The Past, Present, and Future of Molecular Gels. What Is the Status of the Field, and Where Is It Going?

Weiss, Richard G.

doi:10.1021/ja503363v

Cited by 612 publications

(492 citation statements)

References 158 publications

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Section: Introductionmentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

“…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 Picture Gels are ubiquitous soft solids that are widely used in everyday life. Most gels are based on polymeric materials, as either entangled biopolymers or covalently crosslinked networks.…”

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confidence: 99%

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

Draper

Adams

2017

Chem

525

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%

mentioning

confidence: 99%

mentioning

confidence: 99%

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

Draper

Adams

2017

Chem

525

469

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“…A key issue in the area of low molecular weight gelators is the lack of available design rules for their design. 45 This work points to important contributions of different parts of the molecule to the organisation of both molecular structure within individual filaments and their lateral association and packing. However, we note that it is not possible to link the molecular structure to the bulk properties of the gels.…”

Section: Articlementioning

confidence: 88%

Structural determinants in a library of low molecular weight gelators

et al. 2015

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ARTICLELow molecular weight hydrogels are formed by molecules that form a matrix that immobilises water to form a self-supporting gel. Such gels have uses as biomaterials such as molecular scaffolds and structures for tissue engineering. One class of low molecular weight gelators (LMWG), naphthalene-conjugated dipeptides, has been shown to form hydrogels via selfassembly following a controlled drop in pH. A library of naphthalene-dipeptides has been generated previously although the relationship between the precursor sequence and the resulting self-assembled structures remained unclear. Here, we have investigated the structural details of a set of dipeptide sequences containing alanine (A) and valine (V) conjugated to naphthalene groups substituted with a Br, CN or H at the 6-position. Electron microscopy, circular dichroism and X-ray fibre diffraction shows that these LMWG may be structurally classified by their composition: the molecular packing is determined by the class of conjugate, whilst the chirality of the self-assemblies can be attributed to the dipeptide sequence. This provides insights into the relationship between the precursor sequence and the macromolecular and molecular structures of the fibres that make up the resulting hydrogels. IntroductionThe formation of hydrogels from low molecular weight gelators (LMWG) is a useful route to the production of materials for a wide range of applications. 1, 2 A recent expansion in the number of LMWG systems reported has led to a rapid growth in reports of characterisation and applications of a particular class of this type of molecule, namely aromatic conjugated dipeptide LMWG. 3-8 These systems typically consist of a hydrophobic, often aromatic, dipeptide sequences conjugated to Fmoc (9-fluorenylmethoxycarbonyl) 9, 10 or naphthalene 3, 4 ; further conjugations have also been reported. 11,12 Through the use of an environmental cue, 13 such as an enzymatic trigger, 14 temperature, 15,16 or light 12 some of these conjugates selfassemble into anisotropic fibrils that can eventually cause hydrogelation through the immobilisation of water by the fibrillar network. There are now a large number of systems reported in the literature. 17 It is apparent from previous work that two LMWG molecules that differ only by a single amino acid can give rise to hydrogels with dramatically different rheological and phase properties. 3,4,10,18 However, the structural basis for these differences in material properties is not understood.The short-range molecular architecture of some LMWG systems has been studied. For example, the chirality of assembled naphthalene conjugated dipeptides has been reported to correlate to the D-or L-enantiomer of the incorporated amino acids with left-and right-handed assemblies being formed respectively. 3 Other reports have indicated that proteinaceous additives induce changes to the chiral organisation of the self-assembled hydrogelating molecules. 19 In addition to the plethora of molecular hydrogels with varying material properties available, the...

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“…[1][2][3][4] The increasing attention paid to supramolecular gels is related to their applicability as new soft materials in areas such as molecular electronics, controlled release, tissue engineering or catalysis among others. [2][3][4][5][6][7] Several approaches have addressed the inclusion of photonic functionalities into supramolecular gels. 8 For example, gels with chromophore units have been used as photocatalysts 9,10 and excitation energy transfer has been studied in supramolecular gels formed by photoactive fibers which contained entrapped dyes.…”

Section: Introductionmentioning

confidence: 99%

Multimodal Light-Harvesting Soft Hybrid Materials: Assisted Energy Transfer upon Thermally Reversible Gelation

et al. 2017

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Multimodal light-harvesting soft systems able to absorb UV-to-NIR radiations and convert into visible emissions have drawn much attention in the last years in order to explore new areas of application in energy, photonics, photocatalysis, sensors and so forth. Here, we present a new hybrid system combining a supramolecular photonic gel of naphthalimide-derived molecules self-assembled into fibers and upconverting NaYF 4 :Yb/Tm nanoparticles (UCNPs). The hybrid system presented here manipulates light reversibly as a result of an optical communication between the UCNPs and the photoactive gel network. Upon UV irradiation, the system shows the characteristic emission at 410 nm from the photoactive organomolecule. This emission is also activated upon 980 nm excitation thanks to an efficient energy transfer from the UCNPs to the fibrillary network. Interestingly, the intensity of this emission is thermally regulated during the reversible assembly or disassembly of the organogelator molecules, in such a way that gelator emission is only observed in the aggregated state. Additionally, the adsorption of the UCNPs with the supramolecular gel fibers enhance their emissive properties, a behavior ascribed to the isolation from solvent quenchers and surface defects, as well as an increased IR light scattering promoted by the fibrillary network. The reported system constitutes a unique case of a thermally regulated, reversible, dual UV and IR light harvesting hybrid soft material.3

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The Past, Present, and Future of Molecular Gels. What Is the Status of the Field, and Where Is It Going?

Cited by 612 publications

References 158 publications

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

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

Structural determinants in a library of low molecular weight gelators

Multimodal Light-Harvesting Soft Hybrid Materials: Assisted Energy Transfer upon Thermally Reversible Gelation

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