Shimalactone Biosynthesis Involves Spontaneous Double Bicyclo-Ring Formation with 8π-6π Electrocyclization

Shimalactones A and B are neuritogenic polyketides possessing characteristic oxabicyclo[2.2.1]heptane and bicyclo[4.2.0]octadiene ring systems that are produced by the marine fungus Emericella variecolor GF10. We identified a candidate biosynthetic gene cluster and conducted heterologous expression analysis. Expression of ShmA polyketide synthase in Aspergillus oryzae resulted in the production of preshimalactone. Aspergillus oryzae and Saccharomyces cerevisiae transformants expressing ShmA and ShmB produced shimalactones A and B, thus suggesting that the double bicyclo-ring formation reactions proceed non-enzymatically from preshimalactone epoxide. DFT calculations strongly support the idea that oxabicyclo-ring formation and 8π-6π electrocyclization proceed spontaneously after opening of the preshimalactone epoxide ring through protonation. We confirmed the formation of preshimalactone epoxide in vitro, followed by its non-enzymatic conversion to shimalactones in the dark.     

Modeling of the elementary gas-phase reaction during chemical vapor deposition of silicon carbide from CH3SiCl3/H2

We established a gas-phase, elementary reaction model for chemical vapor deposition of silicon carbide from methyltrichlorosilane (MTS) and H₂, based on the model developed at Iowa State University (ISU). The ISU model did not reproduce our experimental results, decomposition behavior of MTS in the gas phase in an environment with H₂. Therefore, we made several modifications to the ISU model. Of the reactions included in existing models, 236 were lacking in the ISU model, and thus were added to the model. In addition, we modified the rate constants of the unimolecular reactions and the recombination reactions, which were treated as a high-pressure limit in the ISU model, into pressure-dependent rate expressions based on the previous reports (to yield the ISU+ model), for example, H₂(+M) → H + H(+M), but decomposition behavior remained poorly reproducible. To incorporate the pressure dependencies of unimolecular decomposition rate constants, and to increase the accuracies of these constants, we recalculated the rate constants of five unimolecular decomposition reactions of MTS using the Rice-Ramsperger-Kassel-Marcus method at the CBS-QB3 level. These chemistries were added to the ISU+ model to yield the UT2014 model. The UT2014 model reproduced overall MTS decomposition. From the results of our model, we confirmed that MTS mainly decomposes into CH₃ and SiCl₃ at the temperature around 1000°C as reported in the several studies.     

Biphenyl ether and biphenyl quinolizidine lactone alkaloids from Heimia salicifolia

Three new biphenyl ether quinolizidine lactone alkaloids (1–3) and 13 new biphenyl quinolizidine lactone alkaloids (4–16) were isolated from Heimia salicifolia (Lythraceae) together with seven known alkaloids. Their structures were determined by spectroscopic analyses and chemical conversions.     

Melt crystallization and crystal transition of poly(butylene adipate) revealed by infrared spectroscopy

The structure evolution of poly(butylene adipate) (PBA) during isothermal melt crystallization and phase transition processes is investigated by Fourier transform infrared spectroscopy (FTIR). Detailed IR spectra analysis and band assignment are performed to disclose the bands sensitive to the alpha-form crystalline order of PBA. It is revealed from the in situ IR study that the functionalities within PBA chains alter simultaneously during the melt crystallization process. From the analysis of the spectral changes, it is found that band shifts take place during the phase transition process of PBA from its metastable beta-form crystal to the stable alpha-form. Notable band shifts in the 1300-1100 cm(-1) region indicate that the twist of polymer chains in the alpha-form is located in the C-O-C and C-O linkages. Moreover, the results elucidated that the different segments of molecular chains tune up their conformations synchronously during the beta to alpha crystal transition process of PBA. It is suggested that the betaalpha phase transition process proceeds randomly throughout the solid at a constant rate.     

Encapsulated molecular catalysts in polysiloxane gels: ruthenium cluster-catalyzed isomerization of alkenes

Novel ruthenium-encapsulating polysiloxane gels are prepared by treatment of polymethylhydrosiloxane with diols in the presence of (mu(3),eta(2),eta(3),eta(5)-acenaphthylene)Ru(3)(CO)(7), and act as reusable catalysts in the isomerization of alkenes without leakage of the catalyst species.     

Correlation between surface tension and void fraction in ionic liquids

An effort to systematize published and new data on the surface tension gamma of ionic liquids (ILs) is based on the hypothesis that the dimensionless surface tension parameter gamma V v (2/3)/ kT is a function of the void fraction x v = V v/ V m. The void volume V v is defined as the difference between the liquid volume V m occupied by an ion pair (known from cationic and anionic masses and liquid density measurements) and the sum V (+) + V (-) of the cationic and anionic volumes (known from crystal structures), while kT is the thermal energy. Our hypothesis that gamma V m (2/3)/ kT = G( x v) is initially based on cavity theory. It is then refined based on periodic lattice modeling, which reveals that the number N of voids per unit cell (hence the dimensionless surface tension) must depend on x v. Testing our hypothesis against data for the five ILs for which surface tension and density data are available over a wide range of temperatures collapses all of these data almost on a single curve G( x v), provided that slight (4%) self-consistent modifications are introduced on published crystallographic data for V (+) and V (-). An attempt to correlate the surface tension vs temperature data available for inorganic molten salts is similarly successful, but at the expense of larger shifts on the published ionic radii (8.8% for K; 3.3% for I). The collapsed G( x v) curves for ILs and inorganic salts do not overlap anywhere on x v space, and appear to be different from each other. The existence of a relation between gamma and x v is rationalized with a simple capillary model minimizing the energy. Our success in correlating surface tension to void fraction may apply also to other liquid properties.     

Quick analysis of baicalin in Scutellariae Radix by enzyme-linked immunosorbent assay using a monoclonal antibody

To establish an immunoassay for baicalin (BA), a hybridoma cell line (9D6) secreting a monoclonal antibody (MAb) against BA was prepared by cell fusion with splenocytes derived from a mouse immunized with BA-bovine serum albumin (BSA) conjugate and a myeloma cell line, SP2/0-Ag14. MAb 9D6 shows specific reactivity against BA and its aglycone, baicalein, but not against other natural products. We developed an enzyme-linked immunosorbent assay (ELISA) using MAb 9D6 in a competitive manner, ranging from 200 ng/mL to 2 μg/mL. After validating the developed ELISA on the basis of intra- and inter-assays and a recovery experiment, it was found that the ELISA was not only simple, but also sufficiently reliable and accurate for quality control of Scutellariae Radix. It allowed determination of BA in complex and mixed materials, such as Kampo medicines.     

Development of pyrrole-imidazole polyamide for specific regulation of human aurora kinase-A and -B gene expression

Pyrrole-imidazole polyamide (PIP) is a nuclease-resistant novel compound that inhibits gene expression through binding to the minor groove of DNA. Human aurora kinase-A (AURKA) and -B (AURKB) are important regulators in mitosis during the cell cycle. In this study, two specific PIPs (PIP-A and PIP-B) targeting AURKA and AURKB promoter regions were designed and synthesized, and their biological effects were investigated by several in vitro assays. PIP-A and PIP-B significantly inhibited the promoter activities, mRNA expression, and protein levels of AURKA and AURKB, respectively, in a concentration-dependent manner. Moreover, 1:1 combination treatment with both PIPs demonstrated prominent antiproliferative synergy (CI value [ED(50)] = 0.256) to HeLa cells as a result of inducing apoptosis-mediated severe catastrophe of cell-cycle progression. The novel synthesized PIP-A and PIP-B are potent and specific gene-silencing agents for AURKA and AURKB.     

Nanomechanical properties of reversed surfactant bilayers formed in micrometre-sized holes

Nanomechanical properties of free-standing reversed surfactant bilayers, dried foam films (DFFs), were examined via AFM by fitting local force-indentation curves with a Hertzian model. The Young's moduli of four kinds of bilayers were in a range of 10-30 MPa.     

Structures and bonding on a colloidal silver surface of the various length carboxyl terminal fragments of bombesin

Raman (RS) and surface-enhanced Raman scattering spectra (SERS) were measured for various length carboxyl terminal fragments (X-14 of amino acid sequence) of bombesin ( BN): BN13-14, BN12-14, BN11-14, BN10-14, BN9-14, and BN8-14 in silver colloidal solutions. Density functional theory (DFT) calculations of Raman wavenumbers and intensities with extended basis sets (B3LYP/6-31++G**) were performed with the aim of providing the definitive band allocations to the normal coordinates. The proposed band assignment is consistent with the assignment for similar compounds reported in the literature. The nonadsorbed and adsorbed molecular structures were deducted by detailed spectral analysis of the RS and SERS spectra, respectively. This analysis also allowed us to propose the particular surface geometry and orientation of these peptides on silver surface, and their specific interaction with the surface. For example, a SERS spectrum of BN8-14 indicates that the interaction of a thioether atom and Trp8 with the silver surface is favorable and may dictate the orientation and conformation of adsorbed peptide. One of the most prominent and common features in all of the fragments' SERS spectra is a approximately 692 cm (-1) band due to nu(C-S) accompanied by two or three bands of different C-S conformers for all, except BN8-14, which suggests that all of the above-mentioned compounds adsorb on the silver surface through the thioether atom and that the attachment of Trp8 produces limitation in a number of possible C-S conformers adopted on this surface. Our results also show clearly that His12 and CO do not interact with the colloid surface, which supports our earlier results.