Effect of oxychlorination treatment on the regeneration of Pt–Sn/Al2O3 catalyst for propane dehydrogenation

Research on Chemical Intermediates - Propane dehydrogenation and regeneration of Pt–Sn/θ-Al2O3 catalysts was evaluated with oxychlorination treatment. It was observed that the catalytic...     

Microfluidic self-assembly of insulin monomers into amyloid fibrils on a solid surface

We report the self-assembly of insulin monomers into amyloid fibrils within microchannels. To demonstrate the microfluidic amyloid formation and fibril growth on a solid surface, we seeded the internal surfaces of the microchannels with insulin monomers via N-hydroxysuccinimide ester activation and continuously flushed a fresh insulin solution through the microchannels. According to our analysis using optical and fluorescence microscopy, insulin amyloid preferentially formed in the center of the microchannels and, after reaching a certain density, spread to the side walls of the microchannels. By using ex situ atomic force microscopy, we observed the growth of amyloid fibrils inside the microchannels, which occurred at a much higher rate than that in bulk systems. After 12 h of incubation, insulin formed amyloid spherulites having "Maltese cross" extinction patterns within the microchannels according to the polarized microscopic analysis. Microfluidic amyloid formation enabled low consumption of reagents, reduction of incubation time, and simultaneous observation of amyloid formation under different conditions. This work will contribute to the rapid analysis of amyloid formation associated with many protein misfolding diseases.     

Alkali metal ion catalysis and inhibition in nucleophilic displacement reactions at phosphorus centers: ethyl and methyl paraoxon and ethyl and methyl parathion

We report on the ethanolysis of the P=O and P=S compounds ethyl and methyl paraoxon (1a and 1b) and ethyl and methyl parathion (2a and 2b). Plots of spectrophotometrically measured rate constants, kobsd versus [MOEt], the alkali ethoxide concentration, show distinct upward and downward curvatures, pointing to the importance of ion-pairing phenomena and a differential reactivity of free ions and ion pairs. Three types of reactivity and selectivity patterns have been discerned: (1) For the P=O compounds 1a and 1b, LiOEt > NaOEt > KOEt > EtO-; (2) for the P=S compound 2a, KOEt > EtO- > NaOEt > LiOEt; (3) for P=S, 2b, 18C6-crown-complexed KOEt > KOEt = EtO(-) > NaOEt > LiOEt. These selectivity patterns are characteristic of both catalysis and inhibition by alkali-metal cations depending on the nature of the electrophilic center, P=O vs P=S, and the metal cation. Ground-state (GS) vs transition-state (TS) stabilization energies shed light on the catalytic and inhibitory tendencies. The unprecedented catalytic behavior of crowned-K(+) for the reaction of 2b is noteworthy. Modeling reveals an extreme steric interaction for the reaction of 2a with crowned-K(+), which is responsible for the absence of catalysis in this system. Overall, P=O exhibits greater reactivity than P=S, increasing from 50- to 60-fold with free EtO(-) and up to 2000-fold with LiOEt, reflecting an intrinsic P=O vs P=S reactivity difference (thio effect). The origin of reactivity and selectivity differences in these systems is discussed on the basis of competing electrostatic effects and solvational requirements as function of anionic electric field strength and cation size (Eisenman's theory).     

Origin of stereoselectivity in the reduction of a planar oxacarbenium

The Kishi reduction of a planar oxacarbenium was investigated theoretically. The high diastereoselectivity for hydride transfer to the oxacarbenium intermediate is attributed to the conformation of the transition state that places the allyl side chain in an equatorial position in the major transition state and axial position in the minor. The minor transition state is destabilized by a 1,3-diaxial strain between the attacking hydride and the syn allyl side chain.     

Aminolysis of 4-nitrophenyl phenyl carbonate and thionocarbonate: effects of amine nature and modification of electrophilic center from C[double bond]O to C[double bond]S on reactivity and mechanism

A kinetic study is reported for the reactions of 4-nitrophenyl phenyl carbonate (5) and thionocarbonate (6) with a series of alicyclic secondary amines in 80 mol% H(2)O-20 mol% DMSO at 25.0 +/- 0.1 degrees C. The plots of k(obsd) vs. amine concentration are linear for the reactions of 5. On the contrary, the plots for the corresponding reactions of 6 curve upward as a function of increasing amine concentration, indicating that the reactions proceed through two intermediates (i.e., a zwitterionic tetrahedral intermediate T(+/-) and its deprotonated form T(-)). The Br?nsted-type plot for 5 the reactions of with secondary amines exhibits a downward curvature, i.e., the slope decreases from 0.98 to 0.26 as the pK(a) of the conjugate acid of amines increases, implying that the reactions proceed through T(+/-) with a change in the rate-determining step (RDS). The k(N) values are larger for the reactions of with secondary amines than for those with primary amines of similar basicity. Dissection of k(N) values for the reactions of 5 into the microscopic rate constants (i.e., k(1) and k(2)/k(-1) ratio) has revealed that k(1) is larger for the reactions with secondary amines than for those with isobasic primary amines, while the k(2)/k(-1) ratio is nearly identical. On the other hand, for reactions of 6, secondary amines exhibit larger k(1) values but smaller k(2)/k(-1) ratios than primary amines. The current study has shown that the reactivity and reaction mechanism are strongly influenced by the nature of amines (primary vs. secondary amines) and electrophilic centers (C[double bond]O vs. C[double bond]S).     

Evaluation of Enzyme Mixtures in Releasing Fermentable Sugars from Pre-pulping Extracts of Mixed Northeast Hardwoods

One near-term option to developing a forest product biorefinery is to derive pre-pulping extract from incoming wood chips before the main pulping step. The release of monomer sugars from a xylan-rich extract, creating a fermentable substrate is a prerequisite for utilization of pre-pulping extract for production of ethanol or other value-added products. This study examined the individual and mixture efficiencies of two hemicellulolytic microbial enzymes and two xylanase preparations in catalyzing degradation of green liquor (GL) and hot water (HW) pre-pulping extracts. The effects of four commercial enzyme preparations were determined by assessing yields of xylose + galactose + mannose (xmg) obtained under different reaction conditions. Of the individual enzyme preparations tested, a sample NS 50012 was superior to the other enzyme preparations in releasing xmg under conditions optimized for separate hydrolysis and fermentation and for simultaneous saccharification and fermentation. In comparison to pre-pulping extracts treated with HW, extract treated with GL was found to inhibit the action of all tested enzymes. This inhibition may be related to higher salt and lignin phenol in the GL extract. On both types of extracts, the mixture constituted by NS 50012 and NS 50030 provided the highest yield of hemicellulose conversion at 55 °C and pH 5.5. The generated digestibility thus signified that the synergistic effectiveness in xylan + galactan + mannan (XMG) hydrolysis between NS 50012 (from Aspergillus aculeatus) and NS 50030 (from Aspergillus oryzae) is the result of an interaction mechanism involving different XMG-degrading enzyme activities in the two enzyme preparations.     

Interleukin-1�� promotes the expression of monocyte chemoattractant protein-1 in human aorta smooth muscle cells via multiple signaling pathways

Monocyte chemoattractant protein-1 (MCP1) plays a key role in monocyte/macrophage infiltration to the sub-endothelial space of the blood vessel wall, which is a critical initial step in atherosclerosis. In this study, we examined the intracellular signaling pathway of IL-1β-induced MCP1 expression using various chemical inhibitors. The pretreatment of a phosphatidylcholine (PC)-specific PLC (PC-PLC) inhibitor (D609), PKC inhibitors, or an NF-κB inhibitor completely suppressed the IL-1β-induced MCP1 expression through blocking NF-κB translocation to the nucleus. Pretreatment with inhibitors of tyrosine kinase or PLD partially suppressed MCP1 expression and failed to block nuclear NF-κB translocation. These results suggest that IL-1β induces MCP1 expression through activation of NF-κB via the PC-PLC/PKC signaling pathway.     

Effects on the Reactivity by Changing the Electrophilic Center from CO to CS: Contrasting Reactivity of Hydroxide,p‐Chlorophenoxide,and Butan‐2,3‐dione Monoximate in DMSO/H2O Mixtures

Second‐order rate constants have been measured spectrophotometrically for the reactions of O‐p‐nitrophenyl thionobenzoate ( 1 , PNPTB) with HO^?, butan‐2,3‐dione monoximate (Ox^?, α‐nucleophile), and p‐chlorophenoxide (p‐ClPhO^?, normal nucleophile) in DMSO/H₂O of varying mixtures at (25.0±0.1) °C. Reactivity of these nucleophiles significantly increases with increasing DMSO content. HO^? is less reactive than p‐ClPhO^? toward 1 up to 70 mol % DMSO although HO^? is over six pK_a units more basic in these media. Ox^? is more reactive than p‐ClPhO^? in all media studied, indicating that the α‐effect is in effect. The magnitude of the α‐effect (i.e., k/k_p) increases with the DMSO content up to 50 mol % DMSO and decreases beyond that point. However, the dependency of the α‐effect profile on the solvent for reactions of 1 contrasts to that reported previously for the corresponding reactions of p‐nitrophenyl benzoate ( 2 , PNPB); reactions of 1 result in much smaller α‐effects than those of 2 . Breakdown of the α‐effect into ground‐state (GS) and transition‐state (TS) effects shows that the GS effect is not responsible for the α‐effect across the solvent mixtures. The role of the solvent has been discussed on the basis of the bell‐shaped α‐effect profiles found in the current study as well as in our previous studies, that is, a GS effect in the H₂O‐rich region through H‐bonding interactions and a TS effect in the DMSO‐rich media through mutual polarizability interactions.     

Quantum mechanical investigation of the effect of catalyst fluorination in the intermolecular asymmetric Stetter reaction

The asymmetric intermolecular Stetter reaction was investigated using the B3LYP and M06-2X functionals. Fluorination of a triazolium bicyclic catalyst had been found to significantly influence reaction yields and enantiomeric ratios. Computations indicate that the improved reactivity of the fluorinated catalyst is due to better electrostatic interactions between the nitroalkene and catalyst. Computational investigations of preferred conformations of the ground state catalyst and acyl anion equivalent, and the transition structures leading to both enantiomers of the products, are reported.     

Plastoquinones from Sargassum yezoense; chemical structures and effects on the activation of peroxisome proliferator-activated receptor gamma

Four new plastoquinones, together with two known compounds, sargahydroquinoic acid and sargaquinoic acid, were isolated from the brown alga, Sargassum yezoense collected from the eastern coast of Korea. The structures of these compounds were elucidated based on spectroscopic analyses including NMR and MS. Their structures designated as meroterphenol A (1), B (2), C (3) and D (4) were characterized by a 6-methyl-1,4-benzohydroquinone moiety with an oxygenated diterpenoic acid chain. Meroterphenols A-D showed potent activation effects on peroxisome proliferator-activated receptor gamma (PPARγ).