Effects of Acetone, Ethanol, Isopropanol, and Dimethyl Sulfoxide on Amylose-Iodine Complex

Barrett, Albert J.; Barrett, Karen L.; Khan, Arshad

doi:10.1080/10601329808002007

Cited by 6 publications

(4 citation statements)

References 17 publications

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“…The nature of the blue complex of amylose with iodine (λ max = 615 nm) has been a focus of research for many decades [1]. The left-handed helix, with an outer diameter of ~13 Å and a pitch of 8 Å (six 1,4-glucose units per pitch), hosts an internal cavity of ~5 Å where the iodine alongside iodide is hosted with I-I distances of ~3.1 Å [2][3][4][5][6][7][8][9][10]. Slight differences in the blue color are seen depending on the size (and, implicitly, biological source) of amylose; similar complexes are seen with many related poly and oligo saccharides, or even with other organic polymers [11][12][13][14][15][16][17][18][19][20][21].…”

Section: Introductionmentioning

confidence: 99%

On the Origin of the Blue Color in The Iodine/Iodide/Starch Supramolecular Complex

et al. 2022

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The nature of the blue color in the iodine-starch reaction is still a matter of debate. Some textbooks still invoke charge-transfer bands within a chain of neutral I2 molecules inside the hydrophobic channel defined by the interior of the amylose helical structure. However, the consensus is that the interior of the helix is not altogether hydrophobic—and that a mixture of I2 molecules and iodide anions reside there and are responsible for the intense charge-transfer bands that yield the blue color of the “iodine-starch complex”. Indeed, iodide is a prerequisite of the reaction. However, some debate still exists regarding the nature of the iodine-iodine units inside the amylose helix. Species such as I3-, I5-, I7- etc. have been invoked. Here, we report UV-vis titration data and computational simulations using density functional theory (DFT) for the iodine/iodide chains as well as semiempirical (AM1, PM3) calculations of the amylose-iodine/iodide complexes, that (1) confirm that iodide is a pre-requisite for blue color formation in the iodine-starch system, (2) propose the nature of the complex to involve alternating sets of I2 and Ix- units, and (3) identify the nature of the charge-transfer bands as involving transfer from the Ix- σ* orbitals (HOMO) to I2 σ* LUMO orbitals. The best candidate for the “blue complex”, based on DFT geometry optimizations and TD-DFT spectral simulations, is an I2-I5-I2 unit, which is expected to occur in a repetitive manner inside the amylose helix.

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Section: Introductionmentioning

confidence: 99%

On the Origin of the Blue Color in The Iodine/Iodide/Starch Supramolecular Complex

et al. 2022

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“…Eight hydration water molecules were found per unit cell, located in the amylose helices. The amylose left-handed helix was reported to have an outer diameter of~13 Å and a pitch of 8 Å (six 1,4-glucose units per pitch), hosting an internal cavity of ~5 Å [28,[30][31][32]34,36,[94][95][96][97]. Some statistical disorder was noted within the polyiodide chain, with an average iodine-iodine distance of ~3.1 Å.…”

Section: Geometrical Datamentioning

confidence: 99%

The Iodine/Iodide/Starch Supramolecular Complex

Pesek,

Silaghi-Dumitrescu

2024

Molecules

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The nature of the blue color in the iodine–starch reaction (or, in most cases, iodine–iodide-starch reaction, i.e., I2 as well as I− are typically present) has for decades elicited debate. The intensity of the color suggests a clear charge-transfer nature of the band at ~600 nm, and there is consensus regarding the fact that the hydrophobic interior of the amylose helix is the location where iodine binds. Three types of possible sources of charge transfer have been proposed: (1) chains of neutral I2 molecules, (2) chains of poly-iodine anions (complicated by the complex speciation of the I2-I− mixture), or (3) mixtures of I2 molecules and iodide or polyiodide anions. An extended literature review of the topic is provided here. According to the most recent data, the best candidate for the “blue complex” is an I2-I5−-I2 unit, which is expected to occur in a repetitive manner inside the amylose helix.

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“…The amylose left-handed helix was reported to have an outer diameter of~13 Å and a pitch of 8 Å (six 1,4-glucose units per pitch) hosting an internal cavity of ~ 5 Å. 24,25,27,28,30,32,[92][93][94][95] Some statistical disorder was noted within the polyiodide chain, with an average iodine-iodine distance of ~3.1 Å. This value is larger than 2.67 Å in molecular I2 as well as than the 2.90 Å in ionic I3 -, but distinctly shorter than the 4.3 Å sum of van der Waals radii for two iodine atoms.…”

Section: Geometrical Datamentioning

confidence: 99%

The Iodine/Iodide/Starch Supramolecular Complex

Silaghi-Dumitrescu,

Pesek

2023

Preprint

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The nature of the blue color in the iodine-starch reaction (or, in most cases, iodine-iodide-starch reaction, i.e. as I2 as well as I- are typically present) has for decades elicited debate. The intensity of the color suggests a clear charge-transfer nature of the band at ~600 nm, and there is consensus regarding the fact that the hydrophobic interior of the amylose helix is the location where iodine binds. Three types of possible sources of charge transfer have been proposed: (1) chains of neutral I2 molecules, (2) chains of poly-iodine anions (complicated by the complex speciation of the I2 - I- mixture), or (3) mixtures of I2 molecules and iodide or polyiodide anions. An extended literature review of the topic is provided here. According to the most recent data, the best candidate for the “blue complex” is a I2-I5-I2 unit – expected to occur in repetitive manner inside the amylose helix.

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Effects of Acetone, Ethanol, Isopropanol, and Dimethyl Sulfoxide on Amylose-Iodine Complex

Cited by 6 publications

References 17 publications

On the Origin of the Blue Color in The Iodine/Iodide/Starch Supramolecular Complex

On the Origin of the Blue Color in The Iodine/Iodide/Starch Supramolecular Complex

The Iodine/Iodide/Starch Supramolecular Complex

The Iodine/Iodide/Starch Supramolecular Complex

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