Anion tuning of chiral bis(urea) low molecular weight gels

Lloyd, Gareth O.; Piepenbrock, Marc‐Oliver M.; Foster, Jonathan A.; Clarke, Nigel; Steed, Jonathan W.

doi:10.1039/c1sm06448g

Cited by 79 publications

(66 citation statements)

References 124 publications

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“…400 By fitting this model to the rheological profiles of chiral bis(urea) organogels, and assuming the gel fibres to be equal in density to the corresponding single crystals, Lloyd et al were able to estimate values for ES in the range 1-2 GPa. 401 Helical nanofibres of a tripodal tris(urea) were found by Stanley et al to exhibit similar mechanical properties, but in this system the mechanism of gel collapse in the region of δ was also considered. 402 Noting that the observed values of δ are an order of magnitude lower than expected if failure occurs through elastic buckling, it was proposed that fibre networks collapse via plastic deformation, with individual fibres displaying a plastic yield stress on the order of 1 MPa.…”

Section: Gels Under Stressmentioning

confidence: 99%

“…For instance, Lloyd et al observed that interconnections between fibres in a chiral bis(urea) gel become thinned after shearing and self-repair, resulting in a Gʹ value 45% lower than that of the parent material. 401 It is worth noting that the self-healing capacity of a gel may not be correlated with its initial resistance to mechanical disruption. In one study, Terech et al showed that a decane gel of 12-hydroxysteraic acid deforms ten times more slowly than a DMF gel of terpyridyl ligand 42 and nickel(II) chloride but exhibits strain recovery of just 32%, compared with 72% in the metal-containing system (Fig.…”

Section: Gels Under Stressmentioning

confidence: 99%

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Gels with sense: supramolecular materials that respond to heat, light and sound

2016

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. (2016) 'Gels with sense : supramolecular materials that respond to heat, light and sound.', Chemical society reviews., 45 (23). pp. 6546-6596. Further information on publisher's website:https://doi.org/10.1039/C6CS00435KPublisher's copyright statement:Additional information: Use policyThe 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. Advances in the field of supramolecular chemistry have made it possible, in many situations, to reliably engineer soft materials to address a specific technological problem. Particularly exciting are "smart" gels that undergo reversible physical changes on exposure to remote, non-invasive environmental stimuli. This review explores the development of gels which are transformed by heat, light and ultrasound, as well as other mechanical inputs, applied voltages and magnetic fields. Focusing on small-molecule gelators, but with reference to organic polymers and metal-organic systems, we examine how the structures of gelator assemblies influence the physical and chemical mechanisms leading to thermo-, photo-and mechano-switchable behaviour. In addition, we evaluate how the unique and versatile properties of smart materials may be exploited in a wide range of applications, including catalysis, crystal growth, ion sensing, drug delivery, data storage and biomaterial replacement.

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Section: Gels Under Stressmentioning

confidence: 99%

Section: Gels Under Stressmentioning

confidence: 99%

Gels with sense: supramolecular materials that respond to heat, light and sound

2016

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“…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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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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“…13 In contrast, anions, particularly strong hydrogen bond acceptors such as chloride and acetate, tend to 'turn off' gelation by competitive hydrogen bonding to the urea NH groups. 19,20 Indeed reports of anion-promoted gelation are very rare. 21,22 We anticipate that changing from pyridyl ureas to simple pyridinylmethyl ureas (Scheme 1) should radically change the aggregation behaviour of the urea since the introduction of a methylene spacer between the urea and heterocycle means that the oxygen acceptor is no longer sterically hindered, hence markedly favouring urea···urea hydrogen bonding via the 2 1 (6) urea -tape motif.…”

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