Tricalysiolides A-F, new rearranged ent-kaurane diterpenes from Tricalysia dubia

Six rearranged ent-kaurane diterpenes, tricalysiolides A-F, having the cafestol-type carbon framework were isolated from the wood of Tricalysia dubia (Rubiaceae). Their absolute structures were determined on the basis of the 2D NMR spectroscopy, X-ray crystallographic analysis, and chemical methods.     

Photochemistry of cyclohexane on Cu(111)

The photochemistry of cyclohexane on Cu(111) and its excitation mechanism have been studied by temperature-programmed desorption, ultraviolet and X-ray photoelectron spectroscopy. Cyclohexane weakly adsorbed on Cu(111) has been known to show a broadened and redshifted CH stretching band, i.e., CH vibrational mode softening. Although no dehydrogenation takes place thermally on this surface and by the irradiation of photons at 5.0 eV, adsorbed cyclohexane is dissociated to cyclohexyl and hydrogen by the irradiation of photons at 6.4 eV. This is a marked contrast to cyclohexane in the gas phase where the onset of absorption is located at 7 eV. When the surface irradiated by 6.4-eV photons is further annealed, cyclohexyl is dehydrogenated to form cylcohexene that desorbs at 230 K. The systematic measurements of photochemical cross sections at 6.4 eV with linearly polarized light as a function of incident angle indicate that the electronic transition from the highest occupied band of cyclohexane to a partially occupied hybridized band near the Fermi level is responsible for the photochemistry. The hybridized band is formed by the interactions between the electronic states of cyclohexane and the metal substrate. The role of the hybridized band in the photochemistry and the CH vibrational mode softening is discussed.     

Estimation of Silica Species’ Concentrations in Lithium and Magnesium Chloride Solutions from the Peak Intensities Observed by FAB-MS

The concentrations of dissolved silica species in electrolyte solutions were derived from the relative intensities of silica species, obtained from FAB-MS measurements (fast atom bombardment mass spectrometry), and the total concentration of dissolved silica. Generally, silica species in aqueous solutions form various complexes with cations such as sodium (Na⁺) or calcium (Ca²⁺), and it has been difficult to determine the concentration of each species. From the observed results from FAB-MS, the chemical species of silica dissolved in lithium chloride (LiCl) and magnesium chloride (MgCl₂) solutions do not include complexes with these cations, and thus Li⁺ and Mg²⁺ do not replace protons of the silanol groups in silica. Therefore, in LiCl and MgCl₂ solutions, all of the simple structures of silicate species can be identified. The concentration of each silica species was estimated on the basis of its mass spectra peak intensities and the total concentration of silica as determined by colorimetry. This study yields the concentration of each silica species within small errors, whereas conventional methods (such as ²⁹Si-NMR) have not yielded the concentrations of individual silica species. From these results, dimers and cyclic tetramers are concluded to be the main species in silica solutions with concentrations of at most 0.1 to 0.2 μmol⋅dm⁻³. This tendency should also occur in NaCl and CaCl₂ solutions, which are major electrolytes in natural waters.     

Iterative molecular assembly based on the cation-pool method. Convergent synthesis of dendritic molecules

An iterative method for molecular assembly has been developed based on the cation-pool method using (trimethylsilyl)diphenylmethane as a building block. The silyl group works as both an activating group of the benzene ring in the Friedel-Crafts type reaction and an electroauxiliary in the subsequent low temperature anodic oxidation to generate dendritic diarylcarbenium ions, which were well characterized by low-temperature NMR spectroscopy. The convergent synthesis of dendritic molecules has been achieved by repeating the sequence.     

Calorimetric study of the cubic mesogen,ACBC(16)

The heat capacity of the cubic mesogen ACBC(16) was measured between 16 and 500?K by adiabatic calorimetry. As well as the known condensed phases, a new crystalline phase was found to undergo a glass transition at around 165?K. Phase transitions between crystal, SmC, cubic, and isotropic liquid phases took place at 399.16, 431.15, and 474.30?K, respectively. As in the case of ANBC, a broad hump was observed in the heat capacity of the isotropic liquid phase. The first order nature of the SmC–cubic phase transition was confirmed for the first time by the observation of supercooling of the cubic phase. The broad hump in the isotropic liquid phase was shown to extend to a low temperature side if the isotropic liquid was supercooled, suggesting that the event occurring at the hump is not directly related to the cubic–isotropic liquid phase transition.     

Heat-Resistant Polymer-Grafted Carbon Black: Grafting of Poly(Amide-Imide) Onto Carbon Black

Aromatic poly(amide-imide) with terminal isocyanate groups (PAINCO) was prepared by the polycondensation of trimellitic anhydride and a slight excess of 4,4′-diphenylmethane diisocyanate in N-methyl-2-pyrrolidone (NMP) at 160°C for 20 h. PAI was effectively grafted onto the surface by the reaction of PAI-NCO with carbon black: the percentage of grafting onto FW 200 and Neospectra II was determined to be 41.2 and 39.5%, respectively. When the carboxyl and phenolic hydroxyl groups on carbon black were blocked by treatment with diazomethane, the grafting of PAI-NCO onto the treated carbon black does not proceed. Therefore, it is concluded that PAI-NCO reacts with the carboxyl and phenolic hydroxyl groups on carbon black and PAI is grafted through amide and urethane bonds, respectively. The reaction of PAI-NCO with carbon black was accelerated by the addition of amines as catalyst and by raising of the reaction temperature. Thermogravimetric analysis indicated that PAI-grafted carbon black was stable in air up to about 300°C. The PAI-grafted carbon black was found to give a stable colloidal dispersion in NMP.     

An Acid-Activatable Fluorescence Probe for Imaging Osteocytic Bone Resorption Activity in Deep Bone Cavities

A rationally designed pH-activatable fluorescent probe (pHocas-RIS) has been used to measure localised pH levels in osteocytic lacunae in bone tissue. Conjugation of the moderate bone-binding drug risedronate to a pH-activatable BODIPY fluorophore enables the probe to penetrate osteocytic lacunae cavities that are embedded deep within the bone matrix. After injection of pHocas-RIS, any osteocytic lacunae caused by bone-resorbing osteocytes cause the probe to fluoresce in vivo, thus allowing imaging by intravital two-photon excitation microscopy. This pH responsive probe enabled the visualization of the bone mineralizing activities of acid producing osteocytes in real time, thus allowing the study of their central role in remodeling the bone-matrix in healthy and disease states.     

An Ultrastable,Small {Ag7}5+ Nanocluster within a Triangular Hollow Polyoxometalate Framework

Small Ag_n nanoclusters (n<10) have been emerging as promising materials as sensing, biolabeling, and catalysis because of their unique electronic states and optical properties. However, studying synthesis, structure determination, and exploration of their properties remain major challenges as a result of the low stability of small Ag nanoclusters. Herein, we synthesized an atomically precise face-centered-cubic-type small {Ag₇}⁵⁺ nanocluster supported by a novel triangular hollow polyoxometalate (POM) framework [Si₃W₂₇O₉₆]¹⁸⁻. The cluster showed unique {Ag₇}⁵⁺-to-POM charge transfer bands in both visible and UV light regions. Furthermore, this small {Ag₇}⁵⁺ nanocluster exhibited an unprecedented ultrastability in solution, despite having exposed Ag sites that can be accessed by small molecules, such as O₂, water, and solvents.     

Ground state potential energy surface between cyclobutadiene and tetrahedrane looked down from S1/S0 conical intersections

We have explored the singlet ground state potential energy surface (S₀ PES) between cyclobutadiene (CBD) and tetrahedrane (THD) looked down from S₁/S₀ conical intersections through multi-configuration self-consistent field theory. On the basis of the obtained S₀ PES, we propose the revised process of the THD to CBD symmetry-forbidden reaction. According to the present result, the THD to CBD rearrangement occurs via plural steps similarly to previous suggestions, but via a tetra-radical species (instead of an endo-species), which is considered for the first time in this paper. Since the endo-species is significantly destabilized when hydrogen atoms are replaced by bulky substituents (such as tert-butyl group), the present one, where endo-species are not involved, would be realized in actual systems having bulky substituents.     

Olefin polymerization by (cyclopentadienyl)(ketimide)titanium(IV) complexes of the type, Cp′TiCl2(N=CBu2)-methylaluminoxane (MAO) catalyst systems

Effects of substituents on cyclopentadienyl group for homopolymerization of ethylene, 1-hexene, and for ethylene/1-hexene copolymerization using a series of nonbridged (cyclopentadienyl)(ketimide)titanium complexes of the type, Cp′TiCl₂(N=C^tBu₂) [Cp′ = Cp (1), ^tBuC₅H₄ (2), C₅Me₅ (Cp^*, 3), and indenyl (4)] have been explored in the presence of methylaluminoxane (MAO) cocatalyst. Complexes 1–3 showed the similar catalytic activities for ethylene polymerization although the activity by 4 was somewhat low, whereas the activity for 1-hexene polymerization increased in the order 1 > 4 2 > 3. These complexes showed significant activities for ethylene/1-hexene copolymerization affording high molecular weight poly(ethylene-co-1-hexene)s with unimodal molecular weight distributions, and the activity increased in the order: 4 > 1 2, 3. The r_Er_H values in the polymerization by 1–3 at 40 °C were 0.35–0.52 which clearly indicate that the 1-hexene incorporation in the copolymerization did not proceed in a random manner. The r_E values by 1–3 were 6.0–6.4 and the values were independent upon the cyclopentadienyl fragment employed; the r_E values by 4 at 40 °C were 10.2–10.9 which were close to those by ansa-metallocene complex catalysts. These values were influenced by the polymerization temperature, and the 1-hexene incorporation by 1–4 became inefficient at higher temperature, although the observed activities especially by 1, 4 were highly remarkable.