Manning free counterion fraction for a rodlike polyion: aqueous solutions of short DNA fragments in presence of very low added salt.
Phys Rev E Stat Nonlin Soft Matter Phys
; 83(4 Pt 1): 041803, 2011 Apr.
Article
em En
| MEDLINE
| ID: mdl-21599194
ABSTRACT
We quantified the Manning free (uncondensed) counterions fraction θ for dilute aqueous solutions of rodlike polyions 150 bp DNA fragments, in the presence of a very low concentration of monovalent salt c(salt)<0.05 mM. Conductivity measurements of these solutions for DNA base pair concentration range 0.015≤c≤8 mM were complemented by fluorescence correlation spectroscopy (FCS) measurements of the DNA polyion diffusion coefficient D(p)(c). We observed a crossover in the normalized conductivity σ(c)/c that nearly halved across the c=0.05-1 mM range, while D(p)(c) remained rather constant, as we established by FCS. Analyzing these data we extracted θ(c)=0.30-0.45, and taking the Manning asymmetry field effect on polyelectrolyte conductivity into account we got θ(c)=0.40-0.60. We relate the θ(c) variation to gradual DNA denaturation occurring, in the very low salt environment, with the decrease in DNA concentration itself. The extremes of the experimental θ(c) range occur toward the highest, above 1 mM, and the lowest, below 0.05 mM, DNA concentrations and correspond to the theoretical θ values for dsDNA and ssDNA, respectively. Therefore, we confirmed Manning condensation and conductivity models to be valuable in description of dilute solutions of rodlike polyions.
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Assunto principal:
Sais
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DNA
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Água
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Modelos Moleculares
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Íons
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Modelos Químicos
Idioma:
En
Revista:
Phys Rev E Stat Nonlin Soft Matter Phys
Ano de publicação:
2011
Tipo de documento:
Article