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Formation of Complex Ions

Formation of Complex Ions

A type of Lewis acid-base chemistry involves the formation of a complex ion (or a coordination complex) comprising a central atom, typically a transition metal cation, surrounded by ions or molecules called ligands. These ligands can be neutral molecules like H2O or NH3, or ions such as CN− or OH−. Often, the ligands act as Lewis bases, donating a pair of electrons to the central atom. These types of Lewis acid-base reactions are examples of a broad subdiscipline called coordination...

Complexation Equilibria: Overview

Complexation Equilibria: Overview

Complexation reactions take place when dative or coordinate covalent bonds form between metal ions and ligands. The compounds formed in these reactions are called coordination compounds. The number of bonds formed between the metal ion and the ligands is called its coordination number. Generally, most metal ions in an aqueous solution are solvated by water molecules and thus exist as aqua complexes.
The equilibrium constant of the complexation reaction is represented as the formation constant...

Complexometric Titration: Overview

Complexometric Titration: Overview

Complexometric titration involves the formation of a complex by reacting a metal ion with one or more ligands. A visual indicator often detects the end point of a complexometric titration. It is added to the metal solution before the titration, forming a stable metal–indicator complex and imparting color to the solution. As the titration approaches the equivalence point, the excess of the added ligand displaces the indicator from the metal–indicator complex, releasing the free indicator. The...

EDTA: Auxiliary Complexing Reagents

EDTA: Auxiliary Complexing Reagents

EDTA titrations are usually carried out in highly basic conditions, where the fully deprotonated form of EDTA, Y4−, actively complexes with the free metal ions in the solution. Several metal ions precipitate as hydrous oxide (hydroxides, oxides, or oxyhydroxides) under these conditions, lowering the concentration of free metal ions in the solution. For this reason, auxiliary complexing agents or ligands such as ammonia, tartrate, citrate, or triethanolamine are used in EDTA titrations to...

Complexometric EDTA Titration Curves

Complexometric EDTA Titration Curves

EDTA titration curves determine the free metal ion concentration. The titration curve represents the change in concentration of free metal ions (p function) as a function of the volume of EDTA added. This curve consists of three regions: before, at, and after equivalence points. Excess free metal ions are present before the equivalence point. Equal concentrations of metal ions and EDTA are present at the equivalence point. After the equivalence point, excess EDTA exists. This means slight...

Complexometric Titration: Ligands

Complexometric Titration: Ligands

Different monodentate and polydentate ligands are used as complexing agents in complexometric titration reactions. The formation of complexes by mono- and bidentate ligands involves two or more intermediate steps, limiting their use as complexing agents. In comparison, polydentate ligands can form complexes with metal ions in a single-step process, facilitating sharper end points. This means polydentate ligands, such as amino carboxylic acid derivatives, are most commonly employed in...

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T-wave Ion Mobility-mass Spectrometry: Basic Experimental Procedures for Protein Complex Analysis

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Polyelectrolyte complexation with biofunctionalized multivalent ions: Coarse-grained model and isothermal titration

Hervé Hillaireau¹, Federica Costamagna¹, Adrouchan Hotier¹

¹Institut Galien, Université Paris-Saclay, Orsay, France.

The Journal of Chemical Physics

|March 24, 2026

Summary

A new model accurately predicts nanoparticle formation from polyelectrolytes and multivalent ions, crucial for drug delivery. It combines electrostatic and short-range interactions, validated by isothermal titration calorimetry (ITC) experiments.

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T-wave Ion Mobility-mass Spectrometry: Basic Experimental Procedures for Protein Complex Analysis

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Isothermal Titration Calorimetry for Measuring Macromolecule-Ligand Affinity

Isothermal Titration Calorimetry for Measuring Macromolecule-Ligand Affinity

Published on: September 7, 2011

Area of Science:

* Materials Science
* Biotechnology
* Physical Chemistry

Background:

* Nanoparticle formation via polyelectrolyte and multivalent ion complexation is vital for biomedical applications like drug delivery.
* Predicting this complexation quantitatively remains a significant challenge.
* Isothermal titration calorimetry (ITC) offers insights into counterion release entropy and polyelectrolyte-ion interaction energy, but current models are limited.

Purpose of the Study:

* To develop a theoretical model for polyelectrolyte-ion complexation that accounts for both electrostatic and non-electrostatic interactions.
* To interpret isothermal titration calorimetry (ITC) data more accurately.
* To investigate the influence of model parameters on ion condensation and validate against experimental data.

Main Methods:

* Developed a theoretical model incorporating Manning theory for long-range electrostatic interactions and translational ion entropy.
* Included short-range non-electrostatic interactions (van der Waals, hydrogen bonding).
* Tested the model against ITC experimental measurements of chitosan and iron-functionalized chitosan complexing with specific nucleotides/analogs.

Main Results:

* The theoretical model demonstrated excellent agreement with experimental ITC data.
* Identified key parameters influencing ion condensation.
* Showed that iron functionalization enhances short-range attractive forces and increases the entropic penalty in ion-chitosan interactions.

Conclusions:

* The developed model provides a robust framework for understanding and predicting polyelectrolyte-ion complexation.
* The findings offer valuable insights into the mechanisms governing nanoparticle formation for biomedical applications.
* Iron functionalization significantly alters the interaction thermodynamics between chitosan and multivalent ions.