Comparison of retention behavior of oligolysine and oligoarginine in ion-pairing chromatography using heptafluorobutyric acid
2013
Xie, Wenchun | Qin, Xu | Teraoka, Iwao | Gross, Richard A.
This paper describes the retention behavior of oligolysine and oligoarginine peptides of different lengths as a function of heptafluorobutyric acid (HFBA) concentration in ion-pairing reversed-phase chromatography in isocratic elution. A mixture of oligolysine and a mixture of oligoarginine with number of amino acid residues (dp) from two to eight were conveniently prepared by one-pot protease-catalyzed synthesis. Analysis of the logarithm of the retention factor k as a function of [HFBA] for each oligopeptide component, using a closed pairing model, provided values for (1) number (n) of paired HFBA anions per peptide molecule, (2) equilibrium constant (Kᵢₚ,ₘ) for ion pairing between oligopeptides and HFBA anions, and (3) product of the phase ratio and the distribution constant of the paired oligopeptide between the mobile and stationary phases (βKd,ᵢₚ). We found that βKd,ᵢₚof oligoarginine is larger compared with oligolysine having the same dp. A linear relationship was obtained for ln βKd,ᵢₚas a function of n + g · dp. By optimizing constant g separately for oligolysine and oligoarginine, we determined that g is larger for oligoarginine, in agreement with the higher hydrophobicity of arginine residues. Plotting the fraction of paired oligoarginine and oligolysine as a function of [HFBA] shows that the cooperative effect in forming ion pairs is greater for oligoarginine than oligolysine.
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