Reactants or Reagents, Various Definations
A reagent or Reactant: Is
a substance or compound added to a system (Matter) to cause a chemical reaction, or
added to test if a reaction occurs.
The terms
reactant and reagent are often used interchangeably—however, a reactant is more
specifically a substance consumed in the course of a chemical reaction.
Solvents (Carrier of reactant) ,
though involved in the reaction, are usually not called reactants. Similarly,
catalysts (Substance that aid the rate of chemical reaction but remain unchanged after the reaction) 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.
In organic
chemistry, the term "reagent" denotes a chemical ingredient (a
compound or mixture, typically of inorganic or small organic molecules)
introduced to cause a desired transformation of an organic substance.
Examples
include the Collins reagent, Fenton's reagent, and Grignard reagents. 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
concentration of a substance, e.g.
by
colorimetry. Examples include Fehling's reagent, Millon's reagent, and Tollens'
reagent.
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. (American Society for Testing And Materials).
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.
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.
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.
Tool compounds
are also important reagents in biology; they are small molecules or
biochemicals like siRNA or antibodies that are known to affect a given
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.
Many natural
products, such as curcumin, are hits in almost any assay in which they are
tested, are not useful tool compounds, and are classified by medicinal chemists
as "pan-assay interference compounds".
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