Liquid-crystalline phases formed by DNA duplexes containing pyrophosphate groups
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AL, NONLINEAR, AND SOFT MATTER PHYSICS
Liquid-Crystalline Phases Formed by DNA Duplexes Containing Pyrophosphate Groups Yu. S. Volkova*, V. L. Goloa, E. I. Katsb, and S. A. Kuznetsovac a
b
Moscow State University, Moscow, 119992 Russia Landau Institute for Theoretical Physics, Russian Academy of Sciences, Chernogolovka, Moscow oblast, 142432 Russia c Institut Laue–Langevin, 38000 Grenoble, France *e-mail: [email protected] Received July 15, 2008
Abstract—We have studied the interaction between synthetic DNA molecules containing pyrophosphate (PP) groups in various positions, which makes it possible to control the charge distribution along the DNA chain. The PP groups were either symmetrically arranged at the ends or at the center of DNA molecules or uniformly distributed along these molecules. It is shown that, similar to nonmodified DNA, the synthetic PP-modified DNA molecules can form cholesteric liquid crystals. Minima of the pair interaction potential are found, conditions of the symmetry of this potential are formulated, and the dependence of conformation angles on the effective charge is determined. The results of calculations show that the system exhibits polymorphism (i.e., several phases of cholesteric liquid crystals can exist in DNA solutions). PACS numbers: 87.15.-v DOI: 10.1134/S1063776109030133
1. It is well known that, as has been proved by Onsager [1] and later repeatedly confirmed by numerical simulations and experiments (see, e.g., [2]), rigid rodlike molecules in a certain range of thermodynamic parameters (density, pressure) are capable of spontaneous ordering so that they acquire a nematic orientation order. It is also well known [2] that a chiral nematic phase (i.e., a cholesteric liquid crystal) is formed in cases where these rigid molecules are chiral. Double-helix DNA molecules are a very useful example of such chiral molecules. There are numerous observations and experimental investigations of cholesteric phases formed by DNA duplexes [3, 4–6], as well as repeated attempts to theoretically describe these systems [7–11]. Unfortunately, even in cases where the experimental data and theoretical calculations show formal agreement, it should be borne in mind that this agreement is achieved either using phenomenological coefficients not known a priori or by making assumptions that are neither macroscopically justified nor have the known region of validity. The same kind of doubt is related to experimental observations in which the conditions important for liquid-crystalline DNA phases to form can by no means always be controlled. Liquid-crystalline suspensions of DNA molecules are especially complex systems, in which the molecules are strongly charged and, hence, electrostatic interactions (and their screening in aqueous solutions) play a dominant role, thus determining the most important
characteristics of the structure and other physical properties of condensed phases. This situation makes it necessary to consider, prior to studying complex condensed systems, the initial molecular proble
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