Counterion and pH-Mediated Structural Changes in Charged Biopolymer Gels
Ferenc Horkay1, Peter J Basser, Anne-Marie Hecht
1Section on Tissue Biophysics and Biomimetics, Program in Physical Biology, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, 13 South Drive, Bethesda, MD 20892, USA.
Macromolecular Symposia
|November 6, 2012
Summary
DNA gels exhibit complex behaviors with multivalent ions and pH changes. Calcium ions and decreasing pH differently affect DNA gel osmotic pressure and structure, revealing distinct responses in these DNA solutions.
Area of Science:
- Biophysics
- Polymer Science
- Materials Science
Background:
- DNA solutions and gels display complex phenomena, including attraction between charged strands in the presence of multivalent counterions.
- Changes in ion concentration or pH significantly alter DNA gel properties, affecting osmotic pressure and potentially leading to phase transitions or precipitation.
Purpose of the Study:
- To analyze osmotic swelling pressure and small-angle neutron scattering (SANS) measurements on cross-linked DNA gels.
- To compare the effects of calcium ions versus decreasing pH on DNA gel behavior in physiological salt solutions.
Main Methods:
- Osmotic swelling pressure measurements.
- Small-angle neutron scattering (SANS) measurements on chemically cross-linked DNA gels.
- Analysis of DNA gels swollen in near physiological salt solutions with varying calcium ion concentrations and pH levels.
Main Results:
- Both increasing calcium ion concentration and decreasing pH led to a decrease in osmotic pressure of the DNA gels.
- Significant differences were observed in the concentration dependence of osmotic pressure between calcium ion treatment and pH reduction.
- Small-angle neutron scattering (SANS) responses also showed distinct variations depending on whether calcium ions or pH was altered.
Conclusions:
- The study highlights that calcium ions and decreasing pH induce different responses in DNA gels, despite both affecting osmotic pressure.
- The observed differences in osmotic pressure and SANS patterns underscore the distinct mechanisms by which ion valence and protonation state influence DNA gel structure and behavior.
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