Christian V. Stevens

Bio: Christian V. Stevens is an academic researcher from Ghent University. The author has contributed to research in topics: Ionic liquid & Bicyclic molecule. The author has an hindex of 45, co-authored 467 publications receiving 11742 citations. Previous affiliations of Christian V. Stevens include Katholieke Universiteit Leuven & University of Minnesota.

Synthesis and Biological Evaluation of Bolaamphiphilic Sophorolipids

Abstract: New synthetic pathways are proposed for the synthesis of a new set of bolaamphiphilic derivatives starting from microbiologically produced sophorolipids. A total set of 43 new derivatives was synthesized via reductive amination of a previously synthesized sophorolipid aldehyde with diamines and primary amines. The new derivatives were evaluated for their antimicrobial activity against Gram-negative and Gram-positive bacteria. Minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values were determined for the active compounds. Transfection efficiencies were also evaluated for some of the deprotected derivatives via the assessment of their capacity to transfect three different eukaryotic cell lines in vitro. Finally, the self-assembly properties were evaluated for the deprotected derivatives. Antimicrobial activities were mostly observed for the peracetylated mono- or dicationic bolaamphiphiles, and only the deprotected monocationic bolaamphiphile with an octadecyl chain on th...

A New Benzotriazole‐Mediated Stereoflexible Gateway to Hetero‐2,5‐diketopiperazines

Abstract: Open chain Cbz-L-aa(1)-L-Pro-Bt (Bt=benzotriazole) sequences were converted into either the corresponding trans- or cis-fused 2,5-diketopiperazines (DKPs) depending on the reaction conditions. Thermodynamic tandem cyclization/epimerization afforded selectively the corresponding trans-DKPs (69-75%). Complementarily, tandem deprotection/cyclization led to the cis-DKPs (65-72%). A representative set of proline-containing cis- and trans-DKPs has been prepared. A mechanistic investigation, based on chiral HPLC, kinetics, and computational studies enabled a rationalization of the results.

Increasing Uniformity of Biosurfactant Production in Starmerella bombicola via the Expression of Chimeric Cytochrome P450s

Abstract: Sophorolipids are one of the best known microbial biosurfactants and are produced by several yeast species. The best studied producer is Starmerella bombicola, a non-pathogenic yeast associated in nature with bumblebees. Sophorolipids are built up of the rare disaccharide sophorose, which is attached to a fatty acid through a glyosidic bound. Sophorolipids produced by S. bombicola mainly contain oleic acid as the incorporated hydrophobic group. Other chain lengths can, to a certain content, be incorporated by feeding the yeast with substrates of alternative chain lengths. However, the efficiency for such substrates is low as compared to the preferred C18 chain length and defined by the substrate specificity of the first enzymatic step in sophorolipid biosynthesis, i.e., the cytochrome P450 enzyme CYP52M1. To increase product uniformity and diversity at the same time, a new strain of S. bombicola was developed that produces sophorolipids with a palmitic acid acyl chain. This was achieved by heterologous expression of the cytochrome P450 cyp1 gene of Ustilago maydis and feeding with palmitic acid. Optimization of the production was done by protein and process engineering.

Sophorolipid Amine Oxide Production by a Combination of Fermentation Scale-up and Chemical Modification

Abstract: Production scale-up of high-purity diacetylated C18:1 sophorolipid lactone was demonstrated from lab to pilot scale with the Starmerella bombicola lactone esterase overexpression strain (oe sble) as production organism. The 150 L fermentation using oleic acid and yeast extract, characterized by a titer of 199 g/L and a volumetric productivity of 0.9 g/L·h, was most successful in obtaining a highly pure (>98%) and uniform (96% C18:1 SL lactone) sophorolipid product suitable for chemical derivatization. The fermentation product was subsequently modified to produce sophorolipid amine oxides, which cannot be produced enzymatically. First, the fermentation product was transformed into an intermediate sophorolipid aldehyde via methanolysis and protection of the sugar head through acetylation and ozonolysis. This aldehyde intermediate was then used for the synthesis of the sophorolipid amine oxides via reductive amination, oxidation, and deprotection of the sugar head. The total yield of this synthetic pathway a...

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Production of first and second generation biofuels: A comprehensive review

Abstract: Sustainable economic and industrial growth requires safe, sustainable resources of energy. For the future re-arrangement of a sustainable economy to biological raw materials, completely new approaches in research and development, production, and economy are necessary. The ‘first-generation’ biofuels appear unsustainable because of the potential stress that their production places on food commodities. For organic chemicals and materials these needs to follow a biorefinery model under environmentally sustainable conditions. Where these operate at present, their product range is largely limited to simple materials (i.e. cellulose, ethanol, and biofuels). Second generation biorefineries need to build on the need for sustainable chemical products through modern and proven green chemical technologies such as bioprocessing including pyrolysis, Fisher Tropsch, and other catalytic processes in order to make more complex molecules and materials on which a future sustainable society will be based. This review focus on cost effective technologies and the processes to convert biomass into useful liquid biofuels and bioproducts, with particular focus on some biorefinery concepts based on different feedstocks aiming at the integral utilization of these feedstocks for the production of value added chemicals.

Chitosan chemistry and pharmaceutical perspectives.

Abstract: Department of Pharmaceutics, National Institute of Pharmaceutical Education and Research (NIPER), Sector 67, S. A. S. Nagar,Mohali, Punjab-160 062, India, Institute of Biochemistry, Faculty of Medicine, Polytechnic University, Via Ranieri 67, IT-60100 Ancona, Italy,Green Biotechnology Research Group, The Special Division for Human Life Technology, National Institute of Advanced Industrial Science andTechnology, 1-8-31 Midorigaoka, Ikeda, Osaka-563-8577, Japan, and Department of Medicinal Chemistry & Natural Products,The Hebrew University of Jerusalem, School of Pharmacy-Faculty of Medicine, Jerusalem 91120, IsraelReceived March 2, 2004