{{Short description|Macrocylcic molecule}} A '''cyanostar''' (pentacyanopentabenzo[25]annulene) is a shape-persistent macrocycle that binds anions.<ref>{{cite journal |title= Flexibility Coexists with Shape-Persistence in Cyanostar Macrocycles |last1= Liu |first1= Yun |last2= Singharoy |first2= Abhishek |last3= Mayne |first3= Christopher G. |last4= Sengupta |first4= Arkajyoti |last5= Raghavachari |first5= Krishnan |last6= Schulten |first6= Klaus |last7= Flood |first7= Amar H. |journal= J. Am. Chem. Soc. |year= 2016 |volume= 138 |issue= 14 |pages= 4843–4851 |doi= 10.1021/jacs.6b00712 |pmid= 27014837 |pmc= 4957974 }}</ref><ref>{{cite journal |journal= Anal. Chem. |year= 2018 |volume= 90 |issue= 3 |pages= 1925–1933 |doi= 10.1021/acs.analchem.7b04008 |title= Cyanostar: C-H Hydrogen Bonding Neutral Carrier Scaffold for Anion-Selective Sensors |last1= Zahran |first1= EM |last2= Fatila |first2= EM |last3= Chen |first3= CH |last4= Flood |first4= AH |last5= Bachas |first5= LG |pmid= 29356501 }}</ref>
thumb|right|Cyanostar as the central unit of a dendrimer
== Synthesis == 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.<ref name=SLee2013>{{cite journal |first1= Semin |last1= Lee |first2= Chun-Hsing |last2= Chen |first3= Amar H. |last3= Flood |journal= Nature Chemistry |volume= 5 |issue= 8 |pages= 704–710 |year= 2013 |title=A Pentagonal Cyanostar Macrocycle with Cyanostilbene CH Donors Binds Anions and Forms Dialkylphosphate [3]Rotaxanes |doi= 10.1038/nchem.1668 |pmid= 23881503 |bibcode= 2013NatCh...5..704L }}</ref>
== Anion binding == Cyanostar binds anions through hydrogen bonding from the C–H bonds, as the hydrogen has a positive electrostatic potential.<ref name=SLee2013></ref> 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.<ref name=SLee2013/> 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.<ref>{{cite journal |title= Phosphate–phosphate oligomerization drives higher order co-assemblies with stacks of cyanostar macrocycles |first1= Elisabeth M. |last1= Fatila |first2= Maren |last2= Pink |first3= Eric B. |last3= Twum |first4= Jonathan A. |last4= Kartya |first5= Amar H. |last5= Flood |journal= Chem. Sci. |year= 2018 |volume= 9 |issue= 11 |pages= 2863–2872 |doi= 10.1039/C7SC05290A |pmid= 29780454 |pmc= 5941797 }}</ref>
== 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.<ref>{{cite journal |last1= Qiao |first1= Bo |last2= Liu |first2= Yun |last3= Lee |first3= Semin |last4= Pink |first4= Maren |last5= Flood |first5= Amar H. |s2cid= 37747341 |title= High-yield Synthesis and Acid–Base Response of Phosphate-Templated [3]Rotaxanes |journal= Chem. Commun. |volume= 52 |issue= 94 |year= 2016 |pages= 13675–13678 |doi= 10.1039/C6CC08113D |pmid= 27812564 }}</ref>
== References == {{reflist}}
Category:Macrocycles