Arrangement of chromatin in intact chicken erythrocyte nuclei was investigated by small angle neutron scattering. The scattering spectra have revealed that on the scales between 15 nm and 1.5 lm the interior of the nucleus exhibited properties of a mass fractal. The fractal dimension of the protein component of cell nucleus held constant at approximately 2.5, while the DNA organization was biphasic, with the fractal dimension slightly higher than 2 on the scales smaller than 300 nm and approaching 3 on the larger scales.

Smectic ordering in aqueous solutions of monodisperse stiff double-stranded DNA fragments is known not to occur, despite the fact that these systems exhibit both chiral nematic and columnar mesophases. Here, we show, unambiguously, that a smectic-A type of phase is formed by increasing the DNA's flexibility through the introduction of an unpaired single-stranded DNA spacer in the middle of each duplex. This is unusual for a lyotropic system, where flexibility typically destabilizes the smectic phase. We also report on simulations suggesting that the gapped duplexes (resembling chain-sticks) attain a folded conformation in the smectic layers, and argue that this layer structure, which we designate as smectic-fA phase, is thermodynamically stabilized by both entropic and energetic contributions to the system's free energy. Our results demonstrate that DNA as a building block offers an exquisitely tunable means to engineer a potentially rich assortment of lyotropic liquid crystals.

The frequencies of the normal modes of vibration of CoPt 3 and FePd single crystals have been measured using inelastic neutron scattering. The measurements were performed in the L1 2 ordered phase ͑at 300 and 930 K͒ for CoPt 3 and in the L1 0 ordered phase ͑at 300 and 860 K͒ for FePd. Dispersion curves were also measured in the fcc disordered states, at 1060 and 1020 K for CoPt 3 and FePd, respectively. The activation enthalpy of atomic migration has been evaluated from the phonon density of states by applying Schober's model ͓H. R. Schober et al., J. Phys.: Condens. Matter 4, 9321 ͑1992͔͒ and its extension to the L1 2 ordered structure. The phonon properties of FePd 3 reported in the literature have been analyzed similarly and are compared with the results for CoPt 3 and FePd. The contribution of the long-range order to the migration enthalpy estimated in the present analyses agrees well in magnitude with the previous evaluation by Monte Carlo simulation for alloys of the fcc, L1 2 , and L1 0 structures.