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Isoelectric and Isoionic pH definitions

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  • Isoelectric Point
    pH where a polyprotic acid is neutral, does not migrate in an electric field, and exists as a zwitterion.
  • Isoionic Point
    pH where a polyprotic acid exists as an intermediate form, calculated using specific equations for H+ concentration.
  • Zwitterion
    Molecule with both positive and negative charges but overall neutral, common at the isoelectric point of amino acids.
  • Diprotic Acid
    Compound with two ionizable hydrogens, displaying three forms: acidic, intermediate, and basic.
  • Polyprotic Acid
    Compound with more than two ionizable hydrogens, often having multiple intermediate forms and pKa values.
  • pKa
    Negative logarithm of the acid dissociation constant, used to determine the pH at which a group is half dissociated.
  • Cation
    Positively charged ion, formed when an amino acid is in a solution more acidic than its isoelectric point.
  • Anion
    Negatively charged ion, formed when an amino acid is in a solution more basic than its isoelectric point.
  • Carboxyl Group
    Acidic functional group in amino acids, contributing to one of the pKa values and charge states.
  • Amino Group
    Basic functional group in amino acids, can be protonated or deprotonated, affecting overall charge.
  • Alpha Carbon
    Central carbon in amino acids, bonded to the carboxyl group, amino group, hydrogen, and variable R group.
  • Intermediate Form
    Species present between fully protonated and fully deprotonated states in polyprotic acids.
  • Acidic Amino Acid
    Amino acid with three pKa values, isoelectric point calculated using the two lower pKa values.
  • Basic Amino Acid
    Amino acid with three pKa values, isoelectric point calculated using the two higher pKa values.
  • Ion Product of Water
    Constant (Kw) representing the product of H+ and OH- concentrations in water, used in isoionic calculations.