Reconstitution, Solubility and Storage of Peptides 
To ensure that our material retain their integrity, the following guidelines are suggested for storage and use. In general, we do not have to dissolve the peptides in aqueous buffers for our Q.C. Our recommendations are based upon experience and peptide sequences.  

Most regular and charged peptides  
To determine the suitable method of dissolving your peptide, utilize only a small amount of appropriate solvents. Dissolve the peptide in Distilled or deionized sterile (and if possible, oxygen free) water. Only when the peptide has been fully dissolved should required buffer salts/solution be added and the solution diluted to its final concentration, that is, dissolves the peptide first and add the buffer afterwards. 
Bacterial degradation can occur in peptide solutions. 

Always use sterile water to dissolve peptides. 

If required, the peptide solutions may be filtered through a 0.45 um or 0.2 um filter. Do not keep peptide solutions at room temp. 
Amino acids such as Cysteine, Methionine or Tryptophan are susceptible to oxidation and should be dissolved and stored in oxygen free water. This may be prepared by degassing under reduced pressure by sparing with an inert gas such as Nitrogen, Helium or Argon. 
If peptide is insoluble in pure water, sonication may help in breaking up any particles and increase the rate of dissolution.
Caution: Sonication can cause warming of the solution and degradation of the peptide.  

For Highly Basic peptides 
If the peptide contains many basic amino acids (K, R etc), use an aqueous acetic acid solution (1 to 10%) with or without sonication. For very hydrophobic peptides, use 50% aqueous acetic acid. 

For highly acidic peptides  
If the peptide has many acidic amino acids (E, D etc), use an aqueous ammonia solution (1 to 10%) or a volatile basic buffer (up to pH 8) such as N-Ethymorpholine Acetic or Bicarbonate with or without sonicaton. The pH may have to be adjusted before chromatography. 
Propanol or acetonitrile may be used to dissolve some medium sized peptides. If the peptide is to be injected onto a column, the amount of organic solvent, especially propanol must be kept small, or retention time will be greatly affected.  
 

For highly hydrophobic peptides  
If the peptide is highly hydrophobic with aromatic or hydrocarbon-like side chains, such as Val, Leu, Ile, Met, Phe, Try, Ala or if the peptide is neutral, use a chaotropic agent such as DMF/D">
a. High concentration of chaotropic salts to help dissolve the peptide by breaking up the secondary structures. 
b. Chaotropic agents are suitable for preparing solution for analysis, but may interfere with a biological system used for study of the peptide 
c.  The best agents are DMF or DMSO (up to 30%) added drop until the peptide dissolves. 
d. On reverse phase chromatography, the DMF will elute with the buffer front. The peak can be vary high, depending on how much was injected. Most peptides are retained longer than the few minutes it takes for a large DMF peak to elute. If the peptide is very small and elute early, the starting % may have to be decreased when the peptide is injected.  

Storage of lyophilized Peptides  
All peptides should be stored refrigerated, preferably at -20 ºC for maximum stability. Most peptides when stored below -20 ºC will remain stable for several months. This applies to many amino acid derivatives, lipids, enzymes and other proteins as well as peptides. The only exception to this is immobilized proteins and peptides. 
When using a refrigerated product, the bottle or the vial should be allowed to warm to room temp. in a desiccators containing fresh desiccant before opening. From -20 ºC this can take an hour or more, depending on the pack size. Failure to do this can cause condensation to form on the product when the bottle or vial is opened and will greatly reduce the stability of the material. Once opened, the required quantity should be weighed out to prevent water uptake. This is a particular problem with some hydroscopic peptides.  

Storage of Peptides in Solution  
Peptides in solution are much less stable than lyophilized peptides. For best result please follow the following guidelines. 
1. Avoid repeated thawing and freezing. It is recommended that the stock solution be aliquoted.  Thaw only what is needed. DO not store diluted solutions.
2.  For maximum stability, store at -20 ºC in a sterile, pH 5 to 7 buffered solution.
3.  Amino acids such as Cysteine, Methionine or Tryptophan are susceptible to oxidation and should be dissolved or stored in oxygen free water.

4.  Bacterial contamination degrades peptides, so use sterile water or buffer.