Solvent exposure occurs when a

chemical A chemical substance is a form of matter having constant chemical composition and characteristic properties. Some references add that chemical substance cannot be separated into its constituent elements by physical separation methods, i.e., wit ...

, material, or

person A person (plural, : people) is a being that has certain capacities or attributes such as reason, morality, consciousness or self-consciousness, and being a part of a culturally established form of social relations such as kinship, ownership of pr ...

comes into contact with a

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

. Chemicals can be dissolved in solvents, materials such as

polymers A polymer (; Greek ''poly-'', "many" + '' -mer'', "part") is a substance or material consisting of very large molecules called macromolecules, composed of many repeating subunits. Due to their broad spectrum of properties, both synthetic an ...

can be broken down chemically by solvents, and people can develop certain ailments from exposure to solvents both organic and inorganic. Some common solvents include

acetone Acetone (2-propanone or dimethyl ketone), is an organic compound with the formula . It is the simplest and smallest ketone (). It is a colorless, highly volatile and flammable liquid with a characteristic pungent odour. Acetone is miscible wi ...

, methanol,

tetrahydrofuran Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...

dimethylsulfoxide Dimethyl sulfoxide (DMSO) is an organosulfur compound with the formula ( CH3)2. This colorless liquid is the sulfoxide most widely used commercially. It is an important polar aprotic solvent that dissolves both polar and nonpolar compounds a ...

, and

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

among countless others. In biology, the solvent exposure of an

amino acid Amino acids are organic compounds that contain both amino and carboxylic acid functional groups. Although hundreds of amino acids exist in nature, by far the most important are the alpha-amino acids, which comprise proteins. Only 22 alpha ...

in a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

measures to what extent the amino acid is accessible to the

(usually

) surrounding the protein. Generally speaking,

hydrophobic In chemistry, hydrophobicity is the physical property of a molecule that is seemingly repelled from a mass of water (known as a hydrophobe). In contrast, hydrophiles are attracted to water. Hydrophobic molecules tend to be nonpolar and, ...

amino acids will be buried inside the protein and thus shielded from the solvent, while

hydrophilic A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water.Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon'' Oxford: Clarendon Press. In contrast, hydrophobes are ...

amino acids will be close to the surface and thus exposed to the solvent. However, as with many biological rules exceptions are common and hydrophilic residues are frequently found to be buried in the native structure and vice versa. Solvent exposure can be numerically described by several measures, the most popular measures being

accessible surface area The accessible surface area (ASA) or solvent-accessible surface area (SASA) is the surface area of a biomolecule that is accessible to a solvent. Measurement of ASA is usually described in units of square angstroms (a standard unit of measurement ...

and

relative accessible surface area Relative accessible surface area or relative solvent accessibility (RSA) of a protein residue is a measure of residue solvent exposure. It can be calculated by formula: \text = \text / \text where ASA is the solvent accessible surface area ...

. Other measures are for example: * Contact number: number of amino acid neighbors within a sphere around the amino acid. * Residue depth: distance of the amino acid to the molecular surface. * Half sphere exposure: number of amino acid neighbors within two half spheres around the amino acid.

References

Lee B, Richards F. (1971
The interpretation of protein structures: estimation of static accessibility
J. Mol. Biol. 55:379-400 Greer J, Bush B. (1978
Macromolecular shape and surface maps by solvent exclusion
Proc. Natl. Acad. Sci. USA 75:303-307. Connolly M. (1983
Solvent-accessible surfaces of proteins and nucleic acids
Science 221:709-713 Chakravarty S, Varadarajan R. (1999
Residue depth: a novel parameter for the analysis of protein structure and stability
Structure Fold. Des. 7:723-732. Pintar A, Carugo O, Pongor S. (2003
Atom depth in protein structure and function
Trends Biochem. Sci. 28:593-597. Hamelryck T. (2005
An amino acid has two sides: A new 2D measure provides a different view of solvent exposure
Proteins Struct. Func. Bioinf. 59:38-48. Amino acids Nitrogen cycle Solvents {{chemistry-stub