Capture of highly active anions: supramolecular receptors based on hydrogen bonds

Anion exists widely in nature It not only participates in many reactions in organism, but also directly affects people's health In addition, the acceleration of the industrialization process also makes the anion harm to the environment more and more serious Therefore, anion recognition has been a very active research field in the past decades In addition to the traditional heterocyclic anion acceptors, various supramolecular anion acceptors based on hydrogen bond, electrostatic interaction and ion π interaction have been developed, and they have made remarkable achievements in the field of anion recognition, such as halide ion, oxyacid anion and so on Figure 1 Two anion receptors (picture source: chem SCI.) recently, Michael M Haley, Darren W Johnson and Michael D pluth from the school of chemistry and biochemistry, University of Oregon, United States, jointly reported two receptors for hydrogen selenide anion (HSE -) The hydroselenide anion has great toxicity at high concentration, but many kinds of hydroselenide anion intermediates are produced in the normal metabolism of human body, and hydroselenide anion is a necessity for the synthesis of the 21st amino acid (selenocysteine), However, due to the high reactivity of hydrogen selenide anion to electrophilic reagents and oxygen, general anion receptors can not effectively capture them from solution or biological environment On the basis of hs-anion receptor (Fig 1.1h, 2h), the author developed two kinds of receptors (Fig 1.1tbu, 2cf3) which can effectively capture the hydroselenide anion The results were published in Chemical Science (DOI: 10.1039 / c8sc03968b) under the title of "expanding reversible chalcogenide binding: supramolecular receptors for the hydroselenide (HSE -) an" ）。
The synthesis of anion acceptor 2cf3 can be completed in one step only When tris (2-aminoethyl) amine and 3,5-difluoromethylbenzoyl chloride react overnight in alkaline condition, the higher purity 2cf3 can be obtained However, since the anion acceptors 1 TBU and 2 CF3 are only soluble in organic solution, the General inorganic selenium hydrogen compounds are not suitable for studying their recognition characteristics Therefore, the author obtained NBU 4 sEH which is soluble in organic phase through the reaction of Se with tetrabutylammonium borohydride (NBU 4 BH 4) Fig 2 A) 1-tbu-hse-binding diagram; b) 1-tbu-hse-nmr titration; c) 2-cf3-hse-binding diagram; d) 2-cf3-hse-nmr titration (picture source: chem SCI.), the author studied the binding ability of anion receptor 1-tbu and 2-cf3 to HSE - The NMR titration showed that the corresponding proton peaks on the receptor shifted significantly after HSE - was added to 1 TBU and 2 CF 3 (Fig 2B, d) Therefore, the author speculates that the binding of receptor and anion depends on the hydrogen bond interaction between N-H and anion, but there is another possibility: the chemical reaction between receptor and anion In order to eliminate the latter possibility, the author added an excessive amount of HSE - to the solution of 1 TBU, and the nuclear magnetic spectrum showed that the chemical reaction between the two substances did take place after a long time (3 h) contact, but the reaction between them could be ignored in the titration time range The anion receptor 2cf3 has higher stability After a long time of observation, the author has not observed the reaction between 2cf3 and HSE - In addition, zinc acetate was added to the acceptor solution containing HSE - to remove HSE - the results showed that the NMR spectra of 1 TBU and 2 CF 3 almost returned to the original state, which indicated that the binding of 1 TBU and 2 CF 3 to HSE - was reversible Table 1.1 the binding constants of TBU and 2cf3 with several anions (picture source: chem SCI.) in addition to the study of HSE -, the author also studied the recognition ability of 1bu and 2cf3 to other anions and compared them (Table 1) The results show that both anionic acceptors show the highest affinity for HS - In addition, they can also capture Cl - effectively, which is related to the size and surface charge density of anions Highlight: the two anion receptors reported by the author can effectively capture the highly active anions HSE - and HS - in solution, and the process is reversible Author: hazel a fargher, Nathanael Lau, Lev n Zakharov, Michael M Haley, Darren W Johnson and Michael D pluth