Developments and structures of mesopores in alkaline-treated ZSM-5 zeolites

ZSM-5 zeolites with SiO₂/Al₂O₃ molar ratio of 24 were treated in 0.05 M aqueous sodium hydroxide solution at 325 K in different periods. The samples were characterized by means of nitrogen adsorption at 77 K, field emission scanning electron microscopy, X-ray diffractometry, and Fourier transform infrared spectroscopy. Analysis of the experimental results showed that the alkaline treatment periods have influence on the developments and structures of mesopores in the alkaline-treated ZSM-5 zeolites. Alkaline treatment initially develops mesopores mainly from the boundary portion of MFI zeolites to the bulk, while prolonged treatment destroys the mesopores, and an optimum mesoporosity is obtained by the treatment for 1.5 h. On the other hand, crystallinities and short-range order in alkaline treated zeolites have remained virtually unchanged according to the examination from X-ray diffractometry and Fourier transform infrared spectroscopy.     

Crack-Free,Thick Ceramic Coating Films via Non-Repetitive Dip-Coating Using Polyvinylpyrrolidone as Stress-Relaxing Agent

BaTiO₃ and PZT films were prepared from alkoxide-acetate solutions containing polyvinylpyrrolidone (PVP) by non-repetitive dip-coating. It was demonstrated that PVP incorporated in gel films suppresses crack formation during heating and increases the critical thickness, the maximum thickness achievable without crack formation via single-step deposition. Using PVP crack-free BaTiO₃ and PZT films 1.2 and 0.5 m in thickness could be prepared, respectively, via single-step dip-coating. The films were fairly transparent and dense in microstructure. The tensile stress in heat-treated BaTiO₃ films was also demonstrated to decrease significantly by incorporating PVP in gel films.     

Novel resolution of the anthracyclinone intermediate by the use of (2r, 3r)-(+)- and (2s, 3s)-(-).1,4-bis(4-chlorobenzyloxy)butane-2,3-diol: a simple and efficient synthesis of optically pure 4-demethoxydaunomycinone and 4-demethoxyadriamycinone

(±)-7-Deoxy-4-demethoxydaunomycinone((±)-3) was found to be cleanly resolved by forming a mixture of the diastereomereic acetals((-)-9and(+)-10 or(+)-9 and(-)-10)with the title vicinal-diol(+)-or ( )-5), affording optically pure (R)-( )-3. The resolving agents (( + )- and ( )-5) were readily synthesized from unnatural(2S,3S)-(-)-tartaric acid((-)-6)or D-(-)-mannitol and natural (2R,3R)-(+)-tartaric acid((+)6), respectively. The undesired enantiomer ((S)-(+ )-3) obtained by the optical resolution could be racemized by heating with trifluoromethanesulfonic acid in aq acetic acid. Optically pure (R)-3 was elaborated to optically pure (+)-4-demethoxydaunomycinone ((+)-2b) and (+)-demethoxyadriamycinone ((+)-2a) by featuring highly stereoselective ( ? 20:1) introduction of the OH group into the C₇-position as a key step.     

Synthesis of detoxininolactone derivatives and the revised absolute stereochemistry of detoxinine

A stereospecific synthesis of acetyl-$\text{L}$-valyl-detoxininolactone has been performed and the absolute stereochemistry of detoxinine has been revised to (2$\text{S}$, 3$\text{R}$, 1′$\text{S}$)-2-(2′-carboxy-1′-hydroxyethyl)-3-hydroxypyrrolidine.     

Integration of a flow-type chemiluminescence detector on a glass electrophoresis chip

A glass electrophoresis microchip integrated a flow-type chemiluminescence (CL) detection cell has been developed and evaluated. The chip pattern is a double-T-type electrophoretic sample injection and separation combining with a Y-type chemiluminecent detector. The double-T geometry allows for high-efficiency sample injection and geometric definition of sample plug size. The branch of Y was used as CL reagent channel, and the CL reagent was delivered by a lab-made micropump. Bis[(2,4,6-trichlorophenyl)]oxalate-H₂O₂ CL system was employed to detect dansyl amino acids. On this microchip, dansyl-phenylalanine and -sarcosine were successfully separated by electrophoresis and detected within 250 s. The detection limits (S/N=3) of dansyl-phenylalanine and -sarcosine could reach to 2.8 and 3.2 μM, respectively, due to the vigorous dilution of sample with CL reagent and timely removal of the waste solution from reaction area.     

Fabrication of an integrated PDMS microchip incorporating an LED-induced fluorescence device

A microfluidic device with an integrated fluorescence detection system has been developed in order to miniaturize the entire analytical system. A blue or green light-emitting diode (LED) and an optical fiber were mounted in a polydimethylsiloxane-based microchip. The performance of this device was evaluated by microchip electrophoresis. When a green LED was used as the light source, the calibration curve of Sulforhodamine-101 was linear over the range 1–100 M. The detection limit was found to be 600 nM (240 amol) for a S/N ratio of 3. When using a blue LED, the calibration curve of Fluorescein was linear over the range 0.2–100 M. The detection limit was estimated to be 120 nM (50 amol) (S/N=3). The detection sensitivity per unit power was comparable to that of LIF. The RSD values for the migration time, peak height and peak area were 0.74, 7.18 and 9.45%, respectively. The integrated microfluidic device was successfully used to determine amino acid derivatives.     

Active site mapping of 2-deoxy-scyllo-inosose synthase, the key starter enzyme for the biosynthesis of 2-deoxystreptamine. Mechanism-based inhibition and identification of lysine-141 as the entrapped nucleophile

A key enzyme in the biosynthesis of clinically important aminoglycoside antibiotics including neomycin, kanamycin, gentamicin, etc. is 2-deoxy-scyllo-inosose synthase (DOIS), which catalyzes the carbocycle formation from d-glucose-6-phosphate to 2-deoxy-scyllo-inosose (DOI). To clarify its precise reaction mechanism and crucial amino acid residues in the active site, we took advantage of a mechanism-based inhibitor carbaglucose-6-phosphate (pseudo-dl-glucose, C-6-P) with anticipation of its conversion to a reactive alpha,beta-unsaturated carbonyl intermediate. It turned out that C-6-P clearly showed time- and concentration-dependent inhibition against DOIS, and the molecular mass of the resulting modified-DOIS with C-6-P was 160 mass units larger than that of native DOIS. Thus, the expected alpha,beta-unsaturated intermediate appeared to trap a specific nucleophilic group in the active site through the Michael-type 1,4-addition. The covalently modified amino acid residue was determined to be Lys-141 by means of enzymatic digestion and subsequent LC/MS and LC/MS/MS of the digest. Also discussed are the role of Lys-141 in the substrate recognition and the reaction pathway and comparison with evolutionary related dehydroquinate synthase.     

Modeling of the hysteresis phenomena in finite-sized slitlike nanopores. Revision of the recent results by rigorous numerical analysis

The systematic investigation of the hysteresis phenomena in finite-sized slitlike nanopores via the Aranovich-Donohue (AD) lattice density functional theory (LDFT) is presented. The new reliable quantitative modeling of the adsorption and desorption branch of the hysteresis loop, through the formation and movement of the curved meniscus, is formulated. As a result, we find that our proposal, which closely mimics the experimental findings, can reproduce a rounded shape of the desorption branch of the hysteresis loop. On the basis of the exhausted commutations, we proved that the hysteresis loop obtained in the considered finite-sized slitlike geometry is of the H1 type of the IUPAC classification. This fundamental result and the other most important results do not confirm the results of the recent studies of Sangwichien et al., whereas they fully agree with the recent lattice studies due to Monson et al. We recognize that the nature of the hysteresis loops (i.e. position, width, shape, and the multiple steps) mainly depends on the value of the energy of both the adsorbate-adsorbate and adsorbate-adsorbent interactions; however, the first one is critical for the appearance of hysteresis. Thus, for relatively small adsorbate-adsorbate interactions, the adsorption-desorption process is fully reversible in the whole region of the bulk density. We show that the strong adsorbate-adsorbent interactions produce (also observed experimentally) multiple steps within hysteresis loops. Contrary to the other studies of the hysteresis phenomena in confined geometry via the LDFT formalism, we constructed both ascending and descending scanning curves, which are known from the experimental observations. Additionally, we consider the problem of the stability of both the obtained adsorption and desorption branches of the computed hysteresis loop in finite-sized slitlike nanopores.     

Effect of specific adsorbed anions on the electrode kinetics of the V(III)/V(II) and Eu(III)/Eu(II) couples

Electrochemical kinetic parameters of the V(III)/V(II) and Eu(III)/Eu(II) couples in sulfuric, perchloric, hydrochloric, and hydrobromic acids were measured by potentiostatic and double pulse galvanostatic methods. The ₂ potentials in these solutions were calculated from electrocapillary measurements and the effect of the ₂ potentials on the electrode kinetics was discussed. The kinetic data after the Frumkin correction was applied show a very good agreement in H₂SO₄, HClO₄, and HCl solutions, if we assume that the non-complexed ion, which is partially supplied by the dissociation of complex ions, participates in the electrode reaction. The corrected rate constants in the bromide solution were about ten times larger than those to be expected from the ₂ potentials in the case of the V(III)/V(II) couple and a small acceleration effect was observed for the Eu(III)/Eu(II) couple. The greater reaction rate in the bromide solution is explained by the bridging effect.