Karl Hult

Bio: Karl Hult is an academic researcher from Royal Institute of Technology. The author has contributed to research in topics: Lipase & Candida antarctica. The author has an hindex of 58, co-authored 205 publications receiving 10240 citations. Previous affiliations of Karl Hult include Swedish University of Agricultural Sciences & National Veterinary Institute.

Crystallographic and molecular-modeling studies of lipase B from Candida antarctica reveal a stereospecificity pocket for secondary alcohols.

Abstract: Many lipases are potent catalysts of stereoselective reactions and are therefore of interest for use in chemical synthesis. The crystal structures of lipases show a large variation in the shapes of their active site environments that may explain the large variation in substrate specificity of these enzymes. We have determined the three-dimensional structure of Candida antarctica lipase B (CALB) cocrystallized with the detergent Tween 80. In another crystal form, the structure of the enzyme in complex with a covalently bound phosphonate inhibitor has been determined. In both structures, the active site is exposed to the external solvent. The potential lid-forming helix alpha 5 in CALB is well-ordered in the Tween 80 structure and disordered in the inhibitor complex. The tetrahedral intermediates of two chiral substrates have been modeled on the basis of available structural and biochemical information. The results of this study provide a structural explanation for the high stereoselectivity of CALB toward many secondary alcohols.

Toxicokinetics of ochratoxin A in several species and its plasma-binding properties.

Abstract: The toxicokinetic profile of ochratoxin A was studied after the oral or intravenous administration of 50 ng/g b.w. to fish, quail, mouse, rat and monkey. The elimination half-life varied from 0.68 h after oral administration to fish, up to 840 h after intravenous administration to monkey. The distribution volume ranged from 57 ml/kg in fish to 1500 ml/kg in quail. The plasma clearance was most rapid in quail and fish, 72 and 58 ml/kg.h, respectively, while it was only 0.17 ml/kg.h in monkey. The bioavailability was as low as 1.6% in fish but as high as 97% in mouse. The binding abilities of ochratoxin A to plasma proteins were also studied. From these data we calculated the free fraction of toxin in plasma, which we found to be less than 0.2% in all species investigated (including man) except fish. A similar but smaller investigation on the toxicokinetics and binding properties of ochratoxin B was also performed. Ochratoxin B was more readily eliminated and had a lower affinity for plasma proteins, which partly may explain its lower toxicity.

Carbon-Carbon Bonds by Hydrolytic Enzymes

Abstract: Enzymes are efficient catalysts in synthetic chemistry, and their catalytic activity with unnatural substrates in organic reaction media is an area attracting much attention. Protein engineering has opened the possibility to change the reaction specificity of enzymes and allow for new reactions to take place in their active sites. We have used this strategy on the well-studied active-site scaffold offered by the serine hydrolase Candida antarctica lipase B (CALB, EC 3.1.1.3) to achieve catalytic activity for aldol reactions. The catalytic reaction was studied in detail by means of quantum chemical calculations in model systems. The predictions from the quantum chemical calculations were then challenged by experiments. Consequently, Ser105 in CALB was targeted by site-directed mutagenesis to create enzyme variants lacking the nucleophilic feature of the active site. The experiments clearly showed an increased reaction rate when the aldol reaction was catalyzed by the mutant enzymes as compared to the wild-type lipase. We expect that the new catalytic activity, harbored in the stable protein scaffold of the lipase, will allow aldol additions of substrates, which cannot be reached by traditional aldolases.

Thiol–Ene Click Chemistry

Abstract: Following Sharpless' visionary characterization of several idealized reactions as click reactions, the materials science and synthetic chemistry communities have pursued numerous routes toward the identification and implementation of these click reactions. Herein, we review the radical-mediated thiol-ene reaction as one such click reaction. This reaction has all the desirable features of a click reaction, being highly efficient, simple to execute with no side products and proceeding rapidly to high yield. Further, the thiol-ene reaction is most frequently photoinitiated, particularly for photopolymerizations resulting in highly uniform polymer networks, promoting unique capabilities related to spatial and temporal control of the click reaction. The reaction mechanism and its implementation in various synthetic methodologies, biofunctionalization, surface and polymer modification, and polymerization are all reviewed.

Engineering the third wave of biocatalysis

Abstract: Over the past ten years, scientific and technological advances have established biocatalysis as a practical and environmentally friendly alternative to traditional metallo- and organocatalysis in chemical synthesis, both in the laboratory and on an industrial scale. Key advances in DNA sequencing and gene synthesis are at the base of tremendous progress in tailoring biocatalysts by protein engineering and design, and the ability to reorganize enzymes into new biosynthetic pathways. To highlight these achievements, here we discuss applications of protein-engineered biocatalysts ranging from commodity chemicals to advanced pharmaceutical intermediates that use enzyme catalysis as a key step.

Biocatalysis in ionic liquids

Abstract: Roger Sheldon (1942) received a PhD in organic chemistry from the University of Leicester (UK) in 1967. This was followed by post-doctoral studies with Prof. Jay Kochi in the U.S. From 1969 to 1980 he was with Shell Research in Amsterdam and from 1980 to 1990 he was R&D Director of DSM Andeno. In 1991 he moved to his present position as Professor of organic chemistry and catalysis at the Delft University of Technology (The Netherlands). His primary research interests are in the application of catalytic methodologies—homogeneous, heterogeneous and enzymatic—in organic synthesis, particularly in relation to fine chemicals production. He developed the concepts of E factors and atom utilization for assessing the environmental impact of chemical processes.