Kleinmolekular

kleinmolekular is a German term used in the sciences to describe substances composed of relatively few atoms and possessing a low molecular weight, as opposed to macromolecules such as polymers and proteins. In English-language science, the equivalent term is small molecule. In practice, kleinmolekular denotes chemical compounds with well-defined structures that can usually be synthesized from simple building blocks and purified by standard methods. The typical boundary between small molecules and macromolecules is not fixed; however, many chemists classify small molecules as having molecular weights below roughly 1,000 daltons, with a more stringent commonly used range around 500–900 Da in drug discovery.

In pharmacology and medicinal chemistry, kleinmolekular refers to compounds designed to interact with biological targets, such as enzymes or receptors, by fitting into binding sites. They contrast with biologics, which are large molecules like antibodies. Small molecules generally offer advantages in oral bioavailability, chemical stability, and manufacturing scalability, but may face challenges with selectivity, off-target effects, and metabolic susceptibility.

In materials science, kleinmolekulare entities include organic semiconductors, dyes, and receptor ligands used in supramolecular chemistry and catalysis. The term emphasizes molecular-level control and predictable physicochemical properties.

Etymology: Kleinmolekular derives from German, literally 'small molecule.' The term is used mainly in German-speaking scientific literature and is often translated as small molecule in international contexts.