Supramolecular Gels: Functions and Uses

Sangeetha, N.; Maitra, Uday

doi:10.1002/chin.200602247

Cited by 111 publications

(165 citation statements)

References 44 publications

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“…The gels arise from the self-assembly of small molecules into long, anisotropic structures, most commonly fibers. [1][2][3][4][5] At a sufficiently high concentration, these fibers entangle or otherwise form cross-links, leading to the network that is able to immobilize the solvent through surface tension and capillary forces. 1,2 These gels differ from permanently covalently cross-linked polymer gels because the cross-linking can be reversed by the input of energy, for example, by heating.…”

Section: Introductionmentioning

confidence: 99%

“…There are many reviews that already provide this information. [1][2][3]5,68 Rather here we mainly focus on one example where the process of gelation has been used to lead to significantly different outcomes. This example is hydrogelators; this could be one reason why sufficient data exist on the formation of gels under different conditions because, compared with organic solvents, water as a solvent opens up many additional parameters, including variations in ionic strength, pH, and the addition of background salts.…”

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Low-Molecular-Weight Gels: The State of the Art

Draper

Adams

2017

Chem

536

469

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Low-molecular-weight gels are currently a hugely important class of materials that are attracting significant interest. These gels are formed when small molecules self-assemble into one-dimensional structures that entangle and cross-link to form a network that is capable of immobilizing the solvent. Here, we critically discuss the current state of the art and highlight two key areas where we believe there is significant untapped potential. The first is the observation that the properties of the gels are highly process dependent, which means that it is possible to access materials with very different properties from a single gelator. Second, using multiple gelators offers the opportunity to prepare materials with a high degree of information content and with a wider range of properties. We aim to spark thought and discussion on these aspects. INTRODUCTIONLow-molecular-weight gels (LMWGs), or supramolecular gels, are a fascinating and useful class of material. The gels arise from the self-assembly of small molecules into long, anisotropic structures, most commonly fibers. [1][2][3][4][5] At a sufficiently high concentration, these fibers entangle or otherwise form cross-links, leading to the network that is able to immobilize the solvent through surface tension and capillary forces. 1,2 These gels differ from permanently covalently cross-linked polymer gels because the cross-linking can be reversed by the input of energy, for example, by heating. 6 LMWGs have been around for many years but are receiving considerable current interest. 4 They are also used in industrial products, 7 although this seems rarely discussed in the academic literature.In addition to the industrial applications, many recent advances and uses are being described. [8][9][10][11][12] The specific self-assembly leading to gel formation can be exploited. For example, the fiber formation is a result of molecular stacking, meaning that the self-assembly leads to aggregates that can be suitable for optoelectronic applications. 13,14 The ready reversibility of gelation can be exploited, for example, to release cells from gels on demand in a manner that does not lead to cell death. 15 Ready gel formation by a simple trigger can also be used to allow easy and efficient gel loading. [16][17][18] Unsurprisingly, therefore, there is significant interest in these materials ( Figure 1). This is a fascinating area and in many ways holds attention because of the difficulties in probing and understanding the gels. The gels arise from assembly across many length scales, and understanding all of these is difficult. At the molecular level, the molecules must interact in a manner that leads to the formation of suitable aggregates that can eventually entangle. Thus, one-dimensional growth must be favored. From this perspective, it is very frustrating that it is often extremely difficult to predict whether a molecule will form a gel or not; indeed, gelation has been described as an empirical science. 4 Structurally similar small molecules can exhibitThe Bigger Pict...

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Section: Introductionmentioning

confidence: 99%

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Low-Molecular-Weight Gels: The State of the Art

Draper

Adams

2017

Chem

536

469

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“…Basically, most of the gelation phenomenon arises from the formation of nano-to micrometer-scale fibres or polymer chains either physically branched (in the form of interconnected network) or entangled with each other to trap water via surface tension 8 . Unlike polymer gels where fibres/discrete polymer chains are formed by strong chemical bonds, the strands of small molecule hydrogels are assembled by noncovalent weak interactions that enable small molecule hydrogels thermally reversible 9 .…”

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confidence: 99%

Novel polymer-free iridescent lamellar hydrogel for two-dimensional confined growth of ultrathin gold membranes

et al. 2014

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Hydrogels are generally thought to be formed by nano-to micrometre-scale fibres or polymer chains, either physically branched or entangled with each other to trap water. Although there are also anisotropic hydrogels with apparently ordered structures, they are essentially polymer fibre/discrete polymer chains-based network without exception. Here we present a type of polymer-free anisotropic lamellar hydrogels composed of 100-nm-thick water layers sandwiched by two bilayer membranes of a self-assembled nonionic surfactant, hexadecylglyceryl maleate. The hydrogels appear iridescent as a result of Bragg's reflection of visible light from the periodic lamellar plane. The particular lamellar hydrogel with extremely wide water spacing was used as a soft two-dimensional template to synthesize singlecrystalline nanosheets in the confined two-dimensional space. As a consequence, flexible, ultrathin and large area single-crystalline gold membranes with atomically flat surface were produced in the hydrogel. The optical and electrical properties were detected on a single gold membrane.

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“…10,13 However, the potential of LMWG's as a medium for crystal growth is largely unexplored. [16][17][18] with the exception of some elegant work on the use of LMWG's for the growth of calcium carbonate 19 and other inorganic minerals, 20 as part of studies on biomineralization.…”

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Anion-switchable supramolecular gels for controlling pharmaceutical crystal growth

et al. 2010

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The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Gel media have been utilized for over a century for the growth of inorganic, organic and protein crystals. [1][2][3][4][5] The improved physical characteristics of the resulting crystals (better optical quality, larger size and fewer defects) are usually ascribed to the suppression of convection currents, sedimentation and nucleation afforded by the viscous gel environment. [6][7] In many instances the gel is thought to act as an inert matrix within which crystal growth occurs, however in some cases, the gel structure has been shown to influence the polymorphism, enantiomorphism and habit of crystals. 2 Occasionally gel fibres may become incorporated into the crystal, giving rise to composite materials. 8Conventional gels are formed using polymeric or clay-like materials such as gelatine, solubility were investigated to demonstrate their potential to act as crystallisation media for molecular organic compounds. Compounds 2, and 4 have been reported previously. [23][24] Novel compounds 1 and 3 were prepared by standard methods as detailed in the supplementary information. Gelators 1 -3 were chosen because they reliably form gels in a number of solvents ranging from aqueous systems to toluene. The fibrous nature of the gels is evidenced by SEM images of the dried xerogels ( Figure 1a,b). Compound 4 is a metallogelator which forms blue coloured gels with substoichiometric amounts of CuCl 2 in methanol:water. 23 Between them, these gelators can gel a range of solvents, at different temperatures (T gel ), and with a different critical gelator concentration (CGC). This class of compound has the potential to form the basis of a library of gelators which will allow the selection of gel properties and specific functionalities to match the compound and crystallisation conditions of interest. The synthetic versatility of these gelators could also in principle allow the incorporation of tailored heteronucleating functionality. While we focus upon bis(urea) compounds, the concepts outlined herein equally apply to any LMWG.Crystallisation experiments were undertaken using a range of organic compounds of both drug and non-drug species in parallel in both gel and solution media. We undertook an initial screen using candidate compounds 2-hydroxy benzyl alcohol (HBA, 5), Aspirin (ASP, 6), carbamazepine (CBZ, 7), 1-(3-methylsulfanyl-phenyl)-3-pyridin-2-yl-urea (SPU, 8) and 1,3-bis(m-nitrophenyl)urea (NPU, 9). We then carried out a detailed study on CBZwith all gelators, and a follow up study on gelator ...

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Supramolecular Gels: Functions and Uses

Cited by 111 publications

References 44 publications

Low-Molecular-Weight Gels: The State of the Art

Low-Molecular-Weight Gels: The State of the Art

Novel polymer-free iridescent lamellar hydrogel for two-dimensional confined growth of ultrathin gold membranes

Anion-switchable supramolecular gels for controlling pharmaceutical crystal growth

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