On the physical nature of mesophases of guanosine gels

Physical Chemistry Chemical Physics

Volumn 8, Issue 37, 2006, Pages 4347-4358

  Rudd, Laura ^a   Lee, Dominic J ^a   Kornyshev, Alexei A ^a  

^a IMPERIAL COLLEGE LONDON   (United Kingdom)

Author keywords

[No Author keywords available]

Indexed keywords

2' DEOXYGUANOSINE 3' PHOSPHATE; 2'-DEOXYGUANOSINE 3'-PHOSPHATE; 2'-DEOXYGUANOSINE 5'-PHOSPHATE; DEOXYGUANOSINE PHOSPHATE;

ARTICLE; CHEMISTRY; CONFORMATION; ELECTRICITY; GEL; OSMOSIS; PHASE TRANSITION; STATIC ELECTRICITY; THEORETICAL MODEL;

DEOXYGUANINE NUCLEOTIDES; ELECTROSTATICS; GELS; MODELS, THEORETICAL; MOLECULAR CONFORMATION; OSMOSIS; PHASE TRANSITION; STATIC ELECTRICITY;

EID: 33749660593     PISSN: 14639076     EISSN: None     Source Type: Journal    
DOI: 10.1039/b601018k     Document Type: Article

References (48)

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19. Note that the assumption of torsional rigidity is important writing down eqn (1), if the molecules are allowed to twist, the helical symmetry will be broken. These deviations from an ideal helix are quite small over short lengths. If such distortions are, indeed, slowly varying along the length of the stack we may write an integral over the axial coordinate z where now Δφ depends on z; the interaction energy will be a functional of Δφ (z) [A. Kornyshev and A. Wynveen,. Phys. Rev. E, 2004, 69, 041905]. The effects of torsional elasticity on the pair interaction and the properties of columnar assemblies of helical blocks have been extensively studies for DNA duplexes [D. J. Lee, A. Wynveen and A. A. Kornyshev, Phys. Rev. E, 2004, 70, 051913; A. G. Cherstvy, A. A. Kornyshev and S. Leikin, J. Phys. Chem. B, 2004, 108, 6508; D. J. Lee and A. Wynveen J. Phys: Condens Matter, 2006, 18, 1]. Since this is a first time study of the azimuthal effects of the pair potential and of how that may be used to explain the data on guanosine gels, we will ignore these effects
20. In this theory, bulk water and the cores of macroions are modelled as uniform media of dielectric constants 80 and 2, respectively. Monoionised phosphate groups are modelled in simplest approximation as point charges at the core surface (the latter assumption can easily be and was improved by introducing charge form-factors of phosphates). The net surface charge is screened by a region of oppositely-charged counterions, comprising both those released from the surface and those from dissolved salt. These are treated in terms of a two-state Debye-Bjerrum model, in which the ions of the diffuse electrical double layer around the molecule are described via linearized Poisson-Boltzmann theory, while bound ions are treated as belonging to the molecule. In the simplest approximations the latter may be considered evenly-smeared along the macroion surface, although in principle different kind of adsorbed ion pattern could easily be and were considered in applications of this theory. At high assembly density, Donnan equilibrium will require higher concentration of ions in the aggregate to neutalize the charge of macroins, so the that the effective Debye lengths inside the aggregates will be shorter. Quantitatively this will be taken into account in our calculations below
21. It has been shown that in columnar phase of guanosine gels [P. Mariani, M. M. De Morais, G. Gottarelli, G. P. Spada, H. Delacroix, L. Tondelli, Liq. Cryst, 1993, 15, 757] there is long range order in the plane perpendicular to director field. This is unlike DNA where, in certain cases a line hexatic phase can exist [H. H. Strey, J. Wang, R. Podgornik, A. Rupprecht, L. Yu, V. A. Parsegain, E. B. Sirota, Phys. Rev. Lett., 2000, 84, 3105]. The latter is characterised by long range bond-orientational order, long range nematic order, no smectic layering and liquid like positional 2-D order perpendicular to the nematic director field. However, there does not also seem to be any smectic ordering in guanosine gels. Even though, our calculations are done on a "2-D lattice", as opposed to a proper 3-D system, we do not think this could qualitatively change the effect of thermal azimuthal fluctuations on the force curves; neither will it dramatically affect the lattice distortion
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