Structure of molecule of methyl-N-iminodiacetic acid and hydratation effects

Abstract

Ion exchangers type of ANKB-50, in which iminodiacetic acid as the adsorbent fragments used are
promising materials for ion exchange chromatography. It is believed that amphoteric and complexing
properties of the molecules belonging to chelates ion-exchangers, open the perspectives of using these
materials for the separation of elements that has similar chemical characteristics.
The adsorption capacity of polymeric ion exchangers, and the kinetic energy characteristics of the
adsorbed metal ions in the ion exchange depends strongly on the content of the solvent, in this case on the
water. The aim of this work was a quantum-chemical calculation of possible configurations of different forms
of N-methyl-iminodiacetic acid (cation, zwitterion, monoanion, dianion) in the absence of water and in the
presence of one and two of its molecules. Computer calculations of the molecular structure carried out for Nmethyl-iminodiacetic
acid fragment simulating ion exchanger ANKB-50 by B3LYP method, based on
density functional theory in the basis 6-311G (d, p).
As a result of the calculation was that the ground state of the molecule N-MIDAA has zwitterionic
configuration. Effect of the solvent as a continuous medium does not significantly alter the structure of the
molecule and its cation, and gives a few shifts the energy levels of the single-particle orbitals. A similar
effect was found by adding one or two water molecules in the scope of the molecule. Calculation structure
anion and dianion of N- MIDAA shown that water molecules change their geometry, leading to structural
isomers implemented by the transition of the hydrogen atom from the oxygen atom to the nitrogen atom. The
geometry of the molecule varies considerably and by turns its fragments around chemical bonds.
The energies and atomic structure of the following clusters: molecule N-methyl-iminodiacetic acid
anion, the dianion of the molecule and cation + H2O, 2H2O were calculated. Good agreement between the
calculated and experimental structure of the molecule is shown. The results obtained can be used for sorption
studies of metal ions in the ion exchanger of the type considered.