# Foldamer

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{{short description|Chain molecule which folds in predictable ways while in solution}}
thumbnail|250px|Crystal structure of a foldamer reported in <ref>{{cite journal | last1 = Lehn | first1 = Jean-Marie | authorlink = Jean-Marie Lehn |display-authors=etal | year = 2003 | title = Helicity-Encoded Molecular Strands: Efficient Access by the Hydrazone Route and Structural Features | doi = 10.1002/hlca.200390137 | journal = Helv. Chim. Acta | volume = 86 | issue = 5| pages = 1598–1624 }}</ref>.
thumb|Dynamic view of an alpha-beta foldamer

In [chemistry](/source/chemistry), a '''foldamer''' is a discrete chain molecule ([oligomer](/source/oligomer)) that [folds](/source/Folding_(chemistry)) into a [conformationally](/source/Conformational_isomerism) ordered state in [solution](/source/Solution_(chemistry)).  They are artificial molecules that mimic the ability of [protein](/source/protein)s, [nucleic acid](/source/nucleic_acid)s, and [polysaccharide](/source/polysaccharide)s to fold into well-defined conformations, such as [α-helices](/source/Alpha_helix) and [β-sheet](/source/Beta_sheet)s. The structure of a foldamer is stabilized by [noncovalent interactions](/source/noncovalent_interactions) between nonadjacent [monomers](/source/monomers).<ref name=Foldamer/><ref name=Moore>{{cite journal |last=Hill|first=D. J. |author2=Mio, M. J. |author3=Prince, R. B. |author4=Hughes, T. S. |author5=Moore, J. S. |title=A field guide to foldamers |journal=Chem. Rev. |volume=101 |issue=12 |pages=3893–4012 |year=2001 |pmid=11740924 |doi=10.1021/cr990120t}}</ref>  Foldamers are studied with the main goal of designing large molecules with predictable structures.  The study of foldamers is related to the themes of [molecular self-assembly](/source/molecular_self-assembly), [molecular recognition](/source/molecular_recognition), and [host–guest chemistry](/source/host%E2%80%93guest_chemistry).

==Design==
right|350px|Free energy diagram of the folding of a foldamer.

Foldamers can vary in size, but they are defined by the presence of noncovalent, nonadjacent interactions. This definition excludes molecules like poly(isocyanates) (commonly known as [polyurethane](/source/polyurethane)) and [poly(prolines)](/source/Polyproline_helix) as they fold into helices reliably due to ''adjacent'' covalent interactions.<ref>{{cite journal|last=Green|first=M. M. |author2=Park, J. |author3=Sato, T. |author4=Teramoto, A. |author5=Lifson, S. |author6=Selinger, R. L. B. |author7=Selinger, J. V.|title=The Macromolecular Route to Chiral Amplification|journal=Angew. Chem. Int. Ed.|year=1999|volume=38|issue=21 |pages=3138–3154|doi=10.1002/(SICI)1521-3773(19991102)38:21<3138::AID-ANIE3138>3.0.CO;2-C|pmid=10556885 }}</ref> Foldamers have a dynamic folding reaction (unfolded → folded), in which large macroscopic folding is caused by [solvophobic](/source/solvophobic) effects (hydrophobic collapse), while the final energy state of the folded foldamer is due to the noncovalent interactions. These interactions work cooperatively to form the most stable tertiary structure, as the completely folded and unfolded states are more stable than any partially folded state.<ref name=Manifesto>{{cite journal|last=Gellman|first=S.H.|title=Foldamers: A Manifesto|journal=Acc. Chem. Res.|year=1998|volume=31|issue=4|pages=173–180|doi=10.1021/ar960298r}}</ref>

===Prediction of folding===
The structure of a foldamer can often be predicted from its [primary sequence](/source/primary_sequence). This process involves dynamic simulations of the folding equilibria at the atomic level under various conditions. This type of analysis may be applied to small proteins as well; however, as of 2024, computational technology is unable to simulate all but the shortest of sequences.<ref name="Gunsteren Book">{{cite book|last=van Gunsteren|first=Wilfred F.|title=Foldamers: Structure, Properties, and Applications; Simulation of Folding Equilibria|year=2007|publisher=Wiley-VCH Verlag GmbH & Co. KGaA|pages=173–192| doi = 10.1002/9783527611478.ch6}}</ref>

The folding pathway of a foldamer can be determined by measuring the variation from the experimentally-determined favored structure under different thermodynamic and [kinetic](/source/chemical_kinetics) conditions. The change in structure is measured by calculating the [root mean square](/source/root_mean_square) deviation from the backbone atomic position of the favored structure. The structure of the foldamer under different conditions can be determined computationally and then verified experimentally. Changes in the temperature, solvent [viscosity](/source/viscosity), [pressure](/source/pressure), [pH](/source/pH), and salt concentration can all yield valuable information about the structure of the foldamer. Measuring the kinetics of folding as well as folding equilibria allow one to observe the effects of these different conditions on the foldamer structure.<ref name="Gunsteren Book"/>

Solvents often influence folding. For example, a folding pathway involving [hydrophobic collapse](/source/hydrophobic_collapse) would fold differently in a [nonpolar](/source/nonpolar) solvent. This difference is due to the fact that different solvents stabilize different intermediates of the folding pathway as well as different final foldamer structures based on [intermolecular](/source/intermolecular) noncovalent interactions.<ref name="Gunsteren Book"/>

===Noncovalent interactions===
Noncovalent [intermolecular](/source/Intermolecular_forces) interactions, albeit individually small, collectively alter chemical reactions in major ways. Listed below are common intermolecular forces that chemists have used to design foldamers.

* [Hydrogen bonding](/source/Hydrogen_bonding) (especially with [peptide bond](/source/peptide_bond)s)
* [Pi stacking](/source/Pi_stacking)
* [Solvophobic](/source/Solvophobic) effects, which lead to [hydrophobic collapse](/source/hydrophobic_collapse)
* [Van der Waals force](/source/Van_der_Waals_force)s
* [Electrostatic attraction](/source/Electrostatic_attraction)

==Common designs==
Foldamers are classified into three different categories: [peptidomimetic](/source/peptidomimetic) foldamers, nucleotidomimetic foldamers, and abiotic foldamers.  Peptidomimetic foldamers are synthetic molecules that mimic the structure of proteins, while nucleotidomimetic foldamers are based on the interactions in nucleic acids.  Abiotic foldamers are stabilized by aromatic and charge-transfer interactions which are not generally found in nature.<ref name=Foldamer>"Foldamers: Structure, Properties, and Applications" Stefan Hecht, Ivan Huc Eds. Wiley-VCH, Weinheim, 2007. {{ISBN|9783527315635}}</ref>  The three designs described below deviate from Moore's<ref name=Moore /> strict definition of a foldamer, which excludes helical foldamers.<!--could not decipher: In experimentation, however, helical foldamers are widely designed because helices are seen in biology and, out of the infinite number of possible foldamers, helices are rather predictable. The sections below illustrate foldamer designs.-->

===Peptidomimetic===
Peptidomimetic foldamers often break the previously mentioned definition of foldamers as they often adopt [helical](/source/Helix) structures.  They represent a major landmark of foldamer research due to their design and capabilities.<ref>Anslyn and Dougherty, Modern Physical Organic Chemistry, University Science Books, 2006, {{ISBN|978-1-891389-31-3}}</ref><ref name=Martinek>{{cite journal|last=Martinek|first=T.A.|author2=Fulop, F.|title=Peptidic foldamers: ramping up diversity|journal=Chem. Soc. Rev.|year=2012|volume=41|issue=2|pages=687–702|doi=10.1039/C1CS15097A|pmid=21769415}}</ref>  The largest groups of peptidomimetic consist of β-[peptides](/source/peptides), γ-peptides and δ-peptides, and the possible monomeric combinations.<ref name="Martinek"/> The [amino acids](/source/amino_acids) of these peptides only differ by one (β), two (γ), or three (δ) methylene carbons, yet the structural changes were profound. These peptide sequences are highly studied as sequence control leads to reliable folding prediction. Additionally, with multiple [methylene](/source/Methylene_(compound)) carbons between the [carboxyl](/source/C-terminus) and [amino](/source/Amino_terminus) termini of the flanking peptide bonds, varying [R-group](/source/R_group_(chemistry)) side chains can be designed. One example of the novelty of β-peptides can be seen in the findings of Reiser and coworkers.<ref name=zerbe>{{cite journal|last=De Pol|first=S. |author2=Zorn, C. |author3=Klein, C.D. |author4=Zerbe, O. |author5=Reiser, O.|title=Surprisingly Stable Helical Conformations in alpha/beta-Peptides by Incorporation of cis-beta-Aminocyclopropate Carboxylic Acids|journal=Angew. Chem. Int. Ed.|year=2004|volume=43|issue=4 |pages=511–514|doi=10.1002/anie.200352267|pmid=14735548 }}</ref>  Using a heteroligopeptide consisting of α-amino acids and cis-β-aminocyclopropanecarboxulic acids (cis-β-ACCs), they found the formation of helical sequences in oligomers as short as seven residues and defined conformation in five residues, a quality unique to peptides containing cyclic β-amino acids.<ref>Seebach, D.; Beck, A.K.; Bierbaum, D. J.; Chem. Biodiv., 2004, 1, 1111-1239.</ref><ref>{{cite journal|last=Seebach|first=D.|author2=Beck, A.K. |author3=Bierbaum, D.J. |title=Chemical and Biological Investigations of B-Oligoarginines|journal=Chemistry & Biodiversity|year=2004|volume=1|issue=1|pages=1111–1239|doi=10.1002/cbdv.200490014|pmid=17191776|s2cid=45258727}}</ref><ref>{{Cite web|last=Nizami|first=Bilal|title=FoldamerDB: Database of foldamers|url=http://foldamerdb.ttk.hu/|access-date=2020-07-06|website=foldamerdb.ttk.hu|language=en}}</ref><ref>{{Cite journal|last1=Nizami|first1=Bilal|last2=Bereczki-Szakál|first2=Dorottya|last3=Varró|first3=Nikolett|last4=el Battioui|first4=Kamal|last5=Nagaraj|first5=Vignesh U.|last6=Szigyártó|first6=Imola Cs|last7=Mándity|first7=István|last8=Beke-Somfai|first8=Tamás|date=2020-01-08|title=FoldamerDB: a database of peptidic foldamers|url=https://academic.oup.com/nar/article/48/D1/D1122/5612547|journal=Nucleic Acids Research|language=en|volume=48|issue=D1|pages=D1122–D1128|doi=10.1093/nar/gkz993|pmid=31686102|pmc=7145536|issn=0305-1048|doi-access=free}}</ref>

===Nucleotidomimetic===
Nucleotidomimetics do not generally qualify as foldamers.  Most are designed to mimic single DNA bases, [nucleosides](/source/nucleosides), or [nucleotides](/source/nucleotides) in order to nonspecifically target DNA.<ref>{{cite journal|last=Longley|first=DB|author2=Harkin DP |author3=Johnston PG |title=5-fluorouracil: mechanisms of action and clinical strategies|journal=Nat. Rev. Cancer|date=May 2003|volume=3|issue=5|pages=330–338|doi=10.1038/nrc1074|pmid=12724731|s2cid=4357553}}</ref><ref>{{cite journal|last=Secrist|first=John|title=Nucleosides as anticancer agents: from concept to the clinic|journal=Nucleic Acids Symposium Series|year=2005|volume=49|issue=49|pages=15–16|doi=10.1093/nass/49.1.15|pmid=17150610|doi-access=free}}</ref><ref>{{cite journal|last=Rapaport|first=E.|author2=Fontaine J|title=Anticancer activities of adenine nucleotides in mice are mediated through expansion of erythrocyte ATP pools|journal=Proc. Natl. Acad. Sci. USA|year=1989|pages=1662–1666|doi=10.1073/pnas.86.5.1662|pmid=2922403|volume=86|issue=5|bibcode=1989PNAS...86.1662R|pmc=286759|doi-access=free}}</ref>  These have several different medicinal uses including [anti-cancer](/source/Anti-cancer_drug), [anti-viral](/source/Antiviral_drug), and [anti-fungal](/source/Antifungal_medication) applications.

===Abiotic===
thumb|right|400px|Folding and Coordination of an Oligopyrrole
Abiotic foldamers are again organic molecules designed to exhibit dynamic folding. They exploit a few known key intermolecular interactions, as optimized by their design. One example is [oligopyrrole](/source/oligopyrrole)s that organize upon binding anions like [chloride](/source/chloride) through hydrogen bonding (see figure). Folding is induced in the presence of an anion: the polypyrrole groups have little conformational restriction otherwise.<ref>{{cite journal|last=Sessler|first=J.L.|author2=Cyr, M. |author3=Lynch, V. |title=Synthetic and structural studies of sapphyrin, a 22-.pi.-electron pentapyrrolic "expanded porphyrin"|journal=J. Am. Chem. Soc.|year=1990|volume=112|issue=7|page=2810|doi=10.1021/ja00163a059|bibcode=1990JAChS.112.2810S }}</ref><ref name=juwarker>{{cite journal|last=Juwarker|first=H.|author2=Jeong, K-S.|title=Anion-controlled foldamers|journal=Chem. Soc. Rev.|year=2010|volume=39|issue=10|pages=3664–3674|doi=10.1039/b926162c|pmid=20730154|url=https://zenodo.org/record/889411}}</ref>

===Other examples===
*  ''m''-Phenylene ethynylene oligomers are driven to fold into a helical conformation by [solvophobic force](/source/solvophobic_force)s and [aromatic stacking](/source/Pi-pi_interaction) interactions.
*  [β-peptides](/source/Beta-peptide) are composed of [amino acid](/source/amino_acid)s containing an additional [{{chem|CH|2}} unit](/source/methylene_bridge) between the [amine](/source/amine) and [carboxylic acid](/source/carboxylic_acid).  They are more stable to [enzymatic](/source/enzyme) degradation and have been demonstrated to have antimicrobial activity.
*  [Peptoid](/source/Peptoid)s are ''N''-substituted polyglycines that utilize steric interactions to fold into polyproline type-I-like helical structures.<ref>{{cite journal|last1=Angelici|first1=G.|last2=Bhattacharjee|first2=N.|last3=Roy|first3=O.|last4=Faure|first4=S.|last5=Didierjean|first5=C.|last6=Jouffret|first6=L.|last7=Jolibois|first7=F.|last8=Perrin|first8=L.|last9=Taillefumier|first9=C.|title=Weak backbone CH⋯O=C and side chain ''t''Bu⋯''t''Bu London interactions help promote helix folding of achiral N''t''Bu peptoids|journal=Chemical Communications|date=2016|volume=52|issue=24|pages=4573–4576|doi=10.1039/C6CC00375C|pmid=26940758|hdl=11568/837881|hdl-access=free}}</ref>
*  [Aedamer](/source/Aedamer)s that fold in aqueous solutions driven by hydrophobic and aromatic stacking interactions.
*  [Aromatic oligoamide foldamers](/source/Aromatic_Oligoamide_Foldamers). These examples are some of the largest and best structurally characterized foldamers.<ref>{{cite journal|last1=Delsuc|first1=Nicolas|last2=Massip|first2=Stéphane|last3=Léger|first3=Jean-Michel|last4=Kauffmann|first4=Brice|last5=Huc|first5=Ivan|title=Relative Helix−Helix Conformations in Branched Aromatic Oligoamide Foldamers|journal=Journal of the American Chemical Society|date=9 March 2011|volume=133|issue=9|pages=3165–3172|doi=10.1021/ja110677a|pmid=21306159|bibcode=2011JAChS.133.3165D }}</ref>
* [Arylamide](/source/Arylamide) foldamers,<ref>[http://www.pnas.org/content/early/2009/04/09/0811818106.full.pdf De novo design and in vivo activity of conformationally restrained antimicrobial arylamide foldamers. Choi. 2009]</ref> such as [brilacidin](/source/brilacidin).

==References==
{{Reflist|30em}}

==Further reading==
* {{cite book |author1=Ivan Huc |author2=Stefan Hecht |title=Foldamers: Structure, Properties, and Applications |publisher=Wiley-VCH |location=Weinheim |year=2007 |isbn=978-3-527-31563-5 |url=http://www.wiley-vch.de/publish/dt/books/bySubjectCH00/newTitles200705/3-527-31563-2/?sID=}}
* {{cite journal |vauthors=Goodman CM, Choi S, Shandler S, DeGrado WF |title=Foldamers as versatile frameworks for the design and evolution of function |journal=Nat. Chem. Biol. |volume=3 |issue=5 |pages=252–62 |year=2007 |pmid=17438550 |doi=10.1038/nchembio876|pmc=3810020 }}

===Reviews===
# {{Note|1}} {{cite journal|author=Gellman, S.H. |year=1998 |title=Foldamers: a manifesto |journal=Acc. Chem. Res. |volume=31 |issue=4 |pages=173–180 |url=http://www.chem.wisc.edu/~gellman/pdf/61.pdf |doi=10.1021/ar960298r |url-status=dead |archiveurl=https://web.archive.org/web/20080513115221/http://www.chem.wisc.edu/~gellman/pdf/61.pdf |archivedate=2008-05-13 }}
# {{Note|2}} {{cite journal |vauthors=Zhang DW, Zhao X, Hou JL, Li ZT |title=Aromatic Amide Foldamers: Structures, Properties, and Functions |journal=Chem. Rev. |volume=112 |issue=10 |pages=5271–5316 |year=2012 |pmid=22871167 |doi=10.1021/cr300116k}}
# {{Note|3}} {{cite journal|last=Juwarker|first=H.|author2=Jeong, K-S.|title=Anion-controlled foldamers|journal=Chem. Soc. Rev.|year=2010|volume=39|issue=10|pages=3664–3674|doi=10.1039/b926162c|pmid=20730154|url=https://zenodo.org/record/889411}}

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Adapted from the Wikipedia article [Foldamer](https://en.wikipedia.org/wiki/Foldamer) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Foldamer?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.