Coulombic interactions biopolymers

Delrow, J.J., Gebe, J.A., and Schurr, J.M. (1997) Comparison of hard-cylinder and screened Coulomb interactions in the modeling of supercoiled DNAs. Biopolymers 42, 455 70. 

Ion bridging is a specific type of Coulombic interaction involving the simultaneous binding of polyvalent cations (e.g., Ca, Fe, Cu ) to two different anionic functional groups on biopolymer molecules. This type of ionic interaction is commonly involved in associative self-assembly of biopolymers. As a consequence it is also an important contributory factor in the flocculation (via bridging or depletion) of colloidal particles or emulsion droplets in aqueous media containing adsorbed or non-adsorbed biopolymers (Dickinson and McClements, 1995). 

These interactions are frequently ionic in character. The coulombic forces of interaction between macroions and lower molecular weight ionic species are central to the life processes of the cell. For example, intermolecular interactions of nucleic acids with proteins and small ions, of proteins with anionic lipids and surfactants and with the ionic substrates of enzyme catalyzed reactions, and of ionic polysaccharides with a variety of inorganic cations are all improtant natural processes. Intramolecular coulombic interactions are also important for determining the shape and stability of biopolymer structures, the biological function of which frequently depends intimately on the conformational features of the molecule. 

Theoretical considerations of the coulombic interactions of dissolved biopolymers have produced a complete picture of the distributions of counter and coions under the influence of the electrostatic charge on the macroion(56,57). The counterion condensation theory of Manning(56) has stimulated a great deal of activity in the study of dissolved macroions, especially because it provides a group of limiting laws describing the contribution of electrostatic effects to the thermodynamic and transport properties of polyelectrolyte solutions. Data... 

This model takes into account mainly coulombic forces however, hydrophobic interactions and van der Waals forces (including specific interactions of bases, sugars, or amino acids in nucleoproteins) have a modifying influence. This last general point has a major implication for all conformations of adsorbed biopolymers carrying electron exchange groups. 

Intra-molecular ordering in synthetic polymers also merits consideration vis-a-vis biopolymers. In the natural macromolecules, the superposition of hydrogen bonding, ion-pair formation and hydrophobic interactions is well-known, and the native structures are viewed as accomodations to these and other solvation and coulombic effects. With synthetic polymers, one may focus on a few of these phenomena selectively, and much may be gained from the judicious use of the synthetic macromolecules as analogs to the natural ones. 

Several types of attractive forces between individual molecules can contribute to the interactions occurring in biopolymer systems these include Coulomb forces, van der Waals forces, hydrogen bridges and hydrophobic bonding. 

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