Detailed structural investigations on living cells are problematic because existing structural methods cannot reach high resolutions on non-reproducible objects. Illumination with an ultrashort and extremely bright X-ray pulse can outrun key damage processes over a very short period. This can be exploited to extend the diffraction signal to the highest possible resolution in flash diffraction experiments. Here we present an analysis of the interaction of a very intense and very short X-ray pulse with a living cell, using a non-equilibrium population kinetics plasma code with radiation transfer. Each element in the evolving plasma is modeled by numerous states to monitor changes in the atomic populations as a function of pulse length, wavelength, and fluence. The model treats photoionization, impact ionization, Auger decay, recombination, and inverse bremsstrahlung by solving rate equations in a self-consistent manner and describes hydrodynamic expansion through the ion sound speed. The results show that subnanometer resolutions could be reached on micron-sized cells in a diffraction-limited geometry at wavelengths between 0·75 and 1·5 nm and at fluences of 1011–1012 photons μm−2 in less than 10 fs. Subnanometer resolutions could also be achieved with harder X-rays at higher fluences. We discuss experimental and computational strategies to obtain depth information about the object in flash diffraction experiments.

Surfactants are surface-active, amphiphilic compounds that are water-soluble in the micro- to millimolar range, and self-assemble to form micelles or other aggregates above a critical concentration. This definition comprises synthetic detergents as well as amphiphilic peptides and lipopeptides, bile salts and many other compounds. This paper reviews the biophysics of the interactions of surfactants with membranes of insoluble, naturally occurring lipids. It discusses structural, thermodynamic and kinetic aspects of membrane–water partitioning, changes in membrane properties induced by surfactants, membrane solubilisation to micelles and other phases formed by lipid–surfactant systems. Each section defines and derives key parameters, mentions experimental methods for their measurement and compiles and discusses published data. Additionally, a brief overview is given of surfactant-like effects in biological systems, technical applications of surfactants that involve membrane interactions, and surfactant-based protocols to study biological membranes.

The deposition of amyloid- and amyloid-like fibrils is the main pathological hallmark of numerous protein misfolding diseases including Alzheimer's disease, transmissible spongiform encephalopathy, and type 2 diabetes. Besides the well-established role in disease, recent work on a variety of organisms ranging from bacteria to humans suggests that amyloid fibrils can also convey biological functions. To better understand the molecular mechanisms by which amyloidogenic proteins misfold in disease or perform biological functions, structural information is essential. Although high-resolution structural analysis of amyloid fibrils has been challenging, a combination of biophysical approaches is beginning to unravel the various structural features of amyloid fibrils. Here we review these recent developments with particular emphasis on amyloid fibrils that have been studied using site-directed spin labeling and electron paramagnetic resonance spectroscopy. This approach has been used to define the precise location of fibril-forming core regions and identify local secondary structures within such core regions. Perhaps one of the most remarkable findings arrived at by site-directed spin labeling was that most fibrils that contain an extensive core region of ∼20 amino acids or more share a common parallel in-register arrangement of β strands. The preference for this arrangement can be explained on topological grounds and may be rationalized by the maximization of hydrophobic contact surface.