2,4-Dinitrophenol (2,4-DNP or simply DNP) is an organic compound with the formula HOC6H3(NO2)2. It is a yellow, crystalline solid that has a sweet, musty odor. It sublimates, is volatile with steam, and is soluble in most organic solvents as well as aqueous alkaline solutions. When in a dry form, it is a high explosive and has an instantaneous explosion hazard. It is a precursor to other chemicals and is biochemically active, uncoupling oxidative phosphorylation from the electron transport chain in cells with mitochondria, by allowing hydrogen cations to pass from the intermembrane space into the mitochondrial matrix. Oxidative phosphorylation is a highly regulated step in aerobic respiration that is inhibited, among other factors, by normal cellular levels of ATP. Uncoupling it results in chemical energy from diet and energy stores such as triglycerides being wasted as heat with minimal regulation, leading to dangerously high body temperatures that may develop into heatstroke. Its use as a dieting aid has been identified with severe side-effects, including a number of deaths. Uses Historically, DNP has been used as an antiseptic and as a non-selective bioaccumulating pesticide. DNP was particularly useful as a herbicide alongside other closely related dinitrophenol herbicides like 2,4-dinitro-o-cresol (DNOC), dinoseb and dinoterb. Since 1998 DNP has been withdrawn from agricultural use. Currently, there are no actively registered pesticides containing DNP in the United States or Europe. Dinoseb is used industrially as a polymerisation inhibitor during styrene production. In 2023 after extensive consultation the Home Office couldn't determine any legitimate industrial DNP uses in the United Kingdom. It is a chemical intermediate in the production of sulfur dyes, wood preservatives and picric acid. DNP has also been used to make photographic developers and explosives (see shellite). DNP is classified as an explosive in the United Kingdom and the United States. Although DNP is widely considered too dangerous for clinical use, its mechanism of action remains under investigation as a potential approach for treating obesity. As of 2015, research is being conducted on uncoupling proteins naturally found in humans. Biochemistry In living cells, DNP acts as a proton ionophore, an agent that can shuttle protons (hydrogen cations) across biological membranes. It dissipates the proton gradient across the mitochondria membranes, collapsing the proton motive force that the cell uses to produce most of its ATP chemical energy. Instead of producing ATP, the energy of the proton gradient is lost as heat. DNP is