A cyanostar (pentacyanopentabenzo[25]annulene) is a shape-persistent macrocycle that binds anions. [1] [2]
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A cyanostar (pentacyanopentabenzo[25]annulene) is a shape-persistent macrocycle that binds anions. [1] [2]
The cyanostar structure is synthesized in a one-pot process among five equivalents of a benzaldehyde bearing a meta -cyanomethyl substituent. A series of Knoevenagel condensation reactions catalyzed by various bases stitches them together to make the C5-symmetric structure. [3]
Cyanostar binds anions through hydrogen bonding from the C–H bonds, as the hydrogen has a positive electrostatic potential. [3] It is the first binder to make use of cyanostilbene's electropositive CH groups. The CH bonds create an electropositive region in the center of the macrocycle, creating a binding pocket. Cyanostar strongly binds anions that usually can only be bound weakly. The increased binding arises from the formation of a 2:1 complex, with two cyanostars sandwiching the anion on each side. [3] An extended version of this structural pattern is a 4:3 alternating stack of cyanostar molecules complexing a hydrogen-bonded chain of dihydrogen phosphate units. [4]
Two cyanostars can be threaded onto a phosphate diester structure, forming a rotaxane. Because they have a high affinity for the central phosphate group only when it is in its anionic form, there is a substantial and reversible structural change in response to acid–base changes in solution. [5]
In chemistry, a hydrogen bond is primarily an electrostatic force of attraction between a hydrogen (H) atom which is covalently bonded to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a lone pair of electrons—the hydrogen bond acceptor (Ac). Such an interacting system is generally denoted Dn−H···Ac, where the solid line denotes a polar covalent bond, and the dotted or dashed line indicates the hydrogen bond. The most frequent donor and acceptor atoms are the period 2 elements nitrogen (N), oxygen (O), and fluorine (F).
A rotaxane is a mechanically interlocked molecular architecture consisting of a dumbbell-shaped molecule which is threaded through a macrocycle. The two components of a rotaxane are kinetically trapped since the ends of the dumbbell are larger than the internal diameter of the ring and prevent dissociation (unthreading) of the components since this would require significant distortion of the covalent bonds.
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