1,721,052 research outputs found
Enantiomeric resolution of DNS.amino acids by ligand exchange chromatography: Comparison of different chiral amino acid amides as additives to the mobile phase
No full textA study developing enantiomeric separations by metal chelate additives to the mobile phase in reversed-phase liquid chromatography is reported. In particular the use of Cu(II) complexes of L-prolinamide (L-ProNH2) and L-valinamide (L-ValNH2) is examined and discussed. Interestingly, for a series of DNS-amino acids these selectors show higher enantioselectivity than that obtained with the corresponding nonderivatized amino acid–Cu(II) complexe
Renewable, Sustainable, and Natural Lignocellulosic Carriers for Lipase Immobilization: A Review
Full text linkIt is well-known that enzymes are molecules particularly susceptible to pH and temperature variations. Immobilization techniques may overcome this weakness besides improving the reusability of the biocatalysts. Given the strong push toward a circular economy, the use of natural lignocellulosic wastes as supports for enzyme immobilization has been increasingly attractive in recent years. This fact is mainly due to their high availability, low costs, and the possibility of reducing the environmental impact that can occur when they are improperly stored. In addition, they have physical and chemical characteristics suitable for enzyme immobilization (large surface area, high rigidity, porosity, reactive functional groups, etc.).
This review aims to guide readers and provide them with the tools necessary to select the most suitable methodology for lipase immobilization on lignocellulosic wastes. The importance and the characteristics of an increasingly interesting enzyme, such as lipase, and the advantages and disadvantages of the different immobilization methods will be discussed. The various kinds of lignocellulosic wastes and the processing required to make them suitable as carriers will be also reported
Application of immobilized enzyme reactor in on-line high performance liquid chromatography: A review
No full textThis review summarizes all the research efforts in the last decade (1994-2003) that have been spent to the various application of immobilized enzyme reactor (IMER) in on-line high performance liquid chromatography (HPLC). All immobilization procedures including supports, kind of assembly into chromatographic system and methods are described. The effect of immobilization on enzymatic properties and stability of biocatalysts is considered. A brief survey of the main applications of IMER both as pre-column, post-column or column in the chemical, pharmaceutical, clinical and commodities fields is also reported. (c) 2005 Elsevier B.V. All rights reserved
Phenols removal by immobilized tyrosinase reactor in on-line high performance liquid chromatography
No full textThe development of an immobilized enzyme reactor (IMER) based on tyrosinase immobilized on aminopropyl-controlled pore glass (AP-CPG) for the removal of phenols from model aqueous solutions was reported. To elucidate the influence of the substrate nature, the apparent (V'(max), K'(m)) and the inherent (V-max, K-m) Michaelis-Menten constants were determined by Lineweaver-Burk method and the external diffusional contributions on measured enzyme activities were removed by a graphical method. The dephenolization process was realized by recycling the phenol solutions through the bioreactor connected to a chitosan trap in order to remove the colored quinone-type products of the tyrosinase reactions. The results indicated that a complete removal of phenol derivatives in the range of 150-300 min, with the exception of 60% removal for phenol reached in 400 min, was obtained. The observed sequence: cresol > 4-methylcathecol > catechol > 4-Cl-phenol >> phenol was in accordance to the V'(max)/K'(m) values. (c) 2006 Elsevier B.V. All rights reserved
Spent grain as a sustainable and low-cost carrier for laccase immobilization
Full text linkSpent grain is promising lignocellulosic by-product support for laccase immobilization. The waste digestion with two different approaches (HCl/NaOH and H2SO4/NaOH) was performed. Different procedures (soaking and dropping), based on chemical and physical reactions, were also used to obtain the highest immobilized activity. Results showed that H2SO4/NaOH digestion guaranteed an immobilized activity five times higher than HCl/NaOH digestion. The best immobilization conditions with physical dropping procedure resulted in the highest immobilized activity on digested spent grain (2500 U/Kg). Good reusability (42% of activity retained after four cycles), and lower catalytic efficiency (Vmax/Km) of 0.053 min−1 than free laccase (0.14 min−1) with ABTS as substrate, were also obtained. Besides, when 20 mg of biocatalyst (0.02 U) were tested for syringic acid removal, complete oxidation of the phenol was achieved in just 4 h
A study on the separation of synthetic pyrethroid stereisomer by HPLC
No full textEnantiomer separation of synthetic pyrethroids was carried out on different chiral HPLC columns. In particular, the study provided useful information on the direct resolution of pyrethroids with and without alpha-ciano groups. The study indicated that polymeric chiral stationary phases based on cellulose derivatives are the most appropriate for the stereoisomer separation of cis-Biphenthrin, Resmethrin and (1R)-Phenothrin, whereas multiple-interaction CSPs, like (S)-1-(alpha-naphthyl)-ethylamine/(S)-tert-leucine, are more selective for Cyfluthrin
"Catalytic behaviour of ornithine carbamyl transferase from different mammalian sources"
No full textHPLC study of tyrosinase inhibition by thiopronine
No full textThiopronine (N-2-mercaptopropionyl-glycine, NMPG) inhibits the o-dihydroxy-phenolase activities of mushroom tyrosinase. When d,l-3-4-dihydroxyphenylalanine (DOPA) is employed as substrate, the inhibition was found to be a competitive-type with K(i) of 0.95 micro m. We found in addition that thiopronine interacts with the enzymatic generated product (o-quinone) to form a colourless conjugate compound causing an apparent inhibition. These data suggest that thiopronine inhibits mushroom tyrosinase activity in two ways: (1) by forming an adduct with dopaquinone; and (2) by direct interaction with the enzyme probably towards the copper (II) present in the active site or cysteine-rich domains. This finding was indicated by the presence of a lag period prior to the attainment of an inhibited steady-state rate. Both lag period and steady-state rate were dependent on thiopronine and substrate concentrations. An increase of thiopronine concentration causes longer lag periods as well as a concomitant decrease in the tyrosinase activity. The presence of an excess of copper (II) reverses the inhibition exerted by thiopronin
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