Peptides containing a single free cysteine will be oxidized at pH>7 yielding dimers. This oxidation can be reverted. Peptides containing two or more thiol moieties yield a mixture of products upon oxidation. pH 7.5-8 is the pH optimum for disulfide bond formation. Hence, peptides containing free cysteines are best dissolved in degassed solvents, e.g. buffers pH<7, diluted acetic acid, 0.1% trifluoroacetic acid in aqueous acetonitrile.

DMSO should be avoided, especially with peptide trifluoroacetates.