Dynamic light scattering and

Self-assembling and dynamical properties of deoxyguanosine 5’-monophosphate in isotropic aqueous solutions were studied by 31P NMR spectroscopy and dynamic light scattering (DLS). All solutions had the same c = 4 wt% guanosine concentration, while the added KCl molarity ranged from 0 to 1.5 M. 31P NMR measurements show that potassium ions strongly enhance the stacking process of guanosine tetramers until a saturation is reached at 0.1 M KCl with more than 70% of the molecules aggregated. Polarized light scattering reveals the presence of a fast relaxation mode that arises from the translational dynamics of the self-assembled stacks. The diffusion coefficient of this mode shows a strong dependence on molarity of added salt, which can be described in terms of the coupled mode and counterion condensation theories for polyelectrolyte solutions. Depolarized light scattering reveals the rotational dynamics of the self-assembled stacks which exhibits a pronounced slowing down with increasing the added salt content

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

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

Introducing the azocinnamic acid scaffold into bent-core liquid crystal design: A structure–property relationship study

A series of bent-core liquid crystals possessing the azocinnamoyl unit in both elongating side arms was synthesized. The chain length was kept fixed for each molecule (C12H25), whereas the substituents at the central and outer rings were varied. The LC phases were assigned by polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. The investigated compounds are suitably diverse to reveal some aspects of the relationship between molecular structure and the mesomorphic properties. Namely, non-substituted parent compound is crystalline only and the methyl group in position 2 or the chlorine atom in position 4 of the central ring suppresses LC phase formation. Introduction of the strong electron-withdrawing nitro group between the side arms on the central ring leads to a B7 phase. Compounds possessing a bromine atom or two chlorine atoms in the neighbourhood of the ester groups form LC phases typical for rod-like molecules, namely a nematic – smectic phase sequence. The results are compared with those reported for the azobenzoyl analogues

Phasons and broken symmetries in ferroelectric liquid-crystals

Contains fulltext : 91270.pdf (publisher's version ) (Open Access

Optical second-harmonic generation and scanning tunneling microscopy study of the self-assembly process of cyanine dyes on Br-Ag(111) substrates

Contains fulltext : 92609.pdf (publisher's version ) (Open Access