Only compounds with the
proper surface area will
pass through the
plasma membrane.

True surface area (TSA)

The orientation of molecules depends on the spatial distribution of polar/non-polar moieties. 

Projection of the molecule at the air-water interface (a good model for a lipid membrane) defines the area / adsorbed molecule, representing the true surface area (TSA) of the molecule.

The commonly used parameter PSA is measured by computation and does not correspond to the true surface area, particularly for compounds with a high degree of conformational freedom.   
 

> Too large compounds cannot intercalate into the lipid membrane:

 

• The true surface area is a vital ADME/Tox parameter and a potential indicator why a compound will not pass through the membrane.

• With the high throughput Kibron Delta-8 this property is measured easily and rapidly.