Flüssig/Flüssig-Extraktion: Einsatzgebiete und Lösungsmittel-Auswahl

Liquid/liquid extraction: Applications and choice of solvent . The significance of liquid/liquid extraction has been steadily increasing in recent years as more and more stringent demands are made on the purity, availability, and environmental safety of chemical products. The use and success of this separation process are critically dependent upon the choice of the right extraction agent. Whereas solvent choice was previously mainly empirical, it is now possible to establish the suitability of a given solvent with the aid of molecular-thermodynamic data. This is demonstrated for the extraction of aromatic compounds. The article closes with an account of the formation and stability of emulsions.     

Enzymatic esterification of glycerol II. Lipase-catalyzed synthesis of regioisomerically pure 1(3)-rac-monoacylglycerols

Regioisomerically pure 1(3)-rac-monoacylglycerols are conveniently prepared in high yields (>75%) and in multigram quantities by enzymatic esterification of glycerol in the presence of various lipases(Chromobacterium viscosum, Rhizopus delemar, Rhizomucor miehei) with a variety of different acyl donors, such as free fatty acids, fatty acid alkyl esters, vinyl esters and triacylglycerols, as well as natural fats and oils. All reactions are carried out in aprotic organic solvents with low water content, namelyn-hexane, diethyl ether, tBuOMe or mixtures of these solvents. Essential for the success of these transformations were the following two factors. First, the creation of an artificial interphase between the solvent-immiscible hydrophilic glycerol and the hydrophobic reaction medium by its adsorption onto a solid support. Second, a facile system for the separation of the desired monoacylglycerol from the reaction mixture, coupled with the continuous recycling of acyl donor and undesirable by-products.     

Mass spectrometric glycan rearrangements

Mass spectrometric rearrangement reactions have been reported for a large variety of compounds such as peptides, lipids, and carbohydrates. In the case of carbohydrates this phenomenon has been described as internal residue loss. Resulting fragment ions may be misinterpreted as fragments arising from conventional glycosidic bond cleavages, which may result in incorrect structural assignment. Therefore, awareness of the occurrence of glycan rearrangements is important for avoiding misinterpretation of tandem mass spectra. In this review mass spectrometric rearrangements of both derivatized and underivatized (native) oligosaccharide structures are discussed. Similar phenomena have been reported for glycopeptides, labeled glycan structures and other biomolecules containing a carbohydrate part. Rearrangements in oligosaccharides and glycoconjugates have been observed with different types of mass spectrometers. Most of the observed carbohydrate rearrangement reactions appear to be linked to the presence of a proton. Hence, tandem mass spectrometric analysis of alkali adducts or deprotonated ions often prevents rearrangement reactions, while they may happen with high efficacy with protonated glycoconjugates.     

Structural glycomics using hydrophilic interaction chromatography (HILIC) with mass spectrometry

Hydrophilic interaction chromatography (HILIC) with mass spectrometry is a versatile technique for structural glycomics. Glycans are retained by hydrogen bonding, ionic interactions, and dipole-dipole interactions. Glycopeptides as well as glycans with various modifications and reducing-end labels can be efficiently separated, which often results in the resolution of isobaric species. Chromatography is usually performed with solvent mixtures of organic modifier (often acetonitrile) and volatile (acidic) buffer which are suitable for online-electrospray ionization-mass spectrometry. When performed at the nano-scale, this results in a detection limit for oligosaccharides of approximately 1 femtomol. Alternatively, glycans may be analyzed by offline-MALDI-MS(/MS) in both negative-ion mode and positive-ion mode, which allows the registration of informative fragment ion spectra from deprotonated species and sodium adducts, respectively. (c) 2009 Wiley Periodicals, Inc., Mass Spec Rev 28:192-206, 2009.     

Immunoglobulin 1 (IgG1) Fc-glycosylation profiling of anti-citrullinated peptide antibodies from human serum

In several autoimmune disorders, including rheumatoid arthritis (RA), autoantibodies are thought to be the driving force of pathogenicity. Glycosylation of the Fc-part of human Igs is known to modulate biological activity. Hitherto, glycosylation of human IgG-Fc has been analyzed predominantly at the level of total serum IgG, revealing reduced galactosylation in RA. Given the pathogenic relevance of autoantibodies in RA, we wished, in the present study, to address the question whether distinct Fc-glycosylation features are observable at the level of antigen-specific IgG subpopulations. For this purpose, we have developed a method for the microscale purification and Fc-glycosylation analysis of anti-citrullinated peptide antibodies (ACPA). ACPA represent a group of autoantibodies that occur with unique specificity in RA patients. Their presence is associated with increased inflammatory disease activity and rapid joint destruction. Results indicate that ACPA of the IgG1 subclass vary considerably from total serum IgG1 with respect to Fc-galactosylation, with galactosylation being higher on ACPA than on serum IgG1 for some patients, while other patients show higher galactosylation on serum IgG1 than on ACPA. Using this method, studies can be performed on the biological and clinical relevance of ACPA glycosylation within RA patient cohorts.     

Mining business process variants: Challenges, scenarios, algorithms

During the last years a new generation of process-aware information systems has emerged, which enables process model configurations at buildtime as well as process instance changes during runtime. Respective model adaptations result in a large number of model variants that are derived from the same process model, but slightly differ in structure. Generally, such model variants are expensive to configure and maintain. In this paper we address two scenarios for learning from process model adaptations and for discovering a reference model out of which the variants can be configured with minimum efforts. The first one is characterized by a reference process model and a collection of related process variants. The goal is to improve the original reference process model such that it fits better to the variant models. The second scenario comprises a collection of process variants, while the original reference model is unknown; i.e., the goal is to “merge” these variants into a new reference process model. We suggest two algorithms that are applicable in both scenarios, but have their pros and cons. We provide a systematic comparison of the two algorithms and further contrast them with conventional process mining techniques. Comparison results indicate good performance of our algorithms and also show that specific techniques are needed for learning from process configurations and adaptations. Finally, we provide results from a case study in automotive industry in which we successfully applied our algorithms.     

Securing Passive Objects in Mobile Ad-Hoc Peer-to-Peer Networks

Security and privacy in mobile ad-hoc peer-to-peer environments are hard to attain, especially when working with passive objects (without own processing power, e.g. RFID tags). This paper introduces a method for integrating such objects into a peer-to-peer environment without infrastructure components while providing a high level of privacy and security for peers interacting with objects. The integration is done by associating public keys to passive objects, which can be used by peers to validate proxies (peers additionally acting on behalf of objects). To overcome the problem of limited storage capacity on small embedded objects, ECC keys are used.