Epithalon (AEDG) as a Research Material: Sequence, Mass and What a Certificate Confirms

Epithalon, also spelled Epitalon and often abbreviated AEDG, is a short linear tetrapeptide supplied as a lyophilised powder for laboratory research use only; not for human consumption. Because the molecule is so small, its identity rests entirely on analytical data. This article covers its sequence and charge, its formula and mass, and how a certificate of analysis establishes identity. It also covers practical handling of the powder and of stock solutions at the bench.

Sequence and structure

The sequence in three-letter code is Ala-Glu-Asp-Gly, written N-terminus to C-terminus. In one-letter code it is AEDG. The peptide is linear and unmodified in its common form: a free amine at the alanine N-terminus, a free carboxylic acid at the glycine C-terminus, and three peptide bonds joining the four residues. It has no cysteine, so disulfide formation is not a concern. It has no aromatic residue, which matters for detection, as discussed below.

Two of the four residues are acidic. Glutamic acid and aspartic acid each carry a side-chain carboxyl group. Together with the C-terminal carboxyl, the molecule has three acidic groups against a single basic N-terminal amine. Near neutral pH the carboxyls are largely deprotonated and the amine is protonated, so the net charge is negative, approximately minus two. In practice the peptide is quite polar and usually dissolves readily in water or in a mildly buffered aqueous solvent. Very acidic conditions suppress the carboxylate charges and can reduce solubility somewhat.

Molecular formula and mass

The molecular formula follows from the four residues minus three molecules of water lost on forming the peptide bonds. That gives C14H22N4O9 for the neutral free peptide. Both the monoisotopic mass and the average mass should be taken from the certificate of analysis rather than from memory or a generic database entry.

The distinction between the two masses matters. The monoisotopic figure is what a mass spectrometer resolves as the principal ion. The average figure reflects natural isotope distribution and is used for weighing calculations. If a salt form is supplied, the formula weight of the material in the vial differs from that of the free peptide, and the certificate should make clear which figure applies.

Identity confirmation on a certificate

A white lyophilised cake says nothing about what it contains. AEDG looks the same as almost any other short peptide, a truncated synthesis product, or a mis-sequenced isomer such as AEGD or ADEG, which shares the same formula and mass. For that reason identity is confirmed analytically, and the certificate is the record of that work.

The certificate typically reports two complementary measurements. The first is reversed-phase HPLC, which compares the sample's retention time with a reference standard and reports chromatographic purity as an area value. Because AEDG has no aromatic side chains, detection is normally at low UV wavelengths where the peptide bond absorbs. Mobile-phase choice and baseline handling affect the result at those wavelengths. The second is mass spectrometry showing the expected molecular ion, commonly the protonated species in positive mode or the deprotonated species in negative mode, consistent with the monoisotopic mass.

Sequence isomers share one mass, so a matching molecular ion alone does not distinguish them. Fragmentation data or co-elution with an authentic standard closes that gap. Analytical laboratories have applied LC-MS with selected-reaction monitoring to pick AEDG out of unlabelled preparations. Specific precursor-to-fragment transitions give a far more selective signal than a full-scan mass (PMID: 25535022). Mass-spectrometric methods have also been used to detect the AEDG sequence within a complex polypeptide extract, again relying on characteristic ions rather than bulk properties (PMID: 29124531).

Each certificate reports what one third-party laboratory, named on the report, measured on one batch. It is identified by its Report ID or Laboratory ID. Some batches have results pending, and a certificate should be read for the specific material in hand.

Salt form and net peptide content

Synthetic peptides are often isolated as salts, most commonly acetate or trifluoroacetate, and sometimes as a free acid or sodium salt. For an acidic peptide such as AEDG, the counter-ion and any residual water contribute to the weighed mass. The net peptide content on a certificate, where reported, states the fraction of the gross powder weight that is peptide.

Concentration calculations for a stock solution should use this figure together with the correct formula weight. Otherwise the true peptide concentration will be overstated. Chromatographic purity and net peptide content measure different things and should not be conflated.

Stability, handling and storage

The lyophilised powder is best stored cold, dry and protected from light, with the vial kept sealed. Before opening, a refrigerated or frozen vial should be allowed to reach room temperature. Opening it cold draws in moisture, and many peptide salts take up water readily.

For bench preparation of a stock solution for assay, sterile water or a dilute aqueous buffer is usually adequate given the peptide's polarity. The solvent should be compatible with the downstream method; for example, phosphate buffers should be avoided when the solution is destined for direct MS analysis.

The stock should be divided into single-use aliquots and frozen. Repeated freeze-thaw cycles promote degradation and adsorption losses, and aspartate-containing sequences can undergo slow chemical changes in solution over time. Each aliquot should be labelled with the concentration, solvent, preparation date and the certificate's Report ID. That label lets any analytical result be traced back to the documented material.