What it is
Epitalon is a tetrapeptide: four residues, written AEDG — alanine, glutamic acid, aspartic acid, glycine. It was developed as a synthetic counterpart to a peptide fraction isolated from pineal tissue, and it is among the smallest molecules sold in this category.
| Property | Value | Where it is confirmed |
|---|---|---|
| Residue count | 4 (Ala-Glu-Asp-Gly) | Synthesis record |
| Approximate mass | near 390 g/mol | Certificate of analysis |
| Character | Strongly acidic; two carboxylic side chains | Structure |
| Physical form supplied | Lyophilized solid | Label and batch record |
Why a high purity figure proves less here
A four-residue chain requires three coupling steps. The opportunities for a deletion sequence are correspondingly few, and the chain is short enough that separating a three-residue impurity from the four-residue product is easy chromatographically. Purity figures for this compound are therefore routinely very high — and that is a property of the synthesis, not evidence of unusual care.
The practical inversion is worth stating: on a 44-residue chain a purity figure carries real information because the synthesis is genuinely hard. On a four-residue chain, a high figure is close to guaranteed, so it discriminates between suppliers much less than it appears to. A low figure on a tetrapeptide, by contrast, is unusual and worth asking about.
Where the real question moves
With purity close to a given, identity carries more of the weight — and a small, highly polar molecule is where identity is least comfortable.
- Retention is weak. Two acidic side chains on a four-residue chain make this compound very polar, so it is poorly retained on a standard reversed-phase column and can elute close to the solvent front. A method not adapted for it may not resolve it from unretained material at all. See how to read an HPLC chromatogram on why the solvent front should be excluded from integration.
- Small masses have more near neighbours. At around 390 units, ordinary salts, buffer components and synthesis reagents sit in the same mass region as the product, so a mass result needs the stated formula alongside it to be meaningful.
- Sequence order is not established by mass. Any rearrangement of the same four residues has an identical mass. Retention-time matching against a properly characterised reference standard is what addresses this, which is why a report stating HPLC-RTM should name the standard.
The general point applies beyond this compound: the informative line on a certificate moves with the size of the molecule. Long chains: read the purity and the impurity envelope. Short chains: read the identity and the method.
Storage of the lyophilized solid
Supplied as a freeze-dried solid. Short, highly polar peptides are markedly hygroscopic — the acidic side chains attract water — so an intact seal and equilibration to room temperature before opening matter as much here as for any compound in the library.
Stability is a documented property rather than an assumed one: a laboratory establishes it by holding material under defined conditions and re-analysing at intervals. Where a retest date is stated, the question worth asking is what data supports it. See storing lyophilized research materials.
Scope of this documentation
This page concerns material identification and analytical documentation for laboratory research. It does not recommend personal, human, clinical, therapeutic or veterinary applications. Published research findings do not establish the properties of Arctic stock; use the applicable lot record and its stated methods and limitations.
Related documentation
Material on this site
The documentation this article describes is published per lot for the listings below. Match the lot number on a vial label to its record before relying on it.
- Research materials catalog — current listings with batch status
- Batch COA library — every currently published report with its verification link