Novel X‐ray Method for In Situ Determination of Gelator Strand Structure: Polymorphism of Cholesteryl Anthraquinone‐2‐carboxylate

Ostuni, Emanuele; Kamaras, Peter; Weiss, Richard G.

doi:10.1002/anie.199613241

Cited by 267 publications

(216 citation statements)

References 17 publications

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“…This dependence on cooling rate highlights the close relationship between ordered crystalline material and more disordered gels. 51,52 The structure of the co-crystal material was analysed by single crystal X-ray crystallography, Figure 3. The Xray structure reveals a conventional nearly symmetrical, double, anti-parallel urea -tape hydrogen-bonding motif.…”

Section: Gelation By Competitive Inhibitionmentioning

confidence: 99%

Halogen-bonding-triggered supramolecular gel formation

et al. 2012

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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-prot 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. Tunable gel phase materials with novel properties such as switchable rheology and controlled flow characteristics are an emerging topic of interest in potential applications as diverse as pharmaceutical crystallization, catalysis, drug delivery and controlled release, wound healing, and stabilization of drilling mud [1][2][3][4][5][6][7][8][9] . Within this context supramolecular low molecular weight gelators (LMWG), with their reversible and dynamic intermolecular interactions are achieving increasing prominence [10][11][12][13][14][15] . Work on switchable gels includes 2 systems involving photo-, pH, and redox based switching, ultrasound induced gelation, and switchable catalysis [16][17][18][19][20][21][22][23] . In order to systematically develop smart materials with controllable and well understood changes in bulk properties, an understanding of the intermolecular interactions in the system and the way in which they engage in hierarchical self-assembly in order to produce emergent morphologies with complex behavior is required. The link between even primary supramolecular interactions and bulk material properties is often unclear, however. Recent work has highlighted some simple approaches to controllable or smart materials that have met with considerable success. A key theme in particular is setting up a 'tipping point' in a system comprising competing intermolecular interactions which contribute to either gel assembly or gel dissolution. In this way a number of research groups have shown that anion binding in competition with urea self-assembly can be used to 'turn-down' and ultimately 'turn-off' gelation behavior 24,25 . Interestingly, in alternative systems, anion binding has also been used to induce gelation 26,27 . In a similar way metal coordination has also been used to tune gel properties 25 . In a series of bis(urea) gels we have shown how a combination of metal-and anion-binding can allow comprehensive control over the system. Competitive anion binding reduces gel strength by inhibiting urea -tape hydrogen-bond formation [28][29][30][31] .Conversely, metal coordination in pyridyl-urea compounds results in metal binding to the pyridyl group which suppresses the alternative, gel-inhibiting urea-pyridyl hydrogenbonding interaction, freeing the urea groups to form fibrils, and hence gels, as a result of the urea tape hydrogen-bonding motif [32][33][34] . These competitive interaction modes are summarised in Figure 1. 3

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Section: Gelation By Competitive Inhibitionmentioning

confidence: 99%

Halogen-bonding-triggered supramolecular gel formation

et al. 2012

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“…Here, it is especially difficult to see why there has to necessarily be a link, considering how many properties change on replacing one with another. Even where some crystallinity has been implied in the gel phase, 27 it is not clear how these data can be shown to not arise from simply some (possibly a very small amount of) crystallization within an amorphous gel phase. There is debate here, but to our minds there is no reason to necessarily assume that there is a link between crystallization and gelation.…”

Section: Introductionmentioning

confidence: 99%

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

Draper

Adams

2017

Chem

539

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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“…However, we are reluctant to draw a strong conclusion from this observation because the morph of an LMOG in its gels may differ from that in solids obtained by bulk recrystallizations 40 .…”

Section: -Camentioning

confidence: 86%

“…Previously, a method was devised in our group to provide molecular packing information of LMOGs within their gel superstructures by relating the X-ray diffraction (XRD) pattern of a gel to that of its neat solid phase 40 . When the two patterns are the same and the single-crystal structure of the LMOG is also available, packing in the gel is determined unambiguously.…”

Section: The Structures Of C36 Organo Gel Assemblies At åNgstrom To Mmentioning

confidence: 99%

The quest for the simplest possible organogelators and some properties of their organogels

Abdallah¹,

Weiss²

2000

J. Braz. Chem. Soc.

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Nesse trabalho é apresentada uma revisão sobre esforços recentes na busca pela classe mais simples de moléculas orgânicas capazes de gelificar grandes volumes de líquidos, com ênfase na abordagem adotada pelos autores. Apresentam-se, também, propriedades de alguns destes compostos bem como de seus organogéis. Alguns dos desafios futuros para o desenvolvimento desta área são discutidos.The search for the simplest structural class of organic molecules capable of gelling large amounts of organic liquids is reviewed with an emphasis on the approach taken by the authors. The properties of several of the gelators, as well as their gels with various organic liquids, are presented. Some challenges to future developments in the field are mentioned.

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Novel X‐ray Method for In Situ Determination of Gelator Strand Structure: Polymorphism of Cholesteryl Anthraquinone‐2‐carboxylate

Cited by 267 publications

References 17 publications

Halogen-bonding-triggered supramolecular gel formation

Halogen-bonding-triggered supramolecular gel formation

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

The quest for the simplest possible organogelators and some properties of their organogels

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