zwitterionic

Examples of zwitterionic in the following topics:

• The Favorskii Rearrangement

  • A debate concerning the nature of the carbon-carbon bond formation step now favors direct (synchronous) formation of the cyclopropanone by a 1,3-elimination, as shown, rather than initial ionization of the enolate to a zwitterionic species such as that drawn in the green box.
  • When stereoisomeric substrates were examined, the rearrangement proved to be stereospecific, ruling out a common zwitterionic intermediate.

• The Effect of pH on Solubility

  • The isomer on the right is a zwitterion.

• Peptides & Proteins

  • As expected, the free amine and carboxylic acid functions on a peptide chain form a zwitterionic structure at their isoelectric pH.

• α-Amino Acids

  • The resulting ammonium carboxylate structure, commonly referred to as a zwitterion, is also supported by the spectroscopic characteristics of alanine.
  • As expected from its ionic character, the alanine zwitterion is high melting, insoluble in nonpolar solvents and has the acid strength of a 1º-ammonium ion.
  • In the diagrams above is a display of an L-amino acid in its zwitterionic form.
  • Examples of a few specific amino acids may also be viewed in their favored neutral zwitterionic form.
  • At pH 6.00 alanine and isoleucine exist on average as neutral zwitterionic molecules, and are not influenced by the electric field.

• Preparation of Ylides

  • This bonding stabilization extends to carbanions alpha to phosphonium and sulfonium centers, and the zwitterionic conjugate bases derived from such cations are known as ylides.

• Reactions of Amino Acids

  • Once the carboxyl function is esterified, zwitterionic species are no longer possible and the product behaves like any 1º-amine.
  • Since amides are only weakly basic ( pKa~ -1), the resulting amino acid derivatives do not display zwitterionic character, and may be converted to a variety of carboxylic acid derivatives.

• Extremely Halophilic Archaea

  • The most common compatible solutes are neutral or zwitterionic, and include amino acids, sugars, polyols, betaines and ectoines, as well as derivatives of some of these compounds.

• Ions

  • Zwitterions are neutral and have both positive and negative charges at different locations throughout the molecule.

• Synthesis of Amino Acids

  • If the racemic mixture of amides shown in the green shaded box above is treated with this enzyme, the L-enantiomer (whatever its rotation) will be rapidly converted to its free zwitterionic form, whereas the D-enantiomer will remain largely unchanged.

• The Primary Structure of Peptides

  • A free amine function, usually in equilibrium with zwitterion species, is necessary for the initial bonding to the phenyl isothiocyanate reagent.