Frequently Asked Questions

Orders can be placed by: • phone 1-978-425-5209 • email tides@scitide.com • online www.scitide.com

This is the percentage of peptide that is found in the correct sequence as opposed to truncated, deleted, or incomplete sequences that can arise from peptide synthesis. The purity is determined by high performance liquid chromatography (HPLC).

Net peptide weight is the weight of the total peptide. The net peptide weight is precisely determined by amino acid analysis after acid hydrolysis, HPLC, and/or UV absorption, and the value is indicated clearly on the vial label. The indicated weight is only for the net peptide molecule, and the weights of any constituents are excluded from the quantity. Gross peptide weight is the weight of the peptide and peptide impurities as well as non-peptide components like salts and moisture. Peptides manufactured by SciTide are sold in gross peptide weight unless otherwise ordered.

There is not a universal solvent for dissolving every peptide. Because several solvent systems may be necessary until the desired conditions are achieved, always test a small sample of the peptide to determine the best solvents. When testing, begin with solvents that can be easily removed by lyophilization, such as water and acetonitrile. For this reason, it is not recommended to start with buffers which have high salt concentrations. SciTide provides solubility testing as an additional service for customers, should you desire it. Determine the overall charge Charged amino acids aid solubility in aqueous environments. A sequence with little or no overall charge at any pH is not likely to be water soluble. Hydrophobic amino acids: Ala, Phe, Ile, Leu, Val, Pro, Met, Trp, Tyr, Cys Positive Charges: Lys, Arg, His and Free N-terminus Negative Charges: Asp and Glu and Free C-terminus First, determine if the peptide is charged or neutral by calculating the overall charge of the peptide at pH 7. Calculate overall charge by using the following values: +1 for each basic residue (Lys, Arg, and N-terminus) -1 for each acidic residue (Asp, Glu and C-terminus) If the overall charge of the peptides is negative then the peptide is acidic, if it is positive then it is basic, and if zero then it is neutral. Charged peptides For acidic peptides (and/or if the total number of charges of the peptide at pH 7 is greater than 25% of the total number of residues): use a small amount of 0.1M ammonium bicarbonate to dissolve the peptide, and then dilute it with water to the desired concentration. Maintain pH around 7 and adjust pH as needed. For basic peptides (and/or if the total number of charges of the peptide at pH 7 is between 10-25% of the total number of residues): use a small amount of 25% acetic acid to dissolve the peptide and dilute it with water to the desired concentration. Adjust pH with 8 M NH4OH to desired pH for oxidation (4-7). For neutral peptides (and/or if the number of charges is greater than 25% of the total number of residues): use the strategy described for acidic peptides. Otherwise, the use of organic solvents is recommended. Hydrophobic or neutral peptides Hydrophobic peptides containing 50% to 75% hydrophobic residues may be insoluble or only partially soluble in aqueous solutions, even if the sequence contains 25% charged residues. It is best to first dissolve these peptides in a minimal amount of stronger solvents such as acetonitrile, isopropyl alcohol, ethanol, and/or acetic acid, and then slowly add (drop wise) the solution to a stirred aqueous buffer solution. If the resulting peptide solution begins to show turbidity, you might have reached the solubility limit and it will be futile to proceed. Again, it is important to remember that the initial solvent of choice should be compatible with the experiment. It is important to dissolve the peptide completely in the initial solvent (such as acetic acid, acetonitrile) because the rate of dissolution of peptides into these solvents is usually higher than in a water/solvent mixture. If a water/solvent mixture is used first to dissolve the peptide, the final volume of solution may be larger than necessary. Sonication It may be necessary to sonicate the solution before determining if the solvent choice was appropriate. Sonication should improve solubilization by breaking the solid peptide into smaller particles. If the solution gels, becomes cloudy or turbid, or has visible particulates, the peptide has not dissolved completely but is suspended. At this point, a stronger solvent is necessary and the solvents should be removed. Begin again with the dry sample.

SciTide peptides are shipped as trifluoroacetate (TFA) salt, unless otherwise noted by the customer. Peptides are generally purified by reverse-phase High Performance Liquid Chromatography (rHPLC) using a TFA buffer. The charge on a free amine in the peptide, either on the N-terminus or in a side chain, attracts the TFA counter ion. In cases where TFA is not the desitred salt form an exchange can be completed. Some examples of alternative salt forms are acetate (-OAc) or hydrochloride (HCl). Since converting from a TFA salt form to another salt form requires an additional step and material loss, there is a fee to complete. All products sold by SciTide, Inc. are intended solely for laboratory and research use and should not be used in or on human subjects. User assumes all risk of patent infringement by reason of use of material provided by SciTide. SciTide will not be responsible for damages arising from misuse of any product and is not responsible for the results of research using our products.

Most peptides are shipped at room temperature and delivered to you in a lyophilized state. Once a product arrives at your facility, it should be kept at -20 °C (or cooler) for long-term storage. In a rare instance where a peptide requires shipment at low temperature, a dry ice shipment will be arranged.

Short Term: Store in a desiccator or with a desiccant to maintain a dry environment. Long Term: Store in the freezer at a temperature of -20 °C

The physical state for peptides range from amorphous solid to crystalline powder. Some peptides will appear as a small disk at the bottom of the vial, others may appear fluffy or powdery, and other peptides may not seem visible at all. Particularly, peptides ordered in small quantities such as 0.1 mg or 0.5 mg, may not be visible, especially through an amber glass vial.

Generally, peptides in solid lyophilized form are quite stable. Synthetic peptides, unlike proteins purified from cells, have an extremely low chance of proteinase contamination. Peptides are stable for more than one year if they are stored in a lyophilized state at -20 °C or below and protected from moisture and light. However, following reconstitution of a peptide in solution, stability and storage time will decrease. If a peptide has been in solution for an extended period of time, homogeneity of the peptide must be reconfirmed. Typically, once a peptide is in solution, it should be used within a few weeks, even when stored below -20 °C. For specific information on storage time of a peptide solution, refer to the product sheet that comes with the order. Conditions that can affect peptide stability include the following: Moisture can lead to hydrolysis of the peptide. The peptide should be allowed to warm gradually to room temperature in a desiccator to reduce condensation of water vapor. Constant freeze thaw cycles can compromise peptide integrity; therefore, stock solutions should be aliquoted at single use amounts. O2 can negatively affect Trp, Cys, and Met residues in a peptide. If a peptide contains any of these residues, limit its exposure to air especially when in liquid form. This can be done by blanketing with Nitrogen or another inert gas. SciTide can do an independent evaluation on each peptide sequence to give a more specific approach to storage and handling upon shipment.

A hygroscopic peptide contains charged amino acids (ex: Arg, Asp, Glu, His, Lys), making it vulnerable to exposure to oxygen which can lead to moisture uptake. To prevent the product from liquefying during the weighing process, it should be allowed to warm to room temperature in a desiccator prior to weighing. If possible, weigh in a glove box to prevent exposure to oxygen and blanket vial with an inert gas prior to restorage. If this is not an option, weigh product quickly and close lid tightly to reduce exposure to the air. If you do not have ideal weighing conditions for this product, it is best to purchase smaller aliquoted for single use vial sizes.

The peptide should be allowed to warm gradually to room temperature in a desiccator to minimize condensation of water vapor upon opening the vial or screw-cap bottle. Visually locate the peptide in the container. Tap the vial (vortex or microcentrifuge) to release any product that may have become trapped in the cap. Use sterile buffer or water to reconstitute the peptide. For smaller quantities such as 0.1 or 0.5 mg, it is recommended to use a sterile syringe to inject solvent into the vial as opposed to opening the cap. If DMSO is required for solubilization, be sure to use analytical grade DMSO. DMSO can degrade and become dilute with time because it can take up water from the air so care should be taken when using stock DMSO. Aliquot the remaining peptide solution into single-use sterile glass or high-quality polypropylene vials for storage to prevent repeated freezing and thawing which can be detrimental to the integrity of the peptide. Store stock solution in a freezer, at -20 °C or below, under dry conditions.