Optical Properties of the DNA Particles of Cholesteric and «Re-Entrant» Cholesteric Phases

Abstract

Phase exclusion of DNA molecules from polyethylene glycol (PEG) water-salt solutions leads to formation at room temperature of liquid-crystalline dispersions (LCD) with cholesteric and hexagonal packing of DNA molecules, determined by the osmotic pressure of the PEG solution. LCDs with cholesteric DNA packing (CLCD) have an intense negative band in the circular dichroism (CD) spectrum in the absorption region of nitrogen bases. LCD particles with hexagonal packing have no abnormal band. With increase of the solution temperature containing DNA CLCD particles, a decrease in the abnormal band in the CD spectrum is observed. Cooling of the dispersion leads not only to the restoration of the initial abnormal band, but also increases its amplitude. When the heating LCD with hexagonal DNA packing occurs, such band appears, i.e. there is the "hexagonal packing →"re-entrant"cholesteric packing phase transition. Cooling of the "re-entrant" cholesteric phase (C PEG = 240 mg ml-1) is accompanied by further increase in abnormal optical activity, whereas cooling of the dispersion formed at C PEG = 300 mg ml-1 causes decrease of the abnormal band amplitude. Consequently, equilibrium amplitude values of abnormal bands in CD spectra of these dispersion particles are realized as a result of multidirectional processes. When cooled to room temperature, the kinetic curves designating changes in the spatial structure of LCD particles with the "re-entrante" cholesteric packing of DNA molecules have a wave-like character. Comparison of these curves shows that the osmotic pressure increase of the PEG solution is accompanied by the increase of the wave-like character. Thus, the formation of the "re-entrant" cholesteric phases of DNA is determined not only by the osmotic pressure and temperature of PEG solution, but also by the average distance between DNA molecules in dispersion particles with the original hexagonal packing. Key words: liquid-crystalline ds DNA dispersion particles, circular dichroism, abnormal optical activity, cholesteric packing of ds DNA molecules, hexagonal packing of ds DNA molecules, temperature kinetics of formation of ds DNA cholesteric "re-entrant" phase, hexagonal → "re-entrant" phase of ds DNA transition.

Perturbative density functional methods for cholesteric liquid crystals

“…1 It should be noted that this compact expression derives from a finite-order truncation of the free energy gradient expansion, and is therefore only valid in the limit of long-wavelength director fluctuations -an assumption consistent with the characteristically large values of experimental cholesteric pitches. [25][26][27][28][29][30][31][32] Eq. ( 1) thus provides a natural theoretical framework for the description of smoothly modulated nematic phases, and has been successfully used in recent years for the analytical 59,60 and numerical 59,61 modelling of a number of experimentally-relevant systems.…”

“…A fundamental feature of both systems is the high sensitivity of the pitch P to the chemical structure and thermodynamic state of their constituent particles, which provides the basis for many of the above applications; the nature of this intricate dependence has been intensively investigated experimentally over the last decades in a number of different contexts. [25][26][27][28][29][30][31][32] Conversely, theoretical and numerical descriptions of the cholesteric phase have long been hampered by both the complexity of the microscopic chiral interactions and the multi-scale nature of the problem, as cholesteric pitches measured experimentally are usually several orders of magnitudes larger than typical particle sizes. 1 This large spatial periodicity renders direct atomistic simulations largely impractical, due to both the substantial size of the simulation boxes required and the unsuitability of standard periodic boundary conditions.…”

Designing Liquid‐Crystalline Oligomers to Exhibit Twist‐Bend Modulated Nematic Phases

“…The term liquid crystal (LC) refers to a group of phases of matter with some degree of positional or orientational order. In addition to being widely exploited in display devices, LC phases are also formed by DNA, carbohydrates and lipids, and peptides, as well as suspensions of viral and inorganic particles . The nematic LC phase possesses an average orientational order of its constituent molecules along a vector termed the director lacks positional order (Figure a).…”