polyene
{{Short description|1=Organic compound with ≥3 C=C bonds}}
{{about|the class of chemical compounds|polyenes in antifungal therapy|Polyene antimycotic|the ancient Macedonian writer|Polyaenus}}
In organic chemistry, polyenes are polyunsaturated organic compounds that contain multiple carbon–carbon double bonds ({{chem2|C\dC}}).{{cite book |editor-last1=Sharp |editor-first1=DWA |title=The Penguin Dictionary of Chemistry |date=1990 |publisher=Penguin Books |location=London, England ; New York, N.Y., USA |isbn=9780140512328 |edition=2nd |page=320 |url=https://archive.org/details/penguindictionar00shar/page/320/mode/2up?q=polyenes}}{{cite book |title=Oxford Dictionary of English |date=2005 |publisher=Oxford University Press |location=Oxford ; New York |isbn=9780198610571 |edition=2nd, rev |page=1364 |url=https://archive.org/details/oxforddictionary0000unse_z0z2/page/1364/mode/1up?q=polyene}} Some sources consider dienes to be polyenes,{{cite book |title=Oxford Dictionary of Biochemistry and Molecular Biology |date=1997 |publisher=Oxford University Press |location=Oxford |isbn=9780198506737 |edition=1st, rev |page=520 |url=https://archive.org/details/isbn_9780198506737/page/n530/mode/1up?q=polyene}} whereas others require polyenes to contain at least three carbon–carbon double bonds.{{cite book |last1=Benet‐Buchholz |first1=Jordi |last2=Boese |first2=Roland |last3=Haumann |first3=Thomas |last4=Traetteberg |first4=Marit |title=The Chemistry of Dienes and Polyenes |chapter=Structural Chemistry of Dienes and Polyenes |date=15 March 1997 |pages=25–65 |doi=10.1002/0470857218.ch2}}
Conjugated polyenes contain a conjugated system of alternating single and double carbon–carbon bonds, with characteristic optical properties.
The following polyenes are used as antimycotics for humans: amphotericin B, nystatin, candicidin, pimaricin, methyl partricin, and trichomycin.{{cite journal|title=Polyene macrolide antibiotics and their applications in human therapy |author=Zotchev, Sergey B.|journal=Current Medicinal Chemistry|year=2003|volume=10|issue=3 |pages=211–223|doi=10.2174/0929867033368448|pmid=12570708 }}
Optical properties
Some polyenes are brightly colored, an otherwise rare property for a hydrocarbon. Normally alkenes absorb in the ultraviolet region of a spectrum, but the absorption energy state of polyenes with numerous conjugated double bonds can be lowered such that they enter the visible region of the spectrum, resulting in compounds which are coloured (because they contain a chromophore). Thus many natural dyes contain linear polyenes.
Chemical and electrical properties
Polyenes tend to be more reactive than simpler alkenes. For example, polyene-containing triglycerides are reactive towards atmospheric oxygen. Polyacetylene, which partially oxidized or reduced, exhibits high electrical conductivity. Most conductive polymers are polyenes, and many have conjugated structures. Poly(aza)acetylenes are readily prepared from pyridine precursors without the necessity of a controlled atmosphere, simply by ultraviolet irradiation of a mixture of pyridine and poly(4-vinyl) pyridine.{{citation needed|date=February 2024}} Recent research at the Weizmann Institute and Aix-Marseille University showed a clear transition between ionic and electronic conductivity with increasing UV dose over 30 hours.{{Cite journal |last1=Vaganova |first1=Evgenia |last2=Eliaz |first2=Dror |last3=Shimanovich |first3=Ulyana |last4=Leitus |first4=Gregory |last5=Aqad |first5=Emad |last6=Lokshin |first6=Vladimir |last7=Khodorkovsky |first7=Vladimir |date=January 2021 |title=Light-Induced Reactions within Poly(4-vinyl pyridine)/Pyridine Gels: The 1,6-Polyazaacetylene Oligomers Formation |journal=Molecules |language=en |volume=26 |issue=22 |pages=6925 |doi=10.3390/molecules26226925 |pmid=34834017 |pmc=8621047 |issn=1420-3049|doi-access=free }}
Occurrence
A few fatty acids are polyenes. Another class of important polyenes are polyene antimycotics.{{cite web |url=https://www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=mmed&part=A4050 |title=Polyene Antifungal Drugs |last=NCBI Bookshelf |date=1996 |publisher=The University of Texas Medical Branch at Galveston |access-date=29 January 2010}}
File:Amphotericin B new.svg|Amphotericin B is an example of a polyene antifungal (antimycotic) agent.Torrado, J. J.; Espada, R.; Ballesteros, M. P.; Torrado-Santiago, S. "Amphotericin B formulations and drug targeting", Journal of Pharmaceutical Sciences, 2008, volume 97, pp. 2405–2425. {{doi|10.1002/jps.21179}}.
File:Leukotriene A4.svg|Leukotriene A4 is a regulator of the immune response.
File:Trans-Polyacetylene.svg|Polyacetylenes are a synthetic polymer of theoretical interest because they exhibit metallic properties upon oxidation.Lam, Jacky W. Y.; Tang, Ben Zhong. "Functional Polyacetylenes", Accounts of Chemical Research, 2005, volume 38, pp. 745–754. {{doi|10.1021/ar040012f}}.