O. N. Kompanets

[About the Spatial Organization of Double-stranded DNA Molecules in the Cholesteric Liquid-crystalline Phase and Dispersion Particles of this Phase].

An attempt to generalize the well-grounded published data on the structure of the cholesteric phase that is formed by double-stranded DNA molecules and the authors’ own data concerning the packaging of these molecules in particles of a cholesteric liquid-crystalline dispersion has been made. Comparison of all of the data revealed a high probability of the existence of both “local” positional order and “long-range” orientation order in the arrangement of double-stranded DNA molecules in both the liquid-crystalline phase and a dispersion of particles of this phase formed under certain conditions. The emergence of the orientation order, that is, rotation of “quasinematic” layers of double-stranded DNA molecules by a small angle, determines the formation of a twisted (cholesteric) spatial structure with characteristic physicochemical properties.

The re-entrant cholesteric phase of DNA

The character of packing of double-stranded DNA molecules in particles of liquid-crystal dispersions formed as a result of the phase exclusion of DNA molecules from aqueous salt polyethylene glycol solutions has been estimated by comparing the circular dichroism (CD) spectra of these dispersions recorded at different osmotic pressures and temperatures. It is shown that the first cycle of heating of dispersion particles with hexagonally packed double-stranded DNA molecules leads to the occurrence of abnormal optical activity of these particles, which manifests itself in the form of a strong negative CD band, characteristic of DNA cholesterics. Moreover, subsequent cooling is accompanied by a further increase in the abnormal optical activity, which indicates the existence of the “hexagonal → cholesteric packing” phase transition, controlled by both the osmotic pressure of the solution and its temperature. The result obtained can be described in terms of “quasi-nematic” layers composed of orientationally ordered DNA molecules in the structure of dispersion particles. There are two possible ways of packing for these layers, which determine their hexagonal or cholesteric spatial structure. The second heating → cooling cycle confirms these results and is indicative of possible differences in the packing of double-stranded DNA molecules in the hexagonal phase, which depend on the osmotic pressure of the solution.

Ordering of double-stranded DNA molecules in a cholesteric liquid-crystalline phase and in dispersion particles of this phase

The current notion of the organization of molecules in a cholesteric phase is fairly well substantiated in the case of low-molecular-weight compounds. However, this question is open to discussion in the case of double-stranded nucleic acids. In this work, an attempt to compare the well-known data on the structure of cholesteric phases formed by double-stranded DNA molecules and the results of experimental modeling obtained by the authors has been undertaken. The comparison brings leads to assumption regarding the high probability of the existence of both short-range (positional) and long-range (orientational) order in the arrangement of double-stranded DNA molecules in the liquid crystalline phase. The presence of the orientational order, i.e., the rotation of quasinematic layers of double-stranded DNA molecules through a small angle, determines the formation of a spatially twisted (cholesteric) structure with specific physical and chemical properties. In addition, these results prompt a suggestion on the mode of the ordering of dsDNA molecules in liquid-crystalline dispersion particles and allow these particles to be considered candidate biosensing units.

On the possibility of determining anthracycline antibiotics in aqueous solutions using optical analytical system (biosensor)

We propose a version of the theory describing the circular dichroism spectra of cholesteric liquidcrystal dispersion particles of double-stranded DNA. The basis of the theory is the concept of absorption of electromagnetic waves by large molecular systems. The effect of physical parameters of dispersion particles on their circular dichroism is theoretically determined. It is experimentally demonstrated that circular dichroism can be used as a convenient tool for creating an optical analytical system for the determination of biologically active compounds that interact with DNA molecules.

About Spatial Organization of Double-Stranded DNA Molecules in Cholesteric Liquid-Crystalline Phase

В случае низкомолекулярных соединений ответ на вопрос об организации молекул в холестерической фазе достаточно хорошо обоснован. Однако в случае молекул двухцепочечных (дц) нуклеиновых кислот однозначный ответ на такой вопрос является предметом дискуссий. В работе предпринята попытка обобщить хорошо известные литературные данные о структуре холестерической фазы, образуемой молекулами дц ДНК. Сопоставление этих данных позволяет высказать предположение о высокой вероятности существования как «ближнего» позиционного, так и «дальнего» ориентационного порядка в расположении дц молекул ДНК в жидкокристаллической фазе. Возникновение ориентационного порядка, т. е. поворот «квазинематических» слоев из дц молекул ДНК на небольшой угол, определяет формирование пространственно закрученной (холестерической) структуры с характерными для нее физико-химическими свойствами. Ключевые слова: модельные спиральные структуры и их сечение, срезы хромосом динофлагеллят, сколы (срезы) холестерической жидкокристаллической фазы ДНК.

Analytical system based on liquid-crystalline DNA particles immobilized in content of polymeric hydrogel and a portable dichrometer

Different approaches to constructing sensing units based on nucleic acid (DNA) molecules are considered. These sensing units permit the detection of biologically relevant compounds of various origin. However, the main goal of this report is the description of the peculiarities of multifunctional sensing units based on particles of liquid-crystalline DNA dispersions immobilized in hydrogel. In combination with a portable dichrometer these sensing units form a new type of the bioanalytical system.

In memory of Roman Ivanovich Personov (January 4, 1932–January 17, 2002)

Roman Ivanovich Personov was born and raised in Moscow. He received a higher education at the Faculty of Physics and Mathematics of the Lenin Moscow State Pedagogical Institute (MSPI), from which he graduated with honors in 1955. After graduating from this institute, he stayed there for postgraduate studies at the Chair of Theoretical Physics. In 1955–1956, Personov served in the Soviet Army, then continuing his post-