Low molecular compound

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As a low molecular weight compound ( English molecule small , dt. "Small molecules") is referred to in various fields, a class of substances of low molecular weight. As a rule, they form the opposite group to larger, high molecular weight substances, e.g. B. long chain polymers. Due to the significantly lower molecular mass and spatial expansion, low molecular weight compounds often have different chemical and physical properties and can therefore be used or processed differently.

Pharmacology and biochemistry

In pharmacology and biochemistry , a class of active ingredients is called low molecular weight, the molecular weight of which does not exceed about 800 g · mol −1 . Due to their small size, according to the Rule of Five , small molecules are partially able to penetrate cells and develop their effect there. The currently approved drugs are by far the largest part of low molecular weight molecules.

In the pharmaceutical practice of English-speaking countries, the English term small molecules is primarily used to distinguish biologics , which are mostly proteins and therefore very "large molecules". In this meaning, small molecules primarily refer to the classic pharmaceutical active ingredients, which - in contrast to biologics - can usually be described with a simple structural formula and chemically synthesized. The term small molecules thus encompasses an extremely heterogeneous group of substances that - apart from their small size - have little in common.

These compounds have a variety of biological functions, such as signaling molecules , tools in molecular biology , drugs , pesticides and many more. They can be of natural (e.g. secondary metabolites ) or artificial (e.g. antivirals ) origin and have both positive effects against diseases (e.g. drugs) or harmful effects (e.g. teratogens and carcinogens ).

A very small fraction of the small molecules (around 2%) is able to cross the blood-brain barrier , so that some drugs based on small molecules can be effective against depression , schizophrenia and insomnia . Low molecular weight compounds are also gaining in importance for the treatment of brain tumors and brain metastases.

Electrical engineering

In the electrical one short chain organic molecules with conjugated double bonds referred to as "small molecules" (Engl .: small molecules ) or (less often) low molecular weight compounds. They are among the electrically conductive plastics and, together with long-chain or high-molecular conjugated polymers, form the basis for organic electronics .

These "small molecules" are used, e.g. B. pentacene for organic electrical circuits (see. Organic field effect transistor , OFET) and in organic light-emitting diodes (OLED, in this case also called SOLED or SMOLED ) and organic solar cells . However, many possible areas of application are still in the development stage.

Individual evidence

  1. World Cup Pardridge: The Blood-Brain Barrier: Bottleneck in Brain Drug Development. In: NeuroRx. 2, No. 1, 2005, pp. 3-14, PMID 15717053 .
  2. N. Butowski and SM Chang: Small molecule and monoclonal antibody therapies in neurooncology. In: Cancer Control No. 2, 2005, pp. 116-124, PMID 15855895 .
  3. G. Tomasello et al. a .: Brain metastases in HER2-positive breast cancer: the evolving role of lapatinib. In: Crit Rev Oncol Hematol 75, No. 2, 2010, pp. 110-121, PMID 20004109 .