Reagent

Substance added to a system to cause a chemical reaction

Not to be confused with Regent.

"Reactants" redirects here; not to be confused with Reactance.

Reagents, such as sulfur (pictured), are the starting materials used in chemical reactions.

In chemistry, a reagent (/riˈeɪdʒənt/ ree-AY-jənt) or analytical reagent is a substance or compound added to a system to cause a chemical reaction, or test if one occurs.[1] The terms reactant and reagent are often used interchangeably, but reactant specifies a substance consumed in the course of a chemical reaction.[1] Solvents, though involved in the reaction mechanism, are usually not called reactants. Similarly, catalysts are not consumed by the reaction, so they are not reactants. In biochemistry, especially in connection with enzyme-catalyzed reactions, the reactants are commonly called substrates.

## Definitions

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### Organic chemistry

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In organic chemistry, the term "reagent" denotes a chemical ingredient (a compound or mixture, typically of inorganic or small organic molecules) introduced to cause the desired transformation of an organic substance. Examples include the Collins reagent, Fenton's reagent, and Grignard reagents.[citation needed]

### Analytical chemistry

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In analytical chemistry, a reagent is a compound or mixture used to detect the presence or absence of another substance, e.g. by a color change, or to measure the concentration of a substance, e.g. by colorimetry. Examples include Fehling's reagent, Millon's reagent, and Tollens' reagent.[citation needed]

## Commercial or laboratory preparations

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In commercial or laboratory preparations, reagent-grade designates chemical substances meeting standards of purity that ensure the scientific precision and reliability of chemical analysis, chemical reactions or physical testing. Purity standards for reagents are set by organizations such as ASTM International or the American Chemical Society. For instance, reagent-quality water must have very low levels of impurities such as sodium and chloride ions, silica, and bacteria, as well as a very high electrical resistivity. Laboratory products which are less pure, but still useful and economical for undemanding work, may be designated as technical, practical, or crude grade to distinguish them from reagent versions.[citation needed]

## Biology

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In the field of biology, the biotechnology revolution in the 1980s grew from the development of reagents that could be used to identify and manipulate the chemical matter in and on cells.[2][3] These reagents included antibodies (polyclonal and monoclonal), oligomers, all sorts of model organisms and immortalised cell lines, reagents and methods for molecular cloning and DNA replication, and many others.[3][4]

### Tool compounds

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Tool compounds are an important class of reagent in biology. They are small molecules or biochemicals like siRNA or antibodies that are known to affect a given biomolecule[ambiguous]—for example a drug target—but are unlikely to be useful as drugs themselves, and are often starting points in the drug discovery process.[5][6]

However, many natural substances are hits in almost any assay in which they are tested, and therefore not useful as tool compounds. Medicinal chemists class them instead as pan-assay interference compounds. One example is curcumin.[7][8][9]

## See also

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* Limiting reagent
* Common reagents
* Product
* Reagent bottle
* Substrate
* All pages with titles containing Reagent

## References

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1. ^ a b IUPAC, Compendium of Chemical Terminology, 5th ed. (the "Gold Book") (2025). Online version: (1996) "Reactant". doi:10.1351/goldbook.R05163
2. ^ Fox, Jeffrey L (1 January 1979). "Antibody reagents revolutionizing immunology". Chemical & Engineering News Archive. 57: 15–17\. doi:10.1021/cen-v057n001.p015.
3. ^ a b "Report of the National Institutes of Health (NIH) Working Group on Research Tools". NIH. June 4, 1998. Archived from the original on August 16, 2000.
4. ^ Ishino, S; Ishino, Y (29 August 2014). "DNA polymerases as useful reagents for biotechnology: the history of developmental research in the field". Frontiers in Microbiology. 5: 465. doi:10.3389/fmicb.2014.00465. PMC 4148896. PMID 25221550.
5. ^ Kenakin, T; Bylund, DB; Toews, ML; Mullane, K; Winquist, RJ; Williams, M (1 January 2014). "Replicated, replicable and relevant-target engagement and pharmacological experimentation in the 21st century". Biochemical Pharmacology. 87 (1): 64–77\. doi:10.1016/j.bcp.2013.10.024. PMID 24269285.
6. ^ Lindsley, CW (25 September 2014). "2013 Philip S. Portoghese Medicinal Chemistry Lectureship: drug discovery targeting allosteric sites". Journal of Medicinal Chemistry. 57 (18): 7485–7498\. doi:10.1021/jm5011786. PMC 4174999. PMID 25180768.
7. ^ Baker, Monya (9 January 2017). "Deceptive curcumin offers cautionary tale for chemists". Nature. 541 (7636): 144–145\. Bibcode:2017Natur.541..144B. doi:10.1038/541144a. PMID 28079090.
8. ^ Dahlin, JL; Walters, MA (July 2014). "The essential roles of chemistry in high-throughput screening triage". Future Medicinal Chemistry. 6 (11): 1265–1290\. doi:10.4155/fmc.14.60. PMC 4465542. PMID 25163000.
9. ^ Baell, JB; Holloway, GA (8 April 2010). "New substructure filters for removal of pan assay interference compounds (PAINS) from screening libraries and for their exclusion in bioassays". Journal of Medicinal Chemistry. 53 (7): 2719–2740\. CiteSeerX 10.1.1.394.9155. doi:10.1021/jm901137j. PMID 20131845.

## External links

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* Media related to Reagents at Wikimedia Commons
* The dictionary definition of reactant at Wiktionary

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