Peptide Glossary: Lab & Chemistry Terms

Form & handling

Lyophilized: Freeze-dried. Water is removed from a frozen material under vacuum, leaving a dry powder or cake in a sealed vial. All Rocky Mountain Peptides products are supplied in lyophilized form.
Reconstitution: Dissolving a lyophilized material in a suitable diluent to make a solution for laboratory use. See the reconstitution guide.
Diluent: The liquid used to dissolve a lyophilized material or to dilute a solution to a lower concentration.
Stock solution: A concentrated solution prepared first and then diluted to working concentrations. The concentration calculator shows the concentration of a stock solution and the dilution steps to a working solution.
Concentration (mg/mL): The amount of material per unit volume of solution. 1 mg/mL equals 1,000 µg/mL, or 1 µg per µL.
C1V1 = C2V2: The dilution equation. The amount of material stays the same when diluent is added, so starting concentration × starting volume equals final concentration × final volume.
Aliquot: A measured portion of a solution, divided out so the whole stock does not have to be handled each time.

Peptide structure

Peptide: A chain of amino acids joined by peptide (amide) bonds. Short chains are often named by length: dipeptide (2), tripeptide (3), pentapeptide (5) and so on.Example: GHK is a tripeptide (Gly-His-Lys). Ipamorelin is a pentapeptide.
Residue: A single amino acid unit within a peptide chain. Peptide length is usually given as a residue count.Example: BPC-157 is listed in PubChem with a 15-residue sequence. Thymosin beta4 has 43 residues.
Sequence notation: The order of amino acids from the N-terminus to the C-terminus, written with three-letter codes (Gly-Glu-Pro) or one-letter codes (GEP).Example: MOTS-c is listed in PubChem as H-MRWQEMGYIFYPRKLR-OH.
N-terminus and C-terminus: The two ends of a peptide chain. The N-terminus carries a free amino group and is written first. The C-terminus carries a carboxyl group and is written last.
Free acid (-OH): A C-terminus left as a carboxylic acid. Sequences sometimes show this as -OH at the end, with H- marking an unmodified N-terminus.
C-terminal amidation (-NH2): A C-terminus converted from a carboxylic acid to an amide.Examples: Ipamorelin (…-Lys-NH2), Sermorelin, KPV (Ac-Lys-Pro-Val-NH2).
N-terminal acetylation (Ac-): An acetyl group attached to the N-terminal amino group.Examples: Thymalfasin, Afamelanotide, Melanotan II, KPV.
D-amino acid: The mirror-image (enantiomer) form of an amino acid, written with a D- prefix. Most natural amino acids occur in the L form.Examples: Ipamorelin contains D-Phe and D-2-Nal. GHRP-6 contains D-Trp and D-Phe.
Non-proteinogenic amino acid: An amino acid outside the standard 20 used in protein synthesis.Examples: Aib (2-aminoisobutyric acid) in Ipamorelin, Nle (norleucine) in Afamelanotide and Melanotan II, 2-Nal (3-(2-naphthyl)alanine) in GHRP-2.
Cyclic peptide: A peptide in which part of the chain is joined into a ring.Example: Melanotan II is listed as Ac-Nle-cyclo[Asp-His-D-Phe-Arg-Trp-Lys]-NH2.
Disulfide bridge: A covalent S–S bond between two cysteine residues that closes a ring within the peptide.Example: Oxytocin (cyclic 1–6 disulfide).
Blend: More than one compound supplied together in the same vial, with the amount of each listed per vial. See all blends.

Chemistry & identifiers

Molecular formula: The number of atoms of each element in one molecule, such as C₆₂H₉₈N₁₆O₂₂. See the molecular weight chart.
Molecular weight: The mass of one molecule averaged over natural isotope abundance, in g/mol (daltons).
Monoisotopic and exact mass: The mass calculated from the most abundant isotope of each element. Mass spectrometry results are usually compared against this value.
Salt form (acetate, TFA): Peptides are often isolated as salts with a counter-ion such as acetate or trifluoroacetate (TFA). The counter-ion adds weight, so the gross vial weight is higher than the weight of the peptide alone. PubChem molecular weights are normally given for the free form.
Net peptide content: The share of a lyophilized powder that is the peptide itself, excluding counter-ions and residual moisture.
CAS number: A unique identifier assigned by the Chemical Abstracts Service to a specific substance.
PubChem CID: The compound identifier in PubChem, the open chemistry database of the U.S. National Library of Medicine. Each product page links to its PubChem record.
InChIKey: A fixed-length text identifier derived from a compound's structure, used to match the same compound across databases.
IUPAC name: The systematic chemical name built from the compound's structure under International Union of Pure and Applied Chemistry rules.
Topological polar surface area (TPSA): A computed value, in Å², for the surface area of a molecule's polar atoms. PubChem lists it with other computed properties on each record.

Definitions are general laboratory and chemistry terms. Compound examples use data from PubChem. All products are for laboratory research use only and are not for human or veterinary use.