ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The cooling process of DNA gel (20 wt./wt.%–40 wt./wt.%) with various counterions has been investigated by low frequency Raman spectroscopy and differential scanning calorimetry (DSC). We have found that the dynamics of water of hydration is different among counterion species below 0 °C. For K-, Rb-, Sr-, and Ba-DNA gels, a part of nonfreezing water slowly changes its dynamical structure, when the gel is kept at ∼−30 °C after cooling below −50 °C. This relaxation process can be monitored both by the frequency increment of the lowest Raman band from ∼17 to ∼20 cm−1 and by the intensity increment of an extra endothermic peak in DSC heating curves. We propose that this relaxation process corresponds to the crystallization of a part of nonfreezing water and is caused by the rearrangement of the secondary hydrated water including counterions when the temperature is held at ∼−30 °C. This relaxation process cannot be observed for NH4- and Li-DNA gels. For Na-, Mg-, and Ca-DNA gels, this phenomenon is more complicated. The dynamical behavior of water of hydration in DNA gels is thus concluded to be different among counterion species.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.458430
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