Purification, general procedures polypeptides

The major disadvantage of solid-phase peptide synthesis is the fact that ail the by-products attached to the resin can only be removed at the final stages of synthesis. Another problem is the relatively low local concentration of peptide which can be obtained on the polymer, and this limits the turnover of all other educts. Preparation of large quantities (> 1 g) is therefore difficult. Thirdly, the racemization-safe methods for acid activation, e.g. with azides, are too mild (= slow) for solid-phase synthesis. For these reasons the convenient Menifield procedures are quite generally used for syntheses of small peptides, whereas for larger polypeptides many research groups adhere to classic solution methods and purification after each condensation step (F.M. Finn, 1976). 

Of equal importance, the use of RPC and HIC techniques provides a very powerful avenue to explore the molecular basis of the hydrophobic effect per se that these biomacromolecules exhibit. Since the time of the initial attempts, commencing over 50 years ago, to exploit the hydrophobic effect as part of robust separation procedures, RPC and HIC have thus come to assume a dominant position for the isolation and analysis of many proteins and now represent the techniques par excellence for the purification and analysis of polypeptides prepared by solid- or solution-phase synthetic procedures. Equally, these techniques provide an opportunity to explore the role of the hydrophobic effect in the stabilization and folding of proteins and polypeptides, the molecular forces that are involved in these processes, the thermodynamics of their interaction with relatively well-defined nonpolar surfaces, and the biophysics of peptide or protein nonpolar interactions in general. 

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