Search

Theoretical analysis revealed the mechanism that accelerates base-catalyzed amide hydrolysis inside the octahedral coordination cage via mechanical bond twisting as demonstrated in recent experiments.

When substrates are confined in an isolated cavity, they experience circumstances that are distinctly different from those in a bulk solution. Molecular self-assembly has widened the potential of m...

The properties of rare-earth-metal ions in aqueous media often depend on their various hydration modes, which allow them to exist as monomeric or oligomeric species with different coordination numbers. Capturing rare-earth-metal ions in a confined cavity can fix their hydration modes and thus enable their intrinsic properties to be distinguished. However, the isolation of ionic species from bulk aqueous media is not an easy task due to competitive interaction with bulk water. Here, we report the encapsulation of hydrated rare-earth-metal ions in a hydrophobic cavity of a synthetic cage. Cap-like counter anions located at the cage's portals play an important role in capturing the rare-earth metals at a fixed position via electrostatic interactions. Preferential encapsulation of early lanthanoid (III) ions was observed even though all the rare-earth metals have the same hydration number and geometry, as visualized by the competitive inclusion of a dye molecule. Accordingly, the early lanthanoid ion was selectively extracted from a mixture of two rare-earth-metal ions.

The ability of a cationic coordination cage to encapsulate molecular guests is enhanced by non-covalent capping of the cage portals with tripodal anions. The capped cage provides new cation binding sites at the portals, which enable accommodation of cationic substrates within the cationic cage. In addition, non-covalent capping allows neutral guests in the cage to be exchanged for cationic ones on demand.

In microthermoelectric generators (μTEGs), parasitic thermal resistance must be suppressed to increase the temperature difference across thermocouples for optimum power generation. A thermally conductive (TC) layer is typically used in μTEGs to guide the heat flow from the heat source to the hot junction of each thermocouple. In this study, we investigate the effect of the thermal boundary resistance (TBR) in metal/dielectric TC layers on the power generation of silicon nanowire (SiNW) μTEGs. We prepared various metal/adhesion/dielectric TC layers using different metal, adhesion, and dielectric layers and measured the thermal resistance using the frequency-domain thermoreflectance method. We found that the thermal resistance was significantly different, mainly due to the TBR of the metal/dielectric interfaces. Interface characterization highlights the significant role of the interfacial bonding strength and interdiffusion in TBR. We fabricated a prototype SiNW-μTEG with different TC layers for testing, finding that the power generation increased significantly when the thermal resistance of the TC layer was lowered. This study helps to understand the underlying physics of thermal transport at interfaces and provides a guideline for the design and fabrication of μTEGs to enhance power generation for effective energy harvesting.

We synthesized a double-walled knotted cage from a flexible tripodal ligand. The characteristic double-walled structure provided a unique adaptive behavior of the cavity upon inclusion of organic molecules, which was evidenced by NMR and X-ray measurements. The semiflexible host framework, restricted by the knotted topology, enabled kinetic molecular recognition revealing the sequential binding of two different guests from their mixture.

A molecular host with photosensitizing centers provides photo-responsive host-guest properties based on its molecular recognition ability. Here, we construct a self-assembled photoactive Ir(

A molecular host with photosensitizing centers provides photo-responsive host–guest properties based on its molecular recognition ability. Here, we construct a self-assembled photoactive Ir(iii) cage-shaped complex that contains anion binding pockets on its rim. The anion recognition ability of the complex enables efficient catalysis of the visible-light-induced E–Z isomerization of an anionic styrene derivative.

Mechanically interlocked host frameworks are expected to show dynamic guest inclusion/release without disruption of their inherent structures. Here, we synthesized a double-walled knotted cage from...

Even flexible linear substrates are conformationally fixed within the hydrophobic confined cavities of enzymes. This enables preorganization of the substrates and their positioning in close proximity to the active center to facilitate stereo- and site-selective reactions. Here, we demonstrate the site-selective electrophilic addition of linear diterpenoids within a self-assembled coordination cage. The reactions proceed through folding of the linear substrates into a U-shaped conformation, which results in noncovalent protection of internal C═C bonds to enhance the site selectivity.

For harvesting energy from waste heat, the power generation densities and fabrication costs of thermoelectric generators (TEGs) are considered more important than their conversion efficiency because waste heat energy is essentially obtained free of charge. In this study, we propose a miniaturized planar Si-nanowire micro-thermoelectric generator (SiNW-μTEG) architecture, which could be simply fabricated using the complementary metal–oxide–semiconductor–compatible process. Compared with the conventional nanowire μTEGs, this SiNW-μTEG features the use of an exuded thermal field for power generation. Thus, there is no need to etch away the substrate to form suspended SiNWs, which leads to a low fabrication cost and well-protected SiNWs. We experimentally demonstrate that the power generation density of the SiNW-μTEGs was enhanced by four orders of magnitude when the SiNWs were shortened from 280 to 8 μm. Furthermore, we reduced the parasitic thermal resistance, which becomes significant in the shortened SiNW-μTEGs, by optimizing the fabrication process of AlN films as a thermally conductive layer. As a result, the power generation density of the SiNW-μTEGs was enhanced by an order of magnitude for reactive sputtering as compared to non-reactive sputtering process. A power density of 27.9 nW/cm2 has been achieved. By measuring the thermal conductivities of the two AlN films, we found that the reduction in the parasitic thermal resistance was caused by an increase in the thermal conductivity of the AlN film and a decrease in the thermal boundary resistance.

We propose a planar device architecture compatible with the CMOS process technology as the optimal current benchmark of a Si-nanowire (NW) thermoelectric (TE) power generator. The proposed device is driven by a temperature gradient that is formed in the proximity of a perpendicular heat flow to the substrate. Therefore, unlike the conventional TE generators, the planar short Si-NWs need not be suspended on a cavity structure. Under an externally applied temperature difference of 5 K, the recorded TE power density is observed to be $12~\mu \text{W}$ /cm2 by shortening the Si-NWs length and suppressing the parasitic thermal resistance of the Si substrate. The demonstration paves a pathway to develop cost-effective autonomous internet-of-things applications that utilize the environmental and body heats.

Unusual demethylenation reactions of cyclopropanes under UV-light irradiation were found within a cavity of a photoactive coordination cage. The reaction proceeded via a guest-to-host electron transfer owing to the highly electron-deficient nature of the cage. The reactions were highly chemoselective and enabled late-stage derivatization of a steroid molecule, which led to a totally new un-natural steroid.

In core disruptive accident (CDA) of sodium-cooled fast reactors (SFRs), fuel and steel can melt to form a molten pool. The objective of the present work is to investigate design measures for core of SFR to prevent recriticality. This paper studied core geometry of convex cross-section shape to increase neutron leakage from core surface in case of core compaction. In order to evaluate effective neutron multiplication factor, 70-group neutron diffusion calculations were performed by changing parameters related to the convex core geometry (i.e. ratio of inner height to inner diameter). Neutron diffusion code and nuclear data library employed in those calculations are CITATION and JENDL-3.3, respectively. By optimizing core configuration, the compaction reactivity of the convex shaped core showed drastic reduction from 2.07 % of reference cylindrical core (Japan Sodium-cooled Fast Reactor) to -3.28 %.

A microgram-scale X-ray structure analysis of small molecules was developed by applying a modern high-throughput crystallization technique to classical co-crystallization via acid-base salt formation. The use of an automatic dispensing machine for the crystallization screening reduces the required amount of sample to the microgram scale. Absolute configurations of a chiral alkaloid and three chiral pharmaceutical acids were obtained by X-ray crystallography from 210–530 µg of samples by this renovated method.

When an amide group is distorted from its planar conformation, the conjugation between the nitrogen lone pair and the π* orbital of the carbonyl is disrupted and the reactivity towards nucleophiles is enhanced. Although there are several reports on the synthesis of activated twisted amides, amide activation through mechanical twisting is much less common. Here, we report twisted amides that are stabilized through their inclusion in a self-assembled coordination cage. When secondary aromatic amides are included in a Td-symmetric cage, the cis-twisted conformation is favoured over the trans-planar one-as evidenced by single-crystal X-ray diffraction analysis-revealing that the amide can twist by up to 34°. As a consequence of this distortion, the hydrolysis of amides is significantly accelerated upon inclusion.

Unusual demethylenation reactions of cyclopropanes under UV-light irradiation were found within a cavity of a photoactive coordination cage. The reaction proceeded via a guest-to-host electron transfer owing to the highly electron-deficient nature of the cage. The reactions were highly chemoselective and enabled late-stage derivatization of a steroid molecule, which led to a totally new un-natural steroid.

A best benchmark of Si-nanowire (NW) thermoelectric (TE) power generator has been achieved by our proposed planar device architecture compatible with CMOS process technology. The TE power density corresponds to 12 μW/cm2, which is recorded at an externally applied temperature difference of only 5 K. The demonstration opens up a pathway to cost effective autonomous internet of things (IoT) application utilizing environmental and body heats.

1. Background and purpose Silicon nanowire (SiNW) is a promising candidate for next-generation thermoelectric materials, because they maintain both low-thermal conductance and high electric conductance simultaneously [1]. It has been reported that thermoelectric power is enhanced by miniaturizing the SiNW [2], and it is very important to measure the temperature difference across the SiNW for examination of thermoelectric characteristics. However, it becomes gradually difficult to measure the temperature with miniaturization of the SiNW. From the above, we focused on the temperature measurement using Raman spectroscopy. In this study, we demonstrated the measurement of temperature difference for the SiNW thermoelectric generator using operand Raman spectroscopy, in order to evaluate of thermoelectric characteristics accurately. Experimental method We fabricated SiNWs using an SOI substrate (SOI layer 55 nm/Buried oxide 145 nm/Si substrate 750 μm) via electron beam lithography and ICP-RIE. Thermal oxidation was performed in dry oxygen ambient at 850 oC for 3h, to form 20 nm thick oxide film on the surface of the SiNWs. The height and width of the SiNW were approximately 35 nm and 100 nm, respectively. The length of SiNWs were assigned to 8, 46, and 90 μm. Phosphorus (P) ions were then implanted at an acceleration energy of 25 keV, with a dose of 1.0 × 1015 ions/cm2 followed by activation annealing at 950 °C for 10 min under vacuum conditions. Next, the SiO2 layer at the pad regions was removed via photolithography and a wet-etching process using buffered hydrofluoric acid. Then, the Si pads and both ends of the SiNWs were nickelized by depositing a Ni film followed by rapid thermal annealing at 410 °C for 20 min. Thus, the both ends of the SiNWs were connected to the NiSi pads. Then, thermally conductive AlN film was deposited onto one of the NiSi pads via RF reactive sputtering to facilitate heat conduction from the heat source, where Al and an Ar/N2 mixture are used as the sputtering target and sputtering gas, respectively. Finally, a forming gas anneal was conducted at 400 °C. The fabricated SiNW-μTEG consists of 8 arrays of 400 legs [3]. Temperature measurement was performed using Raman spectrometer equipped with custom-made microthermostat consisting of a heater and a platinum thermometer on an aluminum nitride ceramic plate. Figure 1 shows schematic of operand Raman measurement. The focal length of the Raman spectrometer was 2,000 mm and the wavenumber resolution was approximately 0.1 cm-1. The excitation source was UV (λ = 355 nm) laser with the penetration depth for bulk Si of approximately 5 nm. From obtained Raman spectra of SiNW regions, temperature was estimated. Results and Discussion Figure 2 shows time transition of Raman shift obtained by operand Raman spectroscopy. The Raman shifts were measured at the edge on the heat source side and the middle of the 46 μm-long SiNWs. As shown in Fig. 2, an apparent change in Raman shift was observed, and the Raman peak tends to shift toward lower wavenumbers over time. It has been reported that the Raman spectrum for Si-Si mode shifts toward lower wavenumbers and broadened by a thermal effect as temperature rises. To obtain thermal conductivity properties in detail, the temperature in SiNW region was estimated using the relation dω/dT = −0.024 cm−1/K [4]. Figure 3 shows time transition temperature obtained by operand Raman spectroscopy. As shown in Fig. 3, we confirmed that the temperature increases over time by operand Raman spectroscopy. Moreover, it was found that the heat transfer tends to be delayed at the SiNW region away from the heat source (L=23 μm). Based on the above, we consider that operand Raman spectroscopy is a novel promising technique that can measure the temperature in a very small region. Acknowledgements This work was supported partly by JST CREST Grant Number JPMJCR15Q7 and JPMJCR19Q5, and the Japan Society for the Promotion of Science (JSPS) through a JSPS Fellows (17J08240). References [1] A. I. Hochbaum et al., Nature 451, 163 (2008). [2] M. Tomita et al., IEEE Trans. Electron Devices, 65, 5180 (2017). [3] T. Zhan, Sci. Technol. Adv. Mater. 19, 449 (2018). [4] D. Fan et al., Phys. Rev. B 96, 115307 (2017). Figure 1

The integral kinetic model is applicable to space-dependent kinetic analysis for any weakly couplea system because of its applicability to any geometry. Transient parameters that aescribe tne time distribution of neutron transport between regions in a system are essential for this model. This paper presents a formula for calculating the parameters based on the nonanalog Monte Carlo neutron transport simulation technique. A continuous-energy Monte Carlo code MVP 2.0 was modified to calculate the parameters, and the modification was verified using the static coupled reactor theory. The parameters were calculated in a simple fast-thermal coupled reactor. The results showed a difference in fission starting times between a fast region and a thermal region, which can cause a time lag in the transient behavior between the two regions. The results also revealed the time distribution of neutron energy groups that trigger fissions in each region. A space-dependent kinetic analysis code based on the integral kinetic model is under development, and these parameters can be used in the integral kinetic model to perform space-dependent kinetic analysis for weakly coupled systems.

The nuclear-pumped laser (NPL) is a technology in which laser oscillation is accomplished using the energy of a nuclear reaction. We studied the possibility of developing a pulse reactor system for NPL using low-enriched uranium. It is possible to design a reactor system with 20% enriched uranium by making the pulse cores large, optimizing their position, and increasing their number. Such a system has uniform power distribution in the laser oscillation cells, which is desirable for laser pumping. The potential to solve the limit of energy efficiency and temperature in a nuclear reactor by NPL is also discussed.

Nuclear-pumped laser can directly convert nuclear energy to optical energy. A coupled reactor which consists of two pulse cores with highly enriched metallic uranium and a subcritical thermal laser module with highly enriched metallic uranium is one of the reactors for nuclear-pumped laser. In this paper, criticality analysis of a coupled reactor which consists of pulse cores with 20% enriched metallic uranium and a subcritical thermal laser module with 20% enriched metallic uranium was performed by Monte Carlo calculation. The result of criticality analysis showed the following three points. First, a coupled reactor with 20% enriched metallic uranium can achieve criticality. Second, using eight pulse cores in axial direction is effective to achieve flattened axial power distribution in the laser module. Third, less than 20% of the energy released from fissions in the whole coupled reactor has the possibility to be converted to optical energy for a coupled reactor with 100% enriched uranium, and less than 7% for a coupled reactor with 20% enriched uranium.

Phthalein dyes in the quinone dianion form (pseudo-D3, colored) are transformed into the lactone dianion form (pseudo-T(d), colorless) through encapsulation in a T(d)-symmetric host even under basic conditions (pH ∼10). The compatibility in size and symmetry between the lactone and the cavity is essential to the transformation. Upon addition of a guest that strongly binds to the cavity, the encapsulated phenolphthalein is expelled, the color of the basic solution is regained, and the host-guest complexation is thus visualized.

The confined space inside a self-assembled cage enhanced halogen bonding (XB) between iodoperfluorocarbons (XB donors) and NO3(-) anions or H2O molecules (XB acceptors), as confirmed by NMR spectroscopy in solution and by X-ray crystallography in the solid state. The cavity also bound an XB donor-acceptor pair, C6F3I3 and C6H5NMe2, in a selective pairwise fashion.

Polyfluorinated aliphatic compounds were encapsulated by a self-assembled M6L4 coordination host in aqueous media. NMR titration and X-ray crystallographic analyses clearly revealed that the aggregation of the fluorinated moieties of the guests in the host cavity plays a significant role in the binding. Polyfluorinated aromatics did not show such aggregation in the cavity because of their "nonfluorous" nature.

An overcrowded alkene with an anti-folded conformation was converted to its twisted conformer, accompanied by a dramatic color change from yellow to deep purple, by inclusion in a self-assembled T(d)-symmetric coordination cage. The shape of the caged cavity was suitable and desirable for trapping of the twisted conformer. The twisted conformation was temporarily memorized in the alkene even after guest ejection. Permanent trapping of the twisted conformation was achieved by bromination of the twisted conformer formed in situ in the cage.

Possibility to perform experiments for nuclear pumped laser oscillation by using low enriched uranium is investigated. Kinetic analyses are performed for two types of reactor design, one is using highly enriched uranium and the other is using low enriched uranium. The reactor design is based on the experiment reactor in IPPE. The results show the oscillation of nuclear pumped laser in the case of low enriched uranium reactor is also possible. The use of low enriched uranium in the experiment will make experiment easier.

Under UV-light irradiation, the anti-Markovnikov hydration of internal arylalkynes proceeds in the cavity of an electron-deficient coordination cage to give benzyl ketones; the reaction is triggered by cage-mediated, photo-induced electron transfer from the alkynes to the cage.

This work aims to show the possibility of using the integral kinetic model, which is applicable to any geometry, for general space-dependent kinetic analysis. A space-dependent kinetic analysis met...