View source for Catenane

{{short description|Molecule composed of two or more intertwined rings}}
[[File:Catenane Crystal Structure ChemComm page634 1991 commons.png|thumbnail|230px|Crystal structure of a catenane with a [[cyclobis(paraquat-p-phenylene)|cyclobis(paraquat-''p''-phenylene)]] [[macrocycle]] reported by [[James Fraser Stoddart|Stoddart]] and coworkers.<ref>{{cite journal |last1=Ashton |first1=Peter R. |last2=Brown |first2=Christopher L. |last3=Chrystal |first3=Ewan J. T. |last4=Goodnow |first4=Timothy T. |last5=Kaifer |first5=Angel E. |last6=Parry |first6=Keith P. |last7=Philp |first7=Douglas |last8=Slawin |first8=Alexandra M. Z. |author-link8=Alexandra Slawin |last9=Spencer |first9=Neil |last10=Stoddart |first10=J. Fraser |last11=Williams |first11=David J. |date=1991 |title=The self-assembly of a highly ordered [2]catenane |journal=Journal of the Chemical Society, Chemical Communications |issue=9 |pages=634 |doi=10.1039/C39910000634}}</ref> ]]

[[Image:Cat.ogg|thumbnail|230px|Schematic animation of the template-directed synthesis of the bis-bipyridinium cyclophane / ''para''-phenylene crown ether [2]catenane described in the text.]]

[[Image:Catenane ChemComm 244 1985.png|thumbnail|230px|Crystal structure of a catenane reported by [[Jean Pierre Sauvage|Sauvage]] and coworkers.<ref>{{cite journal|last1=Cesario|first1=M.|last2=Dietrich-Buchecker|first2=C. O.|last3=Guilhem|first3=J.|last4=Pascard|first4=C.|last5=Sauvage|first5=J. P.|title=Molecular structure of a catenand and its copper(I) catenate: complete rearrangement of the interlocked macrocyclic ligands by complexation|journal=Journal of the Chemical Society, Chemical Communications|date=1985|issue=5|pages=244|doi=10.1039/C39850000244}}</ref> ]]

In [[macromolecular chemistry]], a '''catenane''' ({{ety|la|catena|chain}}) is a [[mechanically interlocked molecular architectures|mechanically interlocked molecular architecture]] consisting of two or more interlocked [[macrocycle]]s, i.e. a molecule containing two or more intertwined [[Ring (chemistry)|rings]]. The interlocked rings cannot be separated without breaking the [[covalent bond]]s of the macrocycles. They are conceptually related to other mechanically interlocked molecular architectures, such as [[rotaxane]]s, [[molecular knots]] or [[molecular Borromean rings]]. Recently the terminology "[[mechanical bond]]" has been coined that describes the connection between the macrocycles of a catenane. Catenanes have been [[Chemical synthesis|synthesised]] in two  different ways: statistical synthesis and template-directed synthesis.

== Synthesis ==
There are two primary approaches to the [[organic synthesis]] of catenanes. The first is to simply perform a [[ring-closing reaction]] with the hope that some of the rings will form around other rings giving the desired catenane product. This so-called "statistical approach" led to the first synthesis of a catenane; however, the method is highly inefficient, requiring high dilution of the "closing" ring and a large excess of the pre-formed ring, and is rarely used.

The second approach relies on [[supramolecular chemistry|supramolecular]] preorganization of the macrocyclic precursors utilizing [[hydrogen bond]]ing, metal coordination, [[hydrophobic effect]], or [[Coulomb force|coulombic interactions]].  These non-covalent interactions offset some of the [[entropy|entropic]] cost of association and help position the components to form the desired catenane upon the final ring-closing. This "template-directed" approach, together with the use of high-pressure conditions, can provide yields of over 90%, thus improving the potential of catenanes for applications. An example of this approach used bis-bi[[pyridinium]] salts which form strong complexes threaded through crown ether bis(''para''-phenylene)-34-crown-10.<ref>{{Cite journal |last1=Ashton |first1=Peter R. |last2=Goodnow |first2=Timothy T. |last3=Kaifer |first3=Angel E. |last4=Reddington |first4=Mark V. |last5=Slawin |first5=Alexandra M. Z. |author-link5=Alexandra Slawin |last6=Spencer |first6=Neil |last7=Fraser Stoddart |first7=J. |last8=Vicent |first8=Cristina |last9=Williams |first9=David J. |date=1989-10-01 |title=Ein [2]-Catenan auf Bestellung |journal=Angewandte Chemie |language=en |volume=101 |issue=10 |pages=1404–1408 |bibcode=1989AngCh.101.1404A |doi=10.1002/ange.19891011023 |issn=1521-3757}}</ref>

Template directed syntheses are mostly performed under [[Thermodynamic versus kinetic reaction control|kinetic control]], when the macrocyclization (catenation) reaction is irreversible. More recently, the groups of [[Jeremy Sanders|Sanders]] and [[Sijbren Otto|Otto]] have shown that [[Dynamic combinatorial chemistry|dynamic combinatorial]] approaches using [[Dynamic covalent chemistry|reversible chemistry]] can be particularly successful in preparing new catenanes of unpredictable structure.<ref>{{cite journal |author1=T. S. R. Lam |author2=A. Belenguer |author3=S. L. Roberts |author4=C. Naumann |author5=T. Jarrosson |author6=S. Otto |author7=J. K. M. Sanders | title = Amplification of acetylcholine-binding catenanes from dynamic combinatorial libraries  | journal = Science | volume = 308 |issue=5722 | pages = 667–669 | doi = 10.1126/science.1109999 | pmid=15761119 | date=April 2005|bibcode=2005Sci...308..667L |s2cid=30506228 }}</ref> The thermodynamically controlled synthesis provides an error correction mechanism; even if a macrocycle closes without forming a catenane it can re-open and yield the desired interlocked structure later. The approach also provides information on the affinity constants between different macrocycles thanks to the equilibrium between the individual components and the catenanes, allowing a titration-like experiment.<ref>{{cite journal |author1=Li, J. |author2=Nowak, P. |author3=Fanlo-Virgos, H. |author4=Otto, S. | title = Catenanes from Catenanes: Quantitative Assessment of Cooperativity in Dynamic Combinatorial Catenation | journal = Chem. Sci. | volume = 5 |issue=12 | pages = 4968–4974 | doi = 10.1039/C4SC01998A |year=2014 |url=https://www.rug.nl/research/portal/en/publications/catenanes-from-catenanes(97ed22a2-ef35-42f8-bbef-34f2f32e2cb3).html |hdl=11370/97ed22a2-ef35-42f8-bbef-34f2f32e2cb3 |hdl-access=free }}</ref>

== Properties ==
The interlocked rings rotate with respect to one another. This motion can often be evaluated by [[NMR spectroscopy]], among other methods. When molecular recognition motifs exist in the finished catenane (usually those that were used to synthesize the catenane), the catenane can have one or more [[thermodynamics|thermodynamically]] preferred positions of the rings with respect to each other (recognition sites). In the case where one recognition site is a switchable moiety, a mechanical [[molecular switch]] results. When a catenane is synthesized by coordination of the macrocycles around a metal ion, then removal and re-insertion of the metal ion can switch the free motion of the rings on and off.

If there are more than one recognition sites, it is possible to observe distinct colors depending on the recognition site the ring occupies and thus it is possible to change the color of the catenane solution by changing the preferred recognition site.<ref>{{Cite journal|last1=Sun|first1=Junling|last2=Wu|first2=Yilei|last3=Liu|first3=Zhichang|last4=Cao|first4=Dennis|last5=Wang|first5=Yuping|last6=Cheng|first6=Chuyang|last7=Chen|first7=Dongyang|last8=Wasielewski|first8=Michael R.|last9=Stoddart|first9=J. Fraser|date=2015-06-18|title=Visible Light-Driven Artificial Molecular Switch Actuated by Radical–Radical and Donor–Acceptor Interactions|journal=The Journal of Physical Chemistry A|volume=119|issue=24|pages=6317–6325|doi=10.1021/acs.jpca.5b04570|pmid=25984816|issn=1089-5639|bibcode=2015JPCA..119.6317S}}</ref> Switching between the two sites may be achieved by the use of chemical, electrochemical or even visible light based methods.

Catenanes have been synthesized with many functional units, including redox-active groups (e.g. [[viologen]], TTF=[[tetrathiafulvalene]]), photoisomerizable groups (e.g. [[azobenzene]]), [[fluorescent]] groups and [[Chirality (chemistry)|chiral]] groups.<ref>{{cite journal |last1=Jamieson |first1=E. M. G. |last2=Modicom |first2=F. |last3=Goldup |first3=S. M. |title=Chirality in rotaxanes and catenanes |journal=Chemical Society Reviews |volume=47 |issue=14 |pages=5266–5311 |date=2018 |doi=10.1039/C8CS00097B|pmid=29796501 |pmc=6049620 }}{{open access}}</ref> Some such units have been used to create molecular switches as described above, as well as for the fabrication of [[molecular electronics|molecular electronic]] devices and [[molecular sensor]]s.

==Families==
[[File:KEBKUXcolorcoded.png|thumb|Catenane derived from cyclobis(paraquat-p-phenylene)(a cyclophane with two viologen units) and a cyclic polyether (bis(para-phenylene-34-crown-10)).  Carbon atoms of the two rotaxane components are colored green and purple. Otherwise, O = red, N = blue. H atoms are omitted.<ref>{{cite journal|author1=Ashton, P. R. |author2=Goodnow, T. T. |author3=Kaifer, A. E. |author4=Reddington, M. V. |author5=Slawin, A. M. Z. |author6=Spencer, N. |author7=Stoddart, J. F. |author8=Vicent, C. |author9=Williams, D. J. |title=A [2] Catenane Made to Order|journal=Angewandte Chemie International Edition in English|year=1989|volume=28|issue=10|pages=1396–1399|doi=10.1002/anie.198913961}}</ref>  The second of Nobel Prizes in Chemistry involving crown ethers was awarded for the design and synthesis of [[molecular machine]]s. Many of these "machines" incorporate crown ethers as essential design components.]]
There are a number of distinct methods of holding the precursors together prior to the ultimate ring-closing reaction in a template-directed catenane synthesis.  Each [[noncovalent]] approach to catenane formation results in what can be considered different families of catenanes.

Another family of catenanes are called '''pretzelanes''' or '''bridged [2]catenanes''' after their likeness to [[pretzel]]s with a [[molecular spacer group|spacer]] linking the two macrocycles. In one such system<ref>{{cite journal|last1=Liu|first1=Y.|last2=Vignon|first2=S. A.|last3=Zhang|first3=X.|last4=Bonvallet|first4=P. A.|last5=Khan|first5=S. I.|last6=Houk|first6=K. N.|last7=Stoddart|first7=J. F.|title=Dynamic Chirality in Donor−Acceptor Pretzelanes|journal=The Journal of Organic Chemistry|date=November 2005|volume=70|issue=23|pages=9334–9344|doi=10.1021/jo051430g|pmid=16268606}}</ref> one macrocycle is an electron deficient oligo Bis-bi[[pyridinium]] ring and the other cycle is [[crown ether]] [[cyclophane]] based on [[Poly(p-phenylene)|para phenylene]] or [[naphthalene]]. [[X-ray diffraction]] shows that due to [[pi-pi interaction]]s the aromatic group of the cyclophane is held firmly inside the pyridinium ring. A limited number of (rapidly interchanging) conformers exist for this type of compound.

In handcuff-shaped catenanes,<ref>{{cite journal|last1=Frey|first1=Julien|last2=Kraus|first2=Tomáš|last3=Heitz|first3=Valérie|last4=Sauvage|first4=Jean-Pierre|title=A catenane consisting of a large ring threaded through both cyclic units of a handcuff-like compound|journal=Chemical Communications|date=2005|issue=42|pages=5310–2|doi=10.1039/B509745B|pmid=16244738}}</ref> two connected rings are threaded through the same ring. The bis-macrocycle (red) contains two [[phenanthroline]] units in a [[crown ether]] chain. The interlocking ring is [[molecular self-assembly|self-assembled]] when two more phenanthroline units with [[alkene]] arms coordinate through a [[copper]](I) complex followed by a [[olefin metathesis|metathesis]] ring closing step.

{|
|+'''Families of catenanes'''
|-
| valign="top"|
[[File:CatenaneScheme.svg|left|115px|thumb|Catenanes]]
| valign="top"|
[[File:Pretzelane.svg|right|115px|thumb|Pretzelanes]]
| valign="top"|
[[File:Handcuffcatenane.svg|right|frame|Handcuff-shaped catenanes]]
|}

== Nomenclature ==
In catenane nomenclature, a number in square brackets precedes the word "catenane" in order to indicate how many rings are involved.<ref>{{cite journal|last1=Safarowsky|first1=O.|last2=Windisch|first2=B.|last3=Mohry|first3=A.|last4=Vögtle|first4=F.|title=Nomenclature for Catenanes, Rotaxanes, Molecular Knots, and Assemblies Derived from These Structural Elements|journal=Journal für Praktische Chemie|date=June 2000|volume=342|issue=5|pages=437–444|doi=10.1002/1521-3897(200006)342:5<437::AID-PRAC437>3.0.CO;2-7|doi-access=free}}</ref> Discrete catenanes up to a [7]catenane have been synthesised.<ref>{{cite journal|last1=Black|first1=Samuel P.|last2=Stefankiewicz|first2=Artur R.|last3=Smulders|first3=Maarten M. J.|last4=Sattler|first4=Dominik|last5=Schalley|first5=Christoph A.|last6=Nitschke|first6=Jonathan R.|last7=Sanders|first7=Jeremy K. M.|title=Generation of a Dynamic System of Three-Dimensional Tetrahedral Polycatenanes|journal=Angewandte Chemie International Edition|date=27 May 2013|volume=52|issue=22|pages=5749–5752|doi=10.1002/anie.201209708|pmid=23606312|pmc=4736444}}</ref>

== See also ==
* [[Olympiadane]]
* [[Polycatenane]]

==References==
{{Reflist}}

==External links==
*{{Commons category-inline|Catenanes}}

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[[Category:Supramolecular chemistry]]
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[[Category:Organic semiconductors]]
[[Category:Molecular topology]]
[[Category:Macrocycles]]
[[Category:Cyclophanes]]