Reversed micelles of polymeric surfactants in nonpolar organic solvents. A new microheterogeneous medium for enzymatic reactions

Biocatalytic Synthesis Using Self-Assembled Polymeric Nano- and Microreactors

Biocatalysis is increasingly being explored for the sustainable development of green industry. Though enzymes show great industrial potential with their high efficiency, specificity, and selectivity, they suffer from poor usability and stability under abiological conditions. To solve these problems, researchers have fabricated nano- and micro-sized biocatalytic reactors based on the self-assembly of various polymers, leading to highly stable, functional, and reusable biocatalytic systems. This Review highlights recent progress in self-assembled polymeric nano- and microreactors for biocatalytic synthesis, including polymersomes, reverse micelles, polymer emulsions, Pickering emulsions, and static emulsions. We categorize these reactors into monophasic and biphasic systems and discuss their structural characteristics and latest successes with representative examples. We also consider the challenges and potential solutions associated with the future development of this field.

Molecular Features Influencing the Release of Peptides from Amphiphilic Polymeric Reverse Micelles

Efficient and controlled release of peptides bound to polymeric reverse micelle assemblies can be achieved through the cooperative effects of disassembly and disruption of charge-charge interactions. Through the examination of various peptides and polymer architectures, we have identified the factors that affect the release efficiency of the electrostatically bound peptides. Peptide guests and polymers with a greater number of complementary charges result in less efficient release than peptides and polymers with lower numbers of charges. Interestingly, we find that the presence of adjacent charged groups on the monomeric unit of the polymer exhibits exceptionally low release efficiency, perhaps because of a chelate-like effect, even when the total polymer charge is lower. Overall, our findings inform the design principles for catch-and-release systems based on polymeric reverse micelles, which offer great versatility and tunability.

Self-assemblies of polymer-enzyme conjugates at oil-water interfaces for interfacial biocatalysis

Many biocatalysts have been shown powerful in enabling reactions among a broad range of substrates possessing very different hydrophilicity/hydrophobicity. Biphasic reaction systems, especially oil-water biphasic systems, have been commonly adopted to mediate such reactions. The greatest challenge in conducting an efficient reaction between two substrates that have to be hosted in two immiscible liquid phases is the mass transfer resistance across interfaces. Imaginably, the substrates afford the most extensive interactions at the interfacial region. The interfacial assembled enzymes, developed by conjugating water-soluble enzymes with hydrophobic polymers, are therefore expected to be efficient in catalyzing biotransformation at the organic-aqueous interfaces. This chapter describes a method in preparing and applying of such interface-assembling enzymes. A model enzyme, α-chymotrypsin (CT), is grafted with polystyrene (PS) to introduce an organic affinity, thus leading to a surfactant-like structure. The characterization of the activity and stability of the interface-assembled enzyme is also presented.

Surface functionalisation of PLGA nanoparticles for gene silencing

This work presents a method for decorating the surface of poly (lactide-co-glycolide) (PLGA) nanoparticles with polyethyleneimine (PEI) utilising a cetyl derivative to improve surface functionalisation and siRNA delivery. Sub-micron particles were produced by an emulsion-diffusion method using benzyl alcohol. We demonstrate by x-ray photoelectron spectroscopy (XPS), 2.6 times higher surface presentation of amines using the cetyl derivative compared to non-cetylated-PEI formulations (6.5 and 2.5% surface nitrogen, respectively). The modified particles were shown by spectroscopy, fluorescent microscopy and flow cytometry to bind and mediate siRNA delivery into the human osteosarcoma cell line U2OS and the murine macrophage cell line J774.1. Specific reduction in the anti-apoptotic oncogene BCL-w in U2OS cells was achieved with particles containing cetylated-PEI (53%) with no cellular toxicity. In addition, particles containing cetylated-PEI achieved 64% silencing of TNFalpha in J774.1 cells. This rapid method for surface modification of PLGA nanoparticles promotes its application for alternative cetylated functional derivatives as a strategy to control specific biological properties of nanoparticles.

The preparation of size-controlled functionalized polymeric nanoparticles in micelles

The reverse micellar system of dioctyl-sulfosuccinate (AOT)/octane and toluene have been used as a template for polymerization of acrylamide (AA)/bisacrylamide (BAA)-based functionalized polymeric nanoparticles. Such nanoparticles are typically sized between 20 and 90 nm. They can be synthesized with different functional groups according to the monomers added to the polymerization mixture. In our experiments the nanoparticles carried amino and carboxyl groups following incorporation of allylamine (AAm) or methacrylic acid (MAA) monomers, respectively. The available amine or carboxyl groups can then be used for immobilization of enzymes or other biomolecules. These enzymes, subtilisin, laccase and lipase, were immobilized onto polyAA/BAA/MAA nanoparticles covalently after activating the MAA carboxylic groups with Woodward's K reagent. Non-covalent immobilization via electrostatic interaction was also performed.

Multi-scale features in recent development of enzymic biocatalyst systems

Functional relation among elements of different size scales in a system is probably a main challenge across the areas of the science of engineering ever since their emergence. Multi-scale time and size correlation for description and prediction of complex systems, however, has been systematically examined only recently with the aid of new computational tools. In the pursuit of efficient and sustainable chemical processing technologies, people have seen a growing emphasis on synthetic biotechnology in recent R&D efforts. In particular, industrial enzyme technologies are attracting enormous attention. Having been traditionally developed for food and detergent applications, industrial enzyme technologies are being re-examined and tested to their limits to keep abreast of the challenges in drug, biochemical, and the emerging biorenewable energy industries. Toward that, enzymes are required to function in non-conventional conditions, such as organic solvents, extreme pH, and temperatures; they also have to compete against alternative chemical technologies in terms of costs and efficiency. Accordingly, enzymic biocatalyst systems are being tackled dynamically at all size levels through efforts ranging from molecular level protein engineering and modification, nanoscale structure fabrication, and microenvironment manipulation to the construction of microchip devices and macroscopic industrial bioreactors and devices. These efforts are probably still on a case-to-case trial basis without much consideration of cross-scale correlations. Discovering, understanding, and controlling of the common features that relate functions of biocatalysts at different size scales may eventually be realized in future.

Superficially active water in lipid membranes and its influence on the interaction of an aqueous soluble protease

The purpose of this paper is to demonstrate that the interaction of an aqueous soluble enzyme with lipid membranes is influenced by the lipid composition of the interphase. The results show that the interaction of an aqueous soluble protease, Rennet from Mucor miehei, depends on the exposure of the carbonyl and phosphate groups at the membrane interphase. The changes produced by the protease on the surface pressure of monolayers of dimyristoylphosphatidylcholine (DMPC); dioleoylphosphatidylcholine (DOPC); diphytanoylphosphatidylcholine (DPhPC); dipalmitoylphosphatidylcholine (DPPC); di-O-tetradecylphosphatidyl-choline [D(ether)PC]; dimyristoylphosphatidylethanolamine (DMPE); di-O-tetradecyl-phosphatidylethanolamine [D(ether)PE] were measured at different initial surface pressures. The meaning of the DeltaPi vs. Pi curves was interpreted in the light of the concept of interphase given by Defay and Prigogine [R. Defay, I. Prigogine, Surface Tension and Adsorption, John Wiley & Sons, New York, 1966, pp. 273-277] considering the interphase as a bidimensional solution of polar head groups. With this approach, and based on reported evidences that carbonyls and phosphates are the main hydration sites of the lipid membranes, it is suggested that the mechanism of interaction of aqueous soluble protein involves water beyond the hydration shell. At high surface pressure, only water strongly bound to carbonyl and phosphate groups is present and the interaction is not occurring. In contrast, at low surface pressures, the protease-membrane interaction is a function of acyl chain for different polar groups. This is interpreted, as a consequence of the changes in the interfacial tension produced by the displacement of water confined between the hydrated head groups.

Spraying Enzymes in Microemulsions of AOT in Nonpolar Organic Solvents for Fabrication of Enzyme Electrodes

A new technique suitable for automated, large-scale fabrication of enzyme electrodes by air-spraying enzymes in organic inks is presented. Model oxidoreductases, tyrosinase (Tyr) and glucose oxidase (GOx), were adapted to octane-based ink by entrapment in a system of reverse micelles (RM) of surfactant AOT in octane to separate and stabilize the catalytically active forms of the enzymes in nonpolar organic media. Nonpolar caoutchouk polymer was also used to create a kind of "dry micelles" at the electrode/solution interface. Enzyme/RM/polymer-containing organic inks were air-brushed onto conductive supports and were subsequently covered by sprayed Nafion membranes. The air-brushed enzyme electrodes exhibited relevant bioelectrocatalytic activity toward catechol and glucose, with a linear detection range of 0.1-100 microM catechol and 0.5-7 mM glucose; the sensitivities were 2.41 A M(-1) cm(-2) and 2.98 mA M(-1) cm(-2) for Tyr and GOx electrodes, respectively. The proposed technique of air-brushing enzymes in organic inks enables automated construction of disposable enzyme electrodes of various designs on a mass-production scale.

Novel interface-binding chloroperoxidase for interfacial epoxidation of styrene

A unique interface-binding chloroperoxidase (CPO) was developed and examined for interfacial biocatalysis. Native CPO was conjugated with polystyrene (PS) to form a surfactant-like structure that self assembled at oil-water interfaces. While enantioselectivity of the enzyme was maintained, the interfacial assembly of the enzyme improved its overall catalytic efficiency as compared to that observed with the enzyme contained in the bulk aqueous phase. The PS conjugated CPO (PS-CPO) showed a 2.5-fold enhancement of enzyme productivity versus native CPO under batch reaction conditions for the epoxidation of styrene, whereas a 25-fold improvement was realized in a continuous feeding reaction to reach a productivity of 10 micromol h-1 mg protein-1. The interface-binding enzyme also demonstrated several other advantages such as suppressing unwanted side reactions including the hydrolysis of styrene epoxide products, stabilizing the enzyme by limiting its exposure to both the oxidant H2O2 and epoxide products, and alleviating the deactivating effect of interfacial stress on enzymes by functioning as a surfactant.