Abstract
Several important enzymatic reactions occurring in nature, such as, e.g., the digestion of fat, proceed only at the interface of two immiscible phases. Typically, these systems consist of an organic substrate, dispersed in an aqueous continuous phase, with a specialized enzyme capable of working at the interface. For adopting such a system for organic synthesis, a stable heterophase system with a large interfacial area is required. These prerequisites can be found in so-called miniemulsions. Such liquid-liquid heterophase systems feature droplets with sizes smaller than 500 nm, and more importantly, these emulsions do not suffer from Ostwald ripening, as conventional emulsions do. Consequently, the droplets show long-term stability, even throughout reactions conducted in the droplets. In this review, we will briefly discuss the physicochemical background of miniemulsions, provide a comprehensive overview of the enzymatically catalyzed reactions conducted in miniemulsions and, as data are available, to compare the most important features to conventional systems, as reverse microemulsions, (macro)emulsions and solvent-based systems.
Highlights
The importance of biocatalytic processes and reactions for organic synthesis and the pharmaceutical, food and cosmetics industry has been constantly growing during the last few years [1,2]
The natural environment of enzymes is water and their preferred “natural” operation temperature is the temperature of the respective organism, enzymes are very tolerant against temperature and organic solvents, especially, when the tertiary structure of enzymes is stabilized by immobilization on a solid substrate
We will conclude with some examples of miniemulsion-prepared nanostructures, which are responsive to the presence of an enzyme
Summary
The importance of biocatalytic processes and reactions for organic synthesis and the pharmaceutical, food and cosmetics industry has been constantly growing during the last few years [1,2]. The natural environment of enzymes is water and their preferred “natural” operation temperature is the temperature of the respective organism (typically 20–40 °C), enzymes are very tolerant against temperature and organic solvents, especially, when the tertiary structure of enzymes is stabilized by immobilization on a solid substrate. Such immobilized enzymes have the advantage of easy recovery from a product mixture, e.g., in an industrial process. Reactions between the organic phase and reactants dissolved in water may proceed at the interface or may be facilitated by phase transfer catalysts. We will conclude with some examples of miniemulsion-prepared nanostructures, which are responsive to the presence of an enzyme
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