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An amino acid contains both acidic (carboxylic acid fragment) and basic (amine fragment) centres. The isomer on the right is a zwitterion.

Sulfamic acid isomers, with the zwitterion (right).

In chemistry, a zwitterion (/ˈtsvɪtər.aɪ.ən/ TSVIT-ər-eye-ən; from German zwitter [ˈtsvɪtɐ] "hybrid" and formerly called a dipolar ion) is a neutral molecule with both a positive and a negative electrical charge. Multiple positive and negative charges can be present. Zwitterions are distinct from dipoles, at different locations within that molecule. Zwitterions are sometimes also called inner salts.^[1]

Unlike simple amphoteric compounds that might only form either a cationic or anionic species depending on external conditions, a zwitterion simultaneously has both ionic states in the same molecule.^[2]

Examples

Amino Acids are the best-known examples of zwitterions. These compounds contain an ammonium and a carboxylate group, and can be viewed as arising via a kind of intramolecular acid–base reaction: The amine group deprotonates the carboxylic acid.

NH₂RCHCO₂H NH₃⁺RCHCO₂⁻

The zwitterionic structure of glycine in the solid state has been confirmed by neutron diffraction measurements.^[3] At least in some cases, the zwitterionic form of amino acids also persists in the gas phase.^[4]

In addition to the amino acids, many other compounds that contain both acidic and basic centres tautomerize to the zwitterionic form. Examples, such as bicine and tricine, contain a basic secondary or tertiary amine fragment together with a carboxylic acid fragment. Neutron diffraction measurements show that solid sulfamic acid exists as a zwitterion.^[5] Many alkaloids, such as LSD and psilocybin, exist as zwitterions because they contain carboxylates and ammonium centres.

Many zwitterions contain quaternary ammonium cations. Since it lacks N–H bonds, the ammonium center cannot participate in tautomerization. Zwitterions containing quaternary-ammonium centers are common in biology, a common example are the betaines, which serve as electrolytes in fish. The membrane-forming phospholipids are also commonly zwitterions. The polar head groups in these compounds are zwitterions, resulting from the presence of the anionic phosphate and cationic quaternary ammonium centres.^[6]

The vesicle-forming phospholipid phosphatidylcholine, palmitoyl-oleyl-sn-phosphatidylcholine.

Related compounds

Dipolar compounds are usually not classified as zwitterions. For example, amine oxides, which are often written as R₃N⁺O⁻, are not zwitterions in terms of the definition,^[1] which specifies that there are unit electrical charges on atoms. The distinction lies in the fact that the plus and minus signs on the amine oxide signify formal charges, not electrical charges. Formal charges are used in valence bond theory for some canonical forms used to construct a resonance hybrid. In fact another theoretical representation of an amine oxide uses a dative covalent bond ≡N→O with no formal charges. Other compounds that are sometimes referred to as zwitterions, mistakenly according to the definition above, include nitrones and "dipolar compounds", such as a 1,2-dipole (ylide) and a 1,3-dipole.^[7]

References

^ ^a ^b IUPAC Gold Book zwitterionic compounds/zwitterions
^ Voet, D. and Voet, J, G. (2005). Biochemistry (3th ed.). Hoboken, NJ: John Wiley & Sons Inc. p. 68. ISBN 9780471193500.
^ Jönsson, P.-G.; Kvick, Å. (1972). "Precision neutron diffraction structure determination of protein and nucleic acid components. III. The crystal and molecular structure of the amino acid α-glycine". Acta Crystallogr. B 28 (6): 1827–1833. doi:10.1107/S0567740872005096.
^ Price, William D.; Jockusch, Rebecca A.; Williams, Evan R. (1997). "Is Arginine a Zwitterion in the Gas Phase?". J. Am. Chem. Soc. 119 (49): 11988–11989. doi:10.1021/ja9711627. PMC 1364450. PMID 16479267. text
^ R. L. Sass (April 1960). "A neutron diffraction study on the crystal structure of sulfamic acid". Acta Crystallogr. 13 (4): 320–324. doi:10.1107/S0365110X60000789.
^ Nelson, D. L.; Cox, M. M. "Lehninger, Principles of Biochemistry" 3rd Ed. Worth Publishing: New York, 2000. ISBN 1-57259-153-6.
^ IUPAC Gold Book dipolar compounds

UpToDate Contents

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1. 嫌気性感染症における病態生理：臨床的な手がかり、および微生物の回収方法 pathophysiology clinical clues and recovery of organisms in anaerobic infections

English Journal

Zwitterionic hyperbranched polyester functionalized cardiovascular stent and its biocompatibility.

Wang X1, Miao J1, Shao X2, Mao C3, Shen J4.Author information 1Jiangsu Key Laboratory of Biofunctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, PR China.2Nanjing General Hospital of Nanjing Military Command, Nanjing 210002, PR China.3Jiangsu Key Laboratory of Biofunctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, PR China. Electronic address: maochun@njnu.edu.cn.4Jiangsu Key Laboratory of Biofunctional Materials, College of Chemistry and Materials Science, Nanjing Normal University, Nanjing 210023, PR China. Electronic address: jshen@njnu.edu.cn.AbstractZwitterionic hyperbranched polyester (HBPE) synthesized on bare metal stents (BMS) surface by surface-initiated atom transfer radical polymerization (SI-ATRP) method. The modified BMS obtained was tested for its blood compatibility. The blood compatibility studies were including, platelet adhesion tests, hemolysis assay, morphological changes in RBCs, coagulation tests, PRT assay, complement activation, platelet activation, and the cytotoxicity was also investigated. The modified BMS surface does not cause platelets adherent, red blood cell disruption, hemolysis and does not induce complement and platelets activation. All results indicated that the modified BMS was blood compatible and no cytotoxicity. It has the potential use for biomedical applications.
Journal of colloid and interface science.J Colloid Interface Sci.2014 Apr 15;420:88-96. doi: 10.1016/j.jcis.2014.01.016. Epub 2014 Jan 15.
Zwitterionic hyperbranched polyester (HBPE) synthesized on bare metal stents (BMS) surface by surface-initiated atom transfer radical polymerization (SI-ATRP) method. The modified BMS obtained was tested for its blood compatibility. The blood compatibility studies were including, platelet adhesion t
PMID 24559705

Phenylalanine and tyrosine methyl ester intramolecular interactions and conformational analysis by (1)H NMR and infrared spectroscopies and theoretical calculations.

Cormanich RA1, Ducati LC2, Tormena CF1, Rittner R3.Author information 1Chemistry Institute, University of Campinas, P.O. Box 6154, 13083-970 Campinas, Brazil.2Chemistry Institute, University of São Paulo, P.O. Box 26077, 05508-900 São Paulo, Brazil.3Chemistry Institute, University of Campinas, P.O. Box 6154, 13083-970 Campinas, Brazil. Electronic address: rittner@iqm.unicamp.br.AbstractAmino acid conformational analysis in solution are scarce, since these compounds present a bipolar zwitterionic structure ((+)H3NCHRCOO(-)) in these media. Also, intramolecular hydrogen bonds have been classified as the sole interactions governing amino acid conformational behavior in the literature. In the present work we propose phenylalanine and tyrosine methyl ester conformational studies in different solvents by (1)H NMR and infrared spectroscopies and theoretical calculations. Both experimental and theoretical results are in agreement and suggest that the conformational behavior of the phenylalanine and tyrosine methyl esters are similar and are dictated by the interplay between steric and hyperconjugative interactions.
Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy.Spectrochim Acta A Mol Biomol Spectrosc.2014 Apr 5;123:482-9. doi: 10.1016/j.saa.2013.12.088. Epub 2014 Jan 3.
Amino acid conformational analysis in solution are scarce, since these compounds present a bipolar zwitterionic structure ((+)H3NCHRCOO(-)) in these media. Also, intramolecular hydrogen bonds have been classified as the sole interactions governing amino acid conformational behavior in the literature
PMID 24434201

Zwitterionic fusion in hydrogels and spontaneous and time-independent self-healing under physiological conditions.

Bai T1, Liu S2, Sun F1, Sinclair A1, Zhang L1, Shao Q1, Jiang S3.Author information 1Department of Chemical Engineering, University of Washington, Seattle, WA 98195, USA.2Department of Bioengineering, University of Washington, Seattle, WA 98195, USA.3Department of Chemical Engineering, University of Washington, Seattle, WA 98195, USA; Department of Bioengineering, University of Washington, Seattle, WA 98195, USA. Electronic address: sjiang@uw.edu.AbstractThe biomedical applications of current self-healing materials are largely impeded by their healing conditions, which usually require heating, UV exposure or harsh pH environments. At the same time, for very few existing spontaneously self-healing materials, healing can only be achieved immediately after rupture occurs. Here, we developed a spontaneously healing material, driven by a new mechanism, "zwitterionic fusion", which is repairable independent of time after damage under physiological conditions. We also tested the anti-fatigue property of this zwitterionic hydrogel. Furthermore, we utilized this zwitterionic fusion to link different cell-hydrogel constructs together.
Biomaterials.Biomaterials.2014 Apr;35(13):3926-33. doi: 10.1016/j.biomaterials.2014.01.077. Epub 2014 Feb 20.
The biomedical applications of current self-healing materials are largely impeded by their healing conditions, which usually require heating, UV exposure or harsh pH environments. At the same time, for very few existing spontaneously self-healing materials, healing can only be achieved immediately a
PMID 24559638

Japanese Journal

両性イオンに基づく水和層を固定相とする保水性分離剤の開発

井上嘉則,上茶谷若,山本敦
分析化学 63(2), 79-92, 2014
親水性基材に両性イオン型化合物であるスルホベタイン及びジアリルアミン─マレイン酸共重合体（DAM）を導入した新規な保水性分離剤を調製し，水溶性化合物に対する抽出・分離特性を調べた．これらの保水性分離剤はイオン交換樹脂と同等の保水能力を示し，アセトニトリル中から水溶性化合物を効率よく抽出可能であった．特に，DAM導入分離剤はグルコースや配糖体も定量的に固相抽出可能であった．高速液体クロマトグラフィー …
NAID 130003391223

Double network hydrogels from polyzwitterions : high mechanical strength and excellent anti-biofouling properties

Yin Haiyan,Akasaki Taigo,Sun Tao Lin,Nakajima Tasuku,Kurokawa Takayuki,Nonoyama Takayuki,Taira Toshio,Saruwatari Yoshiyuki,Gong Jian Ping
Journal of Materials Chemistry B 1(30), 3685-3693, 2013-05-23
… In this study, we have successfully synthesized novel single network hydrogels and double network (DN) hydrogels from the zwitterionic monomer, N-(carboxymethyl)-N,N-dimethyl-2-(methacryloyloxy) ethanaminium, inner salt (CDME). …
NAID 120005429603

FACILE SYNTHESIS OF GUAIAZULENE-HETEROCYCLE HYBRIDS VIA MULTICOMPONENT REACTIONS INVOLVING FORMATION OF ZWITTERIONIC INTERMEDIATES

Sato Koichi,Yokoo Erina,Takenaga Naoko
Heterocycles : an international journal for reviews and communications in heterocyclic chemistry 87(4), 807-814, 2013-04-01
NAID 40019621898