{{Short description|Substance added to a system to cause a chemical reaction}} {{Redirect-distinguish|Reactants|Reactance (disambiguation){{!}}Reactance|Regent}} [[File:SulfurReagent.jpg|thumb|Reagents, such as sulfur (pictured), are the starting materials used in chemical reactions.]]
In chemistry, a '''reagent''' ({{IPAc-en|r|i|ˈ|eɪ|dʒ|ən|t}} {{respell|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.<ref name=gold>{{GoldBookRef |title=Reactant |file=R05163 |year=1996}}</ref> A '''reactant''' is a substance or compound that is consumed in a chemical reaction.<ref name="gold" /> The terms ''reactant'' and ''reagent'' are often used interchangeably, but reactant specifies a substance ''consumed'' in the course of a chemical reaction; ''reagent'' is used in the context of chemical analysis, while ''reactant'' is used in the context of reaction itself. 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==
=== Organic chemistry === 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.<ref>{{cite web|url=https://commonorganicchemistry.com/Sidebar/Common_Reagents.htm|title=Common Reagents in Organic Chemistry|publisher=CommonOrganicChemistry.com|access-date=9 March 2026}}</ref>
=== Analytical chemistry === 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.<ref>{{cite web|url=https://reagents.alfa-chemistry.com/products/analytical-reagents.html?srsltid=AfmBOoq2MOEQ3AdLVOiUlD3AtVDjxDWSPwcKVt-TzrWCBGxY0mKqhh6E|title=Analytical Reagents - Analytical Products / Alfa Chemistry|publisher=Alfa Chemistry|access-date=9 March 2026}}</ref>
==Commercial or laboratory preparations== In commercial or laboratory preparations, {{anchor|Reagent_grade}}'''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.<ref>{{cite web|url=https://wp.stolaf.edu/chemical-hygiene/preparing-chemical-solutions-reagents-and-buffers/#:~:text=The%20ability%20to%20prepare%20accurate%20laboratory%20reagents,Calculator**%20Dilutes%20a%20solution%20of%20known%20molarity|title=Preparing Chemical Solutions, Reagents, and Buffers|publisher=St. Olaf College|access-date=9 March 2026}}</ref>
==Biology== 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.<ref>{{cite journal|last1=Fox|first1=Jeffrey L|title=Antibody reagents revolutionizing immunology|journal=Chemical & Engineering News Archive|date=1 January 1979|volume=57 |pages=15–17|doi=10.1021/cen-v057n001.p015}}</ref><ref name=NIHreport1998>{{cite web |title=Report of the National Institutes of Health (NIH) Working Group on Research Tools|url=http://www.nih.gov/news/researchtools/index.htm|publisher=NIH|archive-url=https://web.archive.org/web/20000816014021/http://www.nih.gov/news/researchtools/index.htm |archive-date=August 16, 2000|date=June 4, 1998}}</ref> 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.<ref name=NIHreport1998/><ref>{{cite journal |last1=Ishino |first1=S|last2=Ishino|first2=Y|title=DNA polymerases as useful reagents for biotechnology: the history of developmental research in the field |journal=Frontiers in Microbiology|date=29 August 2014|volume=5|pages=465|pmid=25221550|pmc=4148896|doi=10.3389/fmicb.2014.00465|doi-access=free}}</ref>
<!-- "Tool compound" redirects to this heading --> ===Tool compounds=== Tool compounds are an important class of reagent in biology. They are small molecules or biochemicals like siRNA or antibodies that are known to directly interact with or modulate a specific biomolecule—for example a drug target—but are unlikely to be useful as drugs themselves, and are often starting points in the drug discovery process.<ref>{{cite journal |last1=Kenakin|first1=T|last2=Bylund|first2=DB|last3=Toews|first3=ML|last4=Mullane|first4=K|last5=Winquist|first5=RJ|last6=Williams|first6=M|title=Replicated, replicable and relevant-target engagement and pharmacological experimentation in the 21st century |journal=Biochemical Pharmacology|date=1 January 2014 |volume=87 |issue=1 |pages=64–77 |doi=10.1016/j.bcp.2013.10.024|pmid=24269285}}</ref><ref>{{cite journal|last1=Lindsley|first1=CW|title=2013 Philip S. Portoghese Medicinal Chemistry Lectureship: drug discovery targeting allosteric sites|journal=Journal of Medicinal Chemistry|date=25 September 2014 |volume=57 |issue=18 |pages=7485–7498|pmid=25180768|pmc=4174999|doi=10.1021/jm5011786}}</ref>
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.<ref>{{cite journal|last1=Baker|first1=Monya|title=Deceptive curcumin offers cautionary tale for chemists |journal=Nature |date=9 January 2017|volume=541|issue=7636|pages=144–145|doi=10.1038/541144a|pmid=28079090|bibcode=2017Natur.541..144B|doi-access=free}}</ref><ref>{{cite journal|last1=Dahlin|first1=JL|last2=Walters|first2=MA|title=The essential roles of chemistry in high-throughput screening triage |journal=Future Medicinal Chemistry|date=July 2014|volume=6|issue=11|pages=1265–1290|pmid=25163000|pmc=4465542|doi=10.4155/fmc.14.60}}</ref><ref>{{cite journal|last1=Baell|first1=JB|last2=Holloway|first2=GA|title=New substructure filters for removal of pan assay interference compounds (PAINS) from screening libraries and for their exclusion in bioassays.|journal=Journal of Medicinal Chemistry |date=8 April 2010|volume=53|issue=7|pages=2719–2740|doi=10.1021/jm901137j|pmid=20131845|citeseerx=10.1.1.394.9155}}</ref>
==See also== * Limiting reagent * Common reagents * Product * Reagent bottle * Substrate * {{in title}}
==References== {{reflist}}
==External links== * {{Commonscat-inline2|Reagents}} * {{Wiktionary-inline|reagent|reactant}}
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Category:Reagents Category:Reagents for organic chemistry Category:Biological techniques and tools Category:Chemical reactions Category:Reagents for biochemistry