Micellar Nanoreactors Research Articles

Laser diagnostics of micellar nanoreactors in ZnSO4/water/AOT/heptane reverse microemulsion system

In the article, for the first time, a method has been developed for remote monitoring of the composition of the reaction medium of micellar nanoreactors and for determining the parameters of nanoparticles during their synthesis using Raman spectroscopy. The sensitivity of spectral characteristics to changes in the size of nanoreactors and the concentration of the nanoparticle precursor in reverse ZnSO4/water/AOT/heptane microemulsions has been experimentally established. It has been shown that the intensity of the band of symmetrical S-O stretching vibrations in the Raman spectrum of the ZnSO4/water/AOT/heptane microemulsion can be used to determine the concentration of ZnSO4 in the micelle cores with the accuracy of 2.4 %. The calibration dependence of the center of mass position of the symmetrical O–H stretching vibrations band of the specified microemulsion on the micelles diameter ensures the determination of the sizes of micellar nanoreactors with an accuracy of 11 %.

Biotransformation of t-butyl phenols by micellar nanoreactors of peroxidase/ionic surfactants at mild conditions: nanobiocatalyst performance and kinetic analysis

Recently, some bulk reaction media were substituted by micellar systems. Micellar media can be created by different types of surfactants which generate micellar nanoreactors for diverse reactions. Ionic surfactants can be used as aqueous micellar systems, providing mild conditions for the specified reactions. Ionic surfactants: sodium dodecyl sulfate, sodium decyl sulfate (SDeS), sodium octyl sulfate (SOS), n-dodecyl trimethyl ammonium bromide, and cetyltrimethylammonium bromide were used to prepare aqueous micellar and entrapped peroxidase nanoreactors as biocatalysts. Oxidative coupling reactions were investigated for a series of phenolic hydrogen donors including 2-tert-butyl phenol, 4-tert-butyl phenol, and 2,4-tert-butyl phenol catalyzed by micellar nanoreactors of horseradish peroxidase (HRP) with hydrogen peroxide and/or tert-butyl peroxide as oxidants. Higher oxidation reaction rates were obtained for 2-tert-butylphenol and 4-tert-butylphenol with hydrogen peroxide in 90 mM SDeS (SDeS90) and 150 mM SOS (SOS150) nanoreactors, respectively. Among the micellar nanoreactors studied, the SDeS90 nanoreactor showed excellent protection of the enzyme against the peroxide inactivation effect. The long-term activity of the HRP/SDeS90 nanobiocatalyst was related to the gradual diffusion of peroxide into the nanoreactor. The biocatalytic kinetic parameters: V max, k cat, catalytic efficiency, and suicide-peroxide inactivation rate constants were determined for HRP/SDeS90. Reactions were carried out successfully under mild conditions in the micellar nanoreactors. Results confirmed that substituted functional groups on the benzene ring affect the oxidative reaction routes and products. Excellent protection of the enzyme, enhanced biocatalytic parameters, higher selectivity, and yield, in the peroxidative coupling of alkylphenols, reveal the high potential of such micellar nanoreactors for diverse organic synthesis and biotransformation.

Unusual Phase Behaviour for Organo-Halide Perovskite Nanoparticles Synthesized via Reverse Micelle Templating

Micelle templating has emerged as a powerful method to produce monodisperse nanoparticles. Herein, we explore unconventional phase transformations in the synthesis of organo-halide perovskite nanoparticles utilizing reverse micelle templates. We employ diblock-copolymer reverse micelles to fabricate these nanoparticles, which confines ions within micellar nanoreactors, retarding reaction kinetics and facilitating perovskite cage manipulation. The confined micellar environment exerts pressure on both precursors and perovskite crystals formed inside, enabling stable phases not typically observed at room temperature in conventional synthesis. This provides access to perovskite structures that are otherwise challenging to produce. The hydrophobic shell of the micelle also enhances perovskite stability, particularly when combined with anionic exchange approaches or large aromatic cations. This synergy results in long-lasting stable optical properties despite environmental exposure. Reverse micelle templates offer a versatile platform for modulating perovskite structure and behavior across a broad spectrum of perovskite compositions, yielding unique phases with diverse emission characteristics. By manipulating the composition and properties of the reverse micelle template, it is possible to tune the characteristics of the resulting nanoparticles, opening up exciting opportunities for customizing optical properties to suit various applications.

Micellar Nanoreactors from Amphiphilic Copolymers for Thia-Michael Addition in Water

Micellar Nanoreactors from Amphiphilic Copolymers for Thia-Michael Addition in Water

Micellar Nanoreactors Enabled Site-Selective Decoration of Pt Nanoparticles Functionalized Mesoporous SiO2 /WO3-x Composites for Improved CO Sensing.

Site-selective and partial decoration of supported metal nanoparticles (NPs) with transition metal oxides (e.g., FeOx ) can remarkably improve its catalytic performance and maintain the functions of the carrier. However, it is challenging to selectively deposit transition metal oxides on the metal NPs embedded in the mesopores of supporting matrix through conventional deposition method. Herein, a restricted in situ site-selective modification strategy utilizing poly(ethylene oxide)-block-polystyrene (PEO-b-PS) micellar nanoreactors is proposed to overcome such an obstacle. The PEO shell of PEO-b-PS micelles interacts with the hydrolyzed tungsten salts and silica precursors, while the hydrophobic organoplatinum complex and ferrocene are confined in the hydrophobic PS core. The thermal treatment leads to mesoporous SiO2 /WO3-x framework, and meanwhile FeOx nanolayers are in situ partially deposited on the supported Pt NPs due to the strong metal-support interaction between FeOx and Pt. The selective modification of Pt NPs with FeOx makes the Pt NPs present an electron-deficient state, which promotes the mobility of CO and activates the oxidation of CO. Therefore, mesoporous SiO2 /WO3-x -FeOx /Pt based gas sensors show a high sensitivity (31±2 in 50ppm of CO), excellent selectivity, and fast response time (3.6s to 25ppm) to CO gas at low operating temperature (66°C, 74% relative humidity).

Polymeric architecture as a tool for controlling the reactivity of palladium(II) loaded nanoreactors.

Self-assembled systems, like polymeric micelles, have become great facilitators for conducting organic reactions in aqueous media due to their broad potential applications in green chemistry and biomedical applications. Massive strides have been taken to improve the reaction scope of such systems, enabling them to perform bioorthogonal reactions for prodrug therapy. Considering these significant advancements, we sought to study the relationships between the architecture of the amphiphiles and the reactivity of their PdII loaded micellar nanoreactors in conducting depropargylation reactions. Towards this goal, we designed and synthesized a series of isomeric polyethylene glycol (PEG)-dendron amphiphiles with different dendritic architectures but with an identical degree of hydrophobicity and hydrophilic to lipophilic balance (HLB). We observed that the dendritic architecture, which serves as the main binding site for the PdII ions, has greater influence on the reactivity than the hydrophobicity of the dendron. These trends remained constant for two different propargyl caged substrates, validating the obtained results. Density functional theory (DFT) calculations of simplified models of the dendritic blocks revealed the different binding modes of the various dendritic architectures to PdII ions, which could explain the observed differences in the reactivity of the nanoreactors with different dendritic architectures. Our results demonstrate how tuning the internal architecture of the amphiphiles by changing the orientation of the chelating moieties can be used as a tool for controlling the reactivity of PdII loaded nanoreactors.

Self-Assembled Catalytic Nanoreactors from Molecular Brushes by Utilizing Postpolymerization Modification for Catalyst Attachment

Polymer-based catalytic nanoreactors, with the characteristics of easy preparation, good dispersion, and facile modulation of molecular structures, have been widely applied for various organic transformations. Usually, polymeric nanoreactors are fabricated via the self-assembly of amphiphilic copolymers in water, while the disassembly and instability of the relevant nanoreactors often compromise their potential applicability. Molecular brushes (MBs), as a kind of polymer with high-density grafted side chains on the linear polymer main chain, can be rapidly self-assembled into highly ordered nanostructures even at low concentrations. This study reports the fabrication of catalytic nanoreactors from molecular brushes of poly[norbornene–poly(bromoethyl methacrylate-co-methyl methacrylate)]-co-poly[norbornene polyethylene glycol monomethyl ether] (P[NB-(BEMA-co-MMA)]-co-P[NB-PEG]). The amphiphilic molecular brush was synthesized by combining reversible addition–fragmentation chain transfer (RAFT) polymerization and ring-opening metathesis polymerization (ROMP) techniques. Homogeneous catalysts, such as triethylenediamine and 4-(dimethylamino)pyridine analogues, were introduced by nucleophilic substitution with alkyl bromide on the side chain of molecular brushes. Furthermore, micellar catalytic nanoreactors were fabricated via self-assembly in deionized water. The resulted nanoreactors display high catalytic activities toward the Knoevenagel condensation reaction and acylation reaction of alcohol in water, respectively. This contribution describes a general method for constructing highly efficient molecular brush-based catalytic nanoreactors utilizing postpolymerization modification (PPM) for aqueous catalysis.

Bioorthogonal micellar nanoreactors for prodrug cancer therapy using an inverse-electron-demand Diels-Alder reaction.

Block copolymer micelles functionalized with tetrazine groups can act as nanoreactors to activate a trans-cyclooctene-functionalized prodrug for releasing anticancer drugs via a bioorthogonal inverse-electron-demand Diels-Alder (IEDDA) reaction. In addition, the IEDDA reaction can be accelerated in the micellar nanoreactor system compared to the free tetrazine system. Moreover, In vivo prodrug activation in a mouse tumor model led to the inhibition of tumor growth without significant systemic toxicity. These results demonstrated their potential for applications as bioorthogonal micellar nanoreactors for cancer chemotherapy.

Facile one-step fabrication of DMAP-functionalized catalytic nanoreactors by polymerization-induced self-assembly in water

Fabrication of highly efficient and recyclable micellar nanoreactors for green organic transformation via self-assembly of catalyst-containing amphiphilic copolymers in water has made great progress. These methods commonly include synthesis and functionalized amphiphilic copolymers and then self-assembly. In this study, a straightforward, one-step strategy for the construction of DMAP-functionalized nanoreactors was developed via polymerization-induced self-assembly (PISA). Acrylate hydrophilic monomer and DMAP-functionalized monomer in the presence of hydrophilic macromolecular chain transfer reagent was polymerized through reversible addition-fragmentation chain transfer (RAFT) polymerization in situ in water, leading to simultaneous amphiphilic block copolymer formation and self-assembly. The diameters of the resulted micelles ranged from 20 to 100 nm depending on the type and amount of hydrophilic monomer, and solid content is up to 25%. The high catalytic activity of the micelles as homogeneous, also readily recyclable catalysts is demonstrated through acylation of a variety of alcohols and recovery by simple dialysis. The study offers an one-pot tandem RAFT-PISA process in water for fabricating highly efficient catalytic nanoreactor.

Tuning the Reactivity of Micellar Nanoreactors by Precise Adjustments of the Amphiphile and Substrate Hydrophobicity.

Polymeric assemblies, such as micelles, are gaining increasing attention due to their ability to serve as nanoreactors for the execution of organic reactions in aqueous media. The ability to conduct organic transformations, which have been traditionally limited to organic media, in water is essential for the further development of important fields ranging from green catalysis to bioorthogonal chemistry. Considering the recent progress that has been made to expand the range of organometallic reactions conducted using nanoreactors, we aimed to gain a deeper understanding of the roles of the hydrophobicity of both the core of micellar nanoreactors and the substrates on the reaction rates in water. Toward this goal, we designed a set of five metal-loaded micelles composed of polyethylene glycol–dendron amphiphiles and studied their ability to serve as nanoreactors for a palladium-mediated depropargylation reaction of four substrates with different log P values. Using dendrons as the hydrophobic block, we could precisely tune the lipophilicity of the nanoreactors, which allowed us to reveal linear correlations between the rate constants and the hydrophobicity of the amphiphiles (estimated by the dendron’s cLog P). While exponential dependence was obtained for the lipophilicity of the substrates, a similar degree of rate acceleration was observed due to the increase in the hydrophobicity of the amphiphiles regardless of the effect of the substrate’s log P. Our results demonstrate that while increasing the hydrophobicity of the substrates may be used to accelerate reaction rates, tuning the hydrophobicity of the micellar nanoreactors can serve as a vital tool for further optimization of the reactivity and selectivity of nanoreactors.

Micellar nanoreactors for organic transformations with a focus on “dehydration” reactions in water: A decade update

Although nature uses the aqueous environment in most of its chemical/biochemical transformations, water as solvent was totally neglected in organic transformations till the end of the last century because of its poor ability to solubilize most of the organic compounds. However, growing environmental concerns make it imperative to replace toxic organic solvents with benign solvents like water. Over the last few decades, the use of catalytic amounts of surfactants in the aqueous media has proved to be the best solution to overcome the problem of insolubility and hydrolytic decomposition of many organic compounds in water. The surfactants form a colloidal, micellar, or other organized phases that serve as “nanoreactors” in aqueous media. The field is called “micellar catalysis” that acts as a greener alternative to conventional organic synthesis. The hydrophobic interior of micelles can successfully accomplish the most challenging task of “dehydration reactions” in water. The last two decades have witnessed enormous contributions of “dehydration reactions” in micellar media. In addition, incredible rate acceleration and selectivities have been observed in micellar media. The technology lends advantages of reusability and easy scalability in the synthetic processes towards setting-up a new dimension of benign chemical transformations. The purpose of the present review to capture the enormous contributions of the last decade on “dehydration reactions” in micellar media including various condensation reactions, formation of acid-derivatives, multicomponent reactions, and the formation of heterocycles to give a comprehensive idea to readers on the development of this field. The review also covers a brief account on micelle-assisted reactions other than dehydrations taking the key and recent contributions of various types of reactions such as cross-coupling reactions, C–H activation, asymmetric catalysis, oxidation-reduction, click chemistry etc.

Cross‐Linked Polymeric Micelles as Catalytic Nanoreactors

AbstractCross‐linked micelles have emerged as promising catalyst supports over the past two decades due to their improved structural stability, chemical diversity in multiple domains, and catalyst recovery compared to their uncross‐linked analogues. We highlight the different physicochemical properties that arise by cross‐linking the shell or core‐domain and the subsequent impact on catalysis. Both, shell cross‐linked micelles (SCMs) and core cross‐linked micelles (CCMs) were initially designed to include one catalytic entity. Later on, SCMs were used to compartmentalize catalysts for non‐orthogonal tandem catalysis while CCMs were investigated as phase transfer agents in biphasic catalysis. Current challenges in this field and new design trends for advanced micellar nanoreactors are discussed.

Compartmentalization and Photoregulating Pathways for Incompatible Tandem Catalysis.

This contribution describes an advanced compartmentalized micellar nanoreactor that possesses a reversible photoresponsive feature and its application toward photoregulating reaction pathways for incompatible tandem catalysis under aqueous conditions. The smart nanoreactor is based on multifunctional amphiphilic poly(2-oxazoline)s and covalently cross-linked with spiropyran upon micelle formation in water. It responds to light irradiation in a wavelength-selective manner switching its morphology as confirmed by dynamic light scattering and cryo-transition electron microscopy. The compartmental structure renders distinct nanoconfinements for two incompatible enantioselective transformations: a rhodium-diene complex-catalyzed asymmetric 1,4-addition occurs in the hydrophilic corona, while a Rh-TsDPEN-catalyzed asymmetric transfer hydrogenation proceeds in the hydrophobic core. Control experiments and kinetic studies showed that the gated behavior induced by the phototriggered reversible spiropyran to merocyanine transition in the cross-linking layer is key to discriminate among substrates/reagents during the catalysis. The smart nanoreactor realized photoregulation to direct the reaction pathway to give a multichiral product with high conversions and perfect enantioselectivities in aqueous media. Our SCM catalytic system, on a basic level, mimics the concepts of compartmentalization and responsiveness Nature uses to coordinate thousands of incompatible chemical transformations into streamlined metabolic processes.

Selective palladium nanoparticles-catalyzed hydrogenolysis of industrially targeted epoxides in water

Palladium nanoparticles, with core sizes of ca. 2.5 nm, were easily synthesized by chemical reduction of Na2PdCl4 in the presence of hydroxyethylammonium salts and proved to be efficient for the selective hydrogenolysis of various aromatic, alkylphenyl, aliphatic epoxides in water as green solvent. Capping agents of the metal species were screened to define the most suitable micellar nanoreactors on two target substrates of industrial interest, epoxystyrene and 7,8-epoxy-2-methoxy-2,6-dimethyloctane. In our conditions, the hydrogenolysis of epoxystyrene proved to be pH-dependent, producing either the diol under acidic conditions, or the sweet-smelling 2-phenylethanol in the presence of a base. Promisingly, 7,8-epoxy-2-methoxy-2,6-dimethyloctane was completely and selectively hydrogenated into Florsantol®, a sandalwood odorant at a multigram scale (40 g and up to 175g). A general mechanism for the palladium nanoparticles-catalyzed hydrogenolysis of terminal epoxides was proposed according to steric and electronic properties and finely corroborated with deuterium labelling experiments.

Stereocomplexation of Polymers in Micelle Nanoreactors As Studied by Multiple Detection Thermal Field-Flow Fractionation.

In this study the thermally induced in situ stereocomplexation (SC) of binary blends of symmetrical isotactic and syndiotactic polymethymethacrylates (i- and s-PMMAs) inside micellar nanoreactors (MNR) with polystyrene (PS) shells is investigated using thermal field-flow fractionation (ThFFF) as a separation technique. The MNRs are prepared from three systematic binary blending ratios of pure micelles of i-PMMA-PS and s-PMMA-PS in a nonsolvent for PMMAs in order to produce mixed micelles with a binary microstructural composition of the interior PMMA cores. The SC of these stereoregular PMMA cores inside the MNRs is shown to be thermally induced as a function of annealing temperatures from room temperature up to 150 °C. This SC is initially confirmed by Fourier transform infrared spectroscopy (FTIR), whereby signal shifts are observed in the carbonyl absorption regions. These signal shifts are as a result of SC interactions between adjacent ester and alpha-methyl groups. Furthermore, temperature-dependent dynamic light scattering (DLS) results show that MNRs with more SC domains have a much more drastic reduction in size. Additional corroboration is provided by multiple detection ThFFF results which show significant differences in retentions and sizes between MNRs with stereocomplexed cores and those without. Ratios of i-PMMA:s-PMMA in the order of 1:1, 1:2, and 2:1 were investigated with all ratios exhibiting thermal annealing induced SC, of which the 1:2 ratio is shown to have the highest predisposition to SC.

ROMP synthesis of 1,2,3-triazolyl dendronized polymers with triethylene glycol branches as recyclable nanoreactors for Cu(I) “click” catalysis reaction in water

The design and construction of high-efficiency nanoreactor systems have attracted a great deal of attention for their potential applications in materials science, biomedicine and catalysis. Especially, understanding the relationship between the precise internal structure of nanoreactors and their catalytic performance is essential for catalyst design. Here we report two bulky G2 dendronized norbornene macromonomers 8 and 13 containing nine hydrophilic triethylene glycol (TEG) termini with three and nine, respectively, 1,2,3-triazole (trz) rings, and their controlled polymerizations via the ring-opening metathesis polymerization (ROMP) technique using Grubbs' third-generation olefin metathesis catalyst. The self-assemblies of the obtained dendronized polymers (DPs) 9 and 14 in water then yield novel micellar nanoreactors with different location distribution of the coordinative intradendritic trz ligands. The recyclable nanoreactors are used to support CuI ion generated by in situ reduction of CuSO4·5H2O via sodium ascorbate, and strongly activate the CuI-catalyzed azide alkyne cycloaddition (CuAAC) “click” reactions in water, leading to exceptional TONs up to 250 000 and TOFs up to 16 670 h−1. Remarkably, when the amount of CuI catalysts is less than 50 ppm, 9a-CuI exhibits considerably higher catalytic efficiency than 14a-CuI, which is attributed to the architectural difference of the two used DPs 9 and 14. This work highlights the role of the location of trz ligands in DPs nanoreactors on the catalytic efficiency of CuI catalyst, and the unique advantage of DP-type nanoreactors by less steric inhibition, compared to the congested dendrimers nanoreactors, and also rationalizes optimization in catalyst engineering.

Synthesis and antibacterial activity of water-dispersible silver nanoparticles via micellar nanoreactors

We have synthesized silver nanoparticles (AgNPs) using micelles of sugar fatty acid ester by dissolving the surfactant in a mixture of iso-octane and n-butanol, with solid-liquid extraction. Highly concentrated, water-dispersible AgNPs were obtained after thorough washing with alcohol, to remove excess of sucrose fatty acid ester DK SS and salt, followed by drying. The particles were characterized for their size, morphology and crystallinity using UV-Visible spectrophotometry, Transmission Electron Microscopy and x-ray diffractometry. Antibacterial study, confirmed the activity of nanoparticles against E. coli, P. aeruginosa and S. aureus, which causes diseases including diarrhoea and several life-threatening infections. Antibacterial activity of E. coli and P. aeruginosa was found to be 2.5 fold and for S. aureus 1.6 fold compared to 50 ppm conc. of Silver Nitrate. Our method of producing nanoparticles is employed as a platform technology for synthesizing other inorganic nanoparticles. This is the first report discussing the use of micellar carriers for obtaining silver nanopowder, to the best of our knowledge, which has the potential to overcome limitations during fabrication of AgNPs using reverse/inverse micelles. Our method yielded nano-sized, water-dispersible AgNPs via an easy and economic approach. The one-pot approach possesses advantages in terms of cost and simplicity, as compared with traditional methods of producing powdered AgNPs using energy intensive and expensive techniques like lyophilisation. The developed method, thus, possesses immense potential for commercial synthesis of AgNPs.

A New Mn–Salen Micellar Nanoreactor for Enantioselective Epoxidation of Alkenes in Water

A new chiral Mn–salen catalyst, functionalized with a long aliphatic chain and a choline group, able to act as surfactant catalyst for green epoxidation in water, is here described. This catalyst was employed with a commercial surfactant (CTABr) leading to a nanoreactor for the enantioselective epoxidation of some selected alkenes in water, using NaClO as oxidant. This is the first example of a nanoreactor for enantioselective epoxidation of non-functionalized alkenes in water.

Selective hydrogenation of α-pinene to cis-pinane over Ru nanocatalysts in aqueous micellar nanoreactors

Hydrogenation of α-pinene took place in the lipophilic core between the metal and the hydrogen-containing micelles.

Reductions of aryl bromides in water at room temperature

Micellar nanoreactors derived from commercially available ‘Nok’ (SPGS-550-M), in the presence of Fu’s catalyst and a mild hydride source (NaBH4), are useful for facile debromination of functionalized aromatic derivatives. This mild and environmentally responsible process is utilized in water at room temperature, and the reaction mixtures can be smoothly recycled.