Net peptide content and peptide purity are different concepts. Net peptide content is the percentage of peptide relative to non-peptides, most equilibrium ions, and water. Typically hydrophilic peptides absorb small molecules of water even under stringent lyophilization conditions. The net peptide content changes from one purification and lyophilization step to the next and varies greatly from one salt type to another. Net peptide content can be determined by amino acid analysis.

The purity of peptides is determined by measuring the UV absorption of the peptide bonds in the target peptide using HPLC; water and residual salts are not measured by the UV detector. The main impurities include: residual sequence peptides (short peptides with one or more amino acid residues less than the target peptide), truncated sequences (peptides produced by preventing the production of capping of residual sequence peptides), and incompletely deprotected peptides (peptides produced during synthesis or final cleavage).

In research and development using peptides, how much purity should be chosen and is it better to use peptides of higher purity?

Generally speaking, the price of the same sequence and quantity of peptide will be different because of its purity, the higher the purity, the higher the price per unit quality of peptide.

We can provide different purity levels for customers to choose, from crude to >98% purity. We can provide ultra-pure peptide with purity >98% according to customer's needs.

Crude peptides are not recommended for biological experiments. Crude peptides may contain significant amounts of non-peptide impurities such as residual organic solvents, scavengers, TFA, and other incomplete peptides.TFA cannot be completely eliminated, and the peptides are usually delivered as TFA salts. If residual TFA interferes with your experiments, we recommend other salt forms such as acetate and hydrochloride (see: link for the types of salts we can provide). These salts are usually more than 20-30% more expensive than regular TFA salts. This is due to the fact that more peptide losses occur during the conversion process and more raw materials are required. 
We recommend the following levels of peptide purity for various programs:

For the screened peptide sequences, they can be screened to more active peptide sequences by: multi-site scanning of random peptide libraries, and optimization of peptide sequences.

The design of a single-site scanning matrix is relatively simple. A selected region or site of a peptide is systematically replaced with other amino acids, and such peptide libraries help researchers to discover specific regions with particular effects or activities at a particular position.

Multi-site scanning randomized peptide libraries are relatively complex. This library is designed to replace selected amino acid residues with 20 natural amino acids simultaneously and randomly by the shotgun approach. The peptide library constructs as many mutations as possible in the selected amino acids. Such libraries can be screened for peptide sequences with enhanced activity. The peptide libraries designed by this method have a large library size and a high screening workload, with a library size of 8,000 sequences for simultaneous three-site screening. Using peptidegoTM's proprietary combinatorial chemistry strategy, the number of peptides synthesized and the screening workload can be greatly reduced, and the screening workload and peptide production cost can be reduced to 800 peptides for three-site screening. The peptidegoTM proprietary combinatorial chemistry strategy enables more sites to be scanned simultaneously.

Small molecule active peptides as vaccines, diagnostic reagents, drugs, and drug lead compounds have become a new trend in the field of pharmaceutical research. There are various screening methods for small molecule active peptides: based on phage display peptide libraries, random synthesized peptide libraries, antisense peptide libraries, protein degradation (enzymatic, chemical), MHC-peptide complexes, protein structure and protein structure prediction.

Phage display peptide library screening is a more mature screening method. Through 3 rounds of screening, more desirable strains can be obtained, and their expressed small molecule peptide sequences can be inferred by DNA sequencing, and then the biological activities of small molecule peptides can be verified by directed synthesis. The disadvantage is that the diversity of the library is easily affected by a variety of factors, and what is obtained is a small molecule peptide with lower affinity.

Randomized peptide libraries can be synthesized according to customers' needs, usually with short production cycle and large library capacity, and the library capacity of a peptide library containing 10 amino acids can reach 1012. Usually, randomized peptide libraries can be synthesized by two synthesizing methods: split and mix and amino acid pre-mix. Peptide libraries obtained by the split and mix method have a more consistent content of different sequences and contain only one peptide per resin ball. Peptide libraries obtained by the amino acid pre-mix method contain a wide variety of sequences, which may result in screening failures. Because the library is too large, the structural characterization of the screened active peptides is a very challenging task.

Antisense peptide library screening, antisense peptide libraries are peptide libraries designed according to biological principles, which have a high screening success rate, but need to determine the amino acid sequences of key regions of the target protein. Usually, the amino acid sequence of the key region can be determined by comparison analysis using bioinformatic analysis software such as Clustal X. After the amino acid sequence is determined, the antisense peptide library is designed according to the Meker-Idlis (M-I) theory. At this point, antisense peptide libraries can be synthesized directly for peptide screening, or simulated by software (Discovery Studio) to obtain peptide libraries with smaller capacity. This kind of screening method is easier to screen the target peptide and confirm the structure because of the clear target and small library capacity (a library containing 10 amino acids has a capacity of only 103.).

After screening the target peptide, different peptide libraries can be constructed to confirm the functional regions and screen for more active peptides.