The pH-dependent structures of the ferritin shell (apoferritin, 24-mer) and the ferrihydrite core, under physiological conditions that permit enzymatic activity, were investigated by synchrotron small-angle X-ray scattering (SAXS). The solution structure of apoferritin was found to be nearly identical to the crystal structure. The shell thickness and hollow core volumes were estimated. The intact hollow spherical apoferritin was stable over a wide pH range, 3.40-10.0, and the ferrihydrite core was stable over the pH range 2.10-10.0. The apoferritin subunits underwent aggregation below pH 0.80, whereas the ferrihydrite cores aggregated below pH 2.10 as a result of the disassembly of the ferritin shell under the strongly acidic conditions. As the pH decreased from 3.40 to 0.80, apoferritin underwent stepwise disassembly by first forming a hollow sphere with two holes, then a headset-shaped structure, and, finally, rodlike oligomers. As the pH was increased from pH 1.96, the disassembled rodlike oligomers recovered only to the headset-shaped structure, and the disassembled headset-shaped intermediates recovered only to the hollow spherical structure with two hole defects. The apoferritin hole defects that formed during the disassembly process did not heal as the pH was increased to neutral or slightly basic conditions. The pH-induced apoferritin disassembly and reassembly processes were not fully reversible, although they were pseudoreversible over a limited pH range, between 10.0 and 2.66.

We have investigated for the first time the structure of i-motif DNA in solution at various pH conditions by using synchrotron small-angle X-ray scattering technique. To facilitate direct structural comparison between solution structures of i-motif DNA at various pH values, we created atomic coordinates of i-motif DNA from a fully folded to unfolded atomic model. Under mild acidic conditions, the conformations for i-motif DNA appeared to be similar to that of the partially unfolded i-motif atomic model in overall shape, rather than the fully folded i-motif atomic model. Collectively, our observations indicate that i-motif DNA molecule is structurally dynamic over a wide pH range, adopting multiple conformations ranging from the folded i-motif structure to a random coil conformation. As the i-motif structure has been used as an important component in nanomachines, we can therefore believe that the structural evidence presented herein will promote the development of future DNA-based molecular-actuator devices.

A series of well-defined aniline-chain-end-functionalized regioregular poly(3-hexylthiophene)s (P3HT-NH 2 ) and sulfo-chain-end-functionalized polystyrene (PS-SO 3 H) have been prepared based on quasiliving Grignard metathesis and living anionic polymerization, respectively. Block copolymers via ionic interaction, (P3HT-NH)s, were successfully synthesized, simply by blending P3HT-NH 2 with PS-SO 3 H in toluene. The thermal and optical properties of the block copolymers were investigated by differential scanning calorimetry (DSC) and ultraviolet-visible (UV-vis) spectroscopy. The self-assembly behavior of the (P3HT-NH 3 þ )-b-(PS-SO 3 -) thin film was observed by atomic force microscopy (AFM) and transmission electron microscopy (TEM). In addition, grazing incidence X-ray scattering (GIXS) analysis found the microphase separation of P3HT-NH 3 þ and PS-SO 3 domains as well as the packing behavior of P3HT-NH 3 þ segments in block copolymer thin films. By exploiting the pH-sensitive ionic interaction, the PS-SO 3 domains were selectively etched with ethyl acetate/triethylamine, cleaving the ionic interaction between P3HT-NH 3 þ and PS-SO 3 segments, to obtain the target nanoporous P3HT-NH 2 films. The porosity of the films was confirmed by AFM, scanning electron microscopy (SEM) and GIXS analyses.

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