Research

Oxytocin Explained: the Cyclic Nonapeptide, Its Mass and How to Verify a Batch

3 min read · Research blog · 12 Nov 2026 · By CellMind Research Team

Oxytocin is a peptide hormone of nine amino acids, with the sequence Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2. A disulfide bridge between the two cysteines closes six of the residues into a ring. Its molecular mass is 1,007.19 Da. This guide explains its structure, what the literature covers and how to verify a batch.

Key facts

Type: Cyclic nonapeptide (nine amino acids)
Sequence: Cys-Tyr-Ile-Gln-Asn-Cys-Pro-Leu-Gly-NH2, disulfide bridge between Cys1 and Cys6
Molecular formula: C43H66N12O12S2
Molecular mass: 1,007.19 Da
CAS number: 50-56-6
Supplied as: lyophilized powder in a sealed vial

What is oxytocin

Oxytocin was the first peptide hormone to be sequenced and synthesized, by Vincent du Vigneaud in 1953. Its two cysteines are joined by a disulfide bridge, which gives the molecule a six-residue ring and a three-residue tail ending in an amide. The research material is made by chemical synthesis.

What the scientific literature covers

Published work spans cell assays, tissue preparations and animal models. Laboratory topics include:

Binding and signaling at the oxytocin receptor, a G-protein-coupled receptor
Smooth-muscle contraction in tissue preparations
Social behavior in rodent models
Stability and degradation of oxytocin in solution

These are laboratory findings. CellMind supplies Oxytocin for research purposes only, not for human use. Oxytocin is also the active substance of an approved medicine. CellMind material is a research compound, not a medicine.

How identity and purity are verified

The disulfide ring is what an oxytocin report has to confirm. HPLC separates the target peptide from the open, reduced form, from dimers in which two molecules are joined, and from deamidated by-products. Mass spectrometry confirms 1,007.19 Da; the open form is 2 Da heavier and a dimer weighs about twice as much. Both results must appear on the certificate of analysis (CoA) for the specific batch. Our CoA guide explains how to read one.

Checklist before buying Oxytocin

A CoA for the specific batch
HPLC purity stated as a number, above 99%
Mass of 1,007.19 Da confirmed on the report
A clearly stated amount per vial (5 mg)
A batch number on the vial that matches the report

Common questions about Oxytocin

How is oxytocin different from vasopressin?

Both are nine-amino-acid peptides with the same disulfide ring. They differ at two positions: vasopressin has phenylalanine at position 3 and arginine at position 8, and a mass of about 1,084.2 Da.

Why does the disulfide bridge matter?

It closes the ring that gives oxytocin its shape. If the bridge is open or formed between two different molecules, the product is no longer oxytocin, even though the amino acids are the same.

What mass should an oxytocin report show?

1,007.19 Da for the free peptide. Salt forms weigh more, so the report should state which form was measured.

Storage and handling

Keep lyophilized vials in a cool, dark place. After reconstitution the solution should be refrigerated and used within the planned study period. Avoid repeated temperature changes: they are the most common cause of degradation that nobody notices until results stop matching.