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Soft Matter and Biological Physics

Eur. Phys. J. E 7, 95-102 (2002)
DOI: 10.1140/epje/i200101099

Dynamic light scattering and $\chem{^{31}P}$ NMR spectroscopy study of the self-assembly of deoxyguanosine $\mth{5'}$-monophosphate

L. Spindler1, I. Drevensek Olenik2, M. Copic2, R. Romih3, J. Cerar4, J. Skerjanc4 and P. Mariani5

1  Faculty of Mechanical Engineering, University of Maribor, Smetanova 17, SI-2000 Maribor, Slovenia
2  Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana, Slovenia, and Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia
3  Institute of Cell Biology, Medical Faculty, University of Ljubljana, Lipiceva 2, SI-1000 Ljubljana, Slovenia
4  Faculty of Chemistry and Chemical Technology, University of Ljubljana, Askerceva 5, SI-1000 Ljubljana, Slovenia
5  Istituto di Scienze Fisiche, Facoltà di Medicina e Chirurgia, Università di Ancona, and INFM, via Ranieri 65, I-60131 Ancona, Italy


(Received 13 July 2001 and Received in final form 17 October 2001)

Self-assembling properties of deoxyguanosine 5'-monophosphate in isotropic solutions of concentrations from 0.5 wt% to 15 wt% were investigated by dynamic light scattering (DLS) and $\chem{^{31}P}$ NMR spectroscopy. A slow diffusive mode with a diffusion coefficient $D_{\rm slow} \sim 10^{-12}$ m 2/s was detected by DLS for the whole concentration range. This mode is assigned to the translational motion of large globular aggregates, similar to those observed in DNA and other polyelectrolyte solutions. The existence of such aggregates was confirmed by freeze fracture electron microscopy. Close to the isotropic-cholesteric phase transition, at 4 wt% $ \leqslant
c \leqslant 10$ wt%, also a faster diffusive mode is observed in the polarized DLS response and a very fast mode is detected by depolarized DLS. These modes are related to translational and rotational diffusion of the columnar stacks of guanosine molecules, which are favorably formed in the relatively narrow pretransitional region. The stacking was also revealed from the appearance of a secondary resonance line in the $\chem{^{31}P}$ NMR spectra. Using the hydrodynamic theory of Tirado and Garcia de la Torre, the length of the cylindrical stacks was found to be $L =
364 \pm 78$ Å, which is significantly larger than the values reported for other guanosine derivatives.

81.16.Dn - Self-assembly.
61.30.St - Lyotropic phases.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2002