Selank: salt form, net peptide content and purity

The short answer

Selank is a synthetic heptapeptide with a free-base mass near 752 Da, commonly supplied as a diacetate salt. Because the counterion adds mass, the weighed powder exceeds the free-base figure — which is why net peptide content, not label weight, describes how much peptide is present.

A tuftsin analogue built for stability

Selank is a seven-residue synthetic peptide: the endogenous immunomodulatory tetrapeptide tuftsin extended with a C-terminal Pro-Gly-Pro tripeptide. The extension is the same structural strategy used in Semax, and for the same reason — resistance to rapid enzymatic degradation.

Research is predominantly preclinical, covering anxiety-behaviour models, enkephalin and enkephalinase biochemistry, and serotonin metabolism in rodents. Human data are limited and largely confined to small clinical studies in a specific regional literature.

There is no FDA- or EMA-approved Selank product. Material supplied under this name is a laboratory research compound.

Why the salt form changes what you weigh

Selank is frequently supplied as a diacetate salt rather than as the free base. The acetate counterions contribute mass, so a vial containing a stated weight of salt contains less peptide than that number implies. This is ordinary peptide chemistry, not a defect — but it has to be disclosed to be interpretable.

Net peptide content is the figure that resolves it: a measurement of how much of the powder is peptide, with the balance being counterion and residual water. A certificate reporting net peptide content alongside purity is describing the material completely. One reporting purity alone leaves the mass question unanswered.

This is also why a purity percentage and a content figure can look inconsistent to someone reading quickly. They are not in conflict — a peptide can be 99% pure by chromatography while representing considerably less than 99% of the powder's mass.

Acetate is the usual counterion for a practical reason: peptides are commonly purified by reversed-phase chromatography using trifluoroacetic acid, and an exchange to acetate is a deliberate downstream step because residual trifluoroacetate is undesirable in many experimental systems. A certificate that names the salt form is therefore reporting something about how the material was finished, not merely labelling it. Where counterion content is quantified as well, the relationship between weighed mass and peptide mass stops being an estimate and becomes a measurement — which is the difference between a document that describes a batch and one that merely accompanies it.

An analytical quirk worth knowing

Selank contains no tryptophan or tyrosine, and no sulfur. The practical consequence is weak ultraviolet absorbance at 280 nm, the wavelength often used for peptide quantitation, so analysis is normally performed at 214 to 220 nm where the peptide bond itself absorbs.

This makes the stated wavelength on a certificate more than a formality for this compound. A purity figure is only interpretable alongside the method and detection wavelength that produced it, and for Selank the choice is not arbitrary.

Beyond that, the usual reading applies: identity determined analytically rather than assumed, contamination controls present, lot number matching the vial, and the certificate verifiable with the laboratory that issued it rather than only downloadable from the seller.

The relationship to tuftsin is worth holding onto while reading any Selank analysis. Tuftsin is a naturally occurring tetrapeptide, and Selank is that sequence with a three-residue extension — which means the parent tetrapeptide is a chemically plausible related substance rather than an unrelated contaminant. Truncated species of this kind sit close to the target in both mass and chromatographic behaviour, so they are exactly what a related-substances specification exists to bound. A certificate that reports related substances against a limit is addressing this; one reporting a single purity figure leaves it unstated.

Questions researchers ask

Is Selank sold as an acetate salt or free base?

Commonly as a diacetate salt. The counterions add mass, so weighed powder exceeds the roughly 752 Da free-base figure. A certificate should state the salt form, because it determines how the labelled weight relates to the amount of peptide actually present.

Why does Selank net peptide content differ from the vial weight?

Because part of the powder's mass is acetate counterion and residual water rather than peptide. Net peptide content measures the peptide fraction specifically, which is why it reads below the labelled weight — a disclosure of composition, not a shortfall in quality.

What wavelength should Selank purity be measured at?

Typically 214–220 nm. Selank contains no tryptophan or tyrosine, so it absorbs weakly at the 280 nm often used for peptides. The stated detection wavelength is therefore part of the result, and a purity figure quoted without it is difficult to interpret.

Is Selank an approved medicine?

No. There is no FDA- or EMA-approved Selank product. The research base is largely preclinical, with limited human clinical literature, and material supplied under this name is a research compound for laboratory use only.

At a glance

Class: Synthetic heptapeptide — tuftsin with C-terminal Pro-Gly-Pro
Free-base mass: ≈ 752 Da
Common salt form: Diacetate — weighed mass exceeds free base
Detection: Weak 280 nm absorbance; typically quantified at 214–220 nm
Status: Research use only — no FDA- or EMA-approved product

How our Selank lots test

Applying the same standard described above to our own material. Each certificate below opens on the issuing laboratory's portal— not a PDF hosted here — so you are reading the lab's record, not ours.

10mg · Lot CO700274 · 99.89% pureView verified COA ↗

Sources

Written from primary literature and published standards — never from other suppliers' marketing copy.

Written by Ivory Science. Scientific review: pending appointment of a named reviewer. Until then this page cites its sources directly so every claim can be checked at origin.

Selank in the catalogue All research notes How to judge a supplier

For research use only. Not for human or veterinary use, ingestion or administration. Nothing here is medical advice, and no statement on this page has been evaluated by the FDA. Selank is not an approved medicine.

Selank: salt form, net peptide content and reading a COA