Enzymes are nature's catalyst of choice for the highly selective and efficient coupling of carbohydrates. Enzymatic sugar coupling is a competitive technology for industrial glycosylation reactions, since chemical synthetic routes require extensive use of laborious protection group manipulations and often lack regio-and stereoselectivity. The application of Leloir glycosyltransferases has received considerable attention in recent years and offers excellent control over the reactivity and selectivity of glycosylation reactions with unprotected carbohydrates, paving the way for previously inaccessible synthetic routes. The development of nucleotide recycling cascades has allowed for the efficient production and reuse of nucleotide sugar donors in robust one-pot multi-enzyme glycosylation cascades. In this way, large glycans and glycoconjugates with complex stereochemistry can be constructed. With recent advances, LeLoir glycosyltransferases are close to being applied industrially in multi-enzyme, programmable cascade glycosylations.hydroxynitrile lyases catalyzed the enzymatic hydrolysis of the glycoside amygdalin [3]. Moving almost two centuries forward, the largest volumetric biocatalytic industrial process is the application of glucose isomerase for the production of high fructose syrup for food and drink applications, producing fructose from glucose at 10 7 tons per year [4]. The secret of the success of enzymes in the production or treatment of carbohydrates and glycosides is their exquisite stereo-and regioselectivity. The excellent selectivity of enzymes is required due to the diversity of structural features of carbohydrates [5], comprising d-and l-epimers, ring size, anomeric configuration, linkages, branching, and oxidation state(s). Since drug targets often exhibit specificity for all of these structural features, the production process should not contain any side-products to prevent undesired side-effects [6].The challenge in the synthesis of carbohydrates is their wide variety of functionalities and stereochemistry ( Figure 1). (Poly)hydroxyaldehydes containing a terminal aldehyde are referred to as aldoses and (poly)hydroxyketones are defined as ketoses. In aqueous solutions, monosaccharides form equilibrium mixtures of linear open-chain and ring-closed 5-or 6-membered furanoses or pyranoses, respectively. For aldoses, the asymmetric ring forms at C-1. For ketoses, it closes at C-2 as an axial (α) or equatorial (β) hemiacetal or hemiketal, respectively (commonly defined as the anomeric center). A glycosidic linkage is a covalent O-, S-, N-, or C-bond connecting a monosaccharide to another residue resulting in a glycoside, while glucoside is specific for a glucose moiety. The equatorial or axial position of the glycosidic bond is referred to as α-(axial) or β-linkage (equatorial). The number of carbohydrates linked via glycosidic bonds can be subdivided into oligosaccharides with two to ten linked carbohydrates, while polysaccharides (glycans) contain more than ten glycosidic bonds. A glycan either con...
The alkaline catalysts commonly applied to alkoxylation are characterized by a limited spectrum of activity caused by an irreversible termination of the polyether chains. The presented results show that double metal cyanide (DMC) catalysts reduce or eliminate the aforementioned adverse rearrangement of hydroxyl groups. Moreover, DMC catalysts indicate high activity at low concentrations (ppm range), as expressed by high polymerization rates. It was demonstrated that decreased concentrations of DMC catalyst irreversibly influence its reactivity and the dispersity of the obtained products, as exemplified by the production and determination of selected polyoxypropylenediols at different concentrations of the catalyst. Because of their unique advantages, the DMC catalysts are a very attractive alternative to conventional alkaline catalysts for the polyaddition of oxiranes. The phenomenon was discussed and explained by an alteration of reaction rate coefficients at subsequent polyaddition stages.
Double metal cyanide (DMC) catalysts are commonly applied at industrial ring-opening polymerization of the epoxides, being the initial stage of the polyurethanes manufacturing route. This group of catalysts is frequently used in industry, but the knowledge on the molecular nature of their high activity and selectivity is limited to some phenomenological hypotheses based on overall chemical premises. To shine some light on the relation between structural and chemical properties of DMC catalysts and their activity, the complementary X-ray powder diffraction, X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy and X-ray absorption spectroscopy studies were performed. The comprehensive characterization of DMC catalyst synthesized from ZnCl 2 and potassium hexacyanocobaltate(III) solution, in presence of the organic ligand ( t BuOH), confirmed that a significant part of the catalyst material reveals the features of the non-crystalline structure. Extended X-ray absorption fine structure (EXAFS) analysis established that only Zn atoms are the active metallic centers in the DMC catalyst. The coordination around Zn was changed from octahedral in reference material to tetrahedral in catalysts, and Cl atoms were detected near some of the Zn atoms, but no significant amount of oxygen atoms was detected, which agrees with XPS chemical analysis. The performed experimental studies give direct experimental evidence for the model deduced by Zhang et al., and for the calculation performed by Wojdeł et al. Moreover, the generally accepted formula Zn 3 [Co(CN) 6 ] 2 • xZnCl 2 • ytBuOH • zH 2 O describing this catalyst is not valid, because none of the compounds were detected by XRD or EXAFS techniques.Regarding the relation between structural and chemical activity of catalyst, we conclude that for the chemical activity of DMC catalyst not only is the content of Cl very important, but also the fraction of non-crystalline phase, the formation of which is stimulated by ligand. The non-crystalline fraction of catalyst may offer the easier access to the active center with Cl. Results and discussion X-ray diffractionTrizinc bishexacyanocobaltate(III), used as a reference material, has been reported to be dimorphic, cubic (Fm-3 m) and rhombohedral Catalytic centre in double metal cyanide catalysts
In addition to looking for effective drugs and a vaccine, which are necessary to save and protect human health, it is also important to limit, or at least to slow, the spread of coronavirus. One important element in this action is the use of individual protective devices such as filtering facepiece masks. Currently, masks that use a mechanical filter, such as a HEPA (High Efficiency Particulate Air) filter, are often used. In some countries that do not have a well-developed healthcare system or in exceptional situations, there is a real and pressing need to restore filters for reuse. This article presents technical details for a very simple device for sterilization, including of HEPA polymer filters. The results of biological and microscopic tests confirming the effectiveness of the sterilization performed in the device are presented. The compact and portable design of the device also allows its use to disinfect other small surfaces, for example a small fragment of a floor, table, or bed.
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