A Transition in DNA Molecule's Spatial Ordering Due to Nano-Scale Structural Changes

Abstract

The optical, X-ray-and AFM-properties of the particles of cholesteric liquid-crystalline dispersion (CLCD) formed by double-stranded DNA molecules and treated with gadolinium salts are studied. It is shown that under certain conditions this treatment results in two effects: i)amplification of the abnormal negative band in the CD spectra specific to the initial CLCD, and ii) disappearance of small-angle X-ray scattering specific of ordered DNA molecules. The explanation of these effects is based on a suggestion that gadolinium ions when present at high concentrations not only induce nano-scale changes in the DNA secondary structure, but also overcompensate the DNA negative charges, influencing the efficiency of DNA-DNA interactions in the content of the particles of CLCD. These processes lead to transformation of the spatial structure in particles of CLCD. The resulting structure of particles of DNA CLCD highly enriched in gadolinium is not "liquid-crystalline"; rather it is a rigid construction of practical importance.

The Physicochemical and Nanotechnological Approaches to Creation of “Rigid” DNA Nanoconstructions

“…Thus, one can expect that CLCDs of ds DNA with all phosphate groups neutralized by Gd 3+ ions, become poorly soluble and can exist even in absence of high osmotic pressure of PEG-containing solution [17]. Considering that these ds DNA molecules cannot "leave" the physical volume of CLCD particle and that separation of ds DNA chains in these particles is impossible for steric reasons due to fixed osmotic pressure of PEG-containing solution, we come to the following conclusion.…”

“…The results of AFM measurements show that treatment of ds DNA CLCD particles with the gadolinium salt is not accompanied by alteration in the mean size of the "rigid" NaCs of (DNA-Gd) complexes [16][17][18].…”

“…The results of X-ray measurements show that treatment of DNA CLCD particles with gadolinium salts leads to the onset of a modified secondary structure of ds DNA molecules and to the alteration of the helical twist of the cholesteric structure [17]. The last effect is responsible for amplification of intense negative band in the CD spectrum [7].…”

“…These cations were used for realization of this version [16][17][18]. It was shown that the treatment of ds DNA CLCD with gadolinium salt (GdCl 3 ) is accompanied by increase in amplitude of negative abnormal band ( ~ 270 nm) in the CD spectrum [16].…”

“…Considering that these ds DNA molecules cannot "leave" the physical volume of CLCD particle and that separation of ds DNA chains in these particles is impossible for steric reasons due to fixed osmotic pressure of PEG-containing solution, we come to the following conclusion. The disappearance of the fluidity of individual ds DNA molecules, combined with an increase in shortrange attractive interaction between their fragments with different conformations, induces the transition of overall structure of CLCD particles from "liquid" to "rigid" state [17].…”