查看更多>>摘要：In this paper, a reusable heterogeneous catalyst of papain was prepared and used to catalyze the polymerization for oligo-glutamate. In silico, the 9,9-bis(2,3-epoxypropyl) fluorenyl group (DDI) carried on polystyrene beads (PS-PEG-DDI) showed site-specific binding for sites which are far away the active site of papain. The immobilization of papain on PS-PEG-DDI reached the optimal value of 126 +/- 2.5 mg/g beads and 1726.2 +/- 34 U/g beads at the papain/beads ratio of 1:5 in phosphate buffer (pH 8.0, 200 mM) at 45 degrees C for 4 h. The storage stability, pH stability, thermal stability, solvent tolerance and resistance to metal ions of papain were enhanced by the immobilization. The oligomerization of L-glutamic acid diethyl ester hydrochloride via PS-PEG-DDI immobilized papain in phosphate buffer (pH 8, 200 mM) at 45 degrees C demonstrated the yield of oligo(gamma-ethyl-L-glutamate) reached 78.6 +/- 1.2% under the conditions of 2 U/ml of papain, 60 mg/ml L-glutamic acid diethyl ester hydrochloride for 4 h. The immobilization increased the yield by about 40%. The analysis by mass spectrometry (MS) and H-1 NMR showed an average degree of polymerization (DPavg) of product was approximately 7-8, identical to that produced using free papain. The biocatalytic activity of the PS-PEG-DDI immobilized papain remained stable after 5 repeated uses, all giving a yield of over 70%. The reduced activation energy of the reaction catalyzed by the PS-PEG-DDI immobilized papain suggests a more favorable active conformation was probably achieved following immobilization.
查看更多>>摘要：Decatungstate (DT) is very potential photo-catalyst for the dioxygens (O-2)-based selective oxidation but still needs to be improved in photo-catalytic efficiency and regeneration. This paper discloses that Au nanoparticles (NPs)-loaded DT (Au/DT) is conveniently synthesized via the reduction of chloroauric acids introduced in the synthesis of DT. A series of characterizations and quenching tests support that the doped Au NPs can remarkably improve the visible-light- harvesting and photo-excited quantum efficiencies of DT, and as the excellent electronic transport carriers, they also plays an additional role in converting O-2 into the active superoxide (center dot O-2(-)) anion radical. As a result, the suggested Au/DT exhibits a significantly enhanced photo-catalytic efficiency for the visible-light-triggered selective oxidation of inert hydrocarbons under 25-28 degrees C and 1 atm pure O-2 atmosphere. Under optimized conditions, the best 1%Au/DT achieves 64.2% conversion and 93% acetophenone selectivity in the photo-oxidation of ethylbenzene and it has an outstanding regeneration ability.
NSTL
Elsevier