View source for Oligomer

{{Short description|Molecule composed of copies of a small unit}}
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[[File:15-crown-5 and monomer 3D balls.png|thumb|right|The [[15-crown-5]] [[crown ether]], a cyclic oligomer, and its monomer, [[ethylene oxide]].]]
In [[chemistry]] and [[biochemistry]], an '''oligomer''' ({{IPAc-en|audio=En-us-Oligomer.oga|ə|ˈ|l|ɪ|g|ə|m|ər}}) is a [[molecule]] that consists of a few [[repeating unit]]s which could be derived, actually or conceptually, from smaller molecules, [[monomer|monomers]].<ref name=webster>{{cite web|title=Oligomer|url=http://www.merriam-webster.com/dictionary/oligomer|publisher=[[Merriam-Webster]]|access-date=25 October 2014}}</ref><ref name=Goldbook-Oligomer>{{GoldBookRef |title=oligomer molecule |file=O04286 }}</ref><ref name=IUPAC1966>{{cite journal|title=Glossary of basic terms in polymer science (IUPAC Recommendations 1996)|journal=[[Pure and Applied Chemistry]]|year=1996|volume=68|issue=12|pages=2287–2311|doi=10.1351/pac199668122287|last1=Jenkins|first1=A. D.|last2=Kratochvíl|first2=P.|last3=Stepto|first3=R. F. T.|last4=Suter|first4=U. W.|doi-access=free}}Quote: ''Oligomer molecule: A molecule of intermediate relative molecular mass, the structure of which essentially comprises a small plurality of units derived, actually or conceptually, from molecules of lower relative molecular mass.''</ref>  The name is composed of [[Greek language|Greek]] elements ''[[wikt:oligo-|oligo-]]'', "a few" and ''[[wikt:-mer|-mer]]'', "parts".  An [[adjective]] form is ''oligomeric''.<ref name=IUPAC1966/>  

The oligomer concept is contrasted to that of a [[polymer]], which is usually understood to have a large number of units, possibly thousands or millions. However, there is no sharp distinction between these two concepts. One proposed criterion is whether the molecule's properties vary significantly with the removal of one or a few of the units.<ref name=IUPAC1966/> 

An oligomer with a specific number of units is referred to by the Greek prefix denoting that number, with the ending ''-mer'': thus [[dimer (chemistry)|dimer]], [[trimer (chemistry)|trimer]], [[tetramer]], [[pentamer]], and [[hexamer]] refer to molecules with two, three, four, five, and six units, respectively. The units of an oligomer may be arranged in a linear chain (as in [[Melam (chemistry)|melam]], a dimer of [[melamine]]); a closed ring (as in [[1,3,5-trioxane]], a [[Cyclic compound|cyclic]] trimer of [[formaldehyde]]); or a more complex structure (as in [[tellurium tetrabromide]], a tetramer of {{chem2|TeBr4}} with a [[cube]]-like core). If the units are identical, one has a ''homo-oligomer'';  otherwise one may use ''hetero-oligomer''. An example of a homo-oligomeric protein is [[collagen]], which is composed of three identical protein chains. 

[[File:Tetrapeptide structural formulae v.1.png|thumb|right|A [[tetrapeptide]], a hetero-oligomer of the amino acids [[valine]] (green), [[glycine]] (black), [[serine]] (black), and [[alanine]] (blue). The units were joined by condensation of the [[carboxylic acid]] group –C(=O)OH of one monomer with the [[amine group]] {{chem2|H2N\s}} of the next one.]]
Some biologically important oligomers are macromolecules like [[protein]]s or [[nucleic acids]]; for instance, [[hemoglobin]] is a protein tetramer. An oligomer of [[amino acid]]s is called an oligopeptide or just a [[peptide]]. An [[oligosaccharide]] is an oligomer of [[monosaccharide]]s (simple sugars). An [[oligonucleotide]] is a short single-stranded fragment of [[nucleic acid]] such as [[deoxyribonucleic acid|DNA]] or [[ribonucleic acid|RNA]], or similar fragments of analogs of nucleic acids such as [[peptide nucleic acid]] or [[Morpholino]]s.

[[File:Mpyv vp1 pentamer vp2 1sie 1cn3.png|thumb|right|A pentamer unit of the major capsid protein VP1. Each monomer is in a different color.]]
The units of an oligomer may be connected by [[covalent bond]]s, which may result from bond rearrangement or [[condensation reaction]]s, or by weaker forces such as [[hydrogen bond]]s.
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The term '''multimer''' ({{IPAc-en|ˈ|m|ʌ|l|t|ᵻ|m|ər}}) is used in biochemistry for oligomers of proteins that are not covalently bound. The [[major capsid protein VP1]] that comprises the shell of [[polyomavirus|polyomaviruses]] is a self-assembling multimer of 72 pentamers held together by local electric charges.

Many [[oil]]s are oligomeric, such as [[Liquid paraffin (medicinal)|liquid paraffin]]. [[Plasticizers]] are oligomeric [[ester]]s widely used to soften [[thermoplastics]] such as [[polyvinyl chloride|PVC]]. They may be made from monomers by linking them together, or by separation from the higher fractions of [[crude oil]]. [[Polybutene]] is an oligomeric oil used to make [[putty]]. 

'''Oligomerization''' is a chemical process that converts monomers to macromolecular complexes through a finite [[degree of polymerization]].<ref name=IUPAC1966/> [[Telomerization]] is an oligomerization carried out under conditions that result in [[chain transfer]], limiting the size of the oligomers.<ref name=Goldbook-Telomerization>{{GoldBookRef |title=telomerization |file=T06260 }}</ref><ref name=IUPAC1966 /> (This concept is not to be confused with the formation of a [[telomere]], a region of highly repetitive DNA at the end of a [[chromosome]].)

==Green oil==
In the oil and gas industry, green oil refers to oligomers formed in all C2, C3, and C4 hydrogenation reactors of ethylene plants and other petrochemical production facilities; it is a mixture of C4 to C20 unsaturated and reactive components with about 90% [[aliphatic]] [[diene|dienes]] and 10% of [[alkanes]] plus [[alkenes]].<ref>{{cite web|url=http://www.pall.com/main/fuels-and-chemicals/green-oil-contaminant-separation-37657.page|title=Chemicals & Polymers|website=www.pall.com}}</ref> Different heterogeneous and homogeneous catalysts are operative in producing green oils via the oligomerization of alkenes.<ref>{{cite journal|last1=Ghashghaee|first1=Mohammad|title=Heterogeneous catalysts for gas-phase conversion of ethylene to higher olefins|journal=Rev. Chem. Eng.|volume=34|issue=5|pages=595–655|doi=10.1515/revce-2017-0003|url=https://www.degruyter.com/view/j/revce.ahead-of-print/revce-2017-0003/revce-2017-0003.xml|year=2018|s2cid=103664623 |url-access=subscription}}</ref>

==See also==
* [[GPCR oligomer]]
* [[Merosity|Oligomery (botany)]]
* [[Protein oligomer]]

==References==
{{Reflist}}

==External links==
*{{Commonscatinline}}

[[Category:Polymer chemistry]]
[[Category:Oligomers| ]]