The valence electron density distribution in crystals can be observed with high accuracy by precise electron density analysis using the core differential Fourier synthesis （CDFS） method with high-intensity and high-resolution single crystal X-ray diffraction data obtained at a large synchrotron radiation facility; SPring-8. By observing the spatial distribution of electron density proportional to the square of the wave function, the quantum parameters of the orbital states of can be directly determined. Using this method, not only orbital ordered states and bonding electrons but also degenerate orbital states can be directly observed, which may lead to a new method for structural properties research beyond the conventional structural analysis.

Atomic model refinement and map calculation methods for cryo-EM single particle analysis（SPA）are explained in relation to X-ray crystallography. To make the best use of high-resolution reconstructions from SPA, it is important to calculate interpretable density maps to help build atomic models, and to use all experimental information to refine models. We developed a new program Servalcat to facilitate the structure refinement in reciprocal space. Servalcat performs structure refinement using REFMAC5, followed by calculation of weighted and sharpened F_o and F_o－F_c maps, which are useful in manual model rebuilding.

The past decade has seen revolutionary progress in single particle analysis with cryo-electron microscopes. Steady improvement in resolution has culminated in the reports of atomic resolution（1.2 Å）structures of apoferritin in 2020. This review, as a follow-up to my previous review in 2018, summarizes hardware and software improvements that enabled this milestone achievement. A quantitative analysis of the relationship between the number of particles and the resolution is presented and its practical implication in data collection strategies is discussed.

Single-crystal neutron structure analysis is a powerful technique to observe the position of hydrogen atoms in crystals with high accuracy and reliability because of its high sensitivity to hydrogen atoms. In Japan, the development of single-crystal neutron diffractometers for structure analysis has progressed since the 1990s at the JRR-3 research reactor. Subsequently, the construction of J-PARC MLF, a high intense spallation neutron source, started in the 2000s. The author has developed single-crystal neutron diffractometers at JRR-3 and MLF to make the single-crystal neutron structure analysis of organic and organometallic molecular crystals possible. In addition, the author has also been conducting research based on the reliable observation of hydrogen atoms in molecular crystals. This paper will review the recent development of single-crystal neutron diffractometers and studies in which hydrogen atoms play a crucial role.

Living cells utilize liquid-liquid phase separation （LLPS） to enable the compartmentalization of macromolecules as membrane-less organelles. RNA binding proteins with intrinsically disordered regions play a central role in the biological LLPS. Although LLPS provides an enormous advantage in a mixture of a wide variety of biological macromolecules, misregulation leads to fatal diseases, including Amyotrophic Lateral Sclerosis （ALS）. Phase state of RNA binding protein FUS and its regulation by nuclear import receptor karyopherinβ2 will be discussed.

Here we describe kinetic assembly of porous coordination networks and structural chemistry of interactive molecules which are connected by keyword, “interaction”. Kinetic assembly of coordination networks provides us with interactive sites which is used for encapsulating unstable species and for creating functional materials. The functionality comes from interactivity. On the other hand, interactive organic molecules show unique behaviors such as assembly of anions and memory effect. Here we describe the details of interactive materials.

Hydrogen boride（HB）sheets are the material composed by boron and hydrogen with H/B＝1.0 atomic ratio, which can be formed by exfoliation and complete ion-exchange between protons and magnesium cations in magnesium diboride（MgB₂＋2H^＋ → Mg^2＋＋2HB）at room temperature and ambient pressure. In this article, its synthesis method, structure, and recently clarified wide-variety of functionalities, including photo-induced hydrogen release function, superior solid-acid catalytic activity, and specific reduction function are introduced.

In recent years, a highly efficient ammonia decomposition catalyst using abundant metal such as Ni is strongly required for on-site hydrogen production. In this study, we clarify the role of Ca-N-H materials （e.g. CaNH, Ca（NH₂）₂, and Ca₂NH） for Ni-based ammonia decomposition catalyst. Among these materials, CaNH significantly enhanced the ammonia decomposition performance of Ni catalyst. Ni/CaNH exhibited much greater ammonia decomposition activity than state-of-the-art Ni-based catalysts, and the operating temperature was reduced by ～100℃ than that of the oxide supported Ni-based catalysts. Detailed characterization and measurements revealed that ammonia decomposition reaction takes place at the site of NH^2－ vacancy located at the Ni-CaNH interface.

Aluminum has low hydrogen affinity and aluminum-based alloy hydrides have rarely been reported so far. We have tried to obtain aluminum-based alloy hydride by hydrogenating alloys consisting of metals with low hydrogen affinities only. The first aluminum-based interstitial hydride Al₂CuH was obtained by hydrogenating Al₂Cu alloy at 10 GPa. However, other aluminum-based interstitial hydrides have yet to be obtained. We investigated hydrogenation reactions of other alloys consisting of metals with low hydrogen affinities only and have tried to obtain new classes of aluminum-based hydrides based on the obtained information. We have synthesized a novel hydride Al₃FeH₄. The obtained Al₃FeH₄ was turned out to be thermodynamically stable near ambient conditions. It is likely that unique structural units in Al₃FeH₄ stabilize the hydride.

XRD-data-assimilated approach has been explained in this article. By introducing the penalty function from the similarity between experimental and calculated diffraction pattern, the structures different from the one obtained in the experiment is efficiently destabilized during the simulated annealing from random structures. Also, found that XRD-assimilated simulation is available for hydrogen containing materials, where H atom hardly contributes to XRD pattern.

High intensity neutron total diffractometer （NOVA） was installed at BL21 of J-PARC/MLF and achieved the designated level of performance to study atomic distribution in various materials including liquids, amorphous and crystals. Short time and small sample measurements are feasible for averaged structure analysis, and the real space resolution is enough for local structure （Pair Distribution Function） analysis by high-flux pulsed neutron and low background at NOVA. Averaged and local structure analysis results of NaAlD₄-TiCl₃ and V-H systems are introduced.

White neutron holography is a novel technique which can visualize local atomic structures around particular elements such as dopants. Since most of functional materials, such as semiconductors, the performance can be controlled by for foreign elements doping. Thus, observation of local atomic structure around dopants must be important to understand properties of functional materials. In particular, light elements such as hydrogen can be observed by neutron holography. In this article, brief principle and a recent result of white neutron holography will be presented.