Lab Techniques · Jul 28, 2026
Reading a Peptide Molecular Formula
Molecular formulas get skipped as decoration on a product page. They carry more practical information than almost anything else printed there.
Size, at a glance
Count the carbons. It is a fast proxy for chain length, and chain length drives almost everything else.
- GHK-Cu: C14 — a tripeptide
- Ipamorelin: C38 — a pentapeptide
- BPC-157: C62 — 15 residues
- CJC-1295: C152
- Tesamorelin: C221 — the longest here
More carbons means more coupling steps in synthesis, more deletion sequences to separate, higher price, and wider quality variance between suppliers. That is covered in why prices vary by length.
Sulfur predicts an oxidation route
Look for S at the end of the formula.
| Contains sulfur | No sulfur |
|---|---|
| Semax (C37H51N9O10S) | BPC-157 (C62H98N16O22) |
| TB-500 (C212H350N56O78S) | Ipamorelin (C38H49N9O5) |
| Tesamorelin (C221H366N72O67S) | CJC-1295 (C152H252N44O42) |
Sulfur in a peptide means a methionine or cysteine residue, and both are oxidation-prone. A sulfur-containing peptide has a degradation route that a sulfur-free one does not, so it wants less air exposure, less time in solution, and darker storage.
Nothing on a typical product page says "this one oxidises." The formula does.
A metal changes the class entirely
GHK-Cu is C14H24N6O4Cu. That Cu is copper, coordinated to the peptide. It makes the substance a metal-peptide complex rather than a peptide, which changes:
- Appearance. Copper(II) complexes are blue. A colourless GHK-Cu solution is
- wrong, and that is the only compound here you can partly check by eye.
- Failure modes. The metal can be lost or displaced; chelators strip it.
- What purity means. A purity figure describes the organic part and does not
- confirm the copper is present at correct stoichiometry.
Covered in BPC-157 vs GHK-Cu.
Cross-checking a listing
The formula, the molar mass and the CAS number should agree with each other. If a page lists a formula whose atoms cannot sum to the stated mass, or a CAS number registered to a different formula, something is wrong: sloppy copy at best, a mislabelled product at worst.
It costs nothing to check, and almost nobody does.
Related
Related reading
- What a CAS Number Actually Tells You (and What It Does Not)
A CAS number identifies a substance unambiguously. It says nothing about purity, quality, or whether the vial in front of you contains what the label claims.
- Why a 5 mg Vial Costs More Than Another 5 mg Vial
Two vials, same mass, ten times the price. The answer is chain length, and it is visible in the molecular formula before you ask anyone.
- Why Two Suppliers Quote Different Purity for the Same Peptide
Synthesis route, deletion sequences, counterion content and the difference between HPLC purity and net peptide content — why 99% from one supplier is not 99% from another.
- How to Spot a Forged Certificate of Analysis
Eleven checks that separate a real third-party certificate from a PDF someone made in an afternoon. Run them on any supplier, including us.