Diborynes, which have N-heterocyclic carbene (NHC) ligands, were first synthesized by Braunschweig et al. They reported that CO is easily activated on the B≡B triple bond, which suggests that there exists a charge transfer interaction between the B≡B triple bond and carbon monoxide. If an electron donation and back-donation between the B≡B triple bond and substrates really occur, the breaking of the chemical bond would be possible. In this study, we examine the mechanism of the σ bond cleavage of the polar and the nonpolar molecules, H2, CH4, NH3 and H2O, on the B≡B triple bond of bis(NHC)-stabilized diboryne NHC-B≡B-NHC by the density functional method. Our calculations show that both σ bonds of the nonpolar H2 and CH4 are broken relatively easily through an electron donation and back-donation at one of the B atoms. These are homolytic cleavages, as well-known for transition metals. Meanwhile, the σ bonds of the polar H2O and NH3 are heterolytically broken not on the one site but on the two sites of the B≡B bond, both reactions being also easy. Thus, the B≡B triple bond has high reactivities for both polar and nonpolar molecules, flexibly changing the reaction channels.
We have developed a facile one-step conversion of 2-deoxy-d-glucose to form a disubstituted cyclopentenone through catalyst-free hydrothermal reaction under mild conditions. The use of 2-deoxy-d-glucose in one-pot conversion is to provide the formation of a carbon five-membered ring instead of the common biomass-derived furans such as furfural, 5-HMF, etc. The cyclopentenone has a potential to be a building block for the preparation of chemical products. As one example, we successfully demonstrated the synthesis of prostaglandin E1 methyl ester.
Positively charged Fe3O4 magnetic nanoparticles were obtained by polyethyleneimine (PEI) as a modification agent. Negatively charged platinum nanoclusters (Pt NCs) were prepared with glutathione (GSH) as reducing agent and protective agent. Finally, spherical fluorescent magnetic nano core-shell microspheres Fe3O4@GSH-Pt NCs were produced through electrostatic adsorption. The magnetic strength was 23.9 emu/g and the fluorescence quantum yield was 8.139%. The experimental results showed that the mean diameter of Fe3O4@GSH-Pt NCs was about 110.3 nm. It emitted red fluorescence at the excitation of 465 nm. Latent fingerprints were directly viewed with excellent ridge details due to the superparamagnetism and excellent fluorescent properties of the prepared Fe3O4@GSH-Pt NCs. Consequently, Fe3O4@GSH-Pt NCs showed great potential in fingerprints detection.
The structural isomers of D-π-A-π-D fluorescent dyes 2,5-PD and 2,6-PD which are substituted with two diphenylamine-thienylcarbazole moieties (electron-donating and π-conjugated unit) on 2,5- and 2,6-positions of a pyrazine ring (electron-withdrawing unit) have been developed. It was found that the structural isomers 2,5-PD and 2,6-PD show a significant solvatofluorochromism (λem = 513–614 and 480–588 nm for 2,5-PD and 2,6-PD, respectively). The photophysical and electrochemical measurements, and density functional theory calculations reveal that 2,5-substituted pyrazine dye 2,5-PD possesses stronger photoabsorption and fluorescence properties in a longer wavelength region and at a lower LUMO energy level, compared to the 2,6-substituted structural isomer 2,6-PD.
Nanoporous CeO2 samples as supports were prepared by chemical dealloying Ce-Al amorphous alloy, followed by synthesis of Au-Pd/CeO2 catalysts. The synthesized Au-Pd/CeO2 catalysts showed higher catalytic activity for hydrogen generation from formic acid than catalysts using supports prepared from a crystalline alloy precursor.
Various tetra-acceptor-substituted alkenes possessing unsymmetrical substituents have been effectively synthesized from vicinal tricarbonyl compounds. The alkenes have polyfunctionality and high electron deficiency. In addition, they easily react with pyrroles to give divergent pyrrolizine derivatives via the conjugate addition of pyrroles followed by intramolecular cyclization. We successfully controlled the chemoselectivity of the intramolecular cyclization (ester/ketone attack) to afford a wide range of valuable pyrrolizine derivatives.
A cationic pyridinium group was introduced to a zinc chlorophyll-a derivative at the meso-positions via its (electro)chemically oxidized cationic radical state. The coupling reactions of zinc methyl mesopyropheophorbide-a with pyridine afforded 5-, 10-, and 20-pyridinio-chlorins that were successfully separated by reversed-phase HPLC. Their 1D/2D-NMR showed the major adduct to be the C10–N+C5H5 regioisomer. Substitution with the meso-pyridinio groups red-shifted their visible absorption bands in a solution.
A boehmite sol which contains uniform fibrous nanoparticles has a unique property to form a film by its self-assembling properties. When Tb ions were added to the sol, the film became photoluminescent (PL) and emitted bright green light due to the f–f transition of Tb by UV irradiation. The PL intensity varied with calcination temperature during pretreatment. The best performance was obtained when the sample was treated around 800 °C. The PL performance normalized by the Tb content was higher for samples with a lower Tb content. Structural analysis by TEM, XRD, and XAFS revealed that when the Tb content was lower than Tb/Al = 2.5/97.5 in the atomic ratio, Tb ions were dispersed on the alumina surface isolated from each other, and those Tb species showed a high PL performance. On the other hand, for densely Tb doped samples, excessive Tb ions aggregated and formed Tb oxide nanoparticles, which were supposed to have lower PL efficiencies.
In this account, we demonstrate that DNA duplex is an ideal scaffold for photochemistry, particularly for comparison of photochemical theory with experiments. The well-defined structure of a DNA duplex can be regarded as an aqueous one-dimensional soft crystal composed of a chromophore-like base-pair assembly. When any base pair in the duplex is replaced with a chromophore, orientation, distance, and association number of chromophores can be precisely controlled. We have developed a new methodology for introduction of chromophores into DNA duplexes using d-threoninol. By using the DNA duplex as a scaffold, experiments on exciton interactions of chromophore assemblies can be compared with molecular exciton theory. A fluorescent resonance energy transfer (FRET) system was also constructed by introducing donor pyrene and acceptor perylene into the DNA duplex using d-threoninol monomers. Using this system, we demonstrated orientation-dependent FRET. We found that theories on both exciton interaction and FRET qualitatively coincide with experimental data and revealed the limitation of the point-dipole approximation. We also evaluated the intrinsic quantum yield of photodimerization of stilbene derivatives by suppressing a side reaction. We propose that there is a correlation of quantum yield of photodimerization with the energy gap of HOMO or LUMO, a hypothesis that deserves theoretical investigation.
The cathodic reduction-induced cross-coupling of arenediazonium salts and heteroarenes was employed to prepare heterobiaryl derivatives. This reaction is attractive because it allows the direct arylation of an aromatic C-H bond in a heteroarene derivative. A radical chain mechanism appears to be involved.
It is well known that “diamond” has ultra-high hardness and low electrical conductivity. However, introducing dopants such as boron into the diamond lattice during growth can increase its conductivity. Boron-doped diamond (BDD) with high conductivity is attracting increasing attention as one of the next-generation of superior electrode materials. In particular, it is expected that BDD electrodes can help solve some of our environmental problems and also improve our quality of life through their use in biomedical devices. Here, in this article, recent developments in the electrochemical applications of boron-doped diamond (BDD) electrodes are introduced.
This review paper summarizes our very recent works on the synthesis of multifunctional transparent nanocomposite thin films or coatings based on metal atom clusters by an electrophoretic deposition (EPD) process. Eight different octahedral atom clusters with niobium, molybdenum or tantalum as metallic cores were used to prepare highly transparent thin films in the visible. Green, yellow, orange, red and brown colored films were successfully fabricated by coating on a transparent conductive oxide glass substrate. Transparent nanocomposite films with prominent luminescent properties were obtained by using Mo6 clusters whereas ultra-violet (UV) and near infrared (NIR) filters were realized by using Nb6 or Ta6 clusters. The EPD process appears to be a new strategy to fabricate highly transparent, homogeneous and colored nanocomposite thin films and coatings for smart windows and solar technologies in a very short time (<90 s).
Total ion current chromatograms (TICCs) generated by liquid chromatography-mass spectrometry (LC-MS) are prone to noise from chemical and electronic sources. This noise can severely impact the detection of analytes in a mixture. Recently, we introduced a new variable selection tool based on Pattern Recognition Entropy (PRE) that selects good quality (high signal-to-noise ratio) mass chromatograms from an LC-MS dataset and thereby creates a reduced TICC with low noise and a flat background (J. Chrom. A. 2018, 1558, 21–28). PRE, which is based on Shannon’s entropy, was shown to be a straightforward and powerful shape recognition tool for this problem. However, while the chromatographic signals in the reduced TICC from PRE were well resolved, some noise remained in the TICC, which suggested that the algorithm had selected some false positives, i.e., poor quality mass chromatograms. In this paper, we report an improved version of the PRE algorithm that utilizes a second variable selection filter based on cross-correlation (CC). As a check on the ability of PRE and CC to select high quality mass chromatograms, every mass chromatogram in our data set (1451 in total) was individually inspected and rated as either high quality (green), intermediate quality (yellow), or poor quality (red). A color-coded plot of the CC value vs. the PRE value for the mass chromatograms was created, which shows that, as expected, the higher quality mass chromatograms are localized in its upper left quadrant, which corresponds to lower PRE values and higher CC values. In our original paper on this topic, we recommended a threshold of 0.5 σ for PRE, which caused the algorithm to select 151 mass chromatograms out of 1451. Of these, 98 were of high quality, 6 were of intermediate quality, and 47 were of poor quality. Using a second threshold for CC, the algorithm retains all the high and intermediate quality mass chromatograms, while removing all 47 of the poor quality ones. The resulting TICC from the PRE-CC algorithm shows less noise compared to the TICC generated from the PRE approach alone. The PRE-CC algorithm is arguably a faster, simpler and more intuitive approach as compared to the widely used CODA_DW algorithm.
In the past decades, various nanomaterials have been intensively developed because of their unique electrical, optical, magnetic as well as catalytic properties. In this review, we discuss the plasma-in-liquid process, especially the microwave-induced plasma-in-liquid process (MWPLP), for metal and metal oxide nanoparticle production. Various types of plasma systems have been employed to produce metal, alloy, and metal oxide nanoparticles. Nanoparticle production by plasma processes usually requires fewer chemical additives compared to other chemical processes. After discussing the bottom-up approach and the plasma-in-liquid process for nanoparticle synthesis, we have focused on MWPLP. Various apparatus systems and detailed mechanisms of MWPLP will be discussed and preparation of metal and metal oxide nanoparticles by MWPLP will be introduced in detail. The surface-coated-electrode system, which is a unique system for MWPLP, is also discussed in this review. This system prevents sample contamination due to the metal components, which are usually ejected into the surrounding liquid after plasma ignition during the production of nanoparticles.