A cubic boracite with substituted boron sites, Li4B4M3O12Cl (M = Al, Ga), derived by fully replacing the tetrahedral BO4 units in the parent lithium chloroboracite, Li4B7O12Cl, with AlO4 or GaO4 units, has been discovered. These substituted compounds have the largest unit cell dimensions of known boracites and are formed as the stable primary phase in highly crystalline glass-ceramics derived from the Li2O–B2O3–M2O3–LiCl quarternary system. The conductivity of Li4B4M3O12Cl glass-ceramics at room temperature was ∼10−5 S cm−1, an order of magnitude larger than the highest conductivity recorded for Li4B7O12Cl glass-ceramics. The Li4B4Al3O12Cl glass-ceramic is stable in contact with Li metal and exhibits a wide electrochemical window between 0 and 6 V vs. Li/Li+ and a Li+ ion transport number of ∼1.
Thermostable mononuclear Eu(III) complexes with a π-expanded system, [Eu(btfa)3(DPEPO)] and [Eu(ntfa)3(DPEPO)] (DPEPO: bis[2-(diphenylphosphino)phenyl] ether oxide, btfa: benzoyltrifluoroacetonate, ntfa: 3-(2-naphthoyl)-1,1,1-trifluoroacetonate), are reported. Decomposition temperature (dp) of [Eu(btfa)3(DPEPO)] and that of [Eu(ntfa)3(DPEPO)] are estimated to be 320 °C and 318 °C, respectively. These values are higher than that of the previous [Eu(hfa)3(DPEPO)] (hfa: hexafluoroacetylacetonate, dp = 228 °C). The photosensitized emission quantum yield Φπ–π* and photosensitized energy transfer efficiency ηsens of [Eu(ntfa)3(DPEPO)] (Φπ–π* = 45%, ηsens = 77%) are larger than those of [Eu(btfa)3(DPEPO)] (Φπ–π* = 38%, ηsens = 55%). The thermostable Eu(III) complex with a π-expanded system is expected to be useful for fabrication of LED devices.
Based on the results of rapid-flow electron spin resonance (RF-ESR) and spin-trapping (ST-ESR) measurements, carbonyl-conjugated radicals derived from the vicinal diol moiety (2, i.e., the head-to-head structure) of poly(vinyl alcohol) (PVA) have been proposed to be the most probable intermediate species involved in the initial stages of the graft reaction of PVA with methyl methacrylate (MMA). A modified poly(vinyl alcohol) (PPVA) bearing a 1,2-propanediol pendant moiety (3) with a molar ratio of 8% (based on the monomer unit) was prepared to clarify the role of the carbonyl-conjugated radicals of PPVA in the graft reaction with MMA. The RF-ESR spectra observed for the mixtures composed of PPVA, hydrogen peroxide (HPO) or ammonium persulfate (APS), and Ti2(SO4)3 (pH ca. 2) revealed the formation of four radical species (A, B1, B2, and C) derived from PPVA. By comparison of the RF-ESR spectra observed for PPVA and PVA, species A (g = 2.0041) was confirmed to be the pendant derived radical of PPVA, and species B1 and B2 (g = 2.0023) and C (g = 2.0032) were assigned to be the PVA main-chain derived radicals. Species B1 and B2 were deduced to be a pair of carbonyl-conjugated radicals (4, 5, R1–CH2–CO–•CH–CH2–R2) derived from the vicinal diol (2), and species C was assigned to be the secondary alcohol (1) derived radicals (6, R1–CH2–•COH–CH2–R2). In terms of g value and proton hyperfine coupling constants (hfcc), the molecular structure of species A was ascribed to be the carbonyl-conjugated radical of the pendant moiety (7, •CH2–CO–CHR1R2). The results of ST-ESR measurements using the sodium salt of 3,5-dibromo-4-nitroso-benzene-sulfonate (DBNBS) show that a pair of pendant radicals (7) and (8, O=CH–•CH–CHR1R2) was formed in the graft polymerization reaction solutions containing APS or HPO as an oxidant (80 °C, pH ca. 2). The grafted copolymers of PPVA and PVA (PPVA-g-MMA and PVA-g-MMA) were separated from similar graft reaction solutions composed of APS and MMA after heating at 70 °C for 1 h (pH ca. 2), and the grafting efficiencies of PPVA (PPVAge%) and PVA (PVAge%) were, respectively, estimated to be 4% and 2%. The molecular and electronic structure of the carbonyl-conjugated radicals derived from the main-chain (4, 5) and from the pendant moiety (7, 8) of PPVA will be discussed in relation to the reaction mechanisms of the initial reaction stage of the graft copolymerization with MMA.
A combination of synthetic, organic, and biochemical approaches has been developed to study how protein and nucleic acid assemblies modulate the affinity, specificity and cooperativity of protein–nucleic acid interactions. These strategies have enabled formation of noncovalent peptide dimers on specific DNA sequences. A new framework from RNA and peptide into a stable complex of ribonucleopeptide was also developed to construct receptors and fluorescent sensors for small molecules. Attempts to design novel DNA-binding peptides, receptors and sensors will provide an ultimate test for our understanding of the principle of molecular recognition associated with protein–nucleic acid interactions.
The reactivity of formaldehyde (HCHO) adsorbed in the supercages of zeolite NaY toward α-methylstyrene for the carbonyl-ene reaction was very dependent on the loading amount of HCHO in the NaY pores. We first prepared a series of NaY samples with different amounts of HCHO, and applied them to the carbonyl-ene reaction with excess amounts of α-methylstyrene to evaluate their intrinsic reactivities. It was found that one formaldehyde molecule adsorbed in one supercage of NaY produced 3-phenylbut-3-en-1-ol in the highest yield (83%), while for higher loading amounts of HCHO on NaY, lower yields of the product were obtained because the supercages were narrowed by the HCHO molecules as well as the homoallylic alcohol product and its over-reaction products. We next investigated their states of HCHO adsorbed in the pores by 13C DD/CP MAS NMR analysis. When three HCHO molecules were adsorbed in a supercage, it was clarified that all the HCHO was exclusively encapsulated in a monomeric form, while most of the adsorbed HCHO with much higher loading amounts was transformed into 1,3,5-trioxane inside the supercages of NaY as well as paraformaldehyde outside the supercages.
This research highlights the dehydration of dimethyl amino ethyl azide (DMAZ), parametric optimization, and describes equilibrium and kinetics of water adsorption on 3A sieves. Central composite design (CCD) was successfully employed for experimental design and analysis of the results. It was indicated that the optimum adsorption capacity (191.3 mg/g) was obtained at contact time = 150 min, liquid/solid ratio = 10:1, initial concentration of water = 3 wt% and agitating rate = 150 rpm. Langmuir-Freundlich and intra-particle diffusion models were appropriate to describe isotherms and kinetics of dehydration, respectively. Thermal stability and regeneration behavior of the adsorbent were investigated using XRD and TGA/DSC methods. It was revealed that the best regeneration occurred in the range of 250–300 °C and the zeolite structure was stable up to 400 °C. Also, the thermal analysis verified that DMAZ molecules cannot diffuse into the aforementioned zeolite pores.
Activated carbon monolith (ACM) was obtained from Amygdalus pedunculata shell (APS) and polyacrylonitrile (PAN) via a template-free approach. APS was uniformly distributed into the monolith matrix and an interconnected network was fully established. The present study greatly promotes the close contact between desert reclamation and green energy storage.
Photochemical properties of 4,4′-distyrylbiphenyl (DSBP) derivatives have been studied. While the introduction of methoxy groups at meta-positions does not influence the photoisomerization of DSBP, the introduction of methyl substituents at the biphenyl moiety (MDSBP) changed the photoisomerization from one-way cis-to-trans photoisomerization for DSBP to cis–trans mutual photoisomerization for MDSBP.
A versatile method for the arylboration of internal alkynes with aryl chlorides or bromides and bis(pinacolato)diboron has been developed. This method tolerates various functional groups, including acetyl, methoxycarbonyl, cyano, and fluoro substituents, and affords a range of tri-substituted vinylboronates, which are highly useful intermediates for the synthesis of tetra-substituted ethenes, in high yield and regioselectivity.
Protein dynamics play a fundamental role in allosteric regulation, which is vital to the function of many proteins. In many proteins, rather than a direct interaction, mutual modulation of properties such as ligand affinity at spatially separated sites is achieved through a conformational change. Conformational changes of proteins are thermally activated processes that involve intramolecular and intermolecular energy exchanges. In this account, I review the work of my team on the development and applications of ultrafast time-resolved resonance Raman spectroscopy to observe functionally important protein dynamics. We gained insights into conformational dynamics upon external stimulus and energy flow with a spatial resolution of a single amino acid residue using time-resolved visible and ultraviolet resonance Raman spectroscopy. The results have contributed to a deeper understanding of the structural nature of protein motion and the relationship of dynamics to function. I discuss the protein dynamics and allosteric mechanism in terms of the nature of the high packing density of protein structures. In addition, I present a view of the future of molecular science on proteins.
Adsorption behavior of As(V) and As(III) to an isolated ferric ion combined with Chelex 100 suggested that an isolated ferric ion combined with organic substances plays an important role in the uptake of arsenic in the pedosphere in addition to ferric hydrous oxides (Fe2O3·nH2O) which are ubiquitous inorganic polymers.
In this study, a benzene-fused bis(thiaporphyrin) was synthesized by the retro-Diels–Alder reaction of a bicyclo[2.2.2]octadiene (BCOD)-fused bis(thiaporphyrin) precursor. This precursor was prepared by the double [3+1] porphyrin synthesis of the BCOD-fused dipyrrole with thiatripyrrane. The ultraviolet–visible (UV–vis) spectrum of benzene-fused bis(thiaporphyrin) in dichloromethane was extremely different from that of the corresponding benzene-fused bis(porphyrin). In contrast, extremely similar spectra were obtained in the presence of trifluoroacetic acid. The similar electronic structures in the protonated states were supported by X-ray analysis and time-dependent density-functional theory (TD-DFT) calculations.
By introducing catalyst- and solvent-free graft polymerization of low cost and environmentally benign sulfur to the nano-channels of an imine-linked covalent organic framework (COF), we demonstrated our strategy for functionalization of a conventional COF to yield a redox-active covalent organic framework-graft-polysulfide (COF-graft-PS), which can be utilized as a cathode active material in rechargeable lithium organic batteries. The COF-graft-PS-based batteries showed high capacity (425 mA h g−1 at a rate of 250 mA g−1), excellent rate capability, and good cycling performance over 500 cycles. The design characteristics and synthetic strategy open new possibilities for the preparation of alternative, sustainable, high-performance rechargeable lithium batteries by using abundant and cost-effective materials.
Polymers are a good platform for the production of various functional materials, since functional moieties can be introduced into both the main chain backbone and side chain pendants by elegant molecular design and utilizing efficient synthetic protocols. Highly colored and fluorescent π-systems have often been employed as ion sensing units especially when heteroaromatic rings are included. The heteroaromatic rings can form supramolecular complexes with metal ions or anions, resulting in the visual color changes of absorption and fluorescence. Conjugated polymers have been traditionally employed to this end, because they are highly emissive and very sensitive to various ions. However, most of such conjugated polymers are synthesized by costly cross-coupling polycondensations, which do not meet the green chemistry concepts of this century. Click chemistry is a new concept representing an efficient and atom-economic synthesis, and one of the most common reactions is the Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) yielding 1,2,3-triazole rings. The 1,2,3-triazole derivatives are electronically almost inert, but they possess fluorescent chemosensor properties. Recent examples of polymeric chemosensors based on the 1,2,3-triazole derivatives are introduced. Furthermore, an emerging click chemistry reaction, i.e., the alkyne-acceptor click chemistry, is also introduced. This reaction produces highly colored donor-acceptor (D-A) chromophores on a polymer platform, enabling visual detection of the ion sensing behavior. The polymeric chemosensors with the D-A chromophores show a specific discrimination between hard and soft metal ions by different color changes. These polymers are also useful for anion sensing.
Nickel is one of the most popular first row transition metals for coupling reactions. For the past two decades, catalytic multi-component coupling reactions via nickelacycles have been developed. Although the formation of nickelacycles has been believed an important key step in the catalytic reactions, the generation of nickelacycles by oxidative cyclization has been less studied. Thus, we have been focusing on the formation of nickelacycles from nickel(0) species and development of catalytic reactions without using coupling reagents to construct highly atom economical nickel-catalyzed multi-component connecting reactions.