2.4. Chromatographic procedures Four types of columns were used as follows: 1. Reverse phase C18 columns: 20 × 2 cm (Bulk C18 from Waters, Milford, MA) equilibrated with 10% acetonitrile in 0.1% TFA, and eluted with 50% acetonitrile in 0.1% TFA. 2. Size fractionation Ultrogel columns: 90 × 1.6 cm A