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    Home > Medical News > Medical World News > The seven stars of C&EN in 2019 have been announced, which ones have you guessed?

    The seven stars of C&EN in 2019 have been announced, which ones have you guessed?

    • Last Update: 2019-12-08
    • Source: Internet
    • Author: User
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    In 2000, the ACS global science and Technology Symposium held in San Francisco, USA, discussed the important contribution of organic fluorine chemistry in academic and industrial application fields Fluorine-containing organic compounds often show physical and chemical properties that are not possessed by the non fluorine parent This special effect, called "fluorine magic", attracts many chemists to study and explore the organic fluorine chemistry The slogan of the conference is "small atom with a big ego" An atom can change the world Those who stand out in the dust and haze of the years are even more powerful Some of them were thunderstruck at the beginning of their appearance, just like the treasure of heaven, which caused a great sensation in the academic circle; others were not in a hurry, just like a piece of music getting better, a story telling, waiting for the clouds to open and the moon to shine in their dormancy, waiting for the light and heat to be released at that time Each year, the journal C & en of the American Chemical Society (ACS) selects new molecules that have been published in major journals for one year Recently, seven molecules have made the C & en's molecules of the year for 2019 The academic Jingwei team is here to briefly introduce the unique structure and design concept of these seven molecules All benzene substituted p-polyphenyl structure has good semiconductor properties and is expected to be widely used in the field of organic optoelectronic materials As the name suggests, these molecules are composed of linear condensed benzene core skeleton, and then all condensed benzene C-H bonds are replaced by phenyl In 1996, Professor Robert A Pascal Jr of Tulane University completed the construction of octaphenylnaphthalene and decaphenylanthracene After more than 20 years, they further expanded their molecular structure and synthesized dodecyl substituted tetrabenzenes Source: reference [1] This molecule is the largest total benzo substituted polyphenyl structure that can be obtained by people at present It is dark red and emits strong fluorescence Due to the steric hindrance and electronic effect of the surrounding benzene substituents, the core skeleton of p-tetraphenylene is distorted to a certain extent, which is not a planar conjugate structure, and the torsion angle of the two ends connected end to end can reach 97 degrees Although the molecule is huge and complex, it can be synthesized effectively by three steps with tetraphenylfuran and 1,2,4,5-tetrabromo-3,6-diphenylbenzene as raw materials You may not be unfamiliar with C60, which is one of the allotropes of carbon It has a hollow structure composed of 60 C atoms, and its shape is similar to football, so it is also called Football ene Since there is a hollow molecular cavity in C60, it is also assumed that other small molecules can be embedded into C60 with C60 as the molecular cage In theory, the process is very simple: cut off the C-C bond of several consecutive five membered carbon rings and six membered carbon rings on one side of fullerene by specific chemical means, open a gap, and then introduce small molecules Finally, close the rings one by one by chemical methods, and "sew" the spherical surface In the past, inorganic small molecules such as H2, H2O and HF have been embedded in C60 If we want to "plug" larger molecules into the fullerene, we need to open a larger gap on its surface However, if the opening is too large, it will lead to the failure of further "stitching", thus limiting the size of the embedded molecules Professor Richard J Whitby's team at the University of Southampton, UK, opened a large gap on the side of C60 molecule The gap is a 17 yuan ring, which contains an S atom Then, CH4 was "stuffed" into football olefine under high pressure The next step is the key "suture" step, in which the thioether in the gap is partially oxidized to sulfoxide, which is desulfonylated under the light initiation, and the first "closing" is completed, followed by the reduction of fullerene through the mature cyclization and aromatization process This is the first time to embed organic molecules in C60, and the largest molecule so far CH4 can rotate freely in the molecular cage, and the carbon skeleton structure of fullerene has no obvious deformation Source: reference [1] Of course, it's not just fun, it's not an episode of obsessive-compulsive disorder Using this method, one can study the quantum properties of C in a single CH4 molecule The authors also plan to further embed other molecules such as O2 and NH3 into the fullerene Amar h flood, Professor of Indiana University, designed a molecular cage that can capture chloride ions (Cl -) by using click reaction (Cu (I) - catalyzed cycloaddition of terminal alkynes and azides) In the past, many groups of O-H and N-H bonds which can be used as hydrogen bond donor need to be modified in the structure of this kind of molecular cage That is to say, Cl - is introduced into the molecular cage through the strong hydrogen bond interaction between multiple groups of O-H and N-H bonds and Cl - Source: reference [1] This work is realized by the interaction of C-H bond and Cl - of molecular cage It seems that C-H bond can be used as hydrogen bond donor to overturn people's inherent impression of hydrogen bond Generally, only N, O, F atoms with large electronegativity and small atomic radius can form hydrogen bond interaction with H atoms The electronegativity difference between C and H is only 0.35, and the possibility of forming hydrogen bond is very small However, X-ray crystallography analysis has confirmed that there is a hydrogen bond interaction between C-H bond and Cl - in six groups of triazole structure in the molecular cage; in addition, the C-H bond in three groups of benzene ring also has a weak interaction with Cl -, resulting in the strong affinity of the molecular cage for Cl -, which is better than all other guest molecules at present, and at the same time, it has good performance Good selectivity (Cl - > Br - > NO3 - > I -) If you ask how strong this affinity is, the author confesses that he spent nearly a year trying to isolate molecular cages that do not contain Cl -, but all failed If the molecular cage is purified by means of column chromatography, it will also grab Cl - in silica gel The minimum residue of Cl - can be controlled at about 10% Under normal conditions, Cl - can accelerate the corrosion of iron and steel materials, but the corrosion rate will be greatly reduced when the common steel is coated with a layer of molecular cage film The work described below is quite topological Professor Kenichiro Itami of Nagoya University, Japan, cooperated with Professor yasutomo Segawa to design two kinds of mechanical interlocking structures only composed of benzene rings, one is the double ring hydrocarbon formed by the interlocking of two coupling rings, the other is the trefoil structure woven by one coupling ring Source: reference [1] Mechanical interlocking structure is widely used in the field of molecular machinery It is not difficult to construct two kinds of structures, i.e bicyclic alkanes and trefoil linked rings The difficulty is to design complex topological structure by using only benzene linked rings In general, to complete the above process, we need to use transition metal salt as template, coordinate it with heteroatoms (such as N, O) on the linked ring, or guide the construction of topological structure based on specific organic template molecules It is difficult to establish such a guiding function if the link is only composed of benzene ring The author thought that, after the spirodi (dibenzothiarole) was used as the organic template molecule to guide the synthesis of dicyclohydrocarbons and trefoil linked rings, adding fluoride to eliminate the central silicon atom, the two phenyl of the original dibenzothiarole part would become a part of the linked ring, thus completing the construction of mechanical interlock structure These two kinds of molecules are only composed of the repeat units of the para disubstituted benzene ring (C6H4) In the early days, it was deduced by theoretical calculation that each C atom can bond with only two other C atoms to form a whole carbon ring structure (ring [n] carbon, CN): each C atom forms a C = C double bond with other C atoms, or a C-C single bond and C ≡ C triple bond In 1966, it was proposed that cyclo [18] carbon (C18) may exist, but there has been a lack of effective methods to realize its synthesis and structural characterization Over the past 50 years, Professor Harry L Anderson, Professor Przemyslaw gawel of Oxford University and Leo of IBM research-z ü rich Dr gross et al First used the atomic force microscope (AFM) to detect and image the cyclic carbon oxide c24o6 precursor and reaction intermediate with high resolution, and used the single atom manipulation technology to operate it at the atomic scale, gradually cut off the C = O group by applying voltage pulse to the needle tip, and finally successfully realized the synthesis of C18 Source: reference [1] This kind of all carbon ring is composed of C atom completely Under AFM imaging, there is a closed-loop structure with alternating C-C single bond and C ≡ C three bond This kind of structure can show good semiconductor properties, which means that C18 may play an important role in the field of nano electronic devices However, at present, they can only synthesize one molecule in a single operation To achieve large-scale synthesis of C18, and to ensure that the molecule can remain stable after leaving the low temperature environment and inert matrix, there is still a long way to go More than 100 years ago, French chemist Alfred Werner put forward the "Werner coordination theory", which pioneered the coordination theory in inorganic chemistry For hexa coordinated transition metal complexes, in addition to the common octahedral and triangular coordination structures, he proposed that there should be another plane hexagon structure However, up to now, almost all six coordination transition metal complexes can not escape from the first two coordination configurations, and the third model has not been supported by examples However, after more than a century of ups and downs, this hypothesis was finally verified by the unremitting efforts of Professor Mark R crimmin of Imperial College London For the first time, they have successfully prepared and separated the complexes of palladium magnesium hydride, platinum magnesium hydride and nickel magnesium hydride with six coordination of planar hexagonal ligands The coordination configuration of hexagonal plane is confirmed by X-ray diffraction analysis and DFT calculation Source: reference [1] According to h ü ckel's rule, when the π electron number of a compound is 4N + 2, it shows aromaticity and chemical stability increases, while when the π electron number is 4N, it shows anti aromaticity, chemical stability decreases and reaction activity increases The latter has paramagnetic ring current, which can play a unique role in magnetic materials With the rise of nanoscience research, various nanoscale structures have been designed, ranging from micro nano molecular cages to macro nano porous materials At present, nano molecular cage has been widely used in molecular recognition, separation and other aspects, and can also be used to promote some special chemical reactions The walls of most molecular cages are composed of aromatic molecules Because of the instability of anti aromatic molecules, there is no nano molecular cage composed of such molecules before Professor Jonathan R Nitschke of the University of Cambridge, UK, designed a new nano molecular cage with relatively stable anti aromatic molecules as the cage wall for the first time The nonaromatic molecule is Ni (II) with demethylcarbrole coordination Norcorole is a kind of ring contraction porphyrin, in which two pyrrole rings are directly linked by C-C bond The π electron number of this kind of ring system is 16, so it shows anti aromaticity, but it is stable at room temperature and air atmosphere Nano molecular cage
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