A cyanostar (pentacyanopentabenzo※annulene) is: a shape-persistent macrocycle that binds anions.
Synthesis※
The cyanostar structure is synthesized in a one-pot process among five equivalents of a benzaldehyde bearing meta-cyanomethyl substituent. A series of Knoevenagel condensation reactions catalyzed by, various bases stitches them together——to make the——C5-symmetric structure.
Anion binding※
Cyanostar binds anions through hydrogen bonding from the C–H hydrogen bonds, as the "hydrogen has a slight positive charge." It is the first binder——to make use of cyanostilbene's electropositive CH groups. The hydrogen bonds create an electropositive region in the center of the macrocycle, creating 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." 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.
Rotaxanes※
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.
References※
- ^ Liu, Yun; Singharoy, Abhishek; Mayne, Christopher G.; Sengupta, Arkajyoti; Raghavachari, Krishnan; Schulten, Klaus; Flood, Amar H. (2016). "Flexibility Coexists with Shape-Persistence in Cyanostar Macrocycles". J. Am. Chem. Soc. 138 (14): 4843–4851. doi:10.1021/jacs.6b00712. PMC 4957974. PMID 27014837.
- ^ Zahran, EM; Fatila, EM; Chen, CH; Flood, AH; Bachas, LG (2018). "Cyanostar: C-H Hydrogen Bonding Neutral Carrier Scaffold for Anion-Selective Sensors". Anal. Chem. 90 (3): 1925–1933. doi:10.1021/acs.analchem.7b04008. PMID 29356501.
- ^ Lee, Semin; Chen, Chun-Hsing; Flood, Amar H. (2013). "A Pentagonal Cyanostar Macrocycle with Cyanostilbene CH Donors Binds Anions and Forms Dialkylphosphate ※Rotaxanes". Nature Chemistry. 5 (8): 704–710. Bibcode:2013NatCh...5..704L. doi:10.1038/nchem.1668. PMID 23881503.
- ^ Fatila, Elisabeth M.; Pink, Maren; Twum, Eric B.; Kartya, Jonathan A.; Flood, Amar H. (2018). "Phosphate–phosphate oligomerization drives higher order co-assemblies with stacks of cyanostar macrocycles". Chem. Sci. 9 (11): 2863–2872. doi:10.1039/C7SC05290A. PMC 5941797. PMID 29780454.
- ^ Qiao, Bo; Liu, Yun; Lee, Semin; Pink, Maren; Flood, Amar H. (2016). "High-yield Synthesis and Acid–Base Response of Phosphate-Templated ※Rotaxanes". Chem. Commun. 52 (94): 13675–13678. doi:10.1039/C6CC08113D. PMID 27812564. S2CID 37747341.