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Iodine Chemistry

Voth, Ho

 

From the Cover: Directing macromolecular conformation through halogen bonds.

Voth AR, Hays FA, Ho PS.

Proc Natl Acad Sci U S A. 2007 Apr 10;104(15):6188-93. Epub 2007 Mar 22.

[abstract only]

 

"The halogen bond, a noncovalent interaction involving polarizable chlorine, bromine, or iodine molecular substituents, is now being exploited to control the assembly of small molecules in the design of supramolecular complexes and new materials. We demonstrate that a halogen bond formed between a brominated uracil and phosphate oxygen can be engineered to direct the conformation of a biological molecule, in this case to define the conformational isomer of a four-stranded DNA junction when placed in direct competition against a classic hydrogen bond. As a result, this bromine interaction is estimated to be approximately 2-5 kcal/mol stronger than the analogous hydrogen bond in this environment, depending on the geometry of the halogen bond. This study helps to establish halogen bonding as a potential tool for the rational design and construction of molecular materials with DNA and other biological macromolecules."

 

It’s explained for the layperson by the newspaper Bend Weekly News:

"It’s now understood that this arcane type of chemical bond, which is based on bromine, iodine or chlorine instead of hydrogen, may have characteristics that could be tapped for a new approach to biological engineering.

 

“Natural biological molecules have some powerful capabilities that we might like to take advantage of, such as the ability to convert biological energy to mechanical energy with incredible efficiency,” Ho said. “But to do that, we need ways to carefully control their behavior, movement and function. The halogen bonds might allow us to do this.”

 

"Among the possibilities could be computers that operate at the size of biological molecules, a molecular “walker” that could control the movement of molecules at the nano-scale, or molecular scissors that provide a way to cut molecules. Such systems done with biological materials would act like extraordinarily small machines, and might also be more environmentally friendly."

 

Halogen bonds in biological molecules.

Auffinger P, Hays FA, Westhof E, Ho PS.

Proc Natl Acad Sci U S A. 2004 Nov 30;101(48):16789-94. Epub 2004 Nov 19.

 

"Short oxygen-halogen interactions have been known in organic chemistry since the 1950s and recently have been exploited in the design of supramolecular assemblies. The present survey of protein and nucleic acid structures reveals similar halogen bonds as potentially stabilizing inter- and intramolecular interactions that can affect ligand binding and molecular folding. A halogen bond in biomolecules can be defined as a short C-X...O-Y interaction (C-X is a carbon-bonded chlorine, bromine, or iodine, and O-Y is a carbonyl, hydroxyl, charged carboxylate, or phosphate group), where the X...O distance is less than or equal to the sums of the respective van der Waals radii (3.27 A for Cl...O, 3.37 A for Br...O, and 3.50 A for I...O) and can conform to the geometry seen in small molecules, with the C-X...O angle approximately 165 degrees (consistent with a strong directional polarization of the halogen) and the X...O-Y angle approximately 120 degrees . Alternative geometries can be imposed by the more complex environment found in biomolecules, depending on which of the two types of donor systems are involved in the interaction: (i) the lone pair electrons of oxygen (and, to a lesser extent, nitrogen and sulfur) atoms or (ii) the delocalized pi -electrons of peptide bonds or carboxylate or amide groups. Thus, the specific geometry and diversity of the interacting partners of halogen bonds offer new and versatile tools for the design of ligands as drugs and materials in nanotechnology."

 
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