Ma. Survay et al., OLIGOGLYCINES AND OLIGOALANINES AS TESTS FOR MODELING MOBILITY OF PEPTIDES IN CAPILLARY ELECTROPHORESIS, Journal of chromatography, 636(1), 1993, pp. 81-86
Peptides in homologous series of oligoglycines and oligoalanines with
degree of polymerisation n = 2 to 6 are baseline separated in 20 mM ci
tric acid-lithium citrate buffers in the pH range 2.51 to 3.02. Mobili
ties determined as a function of pH allow calculation of the mobility
mu+ for the fully protonated peptide. Values of mu+ for oligoglycines
are systematically 0.6 . 10(-4) cm2 V-1 s-1 higher than those for olig
oalanines, consistent with the 40% greater partial molar volume of ala
nine than glycine. Since these mobilities are those of peptides with a
constant charge q = 1, semi-empirical models can be systematically te
sted for their predictions on how peptide mobilities vary with chain l
ength or molecular mass. Within each homologous series the equation in
troduced by Grossman et al. [Anal. Biochem., 179 (1989) 28] for scalin
g peptide mobility with chain length, mu nz n-0.43, accounts for vari
ation in mu+ with excellent correlation coefficients (r > 0.996). Scal
ing mu nz M(r)-2-3 according to Offord [Nature, 211 (1966) 591] also
gives excellent correlation coefficients (r > 0.996). Since a wide ran
ge of exponents can be used to describe the data with good precision,
no scaling relationship can be considered uniquely suitable for peptid
e mobility modelling.