Nonresonant and resonant surface-enhanced Raman scatterings (SERS and SERRS) were studied for N-ethyl-N-(2-hydroxyethyl)-4-(4-nitrophenylazo) aniline (Disperse Red 1, or DR1) in poly (methyl methacrylate) on Ag films with surface roughness. DR1 is a chromophore that consists of azobenzene bridged between electron-donating amine and electron-accepting nitro groups, and it has attracted great attention because of its large molecular hyperpolarizability. DR1 hybridized with metal nanoparticles or nanostructures is promising as a building block for nonlinear plasmonics. Our experimental results demonstrated that the Raman cross sections were highly enhanced both at the molecular nonresonant and resonant excitation wavelengths. The spectroscopic properties of SERRS were taken from resonant Raman (RR), and the enhanced RR cross sections were attributed to electromagnetic enhancements due to surface plasmons (SP). The SERS spectrum was also similar to the RR spectrum, rather than the non-resonant Raman (NR) spectrum, even at the molecular non-resonant excitations. A diagram of energy levels was drawn for the DR1/Ag interfaces by using ultraviolet-visible linear absorption and ultraviolet photoelectron spectroscopic data. The enhanced NR cross sections were explained in terms of the electromagnetic enhancements, as well as the metal-to-molecular charge-transfer, by using the energy diagram.
A colorimetric method involving a novel gold nanoparticle-curcumin system is described for determination of melamine in urine. The natural phenol curcumin can reduce chloroauric acid to form well-dispersed gold nanoparticles, while at high concentration of melamine, reduction is suppressed and blue aggregates are quickly formed, which is confirmed by UV-vis spectroscopy and TEM images. The ratio of absorbances at 673 and 546 nm increases linearly in the 0.5 to 4 ppm melamine concentration range, and the detection limit is 0.16 ppm. The assay has been applied to analyze urine samples and showed recoveries with RSDs of <5%. The gold nanoparticle-curcumin based analytical system is simple for one-pot synthesis, convenient for visual detection and rapid requiring only 30 min. Therefore, it is a promising assay approach for melamine adulteration and well suited for homecare testing.
Nanoparticles of samarium(III) oxide (Sm2O3), gadolinium(III) oxide (Gd2O3) and iron(II,III) oxide (Fe3O4), which have different roles in biomedical applications, were synthesized and embedded in biocompatible polydopamine to make them more dispersible, compatible and non-aggregate so as to fully exploit their features in the human body. Herein, the synthesis procedures of the nanoparticles with different sizes and the embedding procedures in polydopamine were investigated in comparison with coating with silica. The particles (60–100 nm diameter) of Sm2O3 and Gd2O3 synthesized by the calcination method were coated by silica shell (80–100 nm thickness) but their dispersibility in water was less. The nanosized particles (4–7 nm) of Sm2O3 and Gd2O3 synthesized by the polyol solvent method were protected by polyol to be dispersed in water. Separately, Fe3O4 nanoparticles (17 nm) were fabricated by co-precipitation reaction. Each nanoparticle was successfully embedded into spheres of polydopamine, although the preparation of composites depended on solvent amount, metal precursor amount and reaction solution pH. The co-embedding of three particles in a polydopamine sphere was also proved by elemental analysis.
New ionic liquid crystals of [n-CxH(2x+1)NEt3][BEt3Me] (abbreviated to [CxNEt3][BEt3Me]) were detected for species with even numbers of 8 ≤ x ≤ 16. In contrast, plastic- and rotator-crystal phases were obtained for [CxNEt3][BEt3Me] species with lower x values of x = 4, 5, and 6, 7, respectively. Because we previously documented plastic phases for the [CxNEt3][BEt3Me] (x = 1–3) species, [CxNEt3][BEt3Me] can be classified as a novel chemical family adopting the entire range of states (mesophases) between solid and isotropic liquid phases (plastic, rotator, and liquid crystals) as a function of the alkyl chain length. Polarized optical microscope (POM) and X-ray diffraction (XRD) measurements revealed that these liquid crystals (x = 8–16 with even numbers of x) form smectic B (x = 8) and A (x = 10), and nematic phases (x ≥ 12) in the liquid-crystal phases. In the case of x = 4, 5, XRD analysis showed that the salts form cubic crystal structures. Furthermore, the NMR line shapes revealed that both the cation and anion underwent isotropic reorientation. In contrast, the NMR spectra showed that the cations rotated about their long axis in the [C6NEt3][BEt3Me] and [C7NEt3][BEt3Me] crystals.
Functional molecular crystals responsive to external stimuli represent a new frontier for material chemistry and crystal engineering. Here, we report on the photoreversible interference color change in single crystals composed of a photochromic diarylethene derivative, 1,2-bis(2-ethyl-5-phenyl-3-thienyl)perfluorocyclopentene (1a). When crystal 1a was observed by rotating the sample stage at 45° from the extinction position under crossed Nicols, it showed an interference color. Upon irradiation with ultraviolet (UV) light, the interference color changed dramatically and instantaneously in response to photoirradiation due to the photocyclization reaction from the open-ring form to the closed-ring form. The change was quite sensitive to the photochromic reaction. It is attributable to the large decrease in retardation induced by the photocyclization reaction in crystals. These results might provide new opportunities for application of photochromic crystals.
In the field of drug delivery, controllability of drug release site and duration are among the most important factors to manipulate the drug efficacy and side effects. In this paper, a series of nano-prodrugs (NPs) composed of anticancer agent SN-38 and various substituent groups were synthesized and fabricated. By increasing the hydrophobicity of the prodrug molecule (calculated logP values exceeded ca. 7) through changing the substituent group, the hydrolysis susceptibility of SN-38 NPs in mouse serum was drastically decreased, thus prolonged the blood retention time of the NPs. In light of this knowledge and the dispersion stability in aqueous media, SN-38 NP modified with cholesterol (SN-38-chol NPs) was selected to be the optimal candidate among the screened NPs. The in vivo pharmacological effect of SN-38-chol NP was about 10 times higher than irinotecan, the clinically used solubilized prodrug analog of SN-38. In addition, SN-38-chol NP has low side effects in evaluating intestinal damage. These NPs possess great potential for clinical application and promise to be a next-generation of drug for cancer treatment.
Here, we report an empirical model for diastereoselective cyclopropanation of fumarate/maleate diesters with chloroacetate, sulfonium ylide, or ammonium ylide. With symmetrical fumarate/maleate diesters, cyclopropanation was found to proceed with a high level of diastereoselectivity in favor of the chiral isomer. In contrast, production of the meso isomer was observed in 38–48% diastereoselectivity when unsymmetrical fumarate/maleate was employed. An improved synthesis of (N-desmethy)dysibetaine CPa in both racemic and enantiomerically pure forms was furthermore achieved. Configurational analysis by experimental and calculated 13C NMR data is also reported.
A concise synthesis of 4-hydroxy-2-(hydroxymethyl)cyclopentenone (1) has been accomplished from D-glucose by a three-step sequence that features a catalyst-free hydrothermal reaction of D-glucal, which is readily obtained from D-glucose. Optimization of the reaction conditions for synthesizing 1 was performed by changing the temperature and reaction time. The treatment of D-glucal under the optimal conditions, i.e., at 120 °C for 24 h, provided 1 in the highest isolated yield of 61%. 1 would become a versatile intermediate for the synthesis of various fine chemicals having a cyclopentenone structure from cellulosic biomass.
Bentonite was purified using a dispersion-sedimentation method for the preparation of organically modified clays toward the possible optimization of their material performance as rheology controlling reagents. It was possible to classify bentonite into fractions of purified montmorillonite from aqueous suspension. Organic modification with dimethyldioctadecylammonium chloride was done by a conventional ion exchange procedure applied for aqueous suspension of the purified bentonite, which was prepared by alteration of raw bentonite by the addition of sodium carbonate and subsequent jet milling. Organic modification of the raw bentonite without the pretreatment using jet milling was also done for comparison. This careful pretreatment followed by the ion exchange with dimethyldioctadecylammonium ion resulted in organophilic clay with improved viscosity and transparency of the suspension in toluene compared with those observed for dimethyldioctadecylammonium-bentonite prepared without the present jet-milling process. Moreover, the modified organophilic clay showed unique temperature dependent variation of viscosity, which is very important for practical application. The present jet-milling process is useful for other applications of organophilic clays and to the pretreatment of different materials.
Since the performance of an organic film device largely depends on the molecular arrangement in the film, control of the arrangement is crucial. Low molecular-weight organic semiconductor compounds, however, tend to have the edge-on orientation spontaneously due to crystallization on an inert surface. In fact, orientation control of a high-crystallinity compound is often difficult especially on an inert surface. In the present study, a face-on crystalline thin film of zinc tetraphenylporphyrin (ZnTPP) has readily been obtained on an inert surface by using solvent annealing (SA) with an appropriate solvent, formamide (FA). The prepared film is carefully analyzed by using the infrared (IR) p-polarized multiple-angle incidence resolution spectrometry (pMAIRS) and grazing incidence X-ray diffraction (GIXD) techniques. The measurements show that an FA molecule coordinated on a zinc atom blocks the stacking interaction sites of the porphyrin ring, and instead the side to side interaction between the C–H group of the porphyrin rings and π orbital of the phenyl rings forms a two-dimensional sheet-like structure realizing face-on orientation.
Dynamic and static structures of water sorbed in ion exchange resins have been investigated by 17O NMR and X-ray diffraction. Rotational motion of water molecules sorbed in ion exchange resins is significantly slowed according mainly to the amount of cross-linkage of polymer which decides the size of micropore surrounded by hydrophobic polymer networks, and not crucially affected by the difference of hydration properties of ion exchange groups. Static structure of water sorbed in anion exchange resin is revealed to be similar to that of pure water, which indicates a clathrate like structure enclosing a hydrophobic tetramethylammonium group. On the other hand the structure of water in cation exchange resin is quite different from that of pure water, but resembles the structure found in aqueous sulfuric acid solution, which is strongly influenced by the highly acidic atmosphere. The structure of silica adsorbed in anion exchange resin has also been observed by X-ray diffraction. Obtained radial distribution function is quite similar to that of bulk silica, which requires the existence of Si-O-Si interaction in quantitative analysis. The present results evidence that silica adsorption in anion exchange resin is not simple ion exchange but combined processes of ion exchange and micro silica gel growth.
The discovery of new extended structures has often led to the development of new fields in chemistry and physics. However, the numerous combinations of metals (or cations) to yield new materials have been largely exhausted. Materials development based on the anion-centered strategy allows us to access several new classes of materials, such as iron oxides with square-planar coordination and mixed-anion oxides including oxyhydrides.
A series of 2,5-bis(5-aryl-2-thienyl)pyrazines with distinct optical properties tuned by the intramolecular charge transfer (ICT) degree based on the donor strength of the aryl groups have been synthesized. It was found that 2,5-bis[5-(4-N,N-dibutylaminophenyl)-2-thienyl]pyrazine exhibits a fluorosolvatochromism that originates from its ICT excited state and proton sensibility with the result that the two-step protonation of the amino nitrogen atoms and pyrazinyl nitrogen atom leads to stepwise solution and emission color changes. Additionally, it should be noted that 2,5-bis[5-(4-hydroxyphenyl)-2-thienyl]pyrazine exhibits a base sensitivity through the obvious emission color change based on the combined process consisting of the deprotonation process of the phenolic hydrogen atoms and the subsequent ICT process. Consequently, by incorporating the N,N-dibutylaminophenyl group (acts as a strong electron donor and proton acceptor) or the phenolic group (acts as a proton donor) into the pyrazine (acts as an electron acceptor and proton acceptor)-cored (D-π)2-A structure, we have constructed an environmentally responsive optical probe.
Novel thermally convertible precursors of tetrabenzoporphyrin (TBP) were synthesized by tetramerization of the corresponding bicyclo[2.2.2]octadiene(BCOD)-fused pyrroles. These precursors showed high solubility and were converted into TBPs by heating at 180–330 °C depending on the structure of BCOD moieties. This strategy provided easy access to pure PtTBP from the precursor with high conversion temperature in a good yield. Organic field effect transistors based on TBP were fabricated by thermal conversion after spin-coating of the precursors.
A N2 coordination to titanocene monochloride, [Cp2TiCl], in an ionic liquid (IL), 1-butyl-1-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate (Pyr4FAP), was detected by frozen solution EPR spectroscopy, although such a formation was not detected in toluene and THF. To understand the effect of IL toward the N2 coordination to [Cp2TiCl], density functional theory (DFT) calculations were carried out applying dielectric permittivity (ε) of solvents (toluene and IL) for the following six model structures; dimeric [(Cp2TiCl)2] in the singlet (1) and triplet states (2), monomeric [Cp2TiCl] (3), [Cp2TiCl(N2)] (4), and [Cp2TiCl(N2)]‡ in the transition state (4-TS). The DFT calculations have revealed that the model complexes, such as 1 and 2, with a small ε value are stabilized by solvents with a small value. To consider the effect of FAP anion toward titanocene complexes, we further performed the calculations for 3, 4 and 4-TS complexes interacting with FAP anion, 3′-FAP, 4′-FAP and 4′-FAP-TS, using empirical corrections (GD3BJ). Although the core structures of titanocenes in 3′-FAP and 4′-FAP are similar to those without FAP anion, F atoms in FAP anion show weak interaction toward H atoms on Cp rings. These findings suggest that the N2 coordination to [Cp2TiCl] in IL could have been induced by interaction of the metal complex with a polar domain in Pyr4FAP.
Two Eu(III) complexes with thienyl-substituted diphosphine dioxide ligands were prepared and their photoluminescence properties were investigated. Quantum yields of Eu(III)(fod)3(DTDOPO) (1) (fod = tris(6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionato) and DTDOPO = dithienyl[3-(dioctylphosphinyl)propyl]phosphine oxide) and Eu(III)(fod)3(DTDBPO) (2) (DTDBPO = dithienyl[5-(dibutylphosphinyl)pentyl]phosphine oxide) in the solid state were remarkably high (ΦTOT (solid) = 0.60 and 0.68, respectively) compared with that of Eu(III)(fod)3(DPDO) (3) (DPDO = diphenyl[3-(dioctylphosphinyl)propyl]phosphine oxide) (ΦTOT (solid) = 0.47). Given that Eu(III)(fod)3(DTDOPO) (1) and Eu(III)(fod)3(DPDO) (3) have the same molecular structure except for their aromatic substituents, substitution of thienyl groups for phenyl groups is effective for increasing the quantum yield of Eu(III) complexes in the solid state. Another noteworthy result regarding the photoluminescence properties of complexes 1 and 2 with thienyl groups is that quantum yields have strong positive linear correlations with concentration in ethyl acetate, and those in the solid state are located on the extended line. This means that no concentration quenching is observed.
Sulfamic acid functionalized PVC-coated nano-silica (NS) catalyst (NS@PVC-EDA-SO3H) was prepared via multi-step treatment processes and characterized by FT-IR, N2 adsorption-desorption, TGA/DTG, XRD, TEM, STEM-EDS, as well as acid-base back-titration. The hydroxyalkylation of phenol with formaldehyde to bisphenol F was employed to evaluate in detail its acid catalysis performances. The results indicated that the newly constructed NS@PVC-EDA-SO3H possessed richer short mesoporous to macroporous channels and highly exposed sulfamic acids and could exhibit excellent hydroxyalkylation activity and reusability owing to fast mass transfer and reaction rates for the conversion of substrates, as well as excellent structural and chemical stabilities. This new solid acid was obviously superior to the conventional homogeneous concentrated sulfuric acid and heterogeneous sulfonated resin catalysts in catalytic activity and reusability, which could achieve a remarkable formaldehyde conversion (99.9%) and selectivity of bisphenol F (94.5%) under optimal hydroxyalkylation conditions. Furthermore, it could also be recovered easily and used repeatedly at least nine times without an obvious decrease in activity.
The design and application of surface-based nanoplasmonic sensors has spurred broad interest from the chemical science community, touching upon diverse topics such as plasmonics, nanoscience, surface chemistry, measurement analysis, and interfacial science. One of the most exciting areas involves taking advantage of the simple instrumental requirements and high surface sensitivity of these sensing devices to study biomacromolecules and biological nanoparticles. In this Account, we present a narrative summary describing our recent work to explore surface-based nanoplasmonic sensors for biointerfacial science applications and outlining our perspective on possible future directions. After introducing the basic design concepts and measurement principles behind surface-based nanoplasmonic sensors, we focus on critically discussing recent application examples from our laboratory, where the high surface sensitivity of surface-based nanoplasmonic sensors proved useful for studying lipid vesicles, supported lipid bilayers, virus-like particles, proteins, and peptides. The potential of integrating surface-based nanoplasmonic sensors with other surface-sensitive measurement techniques is also discussed. Looking forward, there is excellent potential to continue using surface-based nanoplasmonic sensors for biointerfacial science applications and numerous innovation opportunities exist from fundamental and applied perspectives.