Vilon

What Vilon is, structurally

Vilon is a dipeptide: two residues, one peptide bond, a free N-terminal amine and a free C-terminal acid. At 275.30 g/mol it is the smallest compound in this catalogue, and that is not merely a quantitative difference from the tripeptides alongside it. It changes which chemistry dominates.

The formula reconciles exactly. Three nitrogens means two backbone amides plus the lysine's epsilon-amino group. The five oxygens are one backbone carbonyl, two for the C-terminal acid and two on the glutamate side chain. At this size the reconciliation leaves no room for ambiguity.

Charge is close to balanced, unusually so. The lysine side chain and N-terminal amine carry positives; the glutamate side chain and C-terminal acid carry negatives. Two of each in eleven carbons. The peptide is extremely polar and freely water soluble, though no quantitative figure is quoted here.

There is no aspartate, no asparagine or glutamine, no cysteine, no methionine and no aromatic residue. None of the degradation routes that dominate the rest of this family is available, because none of the residues that carry them is present.

Reconstitution and handling

Sterile water is the default solvent, and with no metal centre present PBS or an appropriate assay buffer are equally suitable. Add diluent down the vial wall and swirl gently. A dipeptide of this polarity dissolves readily and needs no encouragement; vortexing achieves nothing.

Prepare near neutral and use solutions promptly. The cyclisation described below begins with an unprotonated N-terminal amine, so raising the pH is precisely what promotes it.

Adsorption is a minor concern here. A molecule this small, polar and charge-balanced has little affinity for polypropylene, though low-protein-binding tubes cost nothing.

This is laboratory preparation chemistry, not dosing, administration, or protocol guidance of any kind.

Storage and stability

Store the lyophilized powder at -20 degrees C, sealed, desiccated and protected from light, and let a cold vial warm before opening. Reconstituted, hold at 2 to 8 degrees C, or aliquot and freeze rather than thawing repeatedly.

Being a dipeptide changes the picture qualitatively rather than by degree. In a longer chain, diketopiperazine formation needs the N-terminal amine to attack the second peptide bond and cleave the remainder away, which largely confines it to sequences with a proline in position two holding the backbone in the right geometry. A dipeptide needs none of that: its amine and carboxyl are already adjacent, so the ring closes directly, releasing one water molecule and giving cyclo(Lys-Glu).

That reaction is the characteristic instability of dipeptides generally, and here it is the only significant route available. It is promoted by alkaline pH, by warmth and by water, so the lyophilized solid is largely protected while solutions are not.

The absence of everything else is genuine rather than a gap here. No aspartate means no isoaspartate rearrangement, no asparagine or glutamine means no deamidation, no sulfur means no oxidation at sulfur. Cold, dry and near-neutral is the whole requirement.

How Vilon is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. With no aromatic residue there is no 280 nm absorbance, so detection sits near 214 nm.

Retention is the practical difficulty, not detection. A charge-balanced dipeptide of 275 g/mol is about as poorly retained as a peptide can be on standard C18, eluting at or near the void volume where it is hard to separate from injection artefacts and salts. High-aqueous conditions, ion pairing or a phase intended for polar analytes are worth considering rather than assuming a routine gradient works.

Area percent is a chromatographic measure rather than peptide content by weight, and on a molecule of this size the counter-ion is a very large proportional share of the vial contents.

Mass spectrometry confirms identity, and unusually it reads the degradation route cleanly. Cyclisation releases water, so the diketopiperazine appears at 257.28 against a parent of 275.30, an eighteen-unit difference that no isotope envelope obscures. Unlike the isoaspartate rearrangements that affect this compound's larger relatives, nothing here is isobaric with the intact molecule.

Handling FAQ

Why is a dipeptide more prone to cyclisation than a longer peptide? Because nothing has to be cleaved. In a longer chain the ring can only close by breaking the molecule and releasing the remainder. In a dipeptide the amine and the carboxyl are already adjacent, so the ring forms by losing a single water molecule and nothing is lost from the compound but that water.

What does a species eighteen mass units lighter indicate? The cyclic diketopiperazine, cyclo(Lys-Glu), at 257.28. It is the expected degradation product rather than a synthesis impurity, and its appearance points to alkaline pH, warmth or prolonged time in solution.

Full specifications for Vilon.