensional COF single crystal based on imine bond was realized for the first time. This method not only solves the structural problems, but also provides important ideas for obtaining reproducible and high-quality COF materials, which contributes to the expansion of COF research into other chemical bond systems

While chemistry has created new substances to improve people’s living conditions, it has also brought new troubles to the earth. “White trash” is the most typical problem. A large number of polymer materials are difficult to be naturally degraded, seriously polluting water sources, soil and atmosphere. Since chemists have opened the “Pandora’s Box,” they have a responsibility to solve these problems. Chen et al. of Colorado State University have prepared plastics that are degradable under readily achievable conditions by designing specific monomers. The monomers they designed were γ-butyrolactone derivatives with a trans-ring fused at the α and β positions, and a very small amount of catalyst was used to efficiently polymerize at room temperature and without solvent. Synthetic polymer plastics not only have excellent performance, but also can be pyrolyzed or chemically degraded into original monomers and recycled many times.

Chinese Chemistry 2018

Chemistry is the dominant discipline of basic research in China. Since 2013, the number of papers published every year has ranked first in the world, and the gap with other countries is still expanding. This is mainly due to the steady growth of research funding and a large chemical industry. Basic research team. Chinese chemists proposed the techniques of aggregation-induced luminescence, single-atomic catalysis, synthetic graphene two-dimensional carbon materials, and non-fullerene organic solar cells. The development of coal-to-liquid and catalytic gas catalytic conversion technologies The energy sector also has significant strategic implications.

In 2018, China’s chemical research reached a new level, producing significant results in various fields, changing the situation of sporadic occurrences in the past. Representative results include: in the field of chemical reaction mechanism and theory, Peking University Jiang Ying, Xu Limei, Gao Yiqin, Peking University/Chinese Academy of Sciences Wang Enge, etc., first obtained atomic-scale resolution images of hydrated sodium ions, and found a hydrated ion transport The magic number effect of the operation, Zhou Mingfei of Fudan University, and Frenking of the University of Madreburg, Germany, observed the alkaline earth metal octacarbonyl compound similar to the transition metal, Wang Xing’an of the University of Science and Technology of China, Sun Zhigang, Zhang Donghui and Yang Xueming of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences. The “geometric phase” effect in chemical reactions was observed; in the field of synthetic chemistry, Zhao Baoguo of Shanghai Normal University and Yuan Weicheng of Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences, etc. realized the bionic asymmetric Mannich reaction using carbonyl catalysis strategy, Southern University of Science and Technology Tan Bin and the University of California, Los Angeles, Houk, etc. realized the four-component Ugi reaction of catalytic asymmetry for the first time. Zuo Zhiwei of Shanghai University of Science and Technology developed an inexpensive and efficient ruthenium-based catalyst and alcohol catalyst for photo-assisted methane conversion. Synergistic catalytic system; In the field of material chemistry, Xing Xianran and Chen Jun of Beijing University of Science and Technology have prepared super-polarized ultra-tetragonal films through phase interface strains. Fan Chunhai from the Shanghai Institute of Applied Physics, Chinese Academy of Sciences and Yan Wei from Arizona State University, USA Precision and controllable DNA-silica solid-state nanostructure preparation, Southeastern University Yumeng and Nanchang University/Southeast University Xiong Rengen found a class of 17 new all-organic perovskite ferroelectrics; in the field of environmental chemistry, Fudan University Lin et al. made important progress in the study of new particle formation in atmospheric atmospheres. In the field of chemical engineering, Li Yingwei of South China University of Technology and Chen Banglin of the University of Texas at San Antonio, USA, prepared highly ordered, macroporous, single-crystal stabilized MOFs. Materials, Li Jinping from Taiyuan University of Technology, Zhou W from the National Institute of Standards and Technology, and Chen Banglin from the University of Texas at San Antonio, USA, used Fe-MOF to achieve ethane/ethylene separation.

In 2018, Ma Dawei of the Shanghai Institute of Organic Chemistry of the Chinese Academy of Sciences, Zhou Qilin of Nankai University and Feng Xiaoming of Sichuan University won the 2018 Future Science Award for Material Science for their creative contribution to the invention of new catalysts and new reactions.

The core task of chemistry is to achieve precise control and regular awareness of chemical synthesis, processes and functions. Through cross-integration with other disciplines, chemistry constantly discovers new problems, develops new methods, and opens up new directions. In addition, chemical research needs to face the society, serve economic development, and national security. There are many important advances in chemistry in 2018. This article focuses on the nature, creation, and transformation of molecules. It is inevitable that there will be a hangover. Others, such as nanometers and optoelectronic functional materials, are limited by the length of the text, and it is regrettable. In 2019, there will be more exciting achievements in chemistry, and we are looking forward to a greater original breakthrough in China’s chemistry.