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From Molecules to Materials: Engineering New Ionic Liquid Crystals Through Halogen Bonding

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Published on: March 24, 2018

The Iodine/Iodide/Starch Supramolecular Complex.

Szilard Pesek¹, Radu Silaghi-Dumitrescu¹

¹Department of Chemistry, Faculty of Chemistry and Chemical Engineering, Babeş-Bolyai University, 11 Arany Janos Street, 400028 Cluj-Napoca, Romania.

Molecules (Basel, Switzerland)

|February 10, 2024

Summary

The blue color in the iodine-starch reaction arises from charge transfer within the amylose helix. Recent data suggests an I2-I5−-I2 unit is the primary component responsible for this complex.

Keywords:

DFT UV-vis amylose iodide iodine starch

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Published on: May 16, 2014

Area of Science:

Biochemistry
Chemical Spectroscopy

Background:

The blue color of the iodine-starch complex is a well-known phenomenon.
The exact nature of the charge transfer responsible for the color has been debated for decades.
Iodine (I2) and iodide (I-) are typically present in the reaction mixture.

Purpose of the Study:

To review the literature on the iodine-starch reaction.
To elucidate the charge-transfer mechanism responsible for the blue color.
To identify the most likely molecular species forming the blue complex.

Main Methods:

Extended literature review of the iodine-starch reaction.
Analysis of spectroscopic data, particularly the band at ~600 nm.
Evaluation of proposed models for charge transfer within the amylose helix.

Main Results:

Consensus exists that iodine binds within the hydrophobic interior of the amylose helix.
Three main hypotheses for charge transfer sources have been proposed: neutral I2 chains, polyiodine anions, or mixtures.
Recent data strongly supports an I2-I5−-I2 unit as the key component.

Conclusions:

The blue color is attributed to charge transfer interactions.
The I2-I5−-I2 unit, repeating within the amylose helix, is the most probable structure for the blue complex.
This finding resolves a long-standing debate in chemical and biochemical studies.