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Large polypeptides are very stable at -20 ° C, especially freeze-dried and stored in a desiccator. The lyophilized polypeptides can be placed at room temperature before they are exposed to air. This will reduce the influence of humidity. When freeze drying is not possible, the best method is to store it in a small working sample.
For peptides containing Cys, Met or TrP, deoxygenation buffer is essential for its dissolution, because this peptide can be easily oxidized by air. Before sealing the bottle, the nitrogen or argon gas slowly flowing through the peptide will also reduce the oxidation. Polypeptides containing Gln or Asn are also easily degraded, and all of these peptides have a limited lifetime compared to those without these problematic glycosides.
Solubility:
The solvent for large peptides is ultrapure pumped water. Dilute acetic acid or ammonia is important for the dissolution of basic or acidic peptides, respectively. Peptides that are insoluble in these methods require DMF, urea, guanidiniam chloride or acetonitin to dissolve. These solvents may have side effects in some experiments. Therefore, we recommend that you pay attention when designing peptides.
The residues Ala, Cys, Ile, Leu, Met, Phe and Val will all increase the difficulty of dissolving the peptide.
If you need special peptides or any technical help, please feel free to contact us. We are completely satisfied with you, and we do not charge for the order that we cannot synthesize properly.
Preservation and handling of peptides. Peptides of 1 mg or less are packed by net weight. The declared vial weight does not contain relevant anti-ions and water. For example, the peptide content determined by amino acid analysis is 80%. In a 1 mg sample, the gross weight in the bottle is 1.25 mg.
A large number of peptides are calculated by gross weight. The marked weight contains relevant anti-ions and water, for example, the percentage of peptide in a 25mg sample is 90%, then the actual peptide amount is 25mg × 90% = 22.5mg
Don't confuse peptide content with purity. The purity of the peptide may be 100%, and the amount of the anti-ion of the charged group (such as Arg, Lys) and the new water of the peptide determine the peptide content. This is an inherent characteristic of synthetic peptides.
Storage of lyophilized peptides All products should be stored in the refrigerator, preferably at -20 ° C. Most peptides can be kept unchanged for several years in this way.
The storage solution of the peptide solution The peptide is far more unstable than the lyophilized form. The solution should be stored at a neutral pH (pH 5-7) at -20 ° C. To avoid repeated freezing and thawing of the sample, it is best to store it in small samples. After a sample is thawed and unused, it should be thrown away. Bacterial degradation may sometimes become a problem for solution peptides. To overcome this, peptides should be dissolved in sterile water, or the peptide solution should be filtered with a 0.2 μM filter.
Reconstruction and operation of peptides Most peptides are dissolved in sterile distilled water. When dissolving for the first time, pay attention to make the initial concentration greater than the required concentration. If the peptide has only limited solubility, this allows the addition of other dissolving agents or buffer salts.
If the solubility of the peptide in water is limited, there are several options to help dissolve:
Dilute acetic acid for basic peptides (including Arg, Lys, His)
Dilute ammonia for acid peptides (including Asp, Glu)
10% organic modifier (Acetonitnile, Methanol) for very hydrophobic peptides
DM50 or DMF for very insoluble peptides
Concentrated solutions of guanicline hydrochloride or urea are also useful. Combined with the above methods, sonication is also an effective means of dissolving peptides.
Unless otherwise specified, the purity of all peptides in the peptide packaging catalogue is 95 ~ 98%. The packaging is a vial of lyophilized powder. Unless otherwise specified, the net weight of the polypeptide is packaged. For example, a 1 mg bottle of β-amyloid 1-40 contains exactly 1 mg of peptide. The net weight of the peptide is calculated from the peptide content obtained by amino acid analysis. For example, a peptide sample has a gross weight of 5 mg, an amino acid content of 85%, and a net peptide weight of 5 mg × 0.85 = 4.25 mg. Please note that the peptide content is not the purity of the peptide, and the nature of the peptide synthesized with the anti-ion like acetate and solvent, especially the amount of water combined. Peptide purity may be up to 100%, but the content of peptides in synthetic products is determined by amino acids, sulfur water, and the exposure of peptides to solvents and ions. Especially in the purification process, no matter how pure the peptide is, the content of lyophilized powder peptide is generally 70 -85%. The remaining 15-30% is composed of other basic non-peptide components.
Peptide application and storage Peptides have a wide range of solubility. The main problem with insoluble peptides is the formation of secondary structures. Except for the most peptides, this will happen, especially in peptides with multiple hydrophobic residues. Salt promotes secondary structure formation. We recommend dissolving the peptide in sterile distilled water or deionized first. If you need to increase the dissolution rate, you can use sonication. There are still problems with dissolution. Adding a small amount of dilute acetic acid (10%) or ammonia will facilitate dissolution.
For long-term storage of peptides, it is best to freeze-dry. The lyophilized powder can be stored at -20 ° C or lower for several years with little or no degradation. The peptides in solution are far from stable. Peptides are susceptible to bacterial degradation and should be dissolved in sterile purified water.
Polypeptide solutions containing Met, Cgs or Try residues have limited life due to oxidation. It should be dissolved in anaerobic solvents. In order to prevent repeated freeze-thaw damage, it is recommended to dissolve excess peptides for experimentation, and the remaining peptides should be stored as solids.
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