Glossary
The vocabulary of peptide chemistry and lab documentation, defined in plain language.
A
- Acetate salt
- The most common counter-ion form for purified research peptides. Positively charged residues pair with acetate anions after ion exchange, replacing the trifluoroacetate left by synthesis and cleavage.
- Aib (α-aminoisobutyric acid)
- A non-coded amino acid with two methyl groups on its α-carbon. Substituting it into a synthetic peptide restricts the backbone conformation.
- Amidation (C-terminal)
- Replacement of the C-terminal carboxylic acid with an amide (-NH2), which removes the negative charge at the C-terminus. Written as -NH2 at the end of a sequence.
- Amino acid residue
- A single amino acid unit within a peptide chain, after it has lost water in forming peptide bonds.
C
- Certificate of analysis (COA)
- A document reporting the test results for a specific production lot, typically including HPLC purity, mass-spec identity, appearance and test date.
- Counter-ion
- An ion of opposite charge that accompanies a charged peptide in its solid salt form, such as acetate, trifluoroacetate or chloride.
D
- D-amino acid
- The mirror-image (enantiomeric) form of a standard L-amino acid, written with a D- prefix in a sequence, for example D-Phe.
- Disulfide bridge
- A covalent bond between the sulfur atoms of two cysteine residues that constrains a peptide's shape.
E
- Endotoxin
- Lipopolysaccharide from the outer membrane of Gram-negative bacteria. Reported on some COAs, measured by the LAL (Limulus amebocyte lysate) test.
F
- Fill weight
- The gross mass of lyophilized powder dispensed into a vial. It includes the peptide, its counter-ion and residual water.
H
- HPLC
- High-performance liquid chromatography. Reverse-phase HPLC separates a peptide from synthesis impurities so purity can be expressed as the main peak's share of total UV absorbance.
- Hygroscopic
- Readily absorbing moisture from the air. Most lyophilized peptides are hygroscopic, which is why vials should warm to room temperature before opening.
I
- In vitro
- Work carried out in laboratory vessels such as test tubes, plates and culture dishes.
L
- Lot number
- A unique identifier for a single production batch. It links a vial to its synthesis record and certificate of analysis.
- Lyophilization
- Freeze-drying. Water is removed from a frozen solution under vacuum by sublimation, leaving a dry, stable powder or cake.
M
- Mass spectrometry (MS)
- An analytical method that measures the mass-to-charge ratio of ions. Used to confirm a peptide's identity by matching its observed mass to the theoretical molecular weight.
- Molecular weight (MW)
- The sum of the atomic weights in a molecule, expressed in g/mol or daltons (Da). Peptide MWs range from a few hundred to several thousand daltons.
N
- Net peptide content
- The fraction of a lyophilized powder's mass that is actually peptide, as opposed to counter-ions and water. Typically 60 to 90 percent of gross weight.
P
- Peptide
- A short chain of amino acids joined by peptide bonds, conventionally fewer than about 50 residues. Longer chains are generally called proteins.
- Peptide bond
- The amide bond formed between the carboxyl group of one amino acid and the amino group of the next.
- Purity (HPLC)
- The percentage of total UV peak area at a set wavelength that belongs to the target peptide. It reflects related-substance impurities, not water or salt content.
R
- Research Use Only (RUO)
- A labeling category for materials supplied solely for laboratory research. RUO materials are not approved or intended for any other use.
S
- Sequence
- The order of amino acid residues in a peptide, written from the N-terminus to the C-terminus using one-letter or three-letter codes.
- Solid-phase peptide synthesis (SPPS)
- The standard method for making synthetic peptides, in which amino acids are added one at a time to a chain anchored on a resin bead, then cleaved off and purified.
T
- TFA (trifluoroacetate)
- The counter-ion left on peptides after cleavage from the synthesis resin with trifluoroacetic acid. Often exchanged for acetate during purification.