Selank / Semax: structure and analysis

What it is

A two-compound blend supplied in a single vial: Selank at 5 mg and Semax at 5 mg. The notation 5/5mg states each component's mass.

Both components are heptapeptides built on the same design principle — a short active fragment extended with a proline-glycine-proline tail that slows enzymatic degradation — but from different parent sequences. Selank derives from tuftsin, Semax from the 4-7 fragment of adrenocorticotropic hormone.

So this vial contains two peptides of identical length and similar design, which is the most analytically awkward arrangement in the catalogue.

How it is produced

Supplied as a blend: the named components are combined and co-lyophilized into a single vial, with the mass of each component stated. The components are produced separately and characterised before combination.

This changes the analytical question. For a single compound, purity asks what share of the detected material was the target. For a blend there are several targets, and what matters is whether each named component is present at its stated mass — per-component identification and quantitation rather than one purity percentage.

Confirming identity

Both components require independent identity confirmation, and here that is genuinely more demanding than for other blends. Two heptapeptides sharing a proline-glycine-proline extension have more in common than a tripeptide and a 43-residue peptide do.

Their masses differ because their active fragments differ, so mass spectrometry distinguishes them — but the margin is smaller than in any other blend here.

Analytical considerations

Two peptides of the same length with a shared structural motif are the hardest pair in the catalogue to resolve chromatographically. Similar size and similar composition mean similar retention, so the separation has to be developed for this specific pair rather than adapted.

There is an asymmetry in stability worth noting. Semax contains an N-terminal methionine and is therefore susceptible to oxidation to the sulfoxide; Selank contains no methionine, cysteine or tryptophan and has no comparable pathway. Methionine sulfoxide is a plausible impurity in this vial, arising from one component only.

That also means the vial's storage conditions are effectively set by Semax, the less chemically robust of the two.

What its certificate reports

A certificate for a lot of this material names the lot, names the issuing laboratory, and states for each parameter both the method used and the specification the result was measured against. Identity and purity are the two core results; net peptide content states how much of the fill weight is actually peptide.

A certificate belongs to a lot, not to a product line. When a new lot is released it is tested again, and the certificate published against it is that lot's certificate — a previous lot's result is never carried forward.

Research use only

This page describes structure and analysis. It makes no claim about what this compound does, and none should be inferred from it. Material is supplied for laboratory research use only: it is not a drug, food, dietary supplement, cosmetic or medical device, it is not for human or veterinary consumption, and no dosing, administration or reconstitution guidance is provided for any such use.