Isomer
Definition
A compound with the same molecular formula as another but a different arrangement of atoms. Isomers share a mass, so mass spectrometry alone cannot separate them and chromatography or a chiral method is required.
Terms used in this definition
Other entries this definition refers to.
What this means for research sourcing
Structure and identity terms are what a certificate of analysis is written in. Every Volta compound ships with its sequence, molecular weight and measured purity, so these terms map directly onto the specification on the product page.
Related Terms in Chemistry & Structure
Molecular Formula
The count of each element in one molecule, written as a string such as C221H342N46O68. It fixes the molecular mass exactly, which is why a formula and a stated mass that disagree indicate an error in one of them.
Molecular Mass
The mass of one molecule, in daltons. The average mass uses the natural mixture of isotopes and the monoisotopic mass uses the lightest of each, and the two diverge by several daltons on a peptide of any size.
CAS Registry Number
A unique identifier assigned to a chemical substance by the Chemical Abstracts Service. It is specific to the exact substance, so a free base and its salt carry different numbers, and many research peptides have never been assigned one.
Fmoc (Fluorenylmethyloxycarbonyl)
The base-labile protecting group that dominates modern solid-phase peptide synthesis, removed with piperidine between couplings. It gives the strategy its name: Fmoc chemistry builds the chain under mild conditions no strong acid step is needed for.
Boc (tert-Butyloxycarbonyl)
An acid-labile protecting group, and the basis of the older synthesis strategy that preceded Fmoc. Boc chemistry requires repeated acid treatment and a harsh final cleavage, which is why it survives mainly for sequences Fmoc handles badly.
Protecting Group
A chemical group fitted to a reactive site so it stays out of the way while a reaction happens elsewhere, then removed. Peptide synthesis is largely the management of these: every amino acid side chain that could react has one.
Side-Chain Protection
Protecting groups on amino acid side chains, as distinct from the one on the alpha-amino group removed at every cycle. Side-chain groups stay on throughout the synthesis and come off together at final cleavage.
Orthogonal Protection
Using protecting groups removed by different chemistry, so one can be taken off while others stay on. It is what makes selective modification possible, including branched and cyclic structures.