| Abstract
| - The relationship between the electrophoretic mobility,μobs, Stokes radius, rs, ionization state, and solutionconformation of the all l-α-polypeptide, 1, the corresponding retro-all d-α-polypeptide, 2, and several truncatedanalogues, 3−5, has been investigated under low pHbuffer conditions by high-performance capillary zonalelectrophoresis (HPCZE) with coated capillaries. Theresults confirm that, under these conditions, the all l-α-polypeptide, 1, and its retro−inverso isomer, 2, exhibitnonidentical electrophoretic mobilities and thus differentStokes radii. At higher pH values, i.e., pH 5.0, theelectrophoretic behavior of this retro−inverso isomer pair,however, converges. These results indicate that variationsin the dipole characteristics of the polypeptide main chainand subtle differences introduced by the spatial constraints of the l-α-Pro → d-α-Pro residue replacement leadto differences in the Stokes radii and electrophoreticmobilities of these polypeptides. Since the observedelectrophoretic mobilities, μobs, reflect the mean of themobilities of each charge species participating accordingto their Stokes radius or their intrinsic charge and molefraction abundances, the results confirm that polypeptideretro−inverso isomers with unmodified amino and carboxy termini are resolvable. This outcome was achieveddespite their notional topographical and conformationalsimilarities as assessed from high-field proton nuclearmagnetic resonance (1H NMR) spectroscopy and circulardichroism (CD) spectroscopy.
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