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This area will be developed as a way of capturing best practices when using the HELM notation. 

Please do let us know if you have an item you would like to add, or a question on HELM. You can use the issue list or email us at or just add a comment to the end of this page!

Handling monomers in lists

HELM allows users to specify lists of alternative monomers or mixtures in any order. So PEPTIDE1{(A+dA)}$$$$V2.0 and PEPTIDE1{(dA+A)}$$$$V2.0 are exactly the same. However this can get confusing when there are long lists of monomers and also make comparisons between HELM strings more difficult.


However, there is no point to doing this as the notation assumes that the ratio of the components are unknown if the proportions are not specified: PEPTIDE1{(A+A+L+L+A+V)}$$$$V2.0 is exactly the same as PEPTIDE1{(A+L+V)}$$$$V2.0. and the latter example is much clearer to read.