Polyelectrolytes, nucleic acids, counterion

Gorin has extended this analysis to include (1) the effects of the finite size of the counterions in the double layer of spherical particles [137], and (2) the effects of geometry, i.e. for cylindrical particles [2]. The former is known as the Debye-Huckel-Henry-Gorin (DHHG) model. Stigter and coworkers [348,369-374] considered the electrophoretic mobility of polyelectrolytes with applications to the determination of the mobility of nucleic acids. 

For solutions of nucleic acids and polyelectrolytes such as polypeptides, an increasing body of results indicates the importance of displacements of counterions along the linear chains of the charged polymers as an important source of polarization. 

At higher temperatures, higher concentrations of counterions are needed to induce folding in nucleic acids. This is so because thermal fluctuations resist the propensity of counterions to condense in the vicinity of the polyelectrolyte [108, 109]. This is in agreement with experiments [31, 108-110]. In fact,... 

Nucleic Acids are Polyelectrolytes Counterion Condensation Theory... 

Counterions around charged groups (phosphates in nucleic acids) play an important part because they induce the essential properties of the polyelectrolyte. Ions in the double layers at the membrane-electrolyte interface are also in a particular category and they introduce specific properties of the interface. If a biomolecule possesses a permanent dipole, the fluctuations of the dipole can create a special type of noise. 

Ionic polymers (polyelectrolytes and polyampholytes) constitute an important class of water-soluble maaomole-cules. ° Their monomer units are capable of ionization in polar solvents, for example, in water. The ionization occurs via either dissociation of hydrogen ions H from the acidic groups or dissociation of water molecules and protonation of the basic groups on the polymer chain. The solubility of polyelectrolytes in polar solvents is determined first of all by a huge gain in translational entropy of the counterions. The majority of bio-maaomolecules (proteins, nucleic acids, and polysaccharides) operating in aqueous environment carry ionizable groups (carboxyl, sulfate, amine, etc.) and are included in this class of polymers. 

Some of the most successful computer simulation studies of nucleic acid systems to date employ models without explicit treatment of counterions, using instead the Manning model for counterion condensation. 4 Manning developed the counterion condensation model from polyelectrolyte theories applied to DNA treated as a charged cylinder. This model, resulting from a series of studies 2,43 is summarized by ... 

Apart from a few exceptions, polyelectrolytes such as proteins and nucleic acids need a definite pH range and the presence of counterions for stability in aqueous solution. Usually this condition is reaUzed by use of dilute salt or buffer solutions. In this case only weak interactions between macromolecules and low-molecular solutes occur, thus reflecting only small contributions from thermodynamic nonideality. 

---