Catalysis in Cyclodextrin-Based Unconventional Reaction Media: Recent Developments and Future Opportunities
Frédéric HapiotStéphane MenuelMichel FerreiraBastien LégerHervé BricoutSébastien TilloyÉric Monflier
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During these last years, cyclodextrins (CDs) have greatly contributed to the development of innovative homogeneous or heterogeneous catalytic processes. More than simple molecular platforms aiming at designing new ligands or interfacial additives, CDs have been employed to generate unconventional reaction media such as supramolecular hydrogels or low melting mixtures (LMMs) capable of stabilizing active catalytic species. By using such alternative and unconventional media, high catalytic activities and selectivities were obtained in various transition metal catalytic reactions. The studied catalytic systems are easy to implement and allow for the remarkable stabilization of organometallic or metal nanoparticle catalysts. Interestingly, the size of metal nanoparticles can be finely tuned through confinement in the network of CD-based supramolecular hydrogels. Additionally, the catalysts can be recovered by a simple phase separation. The catalytic phase can be stored at room temperature under an air atmosphere in the solid state and reused as needed without significant loss of activity. Eventually, such CD-based catalytic systems greatly improve process safety. The present article intends to show the reader the very substantial progress that has recently been made in the field.The relatively weak mechanical properties of hydrogels remain a major drawback for their application as load-bearing tissue scaffolds. Previously, we developed cell-laden double-network (DN) hydrogels that were composed of photocrosslinkable gellan gum (GG) and gelatin. Further research into the materials as tissue scaffolds determined that the strength of the DN hydrogels decreased when they were prepared at cell-compatible conditions, and the encapsulated cells in the DN hydrogels did not function as well as they did in gelatin hydrogels. In this work, we developed microgel-reinforced (MR) hydrogels from the same two polymers, which have better mechanical strength and biological properties in comparison to the DN hydrogels. The MR hydrogels were prepared by incorporating stiff GG microgels into soft and ductile gelatin hydrogels. The MR hydrogels prepared at cell-compatible conditions exhibited higher strength than the DN hydrogels and the gelatin hydrogels, the highest strength being 2.8 times that of the gelatin hydrogels. MC3T3-E1 preosteoblasts encapsulated in MR hydrogels exhibited as high metabolic activity as in gelatin hydrogels, which is significantly higher than that in the DN hydrogels. The measurement of alkaline phosphatase (ALP) activity and the amount of mineralization showed that osteogenic behavior of MC3T3-E1 cells was as much facilitated in the MR hydrogels as in the gelatin hydrogels, while it was not as much facilitated in the DN hydrogels. These results suggest that the MR hydrogels could be a better alternative to the DN hydrogels and have great potential as load-bearing tissue scaffolds.
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This minireview discusses the advantages and challenges in constructing bioinspired double-network hydrogels mimicking the structure and/or properties of biological tissue.
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Abstract Herein we report the spectroscopic, electrochemical, TEM and DLS characterizations of C60 supramolecular inclusion complexes with α‐, β‐and γ‐cyclodextrins prepared using anionic C60. The results indicate that the cyclodextrin itself has little effect on the encapsulated C60 or on the properties of the inclusion complex. Instead, the cyclodextrin has a significant influence on the aggregation behavior of individual complex in aqueous solution, which in turn affects the property of the supramolecular complex of cyclodextrin and C60 greatly. As the cavity dimension of cyclodextrin becomes smaller as it changes from γ‐CD to β‐CD, and finally to α‐CD, it is observed that more aggregation occurs for the corresponding inclusion complex in aqueous solution.
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The relatively weak mechanical properties of hydrogels remain a major drawback for their application as load-bearing tissue scaffolds. Previously, we developed cell-laden double-network (DN) hydrogels that were composed of photocrosslinkable gellan gum (GG) and gelatin. Further research into the materials as tissue scaffolds determined that the strength of the DN hydrogels decreased when they were prepared at cell-compatible conditions, and the encapsulated cells in the DN hydrogels did not function as well as they did in gelatin hydrogels. In this work, we developed microgel-reinforced (MR) hydrogels from the same two polymers, which have better mechanical strength and biological properties in comparison to the DN hydrogels. The MR hydrogels were prepared by incorporating stiff GG microgels into soft and ductile gelatin hydrogels. The MR hydrogels prepared at cell-compatible conditions exhibited higher strength than the DN hydrogels and the gelatin hydrogels, the highest strength being 2.8 times that of the gelatin hydrogels. MC3T3-E1 preosteoblasts encapsulated in MR hydrogels exhibited as high metabolic activity as in gelatin hydrogels, which is significantly higher than that in the DN hydrogels. The measurement of alkaline phosphatase (ALP) activity and the amount of mineralization showed that osteogenic behavior of MC3T3-E1 cells was as much facilitated in the MR hydrogels as in the gelatin hydrogels, while it was not as much facilitated in the DN hydrogels. These results suggest that the MR hydrogels could be a better alternative to the DN hydrogels and have great potential as load-bearing tissue scaffolds.
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With new characteristics of cyclodextrin discovered and more derivatives of cyclodextrin synthesized,the applications of supramolecular cyclodextrin become more and more extensive.This paper summerized the research progress of supramolecular cyclodextrin in molecular recognition,molecular self-assembly and bio-enzyme mimics.And the development tendency of supramolecular cyclodextrin was prospected.
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The construction and application of β-cyclodextrin-Fe3O4 supramolecular systems at present have been reviewed in detail, especially for the application of β-cyclodextrin-Fe3O4 supramolecular systems constructed covalently in the environ- mental pollutants adsorption, drug loading and releasing, sensor construction and detection application, separation and cataly- sis. In all of the section mentioned above, the construction and property of the β-cyclodextrin-Fe3O4 supramolecular systems were discussed systematically which were classified according to the linking groups between β-cyclodextrin and Fe3O4. It was pointed out that the β-cyclodextrin-Fe3O4 supramolecular systems possessed the ability to form inclusion complex with guest molecules, weak catalytic activity and substrate recognition property of β-cyclodextrin unit and the magnetic property of Fe3O4 which could be recovered easily, simultaneously. It was also pointed out that the immobilization of β-cyclodextrin on Fe3O4 nanoparticles to construct heterogeneous β-cyclodextrin-Fe3O4 supramolecular biomimetic catalytic systems will be one of the focus in the construction of nanoscale supramolecular biomimetic catalysts in the future. Keywords cyclodextrin; Fe3O4; supramolecular systems; construction; application
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