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Solid

2,2-Diphenyl-1-picrylhydrazyl is a stable free radical molecule most commonly used as a tool to monitor chemical reactions involving radicals, most notably in antioxidant assay.

DPPH has several crystalline forms which differ by the lattice symmetry and melting point. The commercial powder is a mixture of phases which melts at ~130 °C. DPPH-I (m.p. 106 °C) is orthorhombic, DPPH-II (m.p. 137 °C) is amorphous and DPPH-III (m.p. 128–129 °C) is triclinic.

This picrylhydrazyl derivative, also known as DPPH free radical, presents as a black crystalline powder. Store in a refrigerator - this substance is heat sensitive. 1,1-Diphenyl-2-picrylhydrazyl Free Radical is incompatible with oxidizing agents, strong bases and halogens. This chemical is harmful if swallowed. It may cause allergy or asthma symptoms or breathing difficulties if inhaled and an allergic reaction on the skin.

[1] SIDDARTHA BALIYAN. Determination of Antioxidants by DPPH Radical Scavenging Activity and Quantitative Phytochemical Analysis of Ficus religiosa.[J]. Molecules, 2022. DOI:10.3390/molecules27041326.
[2] G. CLARKE. High Correlation of 2,2-diphenyl-1-picrylhydrazyl (DPPH) Radical Scavenging, Ferric Reducing Activity Potential and Total Phenolics Content Indicates Redundancy in Use of All Three Assays to Screen for Antioxidant Activity of Extracts of Plants from the Malaysian Rainforest[C]//2 1. 2013: 1-10. DOI:10.3390/antiox2010001.
[3] IKUO NAKANISHI Yoshimi S. Electrochemical redox behavior of 2,2-diphenyl-1-picrylhydrazyl radical solubilized by β-cyclodextrin in water[J]. Electrochemistry Communications, 2022, 134: Article 107190. DOI:10.1016/j.elecom.2021.107190.
[4] JAMES BYH BEHRENDORFF. 2,2-Diphenyl-1-picrylhydrazyl as a screening tool for recombinant monoterpene biosynthesis.[J]. Microbial Cell Factories, 2013, 12: 76. DOI:10.1186/1475-2859-12-76.
[5] J. XIE K. M S. Re-evaluation of the 2,2-Diphenyl-1-picrylhydrazyl Free Radical (DPPH) Assay for Antioxidant Activity[J]. Journal of Agricultural and Food Chemistry, 2014, 62 19: 4251-4260. DOI:10.1021/jf500180u.