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Complexation Equilibria: The Chelate Effect

Complexation Equilibria: The Chelate Effect

In complexation reactions, metal atoms or cations interact with ligands to form donor-acceptor adducts called metal complexes. Ligands that bind through one donor site are monodentate, ligands with two donor sites are bidentate, and those with more than two donor sites are polydentate ligands. For example, ethylene diamine is a bidentate ligand that binds through two nitrogen donor atoms, forming a five-membered ring. EDTA is a polydentate ligand that binds through four oxygen and two nitrogen...

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Related Experiment Video

Updated: Jun 24, 2025

Assembly and Characterization of Polyelectrolyte Complex Micelles

Assembly and Characterization of Polyelectrolyte Complex Micelles

Published on: March 2, 2020

Distribution of polyelectrolytes and counterions upon polyelectrolyte complexation.

Giulia Allegri¹, Jurriaan Huskens¹, Ricardo P Martinho²

¹Molecular Nanofabrication Group, Department for Molecules & Materials, MESA+ Institute & Faculty of Science Technology, University of Twente, 7500 AE Enschede, the Netherlands.

Journal of Colloid and Interface Science

|June 12, 2024

Summary

A new NMR methodology quantifies polyelectrolyte complex (PEC) components. Polyelectrolyte complexation is charge-stoichiometric, with excess components and most counterions in the supernatant, driving formation.

Keywords:

Counterion quantification Mass balance NMR spectroscopy Phase separation Polyelectrolyte complexes Polyelectrolyte quantification

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On-chip Isotachophoresis for Separation of Ions and Purification of Nucleic Acids

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Last Updated: Jun 24, 2025

Assembly and Characterization of Polyelectrolyte Complex Micelles

Assembly and Characterization of Polyelectrolyte Complex Micelles

Published on: March 2, 2020

Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by π-π Stacking Interactions

Anionic Polymerization of an Amphiphilic Copolymer for Preparation of Block Copolymer Micelles Stabilized by π-π Stacking Interactions

Published on: October 10, 2016

On-chip Isotachophoresis for Separation of Ions and Purification of Nucleic Acids

On-chip Isotachophoresis for Separation of Ions and Purification of Nucleic Acids

Published on: March 2, 2012

Area of Science:

Polymer Science
Supramolecular Chemistry
Analytical Chemistry

Background:

Polyelectrolyte complexation is crucial in various applications.
Limited understanding of component distribution hinders progress.
Absence of systematic analysis methods for PECs and dilute phases.

Purpose of the Study:

Develop a quantitative methodology for analyzing PEC components.
Determine the distribution of polyelectrolytes and counterions.
Provide a molecular-level understanding of PEC formation.

Main Methods:

Utilized Nuclear Magnetic Resonance (NMR) spectroscopy.
Quantified poly(allylamine hydrochloride) (PAH) and poly(acrylic acid)-sodium salt (PAA) in PEC and supernatant phases via ¹H NMR.
Measured counterion concentrations (²³Na, ³⁵Cl NMR).

Main Results:

Polyelectrolyte complexes are charge-stoichiometric.
Excess polyelectrolytes reside in the supernatant phase.
Majority of counterions are in the supernatant, indicating counterion release as a driving force.
Counterion concentration is higher in the PEC phase than supernatant.
A complete mass balance and molecular picture of PEC formation were achieved.

Conclusions:

The developed NMR methodology enables comprehensive analysis of PECs.
Charge stoichiometry governs PEC formation, with excess components in solution.
Counterion release is a primary thermodynamic driver for PEC formation.
Insights into polyelectrolyte charge states and extrinsic ion pairs within the complex.