Understanding hydrogen-bonding networks in nanocrystals and microcrystals that are too small for X-ray diffractometry is a challenge. Although electron diffraction (ED) or electron 3D crystallography are applicable to determining the structures of such nanocrystals owing to their strong scattering power, these techniques still lead to ambiguities in the hydrogen atom positions and misassignments of atoms with similar atomic numbers such as carbon, nitrogen, and oxygen. Here, we propose a technique combining ED, solid-state NMR (SSNMR), and first-principles quantum calculations to overcome these limitations. The rotational ED method is first used to determine the positions of the non-hydrogen atoms, and SSNMR is then applied to ascertain the hydrogen atom positions and assign the carbon, nitrogen, and oxygen atoms via the NMR signals for
1
H,
13
C,
14
N, and
15
N with the aid of quantum computations. This approach elucidates the hydrogen-bonding networks in
l
-histidine and cimetidine form B whose structure was previously unknown.
We
report on the formation of a bicontinuous double diamond (DD)
structure in ternary blends of poly(styrene-b-isoprene)
(SI) diblock copolymers with chains of different lengths merely in
a polyisoprene block. Certainly, the materials revealing the DD structure
with mesoscopic length scale have strongly been expected due to high
potential for applications; however, it is difficult to form owing
to thermodynamically evident disadvantages such as wider surface area
and larger domain thickness variation, particularly for monodisperse
copolymers. The DD structure was successfully formed for ternary blends
composed of three parent diblock copolymers; SI-L (M = 190k, φs = 0.46), SI-G (M =
151k, φs = 0.62), and SI-C (M =
124k, φs = 0.73), resulting in covering the overall
composition range 0.57 ≤ φs ≤ 0.60, where φss denotes volume fractions of polystyrene
blocks. Four-branched double network structure with space group symmetry
of Pn3̅m was clearly proved
by transmission electron microscopy (TEM) observation aided by computer
simulation, combined with diffracted data by small angle X-ray scattering.
In addition, TEM tomography gave direct information concerning interwoven
double networks and four-branching nature of the diamond framework.
Three-dimensional structures of actin bundles formed with polycations were observed by using transmission electron microtomography and atomic force microscopy. We found, for the first time, that the cross-sectional morphology of actin bundles depends on the polycation species and ionic strength, while it is insensitive to the degree of polymerization and concentration of polycation. Actin bundles formed with poly-N-[3-(dimethylamino)propyl] acrylamide methyl chloride quaternary show a ribbon-like cross-sectional morphology in low salt concentrations that changes to cylindrical cross-sectional morphology with hexagonal packing of the actin filaments in high salt concentrations. Contrastingly, actin bundles formed with poly-L-lysine show triangular cross-sectional morphology with hexagonal packing of the actin filaments. These variations in cross-sectional morphology are discussed in terms of anisotropy in the electrostatic energy barrier.
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