Intercalation (chemistry)

You don't need to be Editor-In-Chief to add or edit content to WikiDoc. You can begin to add to or edit text on this WikiDoc page by clicking on the edit button at the top of this page. Next enter or edit the information that you would like to appear here. Once you are done editing, scroll down and click the Save page button at the bottom of the page.

In chemistry, intercalation is the reversible inclusion of a molecule (or group) between two other molecules (or groups). Examples include DNA intercalation and in graphite intercalation compounds.

DNA intercalation

There are several ways molecules - in this case, also known as "ligands" - can interact with DNA. Ligands may interact with DNA by covalently binding, electrostatically binding, or intercalating.^[1] Intercalation occurs when ligands of an appropriate size and chemical nature fit themselves in between base pairs of DNA. These ligands are mostly polycyclic, aromatic, and planar, and therefore often make good nucleic acid stains. Intensively studied DNA intercalators include ethidium bromide, proflavine, daunomycin, doxorubicin, and thalidomide. DNA intercalators are used in chemotherapeutic treatment to inhibit DNA replication in rapidly growing cancer cells.

In order for an intercalator to fit between base pairs, the DNA must dynamically open a space between its base pairs by unwinding. The degree of unwinding varies depending on the intercalator, for example, ethidium cation (the ionic form of ethidium bromide found in aqueous solution) unwinds DNA by about 26° while proflavine unwinds it by about 17°. This unwinding causes the base pairs to separate, or "rise", creating an opening of about 0.34 nm (3.4 Å). This unwinding induces local structural changes to the DNA strand, such as lengthening of the DNA strand, or twisting of the base pairs. These structural modifications can lead to functional changes, often to the inhibition of transcription and replication and DNA repair processes, which makes intercalators potent mutagens. For this reason, DNA intercalators are often carcinogenic, such as the exo (but not the endo) 8,9 epoxide of aflatoxin B₁, acridines such as proflavine or quinacrine, or ethidium bromide.

Intercalation as a mechanism of interaction between cationic, planar, polycyclic aromatic systems of the correct size (on the order of a base pair) was first proposed by Leonard Lerman in 1961. One proposed mechanism of intercalation is as follows: in aqueous isotonic solution, the cationic intercalator is attracted electrostatically to the polyanionic DNA. The ligand displaces a sodium and/or magnesium cation that always surround DNA (to balance its charge) and forms a weak electrostatic bond with the outer surface of DNA. From this position, the ligand may then slide into the hydrophobic environment found between the base pairs and away from the hydrophilic outer environment surrounding the DNA. The base pairs transiently form such openings due to energy absorbed during collisions with solvent molecules.

Notes

See also

• Stacking (chemistry)
• Molecular tweezers
• Graphite intercalation compound

fr:Intercalation (chimie) ja:インターカレーションuk:Інтеркаляція (хімія)

Acknowledgement and Attribution Regarding Sources of Content

Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .