Search

Tunable high-refractive-index nanostructures are highly desired for realizing photonic devices with a compact footprint. By harnessing the large thermo-optic effect in silicon, we show reversible and wide thermal tuning of both the far- and near-fields of Mie resonances in isolated silicon nanospheres in the visible range. We perform in situ heating in a transmission electron microscope and electron energy-loss spectroscopy to show that the Mie resonances exhibit large spectral shifts upon heating. We leverage the spectral shifts to demonstrate near-field tuning between different Mie resonances. By combining electron energy-loss spectroscopy with energy-dispersive X-ray analysis, we show a reversible and stable operation of single silicon nanospheres up to a temperature of 1073 K. Our results demonstrate that thermal actuation offers dynamic near-field tuning of Mie resonances, which may open up applications in tunable nonlinear optics, Raman scattering, and light emission.

Resonant optical nanomaterials with a high refractive index, such as silicon, have become key elements for controlling free-space light. Here, we show that silicon nanoparticles can manipulate highly confined guided waves in the form of surface plasmon polaritons (SPPs) on a subwavelength scale. Using electron energy-loss spectroscopy in a transmission electron microscope, we demonstrate that SPPs in ultrathin metal films can be efficiently launched due to the strong coupling between the Mie resonances of the nanoparticle and the SPP modes. We find that the SPP excitation wavelength can be tuned across the entire near-infrared by varying the particle size. For insight into the coupling mechanism, we also measure the electron-beam-induced response of the Mie resonances in isolated silicon nanostructures in a broad size range. Finally, we show that the silicon nanoparticles act as scatterers of the SPPs supported by the film. Our results may pave the way for using high-refractive-index dielectric nanoantennas as compact elements for manipulating highly confined SPPs.

We developed a self-limited self-assembly process to produce red-to-near-infrared luminescent supraparticles made from biocompatible silicon (Si) quantum dots (QDs) for fluorescence bioimaging. A starting material is a methanol solution of boron (B) and phosphorus (P) codoped all-inorganic Si QDs. The Si QDs have a heavily B and P codoped amorphous shell, and the shell induces negative potential on the surface, which prevents agglomeration of QDs in polar solvents. By adding toluene to the methanol solution, controlled agglomeration of Si QDs occurs and spherical supraparticles around 100 nm in diameter with a narrow size distribution are grown. The average diameter of supraparticles was controlled by the growth parameters. We also developed a process to stabilize the supraparticles by coating the surface by polyvinylpyrrolidone (PVP) and then by silica. The photoluminescence spectra of PVP- and silica-coated Si QD supraparticles were very similar to those of Si QDs dispersed in solution.

Gel electrophoresis, which is a standard method for separation and analysis of macromolecules such as DNA, RNA and proteins, is applied for the first time to silicon (Si) quantum dots (QDs) for size separation. In the Si QDs studied, boron (B) and phosphorus (P) are simultaneously doped. Codoping induces a negative potential on the surface of a Si QD and makes it dispersible in water. Si QDs with different B and P concentrations and grown at different temperatures (950 °C-1200 °C) are studied. It is shown that native polyacrylamide gel electrophoresis can separate codoped Si QDs by size. The capability of gel electrophoresis to immobilize size-separated QDs in a solid matrix makes detailed analyses of size-purified Si QDs possible. For example, the photoluminescence (PL) studies of the dried gel of Si QDs grown at 1100 °C demonstrate that a PL spectrum of a Si QD solution with the PL maximum around 1.4 eV can be separated into more than 15 spectra with the PL maximum changing from 1.2 to 1.8 eV depending on the migration distance. It is found that the relationship between the PL peak energy and the migration distance depends on the growth temperature of Si QDs as well as the B and P concentration. For all the samples with different impurity concentrations and grown at different temperatures, a clear trend is observed in the relationship between the full width at half maximum (FWHM) and the peak energy of the PL spectra in a wide energy range. The FWHM increases with the increasing peak energy and it is nearly twice larger than those observed for undoped Si QDs. The large PL FWHM of codoped Si QDs suggests that excitons are further localized in codoped Si QDs due to the existence of charged impurities.

The photocatalytic hydrogen (H2) generation by boron (B) and phosphorus (P) codoped silicon quantum dots (Si QDs) with diameters in the quantum confinement regime is investigated. The codoped Si QDs have an amorphous shell made from B, Si and P. The shell induces negative potential on the surface and makes codoped Si QDs dispersible in water. The hydrophilic shell offers enhanced stability and efficiency in photocatalytic H2 generation and provides the opportunity to study the size dependence of the H2 generation rate. A drastic increase of H2 generation rate with decreasing QD size is observed. Analyses based on the Marcus theory reveal that the upper shift of the lowest unoccupied molecular orbital level of Si QDs by the quantum confinement effect is responsible for the enhanced photocatalytic activity.

Boron (B) and phosphorous (P) co-doped colloidal silicon nanocrystals (Si NCs) have unique size-dependent optical properties, which lead to potential applications in optoelectronic and biomedical applications. However, the microstructure of the B and P co-doped colloidal Si NCs – in particular, the exact location of the dopant atoms in real space, has not been studied. A lack of understanding of this underlying question limits our ability to better control sample fabrication, as well as our ability to further develop the optical properties. To study the microstructure, a process enabling atom probe tomography (APT) of colloidal Si NCs was developed. A dispersion of colloidal Si NCs in a SiO2 sol-gel solution and a low temperature curing are demonstrated as the key sample preparation steps. Our APT results demonstrate that a B-rich region exists at the surface of the Si NCs, while P atoms are distributed within the Si NCs. First principles density functional theory calculations of a Si NC embedded in SiO2 matrix reveal that P atoms, which always prefer to reside inside a Si NC, significantly influence the distribution of B atoms. Specifically, P atoms lower the B diffusion barrier at Si/SiO2 interface and stabilize B atoms to reside within individual Si NCs. We propose that the B-modified surface changes the chemical properties of the Si NCs by (i) offering chemical resistance to attack by HF and (ii) enabling dispersibility in solution without aggregation.

Titanium nitride (TiN) nanostructures are promising building blocks for photothermal applications because of the surface plasmon-induced light absorption. However, compared to noble metal nanostruc...

The antimicrobial activity of a hybrid nanoparticle (NP) composed of a silver (Ag) NP core decorated with silicon (Si) nanocrystals (NCs) on the exterior (Ag/Si NPs) is evaluated. The shell of Si NCs effectively protects the surface of Ag NPs, thus the particles are more stable in water and in air compared to conventional organic-capped Ag NPs. The bacterial growth kinetic analysis reveals that the Si NC shell does not suppress the release of Ag ions from the Ag NP surface due probably to the porous structure. For the antimicrobial coating application, a thin film of the hybrid Ag/Si NPs is produced by drop coating the solution on a cover glass. Thanks to the Si NC shell, agglomeration of Ag NPs in the film is prevented and the film shows a very similar optical absorption spectrum to that of the solution. The film exhibits a larger zone of inhibition in an agar diffusion assay of Escherichia coli compared to a film produced from organic-capped Ag NPs.

The effect of molecular reductants on the charge transfer-induced brightening of near-infrared photoluminescence (PL) from silicon (Si) quantum dots (QDs) was studied. Without a molecular reductant, a temporal decrease of the PL quantum yield (QY) during light irradiation in water was observed. The temporal photodarkening was reversed when a molecular reductant [sodium sulfites (Na2SO3)] was added in water. In Na2SO3-dissolved water, the PL QY increased gradually during light irradiation. The photobrightening behavior depended strongly on the amount of reductant molecules, excitation power, and the size of Si QDs. The observed phenomena suggest that an excess hole generated by trapping a photoexcited electron to a trap level is effectively removed by a reductant molecule. The observed charge transfer-induced photobrightening paves way to realize high efficiency and stable Si QDs-based phosphors usable in aqueous media.

The photoelectrochemical response of a photocathode made from a colloidal solution of boron (B) and phosphorus (P) codoped silicon (Si) quantum dots (QDs) 2-11 nm in diameters is studied. Since codoped Si QDs are dispersible in alcohol and water due to the hydrophilic surface, a photoelectrode with a smooth surface is produced by drop-coating the QD solution on an indium tin oxide substrate. The codoping provides high oxidation resistance to Si QDs and makes the electrode operate as a photocathode. The photoelectrochemical response of a Si QD photoelectrode depends strongly on the size of QDs; there is a transition from anodic to cathodic photocurrent around 4 nm in diameter. Below the size, anodic photocurrent due to self-oxidation of Si QDs is observed, while above the size, cathodic photocurrent due to electron transfer across the interface is observed. The cathodic photocurrent increases with increasing the size, and in some samples, it is observed for more than 3000 s under intermittent light irradiation.

A colloidal solution of nanophotonic structures exhibiting optical magnetism is dubbed a liquid-phase metamaterial or an optical metafluid. Over the decades, plasmonic nanoclusters have been explored as constituents of a metafluid. However, optical magnetism of plasmonic nanoclusters is usually much weaker than the electric responses; the highest reported intensity ratio of the magnetic-to-electric responses so far is 0.28. Here, we propose an all-dielectric metafluid composed of crystalline silicon nanospheres. First, we address the advantages of silicon as a constituent material of a metafluid among major dielectrics. Next, we experimentally demonstrate for the first time that a silicon nanosphere metafluid exhibits strong electric and magnetic dipolar Mie responses across the visible to near-infrared spectral range. The intensity ratio of the magnetic-to-electric responses reaches unity. Finally, we discuss the perspective to achieve unnaturally high (>3), low, and even near-zero (

In this work, we present a colloidal Mie resonators consisting of highly crystalline Si nanospheres [1-4]. Such colloidal Mie resonators acting as nanoantennas and building blocks for colloidal metamaterials have advantages in solution-based fabrication of thin film optical devices.

Resonant excitation and manipulation of high-index dielectric nanostructures (such as Silicon, Germanium) provide great opportunities for engineering novel optical phenomena and applications. Here, we report selective excitation and enhancement of multipolar resonances, and non-radiating optical anapoles in silicon nanospheres using cylindrical vector beams (CVBs). Our approach can be used as a spectroscopy tool to enhance and identify multipolar resonances as well as a straightforward alternate route to excite electrodynamic anapoles at the optical frequencies.

The microstructure of boron (B) and phosphorus (P) codoped silicon (Si) nanocrystals (NCs), cubic boron phosphide (BP) NCs and their mixed NCs (BxSiyPz NCs) has been studied using atom probe tomography (APT), transmission electron microscopy (TEM), and Raman scattering spectroscopy. The BxSiyPz NCs inherit superior properties of B and P codoped Si NCs such as high dispersibility in aqueous media and near infrared (NIR) luminescence and those of cubic BP NCs such as high chemical stability. The microanalyses revealed that BxSiyPz NCs are composed of a crystalline core and an amorphous shell. The core possesses a lattice constant between that of Si (diamond-cubic) and BP (cubic). The amorphous shell is comprised of B, Si and P, though the composition is not uniform and there are local B-rich, Si-rich and P-rich domains connected contiguously. The amorphous shell is proposed to be responsible for their superior chemical properties such as high dispersibility in polar solvents and high resistance to acids, and the crystalline core is responsible for the stable NIR luminescence.

Annealing silicon (Si)-rich borophosphosilicate glass (BPSG) at a high temperature results in the growth of core-shell Si quantum dots (QDs) composed of a boron (B) and phosphorus (P) codoped crystalline Si core and an amorphous shell made from B, Si and P (B and P codoped Si QDs) in a BPSG matrix. The amorphous BxSiyPz shell is responsible for many superior properties of codoped Si QDs such as hydrophilicity, high resistance to hydrofluoric acid (HF) etching, stable luminescence in different environment, robustness of the luminescence for chemical treatments, etc. In this work, we study the growth process of the amorphous shell by Raman spectroscopy and transmission electron microscopy. We show that amorphous Si particles are first grown in a BPSG matrix within 30 s of annealing of Si-rich BPSG. After 50 s annealing, a crystalline Si core appears within an amorphous Si particle. The formation of a crystalline Si core is accompanied by the formation of an amorphous BxSiyPz shell. From the annealing time dependence of the volumes of the core and the shell, we show that supersaturated B and P are expelled to the surface of a crystalline Si core during the growth, which increases B and P concentration in an amorphous BxSiyPz shell.

Boron (B) and phosphorus (P) codoped silicon quantum dots (Si QDs) are dispersible in polar solvents without organic ligands and exhibit photoluminescence (PL) in the first (NIR-I) and second (NIR-II) near infrared (NIR) windows in biological tissues due to the optical transition from the donor to acceptor states. We studied the relationship between the PL wavelength, lifetime and quantum yield (QY) of the colloidal solution and the composition of the starting material for the preparation. We found that the PL lifetime and the QY are primarily determined by the composition, while the PL wavelength is mainly determined by the growth temperature. By optimizing the composition, we achieved QYs of 20.1% and 1.74% in the NIR-I and NIR-II regions, respectively, in methanol. We demonstrate the application for time-gated imaging in the NIR-II range.

Nano- and microstructures of silicon (Si) exhibit electric and magnetic Mie resonances in the optical regime, providing a novel platform for controlling light at the nanoscale and enhancing light–matter interactions. In this Review, we present recent development of colloidal Si nanoparticles (NPs) that have wide range of applications in nanophotonics. Following brief summary of synthesis methods of amorphous and crystalline Si particles with high sphericity, optical responses of single Si particles placed on a substrate are overviewed. Then, the capability as a nanoantenna to control light-matter interactions is discussed in different systems. Finally, collective optical responses of Si NPs in solution are presented and the application potentials are discussed.

Charge transfer interaction between colloidal silicon (Si) quantum dots (QDs) and adsorbed molecules was investigated by means of photoluminescence (PL) spectroscopy. The molecule employed is tetrathiafulvalene (TTF), which has the highest occupied molecular orbital (HOMO) near that of Si QDs and can act as an electron donor to Si QDs. The energy difference between the HOMOs of TTF and Si QDs was controlled by changing the size of Si QDs. We found that the PL of Si QDs is strongly modified by the adsorption of TTF and that the PL change is reversible, that is, removal of TTF from a colloidal solution recovers the PL intensity. In the smallest Si QDs, where the HOMO level is expected to be 0.11 eV lower than that of TTF, a 2.5-fold enhancement of the PL was observed. The PL enhancement suggests that Si QDs having p-type behavior are compensated by electron transfer from TTF, similarly to the case of substitutional phosphorus doping in Si QDs. The observed size dependence of the PL enhancement factors sugge...

Background Although in vitro studies show that iron absorption can be inhibited by magnesium laxatives such as magnesium oxide, taking oral iron supplements with magnesium laxatives is not considered a clinical problem. Case presentation A 28-year-old woman diagnosed with anorexia nervosa who overused magnesium laxatives was admitted to our hospital to evaluate her refractory iron deficiency anemia (IDA), despite having taken oral iron replacement therapy for nine months. She had had amenorrhea for years and her fecal occult blood tests were negative. Furthermore, upper gastrointestinal endoscopy showed no suspected gastroduodenal bleeding or gastroenteritis. We considered her IDA to be induced by malabsorption of iron due to magnesium laxative overuse. Psychoeducational intervention stopped the overuse and oral iron replacement therapy was switched to the intravenous route. During outpatient follow-up, her anemia gradually improved; however, when her magnesium laxative overuse began again, her hemoglobin levels suddenly decreased. Conclusions Clinicians should be attentive to the interactions between iron and magnesium laxatives.

Iron(III)- and cobalt(III)-9,10,19,20-tetraphenylporphycenes, which possess bulky phenyl groups at the four meso positions of porphycene, were successfully incorporated into the haem acquisition protein HasA secreted by Pseudomonas aeruginosa. Crystal structure analysis revealed that loops surrounding the haem-binding site are highly flexible, remodelling themselves to accommodate bulky metal complexes with significantly different structures from the native haem cofactor.

The optical response of an assembly of semiconductor quantum dots (QDs) is strongly modified from those of isolated ones by the inter-QD coupling. The strength of the coupling depends on the size, the inter-QD distance and the number of interacting QDs. In this work, we control these parameters of silicon (Si) QD assemblies by layer-by-layer growth of all-inorganic colloidal Si QDs. We perform detailed photoluminescence (PL) and PL decay dynamics studies for the assemblies made from monolayers of Si QDs 3.0 and 6.8 nm in diameters by precisely controlling the interlayer distance and the number of layers. From the analysis of the data with the Forster resonance energy transfer (FRET) model, we quantitatively discuss the relation between the FRET efficiency and the Forster radius in Si QD assemblies.

We analyze phosphorus (P)- and boron (B)-doped silicon nanocrystals (Si NCs) with various compositions of silicon-rich oxide using atom probe tomography. By creating Si iso-concentration surfaces, it is confirmed that there are two types of Si NC networks depending on the amount of excess Si. A proximity histogram shows that P prefers to locate inside the Si NCs, whereas B is more likely to reside outside the Si NCs. We discuss the difference in a preferential location between P and B by a segregation coefficient.

Silicon nanocrystals (Si NCs) are intensively studied for optoelectronic and biological applications due to having highly attractive features such as band engineering. Although doping is often used to control the optical and electrical properties, the related structural properties of solely doped and codoped Si NCs are not well-understood. In this study, we report the boron (B) and/or phosphorus (P) distribution in Si NCs embedded in borosilicate glass (BSG), phosphosilicate glass (PSG), and borophosphosilicate glass (BPSG) using atom probe tomography (APT). We compared solely and codoped Si NCs grown at different temperatures so that we may compare the effects of codoping and temperature on the B and/or P distribution. Proximity histograms and cluster analyses reveal that there exist boron-rich layers surrounding Si NCs and also B–P clusters within the Si NCs. Raman spectra also show a structural change between codoped Si NCs in solids and free-standing codoped Si NCs. These results lead us to understand...

We report a novel and facile self-limiting synthesis route of silicon nanocrystal (Si NC)-based colloidally stable semiconductor-metal (gold, silver and platinum) hybrid nanoparticles (NPs). For the formation of hybrid NPs, we employ ligand-free colloidal Si NCs with heavily boron (B) and phosphorus (P) doped shells. By simply mixing B and P codoped colloidal Si NCs with metal salts, hybrid NPs consisting of metal cores and Si NC shells are spontaneously formed. We demonstrate the synthesis of highly uniform and size controllable hybrid NPs. It is shown that codoped Si NCs act as a reducing agent for metal salts and also as a protecting layer to stop metal NP growth. The process is thus self-limiting. The development of a variety of Si NC-based hybrid NPs is a promising first step for the design of biocompatible multifunctional NPs with broad material choices for biosensing, bioimaging and solar energy conversion.

Silicon (Si) nanostructures allow for the expansion of the application spectrum of this important semiconductor material with respect to the fields of optoelectronics and photonics. At the same time, the significant potential of Si quantum dots (SiQDs) has been revealed in terms of their potential application in the areas of biology and medicine due to their biocompatibility, low toxicity and natural biodegradability, unlike currently used semiconductor quantum dots. As far as this study is concerned, SiQDs co-doped with boron and phosphorus were used for the in vitro evaluation of their cytotoxicity in human osteoblasts. Two chemically identical types of SiQD differing in terms of their size and photoluminescence (PL) were studied. They both display long-lasting dispersion in methanol and even in aqueous media as well as PL which is not sensitive either to changes in the environment or surface modifications. Our experiments revealed significant differences between the two types of SiQD tested in regard to their behavior in a cell culture environment depending on increasing concentration (25–125 μg ml−1) and cultivation conditions (the presence or absence of proteins from the fetal bovine serum – a component of the cultivation medium). A detailed description of their optical parameters and the evaluation of zeta potential enhance the understanding of the complexities of the in vitro results obtained.

Silicon (Si) nanocrystals (NCs) with high boron (B) and phosphorus (P) concentration shells are dispersible in polar solvents without organic ligands. In order to understand the mechanism of the solution dispersibility, the surface structure is studied by infrared absorption spectroscopy. It is shown that water molecules are adsorbed at the B–oxygen (O) bond sites on NC surface with high hydrogen bond strength, and thus B and P co-doped Si-NCs are a kind of hydrate containing large amounts of water molecules (Si-NC·xH2O). The current transport properties of Si-NC films made from the solutions are studied. It is found that the conductivity is very sensitive to the amount of adsorbed water molecules and changes by 8 orders of magnitude. The high affinity of the NC surface with water molecules is considered to be the origin of the high sensitivity.

A crystalline silicon (Si) nanoparticle (NP) of 100-200 nm in diameter exhibits a highly saturated color owing to Mie resonance, and can be a component to realize angle-insensitive structural color covering the entire visible range. However, to date, coloring a substrate by Si nanostructures has only been achieved in a very small area by using electron beam lithography and dry etching processes. In this work, a Si NP color ink capable of coloring a flexible substrate by a painting process is developed. The sphericity of Si NPs is very high; the circularity factor obtained from a transmission electron microscope image reaches 0.97. The average diameter of Si nanospheres is controlled from 95 to 200 nm, and the polydispersity defined by the standard deviation divided by the average diameter is as small as 6%. Because of the high sphericity, high crystallinity, high size purity, and perfect dispersion in solution, the Si nanosphere solutions exhibit vivid colors recognizable by naked eye in a range of blue to orange. The Si nanosphere color inks combined with a polymer binder are capable of coloring flexible substrates by a painting process.

Shallow impurity doping is an efficient route to tailor optical and electronic features of semiconductor quantum dots (QDs). However, the effect of doping is often smeared by the size, shape, and composition inhomogeneities. In this paper, we study optical properties of almost monodispersed spherical silicon (Si) QDs that are heavily doped with boron (B) and phosphorus (P). The narrow size distribution achieved by a size-separation process enables us to extract doping-induced phenomena clearly. The degree of doping-induced shrinkage of the optical band gap is obtained in a wide size range. Comparison of the optical band gap with theoretical calculations allow us to estimate the number of active donor-acceptor pairs in a QD. Furthermore, we found that the size and detection energy dependence of the luminescence decay rate is significantly modified below a critical diameter, that is ∼5.5 nm. In the diameter range above 5.5 nm, the luminescence decay rate is distributed in a wide range depending on the detection energy even in size-purified Si QDs. The distribution may arise from that of donor-acceptor distances. On the other hand, in the diameter range below 5.5 nm the detection energy dependence of the decay rate almost disappears. In this size range, which is smaller than twice of the effective Bohr radius of B and P in bulk Si crystal, the donor-acceptor distance is not a crucial factor to determine the recombination rate.

Heavily boron and phosphorus codoped silicon quantum dots (QDs) are dispersible in water without organic ligands and exhibit near infrared luminescence. We summarize the fundamental properties and demonstrate the formation of a variety of nanocomposites.

A mechanistic study of H2O2-dependent C–H bond hydroxylation by myoglobin reconstituted with a manganese porphycene was carried out. The X-ray crystal structure of the reconstituted protein obtained at 1.5 A resolution reveals tight incorporation of the complex into the myoglobin matrix at pH 8.5, the optimized pH value for the highest turnover number of hydroxylation of ethylbenzene. The protein generates a spectroscopically detectable two-electron oxidative intermediate in a reaction with peracid, which has a half-life up to 38 s at 10 °C. Electron paramagnetic resonance spectra of the intermediate with perpendicular and parallel modes are silent, indicating formation of a low-spin MnV-oxo species. In addition, the MnV-oxo species is capable of promoting the hydroxylation of sodium 4-ethylbenzenesulfonate under single turnover conditions with an apparent second-order rate constant of 2.0 M–1 s–1 at 25 °C. Furthermore, the higher bond dissociation enthalpy of the substrate decreases the rate constant, in...

We report a new synthetic route for cubic boron phosphide (BP) nanocrystals with diameters of 2 to 6 nm. The key concept of the synthesis process is reduction of oxides of B and P in silicon (Si)-rich borophosphosilicate glass (BPSG) into cubic BP crystals by excess Si. The size of the cubic BP crystals is controlled by the composition of the starting materials. Free-standing cubic BP nanocrystals are extracted into solution by etching out BPSG matrices. The successful growth of size controlled cubic BP nanocrystals opens the way for the development of cubic BP nanocrystal-based optoelectronic and thermoelectric devices.

We develop a new type of boron (B)-rich nanocrystals (NCs) for applications in Boron Neutron Capture Therapy (BNCT). Phase separation of oxygen (O) deficient borophosphosilicate glasses (BPSG) by annealing in inert ambient gas results in the growth of different types of B-rich NCs. When the silicon (Si) concentration is much higher than the others, B and phosphorus (P) co-doped Si-NCs are grown. In the opposite case, cubic boron phosphide (BP) NCs are grown. In between two extremes, we demonstrate the growth of a new type of cubic NCs consisting of B, Si and P with an average B concentration up to 36 at%. The B-rich NCs are dispersible in water and exhibit photoluminescence in the biological window. These properties in combination with the capability of the bio-functionalization via the surface Si–hydrogen (H) and Si–O bonds suggest that the B-rich NCs can be a multifunctional biomaterial used for imaging, diagnosis and BNCT.

A sulfur-modified gold-supported palladium material (SAPd) has been developed bearing palladium nanoparticles on its surface. Herein, we report for the first time the use of SAPd to affect a Pd-nanoparticle-catalyzed 1,7-Pd migration reaction for the synthesis of benzotriazoles via C-H bond activation. The resulting benzotriazoles were evaluated in terms of their inhibitory activity toward indoleamine 2,3-dioxygenase.

We present a new route for mass-production of B and P codoped all-inorganic colloidal Si nanocrystals (NCs) from hydrogen silsesquioxane (HSQ). Codoped Si NCs are grown in glass matrices by annealing mixture solutions of HSQ and dopant acids, and then extracted from the matrices by hydrofluoric acid etching. The free-standing NCs are dispersible in methanol without any surface functionalization processes. The structural analyses suggest the formation of heavily B and P doped hydrophilic shells on the surface of Si NCs. The NCs show efficient size-tunable photoluminescence in the near infrared to visible region.

We report a novel method to prepare silicon quantum dots (Si-QDs) having excellent stability in water without organic-ligands by simultaneously doping phosphorus and boron. The codoped Si-QDs in water exhibit bright size-tunable luminescence in a biological window. The luminescence of codoped Si-QDs is very stable under continuous photoexcitation in water.

H-shaped poly(propylene carbonate) (PPC) was synthesized from a tetrafunctional linear PPC. First, a linear α,ω-dihydroxy PPC (1) was synthesized via the alternating copolymerization of carbon dioxide (CO2) and propylene oxide (PO) catalysed by a cobalt porphyrin complex and DMAP system. A subsequent chain-end functionalization with 1,3,5-benzenetricarbonyl trichloride afforded a tetrafunctional linear PPC (2) with dicarboxylic acid groups at both chain ends. H-shaped PPC (3) was synthesized from 2, as the macromolecular chain-transfer agent, by further alternating copolymerization of CO2 and PO. Moreover, the thermal properties of 3, as determined by DSC, indicated that the glass transition temperature (Tg) of 3 (Tg = 21 °C) is significantly lower than that of linear PPC (Tg = 30 °C). This attribute of the H-shaped topology (lowering of Tg) was then applied to a new self-assembly system. Thus, a PPC with two thymine groups at both chain ends (4) and a PPC with a 2,6-diaminopyridine group at the centre of the main chain (5) were synthesized and self-assembled simply by mixing at a 1:2 ratio. Interestingly, the Tg of the self-assembled product (from 4 and 5) was comparable to that of 3, indicating the formation of an H-shaped topology through complementary hydrogen-bonding interactions.

Si1−xGex alloy nanocrystals potentially have superior properties compared to Si nanocrystals such as an enhanced absorption cross-section and wider controllability of the band gap energy. However, reports on the synthesis of Si1−xGex alloy nanocrystals, especially colloidal Si1−xGex alloy nanocrystals, are still very limited and the quality is not as high as that of colloidal Si nanocrystals. Here, we report the development of a new type of luminescent colloidal Si1−xGex alloy nanocrystals of 3 to 6 nm in diameter. The characteristic feature of the Si1−xGex alloy nanocrystals is the formation of a high B and P concentration layer on the surface. The shell provides inorganic atomic ligands and B and P co-doped Si1−xGex nanocrystals can be dispersed in alcohol without any surface functionalization processes.

The surface structure of P and B codoped colloidal Si-NCs are studied by photoluminescence (PL) in hydrofluoric acid (HF) solution and X-ray photoelectron spectroscopy (XPS). We find that codoped Si-NCs are much more stable in HF solution than undoped, P-doped, and B-doped Si-NCs. The PL study combined with XPS results reveal that a high B concentration layer is formed on the surface of codoped Si-NCs and the layer acts as a kind of inorganic atomic ligands for Si-NCs. The high B concentration layer makes Si-NCs hydrophilic and dispersible in polar liquids. Furthermore, the layer effectively protects Si-NCs from oxidation in solution and in air.

Si nanocrystals (Si-NCs) with extremely heavily B- and P-doped shells are developed and their structural and optical properties are studied. Unlike conventional Si-NCs without doping, B and P co-doped Si-NCs are dispersible in alcohol and water perfectly without any surface functionalization processes. The colloidal solution of co-doped Si-NCs is very stable and no precipitates are observed for more than 5 years. The co-doped colloidal Si-NCs exhibit size-controllable photoluminescence (PL) in a very wide energy range covering 0.85 to 1.85 eV. In this paper, we summarize the structural and optical properties of co-doped Si-NCs and demonstrate that they are a new type of environmentally-friendly nano-light emitter working in aqueous environments in the visible and near infrared (NIR) ranges.

Size dependence of the boron (B) acceptor and phosphorus (P) donor levels of silicon (Si) nanocrystals (NCs) measured from the vacuum level was obtained in a very wide size range from 1 to 9 nm in diameter by photoemission yield spectroscopy and photoluminescence spectroscopy for B and P codoped Si-NCs. In relatively large Si-NCs, both levels are within the bulk Si band gap. The levels exhibited much smaller size dependence compared to the valence band and conduction band edges. The Fermi level of B and P codoped Si-NCs was also studied. It was found that the Fermi level of relatively large codoped Si-NCs is close to the valence band and it approaches the middle of the band gap with decreasing the size. The results suggest that below a certain size perfectly compensated Si-NCs, that is, Si-NCs with exactly the same number of active B and P, are preferentially grown, irrespective of average B and P concentrations in samples.

We demonstrate the formation of a new type of surfactant-free colloidal silicon nanocrystal (Si-NC). The characteristic structural feature of the Si-NCs is simultaneous doping of phosphorus (P) and...

Planar-chiral palladium complexes {[[N,N'-[1,4-butanediylbis(oxy-7,1-naphthalenediyl)]bis(2-pyridinecarboxamidato)](2-)-κN(1),κN(1)',κN(2),κN(2)']palladium (PdL(4)) and [[2,2'-[1,4-butanediylbis[[(oxy-7,1-naphthalenediyl)imino]methyl]]dipyrrolato](2-)-κN(1),κN(1)',κN(2),κN(2)']palladium (PdL(5))} were synthesized from achiral tetradentate ligands N,N'-[1,4-butanediylbis(oxy-7,1-naphthalenediyl)]bis(2-pyridinecarboxamide) (H(2)L(4)) and N,N'-bis[(1H-pyrrol-2-yl)methylidene]-7,7'-(1,4-butanediyldioxy)bis(1-naphthalenamine) (H(2)L(5)) bearing two dissymmetric bidentate units at both ends and a Pd(II) ion, respectively. The palladium complexes were crystallized in the monoclinic space group P2(1)/n with the unit cell parameters a = 16.5464(6) Å, b = 11.3534(4) Å, c = 17.6697(7) Å, β = 115.5300(10)°, and Z = 4 for PdL(4) and a = 17.2271(8) Å, b = 10.1016(5) Å, c = 17.9361(9) Å, β = 105.6310(10)°, and Z = 4 for PdL(5). The planar-chiral structures of PdL(4) and PdL(5) were confirmed by single-crystal X-ray analyses, resulting in the fact that the crystals were racemic mixtures. The racemic mixtures were successfully resolved by using chiral high-performance liquid-chromatography techniques. Racemizations of the complexes were found to be drastically dependent on the arrangement of the charged or uncharged metal-binding N atoms of the ligands.

Fabrication of ZnO ceramics with a sustainable antibacterial activity even in the dark has been conducted. Fine ZnO powders were hydrothermally treated in 0.5–3 mol ml−1 Zn(NO3)2 aqueous solutions at 110–180 °C for 3–20 h. After an uniaxial pressing of the ZnO powders thus prepared, they were sintered at 400–600 °C for 1 h in air. Sustainability in antibacterial activity was evaluated using a colony count method with Escherichia coli bacteria on nutrient agar medium (36 °C/24 h) in a Na–P-buffer solution. The best data was attained for the ZnO ceramics prepared from the following conditions: a 3 mol ml−1 zinc nitrate solution for the hydrothermal treatment at 120 °C for 7 h and sintering in air with a step-by-step pattern (470 °C/1 h–485 °C/1 h–500 °C/1 h). ESR and chemical photoluminescence analyses have cleared that radical oxygen of super-oxide ( O2−) originated from the surface of ZnO might exhibit an antibacterial activity even under the dark condition.

Vitamin D 3 (VD 3), a prohormone in mammals, plays a crucial role in the maintenance of calcium and phosphorus concentrations in serum. Activation of VD 3 requires 25-hydroxylation in the liver and 1alpha-hydroxylation in the kidney by cytochrome P450 (CYP) enzymes. Bacterial CYP105A1 converts VD 3 into 1alpha,25-dihydroxyvitamin D 3 (1alpha,25(OH) 2D 3) in two independent reactions, despite its low sequence identity with mammalian enzymes (21% identity). The present study determined the crystal structures of a highly active mutant (R84A) of CYP105A1 from Streptomyces griseolus in complex and not in complex with 1alpha,25(OH) 2D 3. The compound 1alpha,25(OH) 2D 3 is positioned 11 A from the iron atom along the I helix within the pocket. A similar binding mode is observed in the structure of the human CYP2R1-VD 3 complex, indicating a common substrate-binding mechanism for 25-hydroxylation. A comparison with the structure of wild-type CYP105A1 suggests that the loss of two hydrogen bonds in the R84A mutant increases the adaptability of the B' and F helices, creating a transient binding site. Further mutational analysis of the active site reveals that 25- and 1alpha-hydroxylations share residues that participate in these reactions. These results provide the structural basis for understanding the mechanism of the two-step hydroxylation that activates VD 3.

The use of a cobalt porphyrin ((TPP)CoCl, 1) in combination with dimethylaminopyridine (DMAP) for the alternating copolymerization of CO2 and epoxide is described. The (TPP)CoCl (1)−DMAP system quantitatively produced the alternating copolymer from CO2 and cyclohexene oxide (CHO) under optimized conditions (50 atm, 80 °C). This calatyst system also worked satisfactorily for the alternating copolymerization of CO2 and a terminal epoxide, e.g., propylene oxide (PO), without formation of cyclic carbonate to give the polycarbonate. The alternating copolymerization of CO2 and epoxide (CHO, PO) was achieved under very mild conditions, such as at ambient temperature and under CO2 at 1 atm, by using the 1−DMAP catalyst system.

The successful alternating copolymerization of carbon dioxide and cyclohexene oxide was achieved by using a dinuclear zinc Schiff base complex, without forming cyclic carbonate. A remarkable effect of Lewis basic additives on the yield and selectivity of the product was demonstrated. Among the examined Lewis bases, 1,4-dioxane was the best additive, where the copolymerization with the dinuclear zinc Schiff base complex – 1,4-dioxane system produced selectively the perfectly alternating copolymer in high yield.