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di·po·lar i·ons

ions possessing both a negative charge and a positive charge, each localized at a different point in the molecule, which thus has both positive and negative "poles"; amino acids are the most notable dipolar ions, containing a positively charged NH3+ group and a negatively charged COO- group at neutral pH.
Synonym(s): amphions, zwitterions
Farlex Partner Medical Dictionary © Farlex 2012

di·po·lar ions

(dī-pō'lăr ī'onz)
Ions possessing both a negative charge and a positive charge, each localized at a different point in the molecule, which thus has both positive and negative "poles."
Synonym(s): zwitterions.

zwit·ter hy·poth·e·sis

(tsvit'er hī-poth'ĕ-sis)
That an amphoteric molecule (e.g., an amino acid) has, at its isoelectric point, equal numbers of positive and negative charges, thus becoming a zwitterion (dipolar ion).
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


The dipolar ions that form from amino acids when they are in solution at a neutral pH.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005
References in periodicals archive ?
The newly developed liquid crystals contain a zwitterion made up of a negatively charged inorganic portion and a positively charged organic portion.
Tetracycline-containing zwitterions at pH 7 have good adsorption on soils through cationic and anion exchanges.
The purpose of this study is to derive an approximate analytical solution for the prediction of the facilitation factor and permeation rate through liquid membranes for the facilitated transport of C[O.sub.2] where the reaction rate for C[O.sub.2] is expressed by the zwitterions reaction mechanism of Danckwerts (1979) and over a range from the moderate chemical reaction rate region to the chemical equilibrium region.
One was a zwitterion, 3-[4-(p-N,N-didecylaminostyryl 1-pyridinium) propylsulfonate], abbreviated as di-10-ASPPS (Molecular Probes).
Anti-protein-fouling materials are typically one of two types: polyethylene glycol or zwitterions. Polyethylene glycol is, in most biochemical solutions, readily oxidisable, and high temperatures greatly reduce the antiprotein adsorption, so the antifouling property is not maintained over a long time [3].
At a pH value higher than 7.5, the zwitterions form of RDB in water may increase the aggregation of RDB to form a bigger molecular form (dimer) and become unable to enter into the pore structure of the adsorbent surface.
Various previous works have been reported on improvement of an electrical conductivity of PEDOT:PSS films by adding dimethyl sulfate (DMS), zwitterions, methanol, and amphiphilic fluoro-compounds [12-15].
Comparative p[K.sub.a] and critical salt concentration (CSC) values for several zwitterions and their corresponding cyclopolymers.
In aqueous solution, OCT is ionized to form zwitterions. So, we can control the electronic charges of OCT by adjusting the pH of solution.
Three types of hydrophilic groups: cations, anions, and zwitterions, known as "ionogenic groups," are generally employed and form, according to the ionic charges on the polymeric main chain: cationomers (6,7), anionomers (8-11), and zwitterionomers (12), respectively.