The extent of adsorption (Γ2
1) of DNA from aqueous solution on different hydrophobic and hydrophilic
solid surfaces has been compared as a function of pH, temperature, ionic strength of the medium, and
denaturants. Γ2
1 at a given surface (except sephadex) increases with an increase of the nucleotide
concentration (X
2) of DNA in mole fraction units, but it attains a monolayer saturation value Γ2
m
when
X
2 attains a value X
2
m
. In most cases Γ2
1 increases further when X
2 ≫ X
2
m
. Various neutral electrolytes
like LiCl, KCl, CsCl, KBr, CaCl2, and Na2SO4, surfactants like SDS and Triton-X 100, the denaturing
action of heat, and the addition of acid and alkali have been observed to play an important role during
the study of the adsorption of DNA on charcoal powder. Further, a comparative study has been performed
to examine the relative affinity of DNA toward different types of solid surfaces. The significant role of
different types of surfaces in controlling the adsorption process has been explained in terms of Gibbs'
surface excess quantities. The experimental results have been interpreted in terms of maximum work due
to the free energy change of DNA adsorption on various solid surfaces and more quantitatively in terms
of the standard free energy change (ΔG°) for the saturation of the surface by DNA as a result of the change
in the nucleotide concentration in the bulk from zero to unity in mole fraction units.
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