Substrate (chemistry)

Chemical roles and contexts

Substrates appear in several overlapping senses. In homogeneous solution-phase chemistry a substrate is often the organic or inorganic molecule that reacts with a reagent (reagent). In heterogeneous catalysis the substrate can be the solid surface or the adsorbed molecule; in surface science the substrate may be the underlying material that supports a thin film or catalyst. In electrochemistry the electrode material can be called a substrate when layers or films are deposited on it.

Enzymes and biochemistry

In biochemistry the substrate is the specific molecule upon which an enzyme acts. Binding typically occurs at the enzyme's active site, forming an enzyme–substrate complex that proceeds to a transition state and then products. This interaction is central to models of enzyme kinetics such as the Michaelis–Menten framework. For more on biochemical contexts, see: biochemistry and enzyme.

Characteristics and examples

• Specificity: many catalysts and enzymes recognize particular functional groups or shapes on a substrate.
• Reactivity: substrates differ in how readily they form bonds or are transformed under given conditions.
• Physical form: substrates may be dissolved molecules, adsorbed species, or solid supports.

Examples include an alkene serving as a substrate for an addition reaction, glucose as a substrate for hexokinase in metabolism, and a silicon wafer acting as a substrate for thin-film deposition in materials science.

Distinctions and practical importance

"Substrate" is sometimes used interchangeably with "reactant," but it can emphasize the target of a catalyst or the surface role in heterogeneous systems. It is distinct from a catalyst (which is unchanged overall) and from a reagent (which may be added to effect change). Recognizing the intended sense of substrate helps clarify experimental design, mechanistic interpretation, and applied processes such as drug development, industrial catalysis, and surface engineering.