The structure factor of a fragile glass-forming liquid orthoterphenyl was measured in the previously inaccessible intermediate q range between the conventional light scattering (LS) and small-angle x-ray scattering (SAXS) q ranges using the low-angle scattering beam line at the European Synchrotron Radiation Facility. At low q the structure factor exhibits an excess scattering and matches well the LS data. This excess scattering is due to long-range density fluctuations also observed in the isotropic component of scattered light. At high q the structure factor decays to a plateau corresponding to the isothermal compressibility in agreement with the conventional SAXS data. In the intermediate q range, the structure factor exhibits a power law q dependence which indicates that the excess scattering is due to fractal aggregates of denser domains.

No abstract

Fluorescence correlation spectroscopy (FCS) is frequently used to measure the self-diffusion coefficient of fluorescently labeled probes in solutions, complex media, and living cells. In a standard experiment water immersion objectives and window thickness in the range of 0.13-0.19 mm are used. We show that successful FCS measurements can be performed using samples of different refractive index placed in cells having windows of different thickness, even much thicker than nominally allowed. Different water, oil, and silicon oil immersion as well as long working distance dry objectives, equipped with the correction collar, were tested and compared. We demonstrate that the requirements for FCS experiments are less stringent than those for high resolution confocal imaging and reliable relative FCS measurements can be performed even beyond the compensation range of the objectives. All these features open new possibilities for construction of custom-made high temperature and high pressure cells for FCS.

During the past decade, from the vast evidence it became clear that DNA oligomers rich in guanine stretches can form in solution highly ordered forms called G-quadruplexes and G-wires. G-quadruplexes are present in many sites of the human genome, can inhibit telomerase, and can be used as drug delivery supramolecules. G-wires and related structures seem to be an excellent material of biological origin for nanostructures. Therefore, in this paper we have studied the structures formed by specific association of guanosine 5‘-monophosphate (GMP) nucleotide molecules in water solutions by photon correlation spectroscopy and depolarized Rayleigh light scattering. One relaxation process with distinct amplitude was observed, as a function of temperature and sample concentration. It was attributed to the translational diffusion coefficient of the stacks of G-quartets in a range of high concentration and to the stacks of GMP monomer associates for low concentration (less than 40 mg/mL). From the measurements the hydrodynamic radius of GMP molecule has been estimated as r H ≃ 5.4 Å. The bead modeling of the hydrodynamic parameters allowed us to distinguish the wide spectrum of structures formed in solution:  from single GMP nucleotides to stacks of multiassociates of G-quartets of GMP.