Dependence of polyelectrolyte apparent persistence lengths, viscosity, and diffusion on ionic strength and linear charge density

Ion-exclusion controlled size-exclusion chromatography of methacrylic acid-methyl methacrylate copolymers

Controlled ion-exclusion allows compensation of hydrophobic adsorption in size-exclusion chromatography of negatively charged methacrylic acid-methyl methacrylate (Eudragit) polymers using methanol as a mobile phase. Properly selected low-ionic-strength conditions below 5 mM LiCl provide correct separation in the size-exclusion mode. Possible disturbing effects, mainly related to light scattering, under low-salt conditions are discussed and shown to be negligible if on-line concentration-light scattering detection is used. The absence of these disturbances is checked by a comparison of experiments performed in methanol containing 1.25 mM and 2.5 mM LiCl. Molecular mass averages and distributions identical within the experimental error are obtained.

Conformations and flexibility of native and re-natured xanthan in aqueous solutions

The conformation and flexibility of sonicated 'native' and 're-natured' xanthan have been investigated by size exclusion chromatography (SEC) with coupled multi-angle light scattering and viscosity detectors. 'Native' xanthan (NX) refers to xanthan dissolved in moderate ionic strength aqueous solution, which has not been exposed either to high temperature or very low ionic strength, and 're-natured' xanthan (RX) here refers to xanthan which has been heated above the conformational melting temperature and then recooled. The mass distributions of the NX and RX are virtually identical, implying that the RX does not involve aggregates of, or disassociated fragments of, NX. The flexibilities and conformations between NX and RX, however, are strikingly different; RX is far stiffer than NX, the persistence lengths being roughly 1000 A and 300 A, respectively, and the mass per unit length M/L of the RX is roughly double that of NX. With estimated M/L of 200 Da/A and 98 Da/A, respectively, the results strengthen the notion that RX is double stranded, whereas as NX appears single stranded. The nature and mechanism of formation of the double-stranded form is still unclear, and a few speculative scenarios are suggested. Finally, preliminary results on the kinetics of xanthan self-association in HCI are presented which illustrate the complexity of such processes in xanthan.