Solution conformation of model polypeptides with the use of particle beam LC/FT-IR spectrometry and electrospray mass spectrometry

Abstract

Solution conformations of the polypeptides β endorphin ( β-END) and a cysteine peptide (CYSP) were investigated with the use of particle beam LC/FT-IR spectrometry. Gradient elution HPLC with mobile phases that contained acetonitrile with 0.1% TFA (v/v) and 0.1% aqueous TFA (v/v) were used. The conformations of both polypeptides were studied in 0.9% sodium chloride injection USP, 5% dextrose in water injection USP and sterile water for injection USP. Additional conformational studies over a pH range of 2–10, temperatures of 25, 50, 75 and 100°C and after storage for 24 h were investigated. The studies indicated that the two polypeptides did not behave similarly under identical conditions. It was observed that both β-END and CYSP had slightly different conformations in the various parenteral solutions. It was also shown that the conformation of CYSP changed with both pH and temperature while β-END was conformationally stable to both temperature and pH. The identity of the peptides and the conformationally sensitive charge-state intensities of the peptides were investigated with electrospray ionization mass spectrometry (ESI/MS). The combination of IR and MS data allowed an estimation of solution effects on the conformations of the model polypeptides.