Analysis and Characterization of Synthetic Peptides

The molecular weight of most synthetic organic compounds is well below 1000 daltons. The products of peptide synthesis, however, frequently have molecular weights that exceed this number. Calculating with an average residue weight of 115, even a nonapeptide’s molecular weight is more than 1000 and a further increase is caused by the acids (e.g. acetic acid) associated with cations in the side chain of basic residues. In protected intermediates blocking groups contribute in a major way to the size of the molecule. While high molecular weight in itself could be the cause of some difficulties in analysis, the problem is compounded by the similar elemental composition of the amino acid constituents. Thus, incorporation of an additional residue might lead to only minor changes in the values of elemental analysis of an intermediate, or in its physical properties. Moreover, the by-products formed in various operations of synthesis are often quite similar in their composition to the desired peptide derivatives. These complexities obviously increase the need for thorough scrutiny of synthetic peptides, if possible by a battery of tests. In the following paragraphs we will attempt to point out some well established methods of analysis that are useful in this area.