THPTA is a water-soluble, very effective ligand for Cu(I)-catalyzed Alkyne-Azide click chemistry reactions (CuAAC). It serves a dual purpose: 1) Accelaration of the CuAAC reaction by maintain-ing the Cu(I) oxidation state of copper sources and 2) Protection of biomolecules from oxidative damage during the labeling reaction. THPTA is a superior alternative to water-insoluble TBTA. A stock solution can be prepared in ddH 2O and subsequently be stored at -20C. Avoid freeze-thaw cycles.