title: Monte Carlo description of oligoelectrolyte properties of DNA oligomers: range of the end effect and the approach of molecular and thermodynamic properties to the polyelectrolyte limits.
abstract: Applications of the grand canonical Monte Carlo method demonstrate the importance of end effects on fundamental molecular and thermodynamic properties of oligoelectrolyte solutions. Simulations are carried out for a series of solutions containing double-helical DNA oligomers of varying numbers of phosphate charges N (8 less than or equal to N less than or equal to 100) and univalent electrolyte at fixed activity (a +/- = 1.76 mmol/dm3). These results are used to evaluate as follows: C+N(a), the local concentration of cations at various axial positions along the oligomer surface; C+N(a), the axial average of these concentrations; TN, the preferential interaction coefficient expressed per oligomer charge, which is directly related to the fractional thermodynamic extent of association of counterions. A sufficiently long oligomer (N greater than or equal to 48 under the conditions simulated) is characterized by an interior region over which C+N(a) is uniform and equal to C+ infinity (a), the polyion limit. This interior region is flanked by two symmetric terminal regions, in which C+N(a) varies linearly with axial position from the end of the oligomer to a distance approximately 18 monomer units (approximately 3.1 nm) from that end. For long oligomers, the characteristics of the terminal regions [length and axial profile of C+N(a)] do not vary with N and, by inference, also pertain to the polyion under the same conditions. Both C+N(a) and TN approach their polyelectrolyte limits as linear functions of 1/N. These linear dependences can be attributed to the increasing predominance of the contribution due to the polyion-like interior of the oligomer as N increases.
authors: Department of Chemistry, University of Wisconsin, Madison 53706.
authors: M C
authors: MC
authors: Olmsted
authors: C F
authors: CF
authors: Anderson
authors: M T
authors: MT
authors: Record
mesh_terms: D004247:DNA; D009010:Monte Carlo Method; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides; D012996:Solutions; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D009838:Oligodeoxyribonucleotides; D012996:Solutions; D004247:DNA