Semax and Selank are both synthetic peptides that the Prototides catalog groups under Cognitive Research. They are the most closely matched pair in the catalog by size — both are heptapeptides of seven residues, within about sixty daltons of one another — yet they derive from entirely unrelated parent sequences. This reference compares what each molecule is and how each lot is characterized and documented.
It does not compare — and does not describe or imply — any biological effect, activity, outcome, or application of either compound, and neither is presented as preferable to the other. The category name refers to a field of research, not to any effect of the materials. Both are supplied strictly for laboratory research use.
At a Glance
Reference values for each molecule. Lot-specific figures are always those printed on the accompanying Certificate of Analysis, which takes precedence over any general reference.
| Attribute | Semax | Selank |
|---|---|---|
| CAS number | 80714-61-0 | 129954-34-3 |
| Molecular formula | C37H51N9O10S | C33H57N11O9 |
| Reported mass | ~813.9 Da | ~751.9 Da |
| Sequence length | 7 residues (heptapeptide) | 7 residues (heptapeptide) |
| Structural basis | Analogue based on a fragment of adrenocorticotropic hormone (ACTH) | Analogue of the endogenous peptide tuftsin |
| Category | Cognitive Research | Cognitive Research |
| Identity method | LC-MS | LC-MS |
| Purity method | RP-HPLC (area %) | RP-HPLC (area %) |
| Physical form | White lyophilized powder | White lyophilized powder |
| Storage | -20 °C, protected from light | -20 °C, protected from light |
| Classification | Research use only | Research use only |
How the Molecules Differ Structurally
Size is where these two agree; origin is where they diverge. Semax is a heptapeptide of approximately 813.9 Da, structurally an analogue based on a fragment of adrenocorticotropic hormone (ACTH). Selank is a heptapeptide of approximately 751.9 Da, structurally an analogue of the endogenous peptide tuftsin. Despite both running to seven residues, they share no parent sequence.
The compositional difference is visible in the formulas. Semax's formula (C37H51N9O10S) includes sulfur, reflecting a sulfur-containing residue; Selank's (C33H57N11O9) contains none but carries more nitrogen. These are exactly the identifiers LC-MS checks a lot's measured mass against. Both are fully defined synthetic sequences assembled by solid-phase peptide synthesis. For the full per-compound treatment, see the Semax research profile and the Selank research profile.
How Each Is Characterized
The analytical approach is identical for both:
- RP-HPLC separates the target peptide from synthesis-related impurities and reports purity as an area-percent value for the tested sample under a stated method.
- LC-MS confirms identity by measuring molecular mass and comparing it to the theoretical value calculated from the sequence.
Because both are short seven-residue chains, they place a comparable and relatively modest burden on the separation compared with the catalog's longer peptides. Their masses are close enough that the mass check is the decisive identity discriminator between them — which is precisely the kind of question LC-MS answers and RP-HPLC does not. That distinction is covered in how identity and purity are verified.
Documentation — Identical Standard
Both compounds follow the same catalog-wide documentation standard. Each lot ships with:
- A Certificate of Analysis recording the lot's purity result, mass confirmation, and release date — see the guide to Certificates of Analysis.
- The RP-HPLC purity report supporting the figure on the COA.
- An independent third-party analytical report from a separate laboratory.
A unique lot identifier ties these records to the physical container, as described in batch traceability and lot documentation. Because the standard is shared, the two compounds' records can be read side by side using the same criteria.
Storage and Handling
Both are supplied as lyophilized powder, stored at -20 °C and protected from light. The freeze-dried solid is the stable reference form for each; once reconstituted with a solvent appropriate to the protocol, common laboratory practice for both is to divide the stock into single-use aliquots and minimize freeze–thaw cycles. Reconstitution solvent, working concentration, and storage of any prepared solution are determined by the researcher against the requirements of the specific experiment — see cold-chain and -20 °C storage.
What This Comparison Does and Does Not Establish
This is a structural and documentation reference. It does not, on its own, establish any of the following:
- That either compound is more effective, more suitable, or preferable to the other — no effect or activity is claimed for either, so no such comparison is possible or intended.
- Any biological effect, activity, or outcome for either material — none is claimed or implied, and nothing here describes an effect on cognition or any other function.
- That either material is appropriate for a specific research workflow — suitability is a laboratory determination made against institutional SOPs.
- Fitness for human or veterinary use, diagnosis, treatment, or consumption. Both are supplied for laboratory research use only.
Key Takeaways
- Semax (~813.9 Da) and Selank (~751.9 Da) are both seven-residue heptapeptides, closely matched in size but derived from unrelated parent sequences — ACTH fragment and tuftsin respectively.
- Semax's formula contains sulfur; Selank's does not — a compositional difference checked when LC-MS confirms identity.
- Both carry an identical documentation standard: COA, RP-HPLC report, and independent third-party report tied by a lot identifier.
- This reference compares molecules and records only. No effect, activity, or superiority is claimed or implied for either.
