Thermostability

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The thermal stability referred to in the chemistry and in particular organic and biochemistry the property of a compound , relatively high temperatures to withstand (molecular heat resistance ). The opposite of thermostability is thermolability. This thermostability relates primarily to the structure of the molecule, but is also defined in an application-specific manner via the ability to perform a certain function.

Thermostability of plastics

Thermoplastic plastics are heated for processing. To prevent them from decomposing, additives are added to prevent this.

For example, stabilizers of their own are added to polyvinyl chloride in order to increase the thermal stability during processing and to improve resistance to weathering and aging . For this purpose, compounds such as stearates or carboxylates based on heavy metals such as lead , cadmium , tin , barium / zinc , calcium / zinc and calcium / aluminum / zinc such as cadmium stearate or lead stearate are used. Chlorine released in the melting process , which would destroy the plastic (see also chlorine # chemical properties ), destroys the easily split metal compounds, which act as "acid scavengers". The released chlorine is captured and metal chlorides are formed. Cadmium compounds as stabilizers were banned by the EU in 2001, and lead stabilizers are to be replaced by 2015 (according to a source from 2010) (voluntary reduction target). Such metal-containing thermal stabilizers can be replaced by hydrotalcite (a magnesium-aluminum-hydroxycarbonate).

Thermostability of proteins

Enzyme activity as a function of temperature. At the denaturing temperature the enzyme loses its activity.

The term is mainly applied to biomolecules and especially protein structures , as proteins often lose their functionality due to denaturation at comparatively low temperatures. However, since higher temperatures enable a higher metabolic rate in process engineering ( RGT rule ) or these are necessary for other reasons in order to obtain a desired reaction product, the thermostable biomolecules are of great importance here. An example of this is the polymerase chain reaction , in which thermostable DNA polymerases are used by organisms such as Thermus aquaticus . Organisms that have a high temperature optimum due to their thermally stable structures are called thermophilic . Thermostable proteins often have a compact structure for the additional stabilization of their protein folding and increasingly have hydrogen bonds , salt bridges , hydrolysis- less sensitive amino acids and comparatively high affinities of the monomers of a protein complex to one another.

Since protein-based toxins in particular are often heat-labile, toxins can be divided into thermostable and thermolabile toxins. While thermolabile toxins such as some lectins are inactivated by heating, thermostable toxins such as amatoxins survive this treatment without major losses. This is of particular importance for the cooking effect of foods that are toxic in their raw state (e.g. potatoes, beans, lentils and some mushrooms).

Thermal disinfection processes are based on overcoming the thermal stability of the proteins of pathogens .

The thermal stability of proteins can be increased by protein engineering , cross-linking or coupling to polymers .

literature

  • Jeremy M. Berg, John L. Tymoczko, Lubert Stryer : Stryer Biochemistry . 7th edition, Springer-Verlag, Berlin / Heidelberg 2013, ISBN 978-3-8274-2988-9 .
  • Michael T. Madigan, John M. Martinko: Brock Mikrobiologie 11th edition, Pearson Studium, Munich 2006, ISBN 3-8273-7187-2 .

Individual evidence

  1. ↑ Addition (sic!) And fillers for plastics , website about plastics technology, last accessed in February 2020
  2. ↑ General report on treatment and recovery routes for PVC waste ; Federal Ministry of Agriculture, Forestry, Environment and Water Management, Vienna, December, 2002 (PDF file) , last accessed in February 2020
  3. ↑ a b Hans Jürgen Wernicke and Joachim Großmann: “Environmentally friendly stabilization of PVC by synthetic hydrotalcites” ; Current newsreel of the GDCh; 2008, last accessed February 2020
  4. ^ Vinyl 2010. Voluntary commitment by the PVC industry. The European Council of Vinyl Manufacturers (industry association) (PDF file) , last accessed in February 2020
  5. ↑ EP DeBenedictis, E. Hamed, S. ketene: Mechanical Reinforcement of protein with polymer conjugation. In: ACS Nano . Volume 10, Number 2, February 2016, pp. 2259-2267, doi : 10.1021 / acsnano.5b06917 , PMID 26687555 .