Modeling the electrophoresis of oligoglycines

Abstract

The electrophoretic mobility of low molecular mass oligoglycines is examined in this study using a "coarse-grained" bead modeling methodology [Pei, H., Allison, S. A., J. Chromatogr. A 2009, 1216, 1908-1916]. The advantage of focusing on these peptides is that their charge state is well known [Plasson, R., Cottet, H., Anal. Chem. 2006, 78, 5394-5402] and extensive electrophoretic mobility data are also available in different buffers [Survay, M. A., Goodall, D. M., Wren, S. A. C., Rowe, R. C., J. Chromatogr. A 1996, 741, 99-113] and over a broad range of temperatures [Plasson, R., Cottet, H., Anal Chem. 2005, 77, 6047-6054]. Except for assumptions about peptide secondary structure, the B model has no adjustable parameters. It is concluded that the oligoglycines adopt a random configuration at high temperature (50 degrees C and higher), but more compact conformations at lower temperature. It is proposed that triglycine through pentaglycine adopt compact cyclic structures at low temperature (up to about 25 degrees C) in aqueous solution. At 25 degrees C, buffer interactions are also examined and may or may not influence peptide conformation depending on the buffer species. In a borate buffer at high pH, the mobility data are consistent with complex formation between the oligoglycine and borate anion.

Modeling the electrophoresis and transport of peptides: The effective sphere model and complex formation

“…In a companion paper in this issue 1, a coarse grained bead modeling methodology (BMM) was used to study the electrophoretic mobility of low relative molecular mass oligoglycines in a number of BGE solutions. The principle conclusions of this study relevant to the study of peptide conformation are as follows.…”

“…Later comparisons involved insect oostatic peptides 8, where the experimental data came from Solinova et al . 11; and low relative molecular mass oligoglycines 1, where the experimental data comes from two independent sources 2, 12. In the present study, we shall extend this modeling to the problem of complex formation of peptides with components of the BGE and consider, in particular, oligoglycines in a sodium borate buffer at high pH.…”

“…Before considering complex formation, however, it will be useful to consider a model that is substantially simpler than the B model for peptides discussed elsewhere 1, 5–8 and that is the “effective sphere” (ES) model 4. The ES model, in turn, can be adapted to investigate more complex phenomena like complex formation 4.…”

Conductivity and electrophoretic mobility of dilute ionic solutions

“…The ''large ion" approach [31,[33][34][35][36][37]51] also works well provided account is taken of the Brownian motion of all ions present. The ''large ion" model can be applied to larger, more highly charged, and also ''structured" particles [21,26,49,59]. As far as small ion studies are concerned, which approach an investigator chooses to use is largely a matter of personal convenience.…”

“…In recent years, capillary zone electrophoresis [11][12][13][14][15] has become a widely used separation technique for a broad array of ionic species including peptides [16][17][18][19][20][21], organic anions [22,23], proteins [24][25][26], and nanoparticles [27,28]. Although the conductance theories discussed in the previous paragraph [3,[5][6][7] have been applied to mobility studies of small and weakly charged ions [22,23,29,30], they are not appropriate for large or highly charged particles including nanoparticles [27,28] or metal oxide colloidal particles [31].…”