Dielectric spectroscopy is used to investigate fundamental length
scales of 146 bp short-fragment (nucleosomal) dilute Na-DNA solutions.
Two relaxation modes are detected: the high- and the low-frequency mode.
Dependence of the corresponding length scales on the DNA and on the (uni-valent)
salt concentration is studied in detail, being different from the case of long,
genomic DNA, investigated before. In low-added-salt regime, the length scale of
the high-frequency mode scales as the average separation between DNAs, though it
is smaller in absolute magnitude, whereas the length scale of the low-frequency
mode is equal to the contour length of DNA. These fundamental length scales in
low-added-salt regime do not depend on whether DNA is in a double-stranded or
single-stranded form. On the other hand, with increasing added salt, the
characteristic length scale of the low-frequency mode diminishes at low DNA
concentrations probably due to dynamical formation of denaturation bubbles
and/or fraying in the vicinity of DNA denaturation threshold
