Oligomeric proanthocyanidins (OPC) strictly refer to dimer and trimer polymerizations of catechins. The monomer in step-growth polymerization will be consumed very quickly to dimer, trimer or oligomer. Both dimer and trimer domain-swap structures have been solved. Macrophage migration inhibitory factor assembles into a trimer composed of three identical subunits. Gp120 and gp41 assemble as a trimer. Glycoprotein gp120 is closely associated to a trimer of gp41 via van der Waals interactions. It exists as a monomer, trimer, tetramer, octamer or dodecamer, creating multiple functions. Purification by sublimation gives mainly the trimer and tetramer (PNCl). Oats and barley differ in the ratio of trimer and tetramer 1-4 linkages. Paraldehyde is the cyclic trimer of acetaldehyde molecules. In these crystals, the carotenoid bacterioruberin binds to crevices between the subunits of the trimer. Phenylboronic acid can be selfcondensed to the cyclic trimer called triphenyl anhydride or triphenylboroxin. HA trimer is made of three identical monomers. In the case of the cyclic trimer each tetrahedron shares two vertices with adjacent tetrahedra. Laminins are trimeric molecules; laminin-1 is an alpha1 beta1 gamma1 trimer.