Mesoporous silica nanoparticles (MSNs) with colloidal stability have attracted increasing interest because of their important properties, such as high transparency and cell uptake. Colloidal MSNs are comprehensively reviewed from the viewpoints of their preparation, characterization, and applications which include biomedical, catalytic, and optical materials. The following two points have been emphasized. The first point is that this review covers the widest range of introduction and discussion of the preparation and applications of both colloidal and noncolloidal MSNs. The second point is that this account contains a discussion from the viewpoints of both inorganic and colloid chemistries. After the introduction of the historical background of preparation of MSNs, preparative methods of colloidal MSNs and the major factors for the preparation of nanosized and colloidal MSNs are discussed. The methods to control the size, composition, morphology, and pore size of MSNs are also presented. Appropriate methods to obtain MSNs with high colloidal dispersibility are also discussed. Applications of colloidal MSNs are introduced with an emphasis on the colloidal stability. Issues to be addressed for further developments of colloidal MSNs are finally described.
Colloidal mesoporous silica nanoparticles (MSNs) have been reviewed from the viewpoints of their preparation, characterization, and applications. Different from aggregated MSNs, colloidal MSNs have very important properties. The issues to be addressed for further developments of colloidal MSNs are also described.
Effective control of drug release from “nano-prodrugs”, which are nanoparticles composed of water-insoluble prodrug compounds is one of the most important determinants of the balance between drug efficacy and side effects. However, the chemical behaviors of nano-prodrugs in relation to drug release are poorly characterized. We created nano-prodrugs using a series of fatty acid ester (C2–C18) derivatives of 7-ethyl-10-hydroxycamptothecin (SN-38) and found that their in vitro cytotoxic activities decreased as the length of the fatty acid chain increased. The cytotoxicities of these nano-prodrugs were unrelated to particle size or efficacy of cellular uptake, but critically depended on their hydrolysis rate within cancer cells. These results indicated that the drug release rate from nano-prodrugs can be controlled successfully by changing the length of the introduced fatty acid chain.
For use as an electrode material, a new synthetic route to a Martin-type tridentate ligand and hypervalent sulfur anions bearing this ligand has been developed. A battery containing the anions bearing Li+ as a counter-cation shows a stable cycle performance, indicating their utility for cathode-active materials.
The practices to convert electronic absorption spectra into the fourth- and eighth-order derivatives are described to stress their usefulness in quantitative analysis, keeping in mind the applicability to elucidate photochemical behavior of versatile materials. The simulation was carried out in two ways. The first study disclosed that the higher-even-order derivatives are an efficient approach to resolve elementary bands due to rotational energy level transitions (RLT) and, in particular, vibrational energy level transitions (VLT). Electronic absorption bands are determined by full width at half-maximum (FWHM) of and distance (Δλv) between adjacent VLT bands, while there is a critical FWHM as well as Δλv for the sufficient resolution of VLT bands in derivative spectra. The subsequent simulation was performed with aid of Savizky–Golay smoothing of synthetic noisy spectra to know how polynomial order (s) and filter width (p) affect derivative-spectral shapes. It was shown that p should be smaller than 1 + 2 × (Δλv − 1), whereas Δλv is of an electronic absorption band to be analyzed. The simulation results were substantiated by spectral changes due to the photoisomerization of azobenzene in hexane as a model compound, displaying that Δλv values of electronic transitions of S0–S1 and S0–S2 are quite different, respectively.
The characteristics of sublevel transition bands determine the resolution of UV–vis higher-order derivatives so that the optimization of Savizky–Golay smoothing is required to achieve the quantification of photoinduced spectral changes by means of derivative spectroscopy.
The extraction efficiency of betanin as a natural pigment with antioxidant features is significant. The main reason for studying the different aqueous two-phase systems (ATPSs) for betanin extraction is that the selection of an optimum process of separation is possible. In order to develop an efficient method for the extraction of betanin, ATPS composed of polymer and sodium sulfate was investigated. Sodium sulfate is a strong salting-out agent, which has an important effect on the processes of the extraction of biomolecules. The effect of parameters such as temperature, salt and polymer concentrations, and the molecular weight of the polymer was evaluated for the partitioning of betanin. The experimental results showed that the polymer concentrations in ATPS can significantly affect the partitioning of betanin between the top and bottom phases. The recovery percentage of betanin indicated that this system had the ability to improve the betanin recovery in the top phase.
Fluorescence ratio probes are useful tools for quantitative detection of target molecules even if the concentration of probe molecules is unknown. However, a general and widely applicable method for design and synthesis of fluorescence ratio probes has never been established. Here, we developed double-labeled single-chain antibody fragment (scFv) derivatives showing antigen-dependent fluorescence ratio change based on fluorescence resonance energy transfer (FRET) and antigen-dependent fluorescence quenching. Double-labeled scFvs were synthesized by incorporating fluorescent nonnatural amino acids labeled with TAMRA and Rhodamine Green (RhG) as a FRET donor and acceptor pair into N- and C-termini of scFv, respectively, using four-base and amber codons in a cell-free translation system. The resulting double-labeled antibody fragments showed significant fluorescence ratio change upon the antigen-binding. This result was explained by FRET occurring from RhG to TAMRA but TAMRA being quenched by Trp residues in the absence of antigen. The binding of the antigen canceled the quenching of TAMRA without changing FRET efficiency. Double-labeled antibody fragments developed here will be useful as diagnostic and imaging tools.
A new coordination polymer, Fe(hexyl-nicotinate)2[Au(CN)2]2 (1) with Hofmann-type 2D single layers, exhibited 50% spin-crossover (SCO) behavior with transition temperatures near 150 K. Temperature-dependent X-ray absorption fine structure (XAFS) spectra indicated that 1 possessed SCO properties only with iron(II) ions.
The mechanisms for the trimerization of acetylene in the presence of (PH2CH2CH2PH2)IrCl as an active catalyst were investigated by density functional (B3LYP and M06) theory calculations. The reactant bis(acetylene)–Ir complex has a distorted trigonal bipyramid structure, and thus, there are three types of equilibrium structures connected by pseudorotation. The first oxidative coupling takes place between the acetylene molecule coordinating at the axial position and that in the equatorial plane in these reactant complexes to afford square pyramidal iridacyclopentadiene complexes through one of the two favorable transition states. Then, the third acetylene molecule attacks the iridacyclopentadiene intermediate, accompanied by Cl migration, to afford the iridacyclopentadiene–acetylene complex. The formation of a benzene complex from this acetylene complex involves reaction pathways based on intramolecular [4+2] cycloaddition and the Schore mechanism through iridacycloheptatriene, as well as the bicycle mechanism. The most favorable pathway for the formation of the benzene complex is through intramolecular [4+2] cycloaddition to form the η4-benzene–Ir complex, and finally, to the η2-benzene–Ir complex. This reaction mechanism is compared with that for reactions catalyzed by TpIr and CpIr systems.
Pigments in the printing inks employed for Japanese hand-engraved stamps, the first issues of Japanese postage stamps, were analyzed and characterized by means of FTIR, Raman, and XRF spectroscopy. This work has revealed, for the first time, the changes of the pigments used for all colors of the stamps issued during 1871–1876, and it has been recognized that a drastic change in the ink composition occurred in 1872, when the printing of the stamps was transferred from Matsuda to the Government.
Oxygenated cup-stacked carbon nanofibers (ox-CSCNFs), the surface of which provides highly ordered graphene edges and oxygen-containing functional groups, were introduced to a nanoporous TiO2 photoelectrode for enhanced photocatalytic currents. The ox-CSCNFs are characterized by good electric conductivity and high dispersibility in solvents. Under UV irradiation, short-circuit photocurrents based on water oxidation at the photoelectrode and oxygen reduction at a counter electrode were enhanced by about 15 times by introduction of the ox-CSCNFs. The oxygen-containing functional groups, which may facilitate good contact between the ox-CSCNFs and TiO2, are essential for the dramatic enhancement in the photocurrent. Recombination efficiency between excited electrons and generated holes may be reduced by facilitated electron transport from excited TiO2 to a substrate electrode via ox-CSCNFs. Photocurrents for photocatalytic oxidation of glucose were also enhanced by about 20-fold. The present composite materials would be applied to photocatalytic and photovoltaic cells with enhanced performances.
To understand Rh(III) adsorption behaviors of styrene–divinylbenzene copolymer functionalized with N,N,N-trimethylglycine (AMP03), we measured the distribution coefficients (Kd) of Rh(III) and the adsorbed amounts of HNO3 by varying the HNO3 concentration. It was found that the Kd value of Rh(III) decreased with increasing [HNO3], whereas the amount of adsorbed HNO3 increased. To examine the Rh(III) adsorption capabilities of AMP03 in detail, we performed adsorption experiments while varying H+ and NO3− concentrations. The results showed that the Kd value of Rh(III) increased with decreasing [H+] and increasing [NO3−]. Furthermore, we performed Rh(III) adsorption experiments using HNO3 solutions containing amine compounds such as triethylamine (TEA), ethylenediamine (EDA), or tris(2-aminoethyl)amine (Tren). In all systems, drastic increases in Kd were observed with the addition of amine compounds. The amine compounds have relatively high basicity (TEA: pKa = 10.75, EDA: pKa = 6.85 and 9.93, and Tren: pKa = 8.42, 9.44, and 10.1). The Kd increases were attributed to a decrease in [H+] with the protonation of amine compounds. The stoichiometry of the adsorbed Rh(III) species was determined with slope analysis based on ion-exchange equilibria for Rh3+ and H+. Rh3+ was adsorbed with two betaine groups and three NO3−. In contrast, H+ adsorption reactions occurred competitively with those of Rh3+. Our results show that AMP03 effectively adsorbs Rh(III) from HNO3 solutions with low [H+] and high [NO3−].
We synthesized rhodamine-labeled β-lactoside and assessed its rotatory diffusion rates in aqueous media containing various oligosaccharides through fluorescence intensity distribution analysis-polarization measurements to find that its rotatory diffusion rates decrease in the presence of the coexisting oligosaccharides. Especially, the coexisting lactose lowered the rotatory diffusion rate more effectively than the other disaccharides did. This restrained rotatory diffusion arises from intermolecular carbohydrate–carbohydrate interactions between the rhodamine-labeled β-lactoside and the coexisting lactose. We also detected intermolecular bindings between the rhodamine-labeled β-lactoside and monosialyl-disaccharides (3′- and 6′-sialyllactoses). These data clearly show that the fluorescence intensity distribution analysis-polarization-based system is quite advantageous to probe carbohydrate–carbohydrate interactions.