NAD+ is not a peptide, and its COA looks different

The category error on most listings

NAD+ sits in peptide catalogues, is ordered alongside peptides, and is documented as though it were one. It is not a peptide. Nicotinamide adenine dinucleotide is a dinucleotide — two nucleotides joined through their phosphate groups, one carrying a nicotinamide base and the other an adenine — and it has no amide backbone of amino acid residues at all.

That is not pedantry. It changes which analytical methods are appropriate, which impurities are plausible, and what a competent certificate of analysis should contain. A report that applies peptide conventions to this molecule is describing it with the wrong instrument.

Oxidised and reduced are different substances

The plus sign in NAD+ is doing real work. This molecule exists in two interconvertible forms — the oxidised form written NAD+ and the reduced form written NADH — and they are not interchangeable materials. They differ in mass, they differ in colour behaviour, and they differ in how they respond to a detector.

The most useful practical consequence is optical. The reduced form absorbs strongly at around 340 nm; the oxidised form does not. A laboratory can therefore distinguish the two by looking at absorbance at that wavelength, which is a check available on this molecule and on almost nothing else in a peptide catalogue. A report that does not state which form it describes has left out the compound's defining property.

What the analysis should cover

• Purity by HPLC. The separation principle is the same as for a peptide, but the expected impurity set is not. Degradation of this molecule tends toward hydrolysis products — the two halves coming apart — and toward the reduced form, rather than toward deletion sequences, which have no meaning here.
• Identity. Mass agreement against the calculated value, or retention-time matching against a reference standard under the same method. The salt form matters for the arithmetic: a sodium salt weighs more than the free acid, and a report should say which it describes.
• Water content. This molecule is markedly hygroscopic and hydrolyses in the presence of water, so residual moisture is more informative on this certificate than it is on most.

See how to read a certificate of analysis for the sections a report should carry regardless of compound class.

Storage of the lyophilized solid

This material is among the more moisture-sensitive solids in a research catalogue: water does not merely allow degradation, it is a reactant in the hydrolysis that breaks the dinucleotide apart. Cold, dry, sealed storage is doing more work here than for a typical peptide, and a vial opened before it has equilibrated to room temperature will condense atmospheric moisture directly into the solid.

Stability is a documented property rather than an assumed one: a laboratory establishes it by holding material under defined conditions and re-analysing at intervals. Where a retest date is stated, the question worth asking is what data supports it. See storing lyophilized research materials.

Scope of this documentation

This page concerns material identification and analytical documentation for laboratory research. It does not recommend personal, human, clinical, therapeutic or veterinary applications. Published research findings do not establish the properties of Arctic stock; use the applicable lot record and its stated methods and limitations.

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