A peptide rich in hydrophobic residues (leucine, isoleucine, valine, phenylalanine, tryptophan) tends to hide those parts from water by clustering with other molecules. That reduces solubility and promotes aggregation. One rich in charged residues (lysine, arginine, aspartate, glutamate) dissolves easily, as long as the pH is not close to its isoelectric point.
Modifications also count: a fatty-acid chain makes the molecule more amphiphilic and “sticky”; amidation or acetylation remove charges from the ends and can reduce solubility.
In practice, a poorly soluble peptide may need a slightly acidic solvent (for basic peptides) or a slightly alkaline one (for acidic peptides), or a small proportion of an organic solvent in laboratory settings. It should never be forced by shaking.
A cloudy solution after reconstitution does not always mean a faulty product: it may be a solubility problem caused by the chosen solvent or pH. Looking at the sequence composition helps anticipate it.
Related terms
Learn it in depth at the Peptide University
- The lyophilized form and its diluents · Module 8
- From amino acid to peptide · Module 1
- Peptide content, water, counterion and reading the COA · Module 7
Definition for educational and scientific purposes. It is not medical advice or a recommendation for use. NeoPeptidos products are sold labelled for research use only (RUO).