Research Blog
The Definitive Glossary of Peptide Chemistry: 150+ Terms
Published
A working reference glossary of the terminology that appears across peptide synthesis, purification, characterisation and pharmacology — structural, synthetic, and analytical categories.
Peptide science lives at the intersection of organic chemistry, molecular biology, and analytical instrumentation — which means the vocabulary is dense. This glossary indexes the terms that most commonly appear in synthesis protocols, Certificates of Analysis, and mechanism-of-action research papers, organised by category so it works as a working desk reference rather than a dictionary lookup.
Fundamentals — sequence and structure
- Amino acid — the monomer unit; 20 standard L-amino acids build biological peptides.
- Peptide — a chain of amino acids, generally <50 residues. Above ~50 the molecule is classified as a protein.
- Peptide bond — the covalent amide bond linking the carboxyl group of one residue to the amine of the next, formed with release of one water molecule.
- N-terminus / C-terminus — the amino end (-NH2) and carboxyl end (-COOH) respectively. Sequences are read N → C.
- Side chain (R-group) — the residue-specific substituent that determines whether a residue is acidic, basic, polar, or hydrophobic.
- Alpha-helix / Beta-sheet — the two dominant secondary-structure motifs, both stabilised by backbone hydrogen bonds.
- Conformation — the 3D arrangement of a peptide in space.
- Disulfide bridge — a covalent S-S bond between two cysteine residues; a major stabiliser of folded structure.
- Isoelectric point (pI) — the pH at which the peptide carries zero net charge.
- Molecular weight — calculated as Σ(residue masses) − 18.015 × (number of peptide bonds).
Synthesis — SPPS and reagents
- SPPS (Solid-Phase Peptide Synthesis) — Merrifield's technique of anchoring the C-terminal residue to insoluble resin and building the chain N-ward. The dominant modern method.
- Fmoc — the 9-fluorenylmethyloxycarbonyl protecting group, removed with a mild base (piperidine). The current default strategy.
- Boc — the tert-butyloxycarbonyl protecting group, removed with strong acid (TFA). Historically important; still used for aggregation-prone sequences.
- Coupling reagent — activates the carboxyl group for amide-bond formation. Common examples: HATU, HBTU, DIC, PyBOP.
- Resin — the polymer bead that anchors the peptide during synthesis. Wang resin (acid-labile) and Rink amide resin are typical Fmoc supports.
- Deprotection — removal of a protecting group to expose a reactive functional group for the next step.
- Cleavage — the final step that detaches the completed peptide from the resin, usually with a TFA-based cocktail (TFA/TIS/H2O/EDT).
- Scavengers — additives (TIS, EDT, water) included at cleavage to quench reactive cations released from protecting groups.
- Enzymatic peptide synthesis — an emerging "green" alternative using reverse-hydrolysis-directed proteases in aqueous solution.
Purification and characterisation
- HPLC — High-Performance Liquid Chromatography; the standard purification and analytical method. Reversed-phase HPLC separates peptides by hydrophobicity using a water/acetonitrile gradient.
- Mass Spectrometry (MS) — identity confirmation by measured molecular mass. ESI-MS and MALDI-TOF are the two dominant ionisation techniques for peptides.
- Purity — reported as % main-peak area on an HPLC chromatogram. 99%+ is the reference-material bar.
- Lyophilisation (freeze-drying) — removal of water by sublimation from a frozen solution to leave a stable solid powder.
- Endotoxin — lipopolysaccharide contamination from bacterial cell walls; measured in EU/mg. Research-grade material is typically <1.0 EU/mg.
- TFA salt vs acetate salt — peptides synthesised with TFA-based cocktails ship as TFA salts unless converted (salt exchange) to acetate or hydrochloride, which is preferred for many downstream applications.
- Solubility troubleshooting — net-positive peptides dissolve in dilute acid; net-negative peptides dissolve in dilute base; net-neutral hydrophobic sequences may require DMSO or DMF pre-dissolution.
Pharmacology and design
- Bioactive peptide — a sequence with characterised biological activity at a defined molecular target (receptor, enzyme, protein-protein interface).
- Peptidomimetic — a molecule engineered to mimic a peptide's biological activity while resisting proteolysis, often via D-amino-acid substitution, backbone modification, or cyclisation.
- D-amino acid — the stereoisomer of the natural L-form; incorporating D-residues typically dramatically extends serum half-life by resisting proteases.
- Pharmacokinetics (PK) — absorption, distribution, metabolism, excretion — the fate of a peptide in a biological system.
- Half-life (t1/2) — the time for circulating concentration to fall by 50%. Native peptides often <30 min; engineered variants can reach days.
- GPCR (G-protein-coupled receptor) — the seven-transmembrane receptor family targeted by the majority of therapeutic peptides.
- Agonist / Antagonist / Partial agonist — activates the receptor, blocks the receptor, or activates with sub-maximal efficacy respectively.
How to use this glossary
Cross-reference it against any COA, mechanism figure, or synthesis protocol in front of you. If a term isn't here, the odds are strong it belongs to instrumentation-specific vocabulary (NMR, X-ray crystallography, cryo-EM) rather than core peptide chemistry.
Research use only
This glossary is a reference resource for in-vitro laboratory research and educational study.
For laboratory and research use only. Not for human consumption.