bond

In chemistry, the force holding two neighboring atoms in place and resisting their separation; a b. is electrovalent if it consists of the attraction between oppositely charged groups, or covalent if it results from the sharing of one, two, or three pairs of electrons by the bonded atoms.

- acylmercaptan b. —CO—S—; a “high-energy” b. formed by the condensation of a carboxyl group (—COOH) and a mercaptan (or thiol) group (—SH); widely formed in the course of intermediary metabolism, notably in the oxidation of fats, where the —SH is part of coenzyme A and the —COOH is part of the fatty acid being oxidized.

- apolar b. hydrophobic interaction.

- conjugated double bonds two or more double b. separated by each single b..

- coordinate covalent b. SYN: semipolar b..

- disulfide b. a single b. between two sulfurs; specifically, the —S—S— link binding two peptide chains (or different parts of one peptide chain); also occurs as part of the molecule of the amino acid, cystine, and is important as a structural determinant in many peptide and protein molecules, e.g., keratin, insulin, and oxytocin. A symmetric disulfide is R—S—S—R; R′—S—S—R is a mixed or asymmetric disulfide.

- double b. a covalent b. resulting from the sharing of two pairs of electrons, e.g., H₂C=CH₂ (ethylene).

- electrostatic b. b. between atoms or groups carrying opposite charges (or, in some cases, partial charges). SYN: heteropolar b., salt bridge.

- energy-rich b. high-energy compounds, under compound.

- eupeptide b. a peptide b. between the α-carboxyl group of one amino acid and the α-amino group of another amino acid. Cf.:peptide b., isopeptide b..

- heteropolar b. SYN: electrostatic b..

- high energy phosphate b. high-energy phosphates, under phosphate.

- hydrogen b. a b. arising from the sharing of a hydrogen atom, covalently bound to a strongly electronegative element ( e.g., N or O), with another strongly electronegative element ( e.g., N, O, or a halogen). In substances of biologic importance, the most common hydrogen bonds are those in which H links N to O or N; such bonds link purines on one strand to pyrimidines on the other strand of nucleic acid s, thus maintaining double-stranded structures as in the Watson-Crick helix.

- hydrophobic b. hydrophobic interaction.

- isopeptide b. an amide linkage between a carboxyl group of one amino acid and an amino group of another amino acid in which at least one of these groups is not on the α-carbon of one of the amino acid s; for example, the b. between the glutamyl residue and the cysteinyl residue of glutathione. Cf.:peptide b., eupeptide b..

- noncovalent b. b. in which electrons are not shared between atoms; E.G., electrostatic b., hydrogen b..

- peptide b. the common link (—CO—NH—) between amino acid s in proteins, actually a substituted amide, formed by elimination of H₂O between the —COOH of one amino acid and the H₂N— of another. Cf.:eupeptide b., isopeptide b..

- semipolar b. a b. in which the two electrons shared by a pair of atoms belonged originally to only one of the atoms; often represented by a small arrow pointing toward the electron receiver; e.g., nitric acid, O(OH)N→O; phosphoric acid, (OH)₃P→O. SYN: coordinate covalent b..

- single b. a covalent b. resulting from the sharing of one pair of electrons; e.g., H₃C—CH₃ (ethane).

- triple b. a covalent b. resulting from the sharing of three pairs of electrons; e.g., HCΞCH (acetylene).

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bond 'bänd n an attractive force that holds together atoms, ions, or groups of atoms in a molecule or crystal usu. represented in formulas by a line

bond vb

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(bond) 1. the linkage between two atoms or radicals of a chemical compound. 2. a mark used to indicate the number and attachment of the valences of an atom in constitutional formulas; it is represented by a pair of dots or a line between the atoms, e.g., HOH, HCCH or H:O:H, H:C:::C:H.