Intercalation (chemistry)

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Intercalation of small metal atoms between graphite planes.

Under intercalation (from latin intercalare = insert) in the chemical sense is understood to mean the storage of molecules , ions (rarely atoms ) in chemical compounds , which do not substantially alter their this structure during the storage process.

Inorganic chemistry

In inorganic chemistry , intercalation describes the intercalation of atoms, ions or small molecules between the crystal lattice planes of layered crystals, for example the intercalation of alkali metals in graphite (see picture). The resulting compounds are called intercalation complexes .

In order for a crystal structure to be able to form intercalation compounds, the interaction forces within the layers must be large and between neighboring layers small. Strong interactions must be possible between the host lattice and the guest components. The solvation of interlayer cations is particularly suitable for initiating an intercalation reaction . It depends both on the chemical properties of the component to be embedded, but also on the chemical nature of the host lattice, how the storage takes place. In addition to pure van der Waals interactions , Lewis acid-base interactions often play a role.

The host lattices can be varied widely in their chemical nature; from the quasi-metallic layers in graphite or in the transition metal sulfides NbS 2 or TaS 2 , to the semiconducting systems such as TiS 2 and SnS 2 and to non-conductive compounds such as clay minerals (e.g. kaolinite ).

Many layer grids naturally carry negative layer charges, e.g. B. the mica-like sheet silicates . Electrically neutral host grids are rather rare; for example the above-mentioned kaolinite. Some “neutral” host lattices are only able to form intercalation complexes through the use of strong reducing agents. In some cases, the use of non- stoichiometric preparations can also enable storage. The non-stoichiometry is achieved by reducing agents or electrochemical reduction. Methods for this are cyclic voltammetry , electrogravimetry and galvanostatics.

These types of reactions find practical and technical application in, among others

  • Accumulators and batteries
  • Soil, environmental and geochemistry (absorption and storage behavior of soils)
  • Industrial production and packaging of medicines, fertilizers, pesticides

biochemistry

Intercalation of molecules into DNA.

Intercalation into deoxyribonucleic acid (DNA) is when certain molecules , which are completely or partially planar, insert themselves into the double helix of DNA between neighboring base pairs . This storage disrupts the replication and transcription of the DNA. A grid mutation occurs during the replication process . Intercalation is therefore held responsible for the mutagenic effect of many representatives of this class of substances, and the chemotherapeutic effect of antibiotics or cytostatics such as actinomycin or anthracyclines such as daunorubicin is also attributed to intercalation, among other things. In addition to the cytostatics mentioned, the compounds with intercalative properties also include, for example, polyaromatic hydrocarbons and dyes of the phenanthridine type, such as ethidium bromide , or of the proflavine type (Falbe and Regitz, 1992; Mutschler 1996). Also indirubin derivatives intercalate into DNA.

See also

literature