Peptide Handling and Storage- http://www.sigmaaldrich.com/Brands/Sigma_Genosys/Custom_Peptides/Key_Resources/Handling___Storage.html
In general, peptide solutions are stable for up to a week at 4°C. However, if the peptide sequence has inherent instability (Peptide Stability), it might be better to freeze the solution when not in use. Peptide solutions at pH>8 should also be frozen when not in use. Sigma Aldrich. - [Read Peptide Handling and Storage]
Great peptide storage information. Lerner. Peptides are provided as lyophilized product that should be stored as dry powder at -20°C to -70°C in a desiccator, if possible. After lyophilization, peptides retain significant amounts of water. Peptides are slowly degraded particularly the cysteine-containing peptides are oxidized over time at -20°C. - [Read Peptide Storage Information]