Pi-interaction

The most common types of π-interactions involve:

• Metal–π interactions: involves interaction of a metal and the face of a π system, the metal can be a cation (known as cation–π interactions) or neutral
• Polar–π interactions: involves interaction of a polar molecule and quadrupole moment a π system.

File:Polar-pi.svg

• Aromatic–aromatic interactions (π stacking): involves interactions of aromatic molecules with each other.
• Arene–perfluoroarene interaction: electron-rich benzene ring interacts with electron-poor hexafluorobenzene.

File:Areneperfluoroarene.svg

• π donor–acceptor interactions: interaction between low energy empty orbital (acceptor) and a high-energy filled orbital (donor).

File:Donoracceptor.svg

• Anion–π interactions: interaction of anion with π system
• Cation–π interactions: interaction of a cation with a π system
• C–H–π interactions: interaction of C-H with π system: These interactions are well studied using experimental as well as computational techniques.{{cite journal | title = H-π Complexes of acetylene-ethylene: A matrix isolation and computational study |author1=K. Sundararajan |author2=K. Sankaran |author3=K.S. Viswanathan |author4=A.D. Kulkarni |author5=S.R. Gadre | journal = J. Phys. Chem. A | volume = 106 |issue=8 | pages = 1504 | year = 2002 | doi = 10.1021/jp012457g |bibcode=2002JPCA..106.1504S }}{{cite journal | title = H-π Complexes of acetylene-benzene: A matrix isolation and computational study |author1=K. Sundararajan |author2=K.S. Viswanathan |author3=A.D. Kulkarni |author4=S.R. Gadre | journal = J. Mol. Str. (Theochem) | volume = 613 | pages = 209–222 | year = 2002 |issue=1–3 | doi = 10.1016/S0022-2860(02)00180-1 |bibcode = 2002JMoSt.613..209S }}

{{cite journal | title = Simultane Verkapselung: Moleküle unter sich | author = J. Rebek | journal = Angewandte Chemie | volume = 117 | issue = 14 | pages = 2104–2115 | year = 2005 | doi = 10.1002/ange.200462839 | bibcode = 2005AngCh.117.2104R }}

{{ cite journal | title = Simultaneous Encapsulation: Molecules Held at Close Range | author = J. Rebek | journal = Angewandte Chemie International Edition | volume = 44 | issue = 14 | pages = 2068–2078 | year = 2005 | doi = 10.1002/anie.200462839 | pmid = 15761888 | doi-access = free }}{{cite journal | title = Accurate description of van der Waals complexes by density functional theory including empirical corrections | author = S. Grimme | journal = Journal of Computational Chemistry | volume = 25 | issue = 12 | pages = 1463–73 | year = 2004 | doi = 10.1002/jcc.20078 | pmid=15224390| s2cid = 6968902 }}

Buckycatcher JACS 2007 V129 p3843.jpg|A fullerene bound in a buckycatcher through aromatic stacking interactions.{{cite journal | vauthors = Sygula A, Fronczek FR, Sygula R, Rabideau PW, Olmstead MM | title = A double concave hydrocarbon buckycatcher | journal = Journal of the American Chemical Society | volume = 129 | issue = 13 | pages = 3842–3843 | date = April 2007 | pmid = 17348661 | doi = 10.1021/ja070616p | bibcode = 2007JAChS.129.3842S | s2cid = 25154754 }}

File:24 fig. 2.png|The Stoddart synthesis of [2] catenane...

File:QUATERNARY LIGAND BINDING TO AROMATIC RESIDUES IN THE ACTIVE-SITE GORGE OF ACETYLCHOLINESTERASE.png|Tacrine bound to acetylcholinesterase (PDB 1ACJ). A pi stacking interaction between tacrine (blue) and Trp84 (red) is proposed

Polar-pi.svg|Polar π interaction between water molecule and benzene

Areneperfluoroarene.svg|Arene perfluoroarene stacking

SegStackEdgeOnHMTFCQ.jpg|Edge-on view of portion of crystal structure of hexamethyleneTTF/TCNQ charge transfer salt, highlighting the segregated stacking.{{cite journal|author1=D. Chasseau|author2=G. Comberton|author3=J. Gaultier|author4=C. Hauw|journal=Acta Crystallographica Section B|title=Réexamen de la structure du complexe hexaméthylène-tétrathiafulvalène-tétracyanoquinodiméthane|year=1978| volume=34|issue=2|page=689|doi=10.1107/S0567740878003830|doi-access=|bibcode=1978AcCrB..34..689C }}

File:Graphite-layers-side-3D-balls.png

Graphite consists of stacked sheets of covalently bonded carbon.{{cite book |last1=Delhaes |first1=Pierre |chapter=Polymorphism of carbon |editor-last1=Delhaes |editor-first1=Pierre |title=Graphite and precursors |date=2000 |publisher=Gordon & Breach |isbn=9789056992286|pages=1–24}}{{cite book |last1=Pierson |first1=Hugh O. |title=Handbook of carbon, graphite, diamond, and fullerenes : properties, processing, and applications |date=2012 |publisher=Noyes Publications |isbn=9780815517399 |pages=40–41}} The individual layers are called graphene. In each layer, each carbon atom is bonded to three other atoms forming a continuous layer of sp² bonded carbon hexagons, like a honeycomb lattice with a bond length of 0.142 nm, and the distance between planes is 0.335 nm.{{cite book |title= Graphite and Precursors |author= Delhaes, P. |publisher= CRC Press |year= 2001 |url= https://books.google.com/books?id=7p2pgNOWPbEC&pg=PA146 |isbn= 978-90-5699-228-6}}

Cation-π interactions are important for the acetylcholine (Ach) neurotransmitter.{{cite journal|last1=Dougherty|first1=D. A.|title=Cation-pi Interactions in Chemistry and Biology: A New View of Benzene, Phe, Tyr, and Trp|journal=Science|volume=271|issue=5246|pages=163–8|year=1996|pmid=8539615|doi=10.1126/science.271.5246.163|bibcode = 1996Sci...271..163D |s2cid=9436105}}{{cite journal|last1=Kumpf|first1=R.|last2=Dougherty|first2=D.|title=A mechanism for ion selectivity in potassium channels: computational studies of cation-pi interactions|journal=Science|volume=261|issue=5129|pages=1708–10|year=1993|pmid=8378771|doi=10.1126/science.8378771|bibcode = 1993Sci...261.1708K }} The structure of acetylcholine esterase includes 14 highly conserved aromatic residues. The trimethyl ammonium group of Ach binds to the aromatic residue of tryptophan (Trp). The indole site provides a much more intense region of negative electrostatic potential than benzene and phenol residue of Phe and Tyr.

Pi–pi and cation–pi interactions are important in rational drug design.{{cite journal | vauthors = Babine RE, Bender SL | title = Molecular Recognition of Proteinminus signLigand Complexes: Applications to Drug Design | journal = Chemical Reviews | volume = 97 | issue = 5 | pages = 1359–1472 | date = August 1997 | pmid = 11851455 | doi = 10.1021/cr960370z }} One example is the FDA-approved acetylcholinesterase (AChE) inhibitor tacrine which is used in the treatment of Alzheimer's disease. Tacrine is proposed to have a pi stacking interaction with the indolic ring of Trp84, and this interaction has been exploited in the rational design of novel AChE inhibitors.{{cite journal | vauthors = da Silva CH, Campo VL, Carvalho I, Taft CA | title = Molecular modeling, docking and ADMET studies applied to the design of a novel hybrid for treatment of Alzheimer's disease | journal = Journal of Molecular Graphics & Modelling | volume = 25 | issue = 2 | pages = 169–175 | date = October 2006 | pmid = 16413803 | doi = 10.1016/j.jmgm.2005.12.002 }}

File:24 fig. 1.png

\pi - \pi , CH-\pi and \pi -cation interactions are widely observed motifs in supramolecular assembly and recognition.

\pi-\pi concerns the direct interactions between two {{pi}}-systems; and cation-\pi interaction arises from the electrostatic interaction of a cation with the face of the {{pi}}-system. Unlike these two interactions, the CH-\pi interaction arises mainly from charge transfer between the C–H orbital and the {{pi}}-system.

π systems contribute to supramolecular assembly. Some catenanes feature π–π interactions. The major challenge for the synthesis of catenane is to interlock molecules in a controlled fashion. Stoddart and co-workers developed a series of systems utilizing the strong π–π interactions between electron-rich benzene derivatives and electron-poor pyridinium rings.{{cite journal | vauthors = Ashton PR, Goodnow TT, Kaifer AE, Reddington MV, Slawin AM, Spencer N, Stoddart JF, Vicent C, Williams DJ |display-authors=6 |title=A [2] Catenane Made to Order |journal=J. Angew. Chem. Int. Ed. |year=1989 |volume=28 |issue=10 |pages=1396–1399 |doi=10.1002/anie.198913961 }} [2]Catanene was synthesized by reacting bis(pyridinium) (A), bisparaphenylene-34-crown-10 (B), and 1, 4-bis(bromomethyl)benzene (C) (Fig. 2). The π–π interaction between A and B directed the formation of an interlocked template intermediate that was further cyclized by substitution reaction with compound C to generate the [2]catenane product.

{{Anchor|TTF-TCNQ}}

A combination of tetracyanoquinodimethane (TCNQ) and tetrathiafulvalene (TTF) forms a strong charge-transfer complex referred to as TTF-TCNQ.{{cite journal |author1=P. W. Anderson |author2=P. A. Lee |author3=M. Saitoh | journal = Solid State Communications | volume = 13 | year = 1973 | pages = 595–598 | doi = 10.1016/S0038-1098(73)80020-1 | title = Remarks on giant conductivity in TTF-TCNQ |issue=5 | bibcode=1973SSCom..13..595A}} The solid shows almost metallic electrical conductance. In a TTF-TCNQ crystal, TTF and TCNQ molecules are arranged independently in separate parallel-aligned stacks, and an electron transfer occurs from donor (TTF) to acceptor (TCNQ) stacks.{{cite journal |doi=10.1021/acs.jchemed.5b00340|title=Opposites Attract: Organic Charge Transfer Salts |year=2015 |last1=Van De Wouw |first1=Heidi L. |last2=Chamorro |first2=Juan |last3=Quintero |first3=Michael |last4=Klausen |first4=Rebekka S. |journal=Journal of Chemical Education |volume=92 |issue=12 |pages=2134–2139 |bibcode=2015JChEd..92.2134V }}

Anion and π–aromatic systems (typically electron-deficient) create an interaction that is associated with the repulsive forces of the structures. These repulsive forces involve electrostatic and anion-induced polarized interactions.{{cite journal|last1=Schottel|first1=Brandi L.|last2=Chifotides|first2=Helen T.|last3=Dunbar|first3=Kim R.|title=Anion-π interactions|journal=Chemical Society Reviews|volume=37|issue=1|pages=68–83|year=2008|pmid=18197334|doi=10.1039/b614208g}}Ballester P. "Anions and pi–Aromatic Systems. Do they interact

attractively?" Recognition of Anions. Structure and Bonding Series, 129 (2008) 127-174 Berlin. Springer Verlag This force allows for the systems to be used as receptors and channels in supramolecular chemistry for applications in the medical (synthetic membranes, ion channels) and environmental fields (e.g. sensing, removal of ions from water).{{cite journal|last1=Gamez|first1=Patrick|last2=Mooibroek|first2=Tiddo J.|last3=Teat|first3=Simon J.|last4=Reedijk|first4=Jan|title=Anion Binding Involving π-Acidic Heteroaromatic Rings|journal=Accounts of Chemical Research|volume=40|issue=6|pages=435–44|year=2007|pmid=17439191|doi=10.1021/ar7000099}}

The first X-ray crystal structure that depicted anion–π interactions was reported in 2004.{{cite journal|last1=Demeshko|first1=Serhiy|last2=Dechert|first2=Sebastian|last3=Meyer|first3=Franc|title=Anion−π Interactions in a Carousel Copper(II)−Triazine Complex|journal=Journal of the American Chemical Society|volume=126|issue=14|pages=4508–9|year=2004|pmid=15070355|doi=10.1021/ja049458h|bibcode=2004JAChS.126.4508D }} In addition to this being depicted in the solid state, there is also evidence that the interaction is present in solution.{{cite journal|last1=Maeda|first1=Hiromitsu|authorlink2=Atsuhiro Osuka|last2=Osuka|first2=Atsuhiro|last3=Furuta|first3=Hiroyuki|title=Anion Binding Properties of N-Confused Porphyrins at the Peripheral Nitrogen|journal=Journal of Inclusion Phenomena|volume=49|pages=33–36|year=2004|doi=10.1023/B:JIPH.0000031110.42096.d3|s2cid=95180509}}

π-effects have an important contribution to biological systems since they provide a significant amount of binding enthalpy. Neurotransmitters produce most of their biological effect by binding to the active site of a protein receptor. Xation-π interactions are important for the acetylcholine (Ach) neurotransmitter.{{cite journal|last1=Dougherty|first1=D. A.|title=Cation-pi Interactions in Chemistry and Biology: A New View of Benzene, Phe, Tyr, and Trp|journal=Science|volume=271|issue=5246|pages=163–8|year=1996|pmid=8539615|doi=10.1126/science.271.5246.163|bibcode = 1996Sci...271..163D |s2cid=9436105}}{{cite journal|last1=Kumpf|first1=R.|last2=Dougherty|first2=D.|title=A mechanism for ion selectivity in potassium channels: computational studies of cation-pi interactions|journal=Science|volume=261|issue=5129|pages=1708–10|year=1993|pmid=8378771|doi=10.1126/science.8378771|bibcode = 1993Sci...261.1708K }} The structure of acetylcholine esterase includes 14 highly conserved aromatic residues. The trimethyl ammonium group of Ach binds to the aromatic residue of tryptophan (Trp). The indole site provides a much more intense region of negative electrostatic potential than benzene and phenol residue of Phe and Tyr.

File:24 fig. 1.png

{{pi}} systems are important building blocks in supramolecular assembly because of their versatile noncovalent interactions with various functional groups. Particularly, \pi - \pi , CH-\pi and \pi -cation interactions are widely used in supramolecular assembly and recognition.

\pi-\pi concerns the direct interactions between two {{pi}}-systems; and cation-\pi interaction arises from the electrostatic interaction of a cation with the face of the {{pi}}-system. Unlike these two interactions, the CH-\pi interaction arises mainly from charge transfer between the C–H orbital and the {{pi}}-system.

• Noncovalent interaction
• Dispersion (chemistry)
• Cation–pi interaction
• Intercalation (biochemistry)
• Intercalation (chemistry)

• {{cite journal | vauthors = Luo R, Gilson HS, Potter MJ, Gilson MK | title = The physical basis of nucleic acid base stacking in water | journal = Biophysical Journal | volume = 80 | issue = 1 | pages = 140–148 | date = January 2001 | pmid = 11159389 | pmc = 1301220 | doi = 10.1016/S0006-3495(01)76001-8 | bibcode = 2001BpJ....80..140L }}
• [http://www.scs.illinois.edu/denmark/wp-content/uploads/gp/2011/gm-2011-1_18.pdf Larry Wolf (2011): π-π (π-Stacking) interactions: origin and modulation]

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Category:Intermolecular forces

Category:Organic chemistry

Category:Chemical bonding

Category:Supramolecular chemistry