Palladium(0)-catalyzed intramolecular [2+2+2] alkyne cyclotrimerizations with electron-deficient diynes and triynes

In the presence of 2.5 mol % of [Pd(2)(dba)(3)] (dba=dibenzylideneacetone) and 5 mol % of PPh(3), nearly equimolar amounts of dimethyl nona-2,7-diyne-1,9-dioate derivatives (diyne diesters) and dialkyl acetylenedicarboxylates were allowed to react in toluene at 110 degrees C to afford [2+2+2] cycloadducts in moderate-to-good yields. Similarly, dimethyl trideca-2,7,12-triyne-1,13-dioate derivatives (triyne diesters) were catalytically transformed into phthalic acid ester analogues in excellent yields. To gain insight into the mechanism of these intramolecular alkyne cyclotrimerizations, stoichiometric reactions of [Pd(2)(dba)(3)] with a diyne diester and a triyne diester bearing ether tethers were conducted in acetone at room temperature to furnish an oligomeric bicyclopalladacyclopentadiene and a Pd(0) triyne complex, respectively. The structures of these novel complexes were unequivocally determined by Xray structure analysis. The isolated triyne complex was heated at 50 degrees C or treated with PPh(3) in acetone at room temperature to afford the arene product. Furthermore, the same complex catalyzed the triyne cyclization with or without PPh(3).     

Analysis of dynamic surface tension of tetraethyleneglycol monooctyl ether at air/water interface

The dynamic surface tension of the aqueous solutions of tetraethyleneglycol monooctyl ether (C₈E₄), a nonionic surfactant, was measured at different concentrations and temperatures. Present data at 298.15 K clearly indicate that the mechanism of adsorption is purely diffusion controlled at low concentrations (0.1~0.4 mmol/kg), and there is a switchover in adsorption mechanism to the mixed diffusion-kinetic control at higher concentrations. The calculated activation energies increase with concentration, and thus, with surface density, but decrease with temperature. The magnitude of activation energy and its increase with surface density suggest that the barrier is due to the free surface site formation by overcoming mainly the attractive van der Waals forces between the chain of adsorbed C₈E₄ molecules.     

Correlation of spin states and spin delocalization with the dioxygen reactivity of catecholatoiron(III) complexes

A series of catecholatoiron(III) complexes, [Fe(III)L(4Cl-cat)]BPh4 (L = (4-MeO)2TPA (1), TPA (2), (4-Cl)2TPA (3), (4-NO2)TPA (4), (4-NO2)2TPA (5); TPA = tris(pyridin-2-ylmethyl)amine; 4Cl-cat = 4-chlorocatecholate), have been characterized by magnetic susceptibility measurements and EPR, 1H NMR, and UV-vis-NIR spectroscopies to clarify the correlation of the spin delocalization on the catecholate ligand with the O2 reactivity as well as the spin-state dependence of the O2 reactivity. EPR spectra in frozen CH3CN at 123 K clearly showed that introduction of electron-withdrawing groups effectively shifts the spin equilibrium from a high-spin to a low-spin state. The effective magnetic moments determined by the Evans method in a CH3CN solution showed that 5 contains 36% of low-spin species at 243 K, while 1-4 are predominantly in a high-spin state. Evaluation of spin delocalization on the 4Cl-cat ligand by paramagnetic 1H NMR shifts revealed that the semiquinonatoiron(II) character is more significant in the low-spin species than in the high-spin species. The logarithm of the reaction rate constant is linearly correlated with the energy gap between the catecholatoiron(III) and semiquinonatoiron(II) states for the high-spin complexes 1-3, although complexes 4 and 5 deviate negatively from linearity. The lower reactivity of the low-spin complex, despite its higher spin density on the catecholate ligand compared with the high-spin analogues, suggests the involvement of the iron(III) center, rather than the catecholate ligand, in the reaction with O2.     

Bacillus subtilis epoxide hydrolase-catalyzed preparation of enantiopure 2-methylpropane-1,2,3-triol monobenzyl ether and its application to expeditious synthesis of (R)-bicalutamide

Expeditious synthesis of (R)-bicalutamide (1), a synthetic antiandrogen, from enantiopure 2-methylpropane-1,2,3-triol monobenzyl ether (4) was achieved. An engineered Bacillus subtilis epoxide hydrolase worked enantioselectively on the racemic epoxide (7) to provide the above starting material in highly enantiomerically enriched state.     

Small-angle x-ray scattering measurement of a mist of ethanol nanodroplets: an approach to understanding ultrasonic separation of ethanol-water mixtures

Small-angle x-ray scattering measurements using a brilliant x-ray source revealed nanometer sized liquid droplets in a mist formed by ultrasonic atomization. Ultrasonic atomization of ethanol-water mixtures produced a combination of water-rich droplets of micrometer order and ethanol-rich droplets as small as 1 nm, which is 10(-3) times smaller than the predicted size. These sizes were also obtained for mists generated from the pure liquids. These results will help to clarify the mechanism of "ultrasonic ethanol separation," which has the potential to become an alternative to distillation.     

Single laser pulse induced aggregation of gold nanoparticles

Gold nanoparticles with an average diameter of 11 nm (Au(39000)) were prepared in an SDS aqueous solution. A 80-microm liquid droplet (microdroplet) of the solution was ejected into the atmosphere from a microdroplet nozzle. Structural changes of the gold nanoparticles in the microdroplet, after they were irradiated with a focused single-nanosecond laser pulse at the wavelength of 532 nm, were studied by transmission electron microscopy (TEM) and optical absorption spectroscopy. It was revealed that the gold nanoparticles are fragmented into small particles and then the small fragments aggregate with each other. The aggregation was found to be terminated 100 micros after the laser-pulse excitation.     

Biosynthesis‐Assisted Structural Elucidation of the Bartolosides,Chlorinated Aromatic Glycolipids from Cyanobacteria

The isolation of the bartolosides, unprecedented cyanobacterial glycolipids featuring aliphatic chains with chlorine substituents and C‐glycosyl moieties, is reported. Their chlorinated dialkylresorcinol (DAR) core presented a major structural‐elucidation challenge. To overcome this, we discovered the bartoloside (brt) biosynthetic gene cluster and linked it to the natural products through in vitro characterization of the DAR‐forming ketosynthase and aromatase. Bioinformatic analysis also revealed a novel potential halogenase. Knowledge of the bartoloside biosynthesis constrained the DAR core structure by defining key pathway intermediates, ultimately allowing us to determine the full structures of the bartolosides. This work illustrates the power of genomics to enable the use of biosynthetic information for structure elucidation.     

Study on Enzymatic Hydrolysis of Polylactic Acid by Endogenous Depolymerization Model

Enzymatic degradation of polylactic acid is studied experimentally and analytically. Gel permeation chromatography profiles obtained before and after the enzymatic degradation of polylactic acid (PLA) were introduced into the analysis based on a mathematical model. Previously developed techniques were successfully adapted to the analysis of an initial value problem consisting of an endogenous depolymerization model and an initial condition, and an inverse problem to determine the degradation rate for which the solution of the initial value problem also satisfies a final condition. Those problems were solved numerically and numerical results are introduced. Degradabilities of PLA and polyvinyl alcohol are compared.

     

Lyophilized hemoglobin‐albumin cluster with disaccharides: Long‐term storable powder of artificial O2‐carrier

Core‐shell protein cluster comprising a hemoglobin (Hb) in the center and human serum albumins (HSA) at the exterior, Hb‐HSA ₃ cluster, is an artificial O₂‐carrier designed for use as a red blood cell (RBC) substitute. Lyophilization of the Hb‐HSA ₃ cluster solution ([Hb unit] = 5 g/dL) with sucrose and trehalose yielded stable pink powder, which can be stored for 2 years at 4°C. Addition of pure water to the powder regenerated the homogeneous solution. The O₂‐binding properties and oxyHb rate have been unaltered during the storage period. Infrared spectroscopic studies revealed that the hydrogen bond between protein and sugar stabilizes three‐dimensional structure of the cluster.