Asymmetric Hydrogenation of α, β-Unsaturated Carboxylic Acid Over Chiral-Modified Palladium Catalyst

The production of optically pure chemicals through enantioselective catalytic reaction plays a key role a variety of industrials (e.g., pharmaceutical, agrochemical). Among several established methods, chiral-modified supported transition metal catalyst has been addressed attentions since past decades due to an environmental concern. Asymmetric hydrogenation of α, β-unsaturated carboxylic acid over Pd catalyst is of particular interest in this area. Nevertheless, the spectroscopic aspect, as well as the kinetic mechanism of such reaction system are still not clearly understood and require further study. In this work, a model catalytic reaction has been investigated from both spectroscopic and kinetic view. To be specific, the hydrogenation of a model aliphatic unsaturated carboxylic acid (2-methyl-2-pentenoic acid) over cinchonidine (chiral modifier) modified Pd/Al2O3 catalyst has been examined. The adsorption behaviors of the acid and the modifier, as well as the acid-modifier interaction complex over metal and oxide surface have been characterized by in-situ attenuated total reflection infrared (ATR-IR) spectroscopy. It has been found that the substrate acids predominantly adsorb as bridged bidentate at the surface. The active intermediate is preferential in a modifier:acid=1:1 ratio, regardless of solvent. The racemic and enantioselective hydrogenation has been carried out in a batch reactor. Kinetic aspects (e.g., H2 pressure, solvent effect, external mass transfer, modifier effect) have been studied. To summary, the reaction exhibits a strong solvent-dependent behavior, with polar solvent provides higher activity. H2 pressure shows 1st reaction order at low regime (\u3c 8 atm), while become pressure-independent when greater than 20 atm. The substrate shows 1st reaction order at low conversion region (\u3c ca. 60%), but increase to high order (1.5-2) afterward. The presence of chiral modifier (cinchonidine) does not affect reaction order for both reactant and modifier. However, it will dramatically decrease the reaction and lead to e.e. value up to ca. 30%, due to the high occupied percentage of surface metal sites, and rather low TOF of these modified sites. Moreover, the accumulation of product in liquid mixture appears to be the reason for increasing reaction order of acid substrate, although this does not affect the final e.e. value

The Study on Structural Design of Buildings on the Slope

The current code for structures mainly focuses on the flat ground buildings, neglecting the particularity of the structure on the slope due to the lack of targeted control indicators and guidance. Several problems that require special considerations in design and some reference solutions were proposed from three aspects, including seismic design, foundation design and supporting structure design

Mapping the tail fiber as the receptor binding protein responsible for differential host specificity of Pseudomonas aeruginosa bacteriophages PaP1 and JG004.

The first step in bacteriophage infection is recognition and binding to the host receptor, which is mediated by the phage receptor binding protein (RBP). Different RBPs can lead to differential host specificity. In many bacteriophages, such as Escherichia coli and Lactococcal phages, RBPs have been identified as the tail fiber or protruding baseplate proteins. However, the tail fiber-dependent host specificity in Pseudomonas aeruginosa phages has not been well studied. This study aimed to identify and investigate the binding specificity of the RBP of P. aeruginosa phages PaP1 and JG004. These two phages share high DNA sequence homology but exhibit different host specificities. A spontaneous mutant phage was isolated and exhibited broader host range compared with the parental phage JG004. Sequencing of its putative tail fiber and baseplate region indicated a single point mutation in ORF84 (a putative tail fiber gene), which resulted in the replacement of a positively charged lysine (K) by an uncharged asparagine (N). We further demonstrated that the replacement of the tail fiber gene (ORF69) of PaP1 with the corresponding gene from phage JG004 resulted in a recombinant phage that displayed altered host specificity. Our study revealed the tail fiber-dependent host specificity in P. aeruginosa phages and provided an effective tool for its alteration. These contributions may have potential value in phage therapy