Question 1

How do I place an order?

Accepted Answer

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

Question 2

What is peptide purity?

Accepted Answer

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).

Question 3

What is the difference between gross peptide weight and net peptide weight?

Accepted Answer

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.

Question 4

How should a peptide solution be prepared?

Accepted Answer

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.

Question 5

What is a peptide salt form?

Accepted Answer

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.

Frequently Asked Questions

How do I place an order?

What is peptide purity?

What is the difference between gross peptide weight and net peptide weight?

How should a peptide solution be prepared?

What is a peptide salt form?