isoionicadj.
/ʌɪsəʊʌɪˈɒnɪk/ Physical Chemistry and Biochemistry.
Of a solute or solution: giving rise to or containing no noncolloidal ions other than those formed by dissociation of the solvent; isoionic point, †isoionic reaction, the point (usually pH value) at which the average number of hydrogen ions attached to the basic groups of solute molecules is equal to the average number dissociated from the acidic groups. This is the ‘theoretical’ definition of isoionic point; for the ‘practical’ definitions, see quot. 1959.
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isoionic1926
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isoionic point1926
1926 Linderstrøm-Lang & Lund in Compt. Rend. Lab. Carlsberg XVI. v. 22 We will therefore define isoionic reaction as the value of paH, paH0 at which h [sc. the specific hydrogen ionisation of the ampholyte] is 0.
1934 Biochem. Jrnl. 28 1257 At 0°, the isoionic point of crystallised haemoglobin was at pH 7·6.
1943 J. D. Edsall in Cohn & Edsall Proteins xx. 446 If the protein binds no other ions than protons, the isoionic point may correspond to the isoelectric point of the protein... If the protein combines with other ions also, the isoelectric and isoionic points are different.
1949 Jrnl. Physical & Colloid Chem. 53 88 Operationally we may define the isoionic material as the limit approached by successful electro~dialysis.
1949 Jrnl. Physical & Colloid Chem. 53 95 We may..calculate the change in pH of a solution which is not isoionic.
1959 Linderstrøm-Lang & Nielsen in M. Bier Electrophoresis I. ii. 63 According to the first definition the isoionic point is the pH of the protein solution which does not change on the addition of more isoionic protein. According to the second definition the isoionic point is the pH of a solution of the isoionic protein in water, or in a solution which does not produce H+ or OH− ions when dissolved in water alone. Thus a mixture of proteins may be isoionic.
1969 J. H. Ottaway & F. M. Irvine tr. H. Netter Theoret. Biochem. vi. 192 Amino acids and proteins are usually characterised by their isoelectric or isoionic point.
This entry has not yet been fully updated (first published 1976; most recently modified version published online June 2018).
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adj.1926