zwitterionhttp://www.oed.com/dictionary/zwitterion_n%3Ftab%3Dmeaning_and_usezwitterion, n.
First published 1986; not fully revised

zwitterionnoun

Chemistry.
  1. 1906–
    A molecule or ion having separate positively and negatively charged atoms or groups.
    1. 1906
      Ions which are simultaneously electro-positive and electro-negative (Bredig), and which Küster calls ‘Zwitter-ions’, i.e. hermaphrodite-ions. Thus the ‘Zwitter-ion’ of glycocoll is the group H3N—CH2—COO.
      G. Mann, Chemistry of Proteids vi. 210
    2. 1925
      The ‘isomeric change’ now takes the form of a fission of the molecule by the rupture of a bond, the final ionisation of which provides the electric charges which are needed to neutralise those already present in the ‘Zwitterion’.
      Journal of Chemical Society vol. 127 1381
    3. 1937
      One of the greatest advances in the understanding of the physico~chemical behaviour of amino-acids and proteins is due to the zwitterion theory introduced by Bjerrum in 1923.
      Nature 18 September 492/1
    4. 1948
      The products of [penicillin] inactivation are zwitter-ions.
      Endeavour vol. 7 85/2
    5. 1949
      The penicilloic acids are zwitterions with two acid groups and one basic group.
      E. Chain in H. W. Florey et al., Antibiotics vol. II. xxii. 847
    6. 1968
      At the pH of living cells, lecithin forms a balanced zwitterion.
      D. W. Wood, Principles of Animal Physiology iii. 35
    7. 1982
      It is useful to calculate the exact pH at which an amino acid is electrically neutral and in its zwitterion form.
      R. M. Schultz in T. M. Devlin, Textbook of Biochemistry ii. 41

zwitterion, n. was first published in 1986; not fully revised.

zwitterion, n. was last modified in March 2025.