Salt-induced hydrogelation of functionalised-dipeptides at high pH

Chen, Lin; Pont, Guillaume; Morris, Kyle L.; Lötze, Gudrun; Squires, Adam M.; Serpell, Louise C.; Adams, Dave J.

doi:10.1039/c1cc15474e

Cited by 137 publications

(202 citation statements)

References 22 publications

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“…One interesting observation is that the gels formed at high pH by addition of a calcium salt decrease in gel strength dramatically when the pH is decreased, and then become stronger again as the pH drops below the pK a . 79 This implies at the very least that there is a rare gel-to-gel transition as opposed to a gradual change from one type of gel to another.…”

Section: Process Of Assemblymentioning

confidence: 99%

“…Similarly, the nature of the salt added is important. Weak materials are formed when monovalent cations are added (for example, sodium chloride); 79 in analogy with polymer systems, this is probably The low-molecular-weight gel 2NapFF (at high pH, above the pK a , the carboxylate will be formed instead) can form a gel in different ways, leading to different types of networks.…”

Section: Process Of Assemblymentioning

confidence: 99%

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

Draper

Adams

2017

Chem

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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: Process Of Assemblymentioning

confidence: 99%

Section: Process Of Assemblymentioning

confidence: 99%

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

Draper

Adams

2017

Chem

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492

450

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“…Polymorphism in such polymers can be influenced by the careful choice of solution conditions 11,[31][32][33] . For instance, it has been shown that N-(t-butoxycarbonyl)-L-Phe-L-Phe-COOH (Boc-FF) can undergo self-assembly into structurally distinct states on the nanometer length scale as a result of variations in the solvent composition in which the process occurs.…”

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confidence: 99%

Ostwald’s rule of stages governs structural transitions and morphology of dipeptide supramolecular polymers

et al. 2014

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The self-assembly of molecular building blocks into nano-and micro-scale supramolecular architectures has opened up new frontiers in polymer science. Such supramolecular species not only possess a rich set of dynamic features as a consequence of the non-covalent nature of their core interactions, but also afford unique structural characteristics. Although much is now known about the manner in which such structures adopt their morphologies and size distributions in response to external stimuli, the kinetic and thermodynamic driving forces that lead to their transformation from soluble monomeric species into ordered supramolecular entities have remained elusive. Here we focus on Boc-diphenylalanine, an archetypical example of a peptide with a high propensity towards supramolecular self-organization, and describe the pathway through which it forms a range of nano-assemblies with different structural characteristics. Our results reveal that the nucleation process is multi-step in nature and proceeds by Ostwald's step rule through which coalescence of soluble monomers leads to the formation of nanospheres, which then undergo ripening and structural conversions to form the final supramolecular assemblies. We characterize the structures and thermodynamics of the different phases involved in this process and reveal the intricate nature of the transitions that can occur between discrete structural states of this class of supramolecular polymers.

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“…before gelation), presumably associating via hydrophobic interactions lead by the aromatic rings. 43,44 Nonetheless, whilst the naphthalene rings are undoubtedly essential for self-assembly, which interactions lead to the assembly into anisotropic fibres and modulate the nature of the final assembled structure is less clear. A key issue in the area of low molecular weight gelators is the lack of available design rules for their design.…”

Section: Articlementioning

confidence: 99%

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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Salt-induced hydrogelation of functionalised-dipeptides at high pH

Abstract: Addition of divalent cations to a solution of a naphthalene-diphenylalanine that forms worm-like micelles at high pH results in the formation of a rigid, self-supporting hydrogel.

Cited by 137 publications

References 22 publications

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

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

Ostwald’s rule of stages governs structural transitions and morphology of dipeptide supramolecular polymers

Structural determinants in a library of low molecular weight gelators

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